Merge pull request #3 from eugenp/master

merge

README.md

@@ -1,12 +1,16 @@
 
-The "REST with Spring" Classes
+The Courses
 ==============================
 
-Here's the Master Class of REST With Spring (along with the newly announced Boot 2 material): <br/>
-**[>> THE REST WITH SPRING - MASTER CLASS](http://www.baeldung.com/rest-with-spring-course?utm_source=github&utm_medium=social&utm_content=tutorials&utm_campaign=rws#master-class)**
 
-And here's the Master Class of Learn Spring Security: <br/>
+Here's the new "Learn Spring" course: <br/>
-**[>> LEARN SPRING SECURITY - MASTER CLASS](http://www.baeldung.com/learn-spring-security-course?utm_source=github&utm_medium=social&utm_content=tutorials&utm_campaign=lss#master-class)**
+**[>> LEARN SPRING - THE MASTER CLASS](https://www.baeldung.com/learn-spring-course?utm_source=github&utm_medium=social&utm_content=tutorials&utm_campaign=ls#master-class)**
+
+Here's the Master Class of "REST With Spring" (along with the new announced Boot 2 material): <br/>
+**[>> THE REST WITH SPRING - MASTER CLASS](https://www.baeldung.com/rest-with-spring-course?utm_source=github&utm_medium=social&utm_content=tutorials&utm_campaign=rws#master-class)**
+
+And here's the Master Class of "Learn Spring Security": <br/>
+**[>> LEARN SPRING SECURITY - MASTER CLASS](https://www.baeldung.com/learn-spring-security-course?utm_source=github&utm_medium=social&utm_content=tutorials&utm_campaign=lss#master-class)**
 
 
 
@@ -15,7 +19,7 @@ Java and Spring Tutorials
 
 This project is **a collection of small and focused tutorials** - each covering a single and well defined area of development in the Java ecosystem. 
 A strong focus of these is, of course, the Spring Framework - Spring, Spring Boot and Spring Security. 
-In additional to Spring, the following technologies are in focus: `core Java`, `Jackson`, `HttpClient`, `Guava`. 
+In additional to Spring, the modules here are covering a number of aspects in Java. 
 
 
 Building the project
@@ -32,8 +36,15 @@ Running a Spring Boot module
 ====================
 To run a Spring Boot module run the command: `mvn spring-boot:run` in the module directory
 
-#Running Tests
 
+Working with the IDE
+====================
+This repo contains a large number of modules. 
+When you're working with an individual module, there's no need to import all of them (or build all of them) - you can simply import that particular module in either Eclipse or IntelliJ. 
+
+
+Running Tests
+=============
 The command `mvn clean install` will run the unit tests in a module.
 To run the integration tests, use the command `mvn clean install -Pintegration-lite-first`
 

algorithms-miscellaneous-3/src/main/java/com/baeldung/algorithms/stringsortingbynumber/NaturalOrderComparators.java

@@ -0,0 +1,30 @@
+package com.baeldung.algorithms.stringsortingbynumber;
+
+import java.util.Comparator;
+
+public final class NaturalOrderComparators {
+
+    private static final String DIGIT_AND_DECIMAL_REGEX = "[^\\d.]";
+
+    private NaturalOrderComparators() {
+        throw new AssertionError("Let's keep this static");
+    }
+
+    public static Comparator<String> createNaturalOrderRegexComparator() {
+        return Comparator.comparingDouble(NaturalOrderComparators::parseStringToNumber);
+    }
+
+    private static double parseStringToNumber(String input){
+
+        final String digitsOnly = input.replaceAll(DIGIT_AND_DECIMAL_REGEX, "");
+
+        if("".equals(digitsOnly)) return 0;
+
+        try{
+            return Double.parseDouble(digitsOnly);
+        }catch (NumberFormatException nfe){
+            return 0;
+        }
+    }
+
+}

algorithms-miscellaneous-3/src/test/java/com/baeldung/algorithms/stringsortingbynumber/NaturalOrderComparatorsUnitTest.java

@@ -0,0 +1,79 @@
+package com.baeldung.algorithms.stringsortingbynumber;
+
+import com.baeldung.algorithms.stringsortingbynumber.NaturalOrderComparators;
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+import static org.junit.Assert.*;
+
+public class NaturalOrderComparatorsUnitTest {
+
+    @Test
+    public void givenSimpleStringsContainingIntsAndDoubles_whenSortedByRegex_checkSortingCorrect() {
+
+        List<String> testStrings = Arrays.asList("a1", "b3", "c4", "d2.2", "d2.4", "d2.3d");
+
+        testStrings.sort(NaturalOrderComparators.createNaturalOrderRegexComparator());
+
+        List<String> expected = Arrays.asList("a1", "d2.2", "d2.3d", "d2.4", "b3", "c4");
+
+        assertEquals(expected, testStrings);
+
+
+    }
+
+    @Test
+    public void givenSimpleStringsContainingIntsAndDoublesWithAnInvalidNumber_whenSortedByRegex_checkSortingCorrect() {
+
+        List<String> testStrings = Arrays.asList("a1", "b3", "c4", "d2.2", "d2.4", "d2.3.3d");
+
+        testStrings.sort(NaturalOrderComparators.createNaturalOrderRegexComparator());
+
+        List<String> expected = Arrays.asList("d2.3.3d", "a1", "d2.2", "d2.4", "b3", "c4");
+
+        assertEquals(expected, testStrings);
+
+
+    }
+
+    @Test
+    public void givenAllForseenProblems_whenSortedByRegex_checkSortingCorrect() {
+
+        List<String> testStrings = Arrays.asList("a1", "b3", "c4", "d2.2", "d2.f4", "d2.3.3d");
+
+        testStrings.sort(NaturalOrderComparators.createNaturalOrderRegexComparator());
+
+        List<String> expected = Arrays.asList("d2.3.3d", "a1", "d2.2", "d2.f4", "b3", "c4");
+
+        assertEquals(expected, testStrings);
+
+
+    }
+
+    @Test
+    public void givenComplexStringsContainingSeparatedNumbers_whenSortedByRegex_checkNumbersCondensedAndSorted() {
+
+        List<String> testStrings = Arrays.asList("a1b2c5", "b3ght3.2", "something65.thensomething5"); //125, 33.2, 65.5
+
+        List<String> expected = Arrays.asList("b3ght3.2", "something65.thensomething5", "a1b2c5" );
+
+        testStrings.sort(NaturalOrderComparators.createNaturalOrderRegexComparator());
+
+        assertEquals(expected, testStrings);
+
+    }
+
+    @Test
+    public void givenStringsNotContainingNumbers_whenSortedByRegex_checkOrderNotChanged() {
+
+        List<String> testStrings = Arrays.asList("a", "c", "d", "e");
+        List<String> expected = new ArrayList<>(testStrings);
+
+        testStrings.sort(NaturalOrderComparators.createNaturalOrderRegexComparator());
+
+        assertEquals(expected, testStrings);
+    }
+}

algorithms-sorting/src/main/java/com/baeldung/algorithms/shellsort/ShellSort.java

@@ -0,0 +1,20 @@
+package com.baeldung.algorithms.shellsort;
+
+public class ShellSort {
+
+    public static void sort(int arrayToSort[]) {
+        int n = arrayToSort.length;
+
+        for (int gap = n / 2; gap > 0; gap /= 2) {
+            for (int i = gap; i < n; i++) {
+                int key = arrayToSort[i];
+                int j = i;
+                while (j >= gap && arrayToSort[j - gap] > key) {
+                    arrayToSort[j] = arrayToSort[j - gap];
+                    j -= gap;
+                }
+                arrayToSort[j] = key;
+            }
+        }
+    }
+}

algorithms-sorting/src/test/java/com/baeldung/algorithms/shellsort/ShellSortUnitTest.java

@@ -0,0 +1,17 @@
+package com.baeldung.algorithms.shellsort;
+
+import static org.junit.Assert.*;
+import static org.junit.Assert.assertArrayEquals;
+
+import org.junit.Test;
+
+public class ShellSortUnitTest {
+
+    @Test
+    public void givenUnsortedArray_whenShellSort_thenSortedAsc() {
+        int[] input = {41, 15, 82, 5, 65, 19, 32, 43, 8};
+        ShellSort.sort(input);
+        int[] expected = {5, 8, 15, 19, 32, 41, 43, 65, 82};
+        assertArrayEquals("the two arrays are not equal", expected, input);
+    }
+}

axon/pom.xml

@@ -18,12 +18,6 @@
             <groupId>org.axonframework</groupId>
             <artifactId>axon-spring-boot-starter</artifactId>
             <version>${axon.version}</version>
-            <exclusions>
-                <exclusion>
-                    <groupId>org.axonframework</groupId>
-                    <artifactId>axon-server-connector</artifactId>
-                </exclusion>
-            </exclusions>
         </dependency>
 
         <dependency>
@@ -58,7 +52,7 @@
     </dependencies>
 
     <properties>
-        <axon.version>4.0.3</axon.version>
+        <axon.version>4.1.2</axon.version>
     </properties>
 
 </project>

axon/src/main/java/com/baeldung/axon/commandmodel/OrderAggregate.java

@@ -13,6 +13,7 @@ import com.baeldung.axon.coreapi.commands.ShipOrderCommand;
 import com.baeldung.axon.coreapi.events.OrderConfirmedEvent;
 import com.baeldung.axon.coreapi.events.OrderPlacedEvent;
 import com.baeldung.axon.coreapi.events.OrderShippedEvent;
+import com.baeldung.axon.coreapi.exceptions.UnconfirmedOrderException;
 
 @Aggregate
 public class OrderAggregate {
@@ -34,7 +35,7 @@ public class OrderAggregate {
     @CommandHandler
     public void handle(ShipOrderCommand command) {
         if (!orderConfirmed) {
-            throw new IllegalStateException("Cannot ship an order which has not been confirmed yet.");
+            throw new UnconfirmedOrderException();
         }
 
         apply(new OrderShippedEvent(orderId));
@@ -43,12 +44,12 @@ public class OrderAggregate {
     @EventSourcingHandler
     public void on(OrderPlacedEvent event) {
         this.orderId = event.getOrderId();
-        orderConfirmed = false;
+        this.orderConfirmed = false;
     }
 
     @EventSourcingHandler
     public void on(OrderConfirmedEvent event) {
-        orderConfirmed = true;
+        this.orderConfirmed = true;
     }
 
     protected OrderAggregate() {

axon/src/main/java/com/baeldung/axon/coreapi/exceptions/UnconfirmedOrderException.java

@@ -0,0 +1,8 @@
+package com.baeldung.axon.coreapi.exceptions;
+
+public class UnconfirmedOrderException extends IllegalStateException {
+
+    public UnconfirmedOrderException() {
+        super("Cannot ship an order which has not been confirmed yet.");
+    }
+}

axon/src/main/java/com/baeldung/axon/querymodel/OrderedProductsEventHandler.java

@@ -5,6 +5,7 @@ import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 
+import org.axonframework.config.ProcessingGroup;
 import org.axonframework.eventhandling.EventHandler;
 import org.axonframework.queryhandling.QueryHandler;
 import org.springframework.stereotype.Service;
@@ -16,6 +17,7 @@ import com.baeldung.axon.coreapi.queries.FindAllOrderedProductsQuery;
 import com.baeldung.axon.coreapi.queries.OrderedProduct;
 
 @Service
+@ProcessingGroup("ordered-products")
 public class OrderedProductsEventHandler {
 
     private final Map<String, OrderedProduct> orderedProducts = new HashMap<>();

axon/src/main/resources/application.properties

@@ -0,0 +1 @@
+spring.application.name=Order Management Service

axon/src/test/java/com/baeldung/axon/commandmodel/OrderAggregateUnitTest.java

@@ -2,6 +2,7 @@ package com.baeldung.axon.commandmodel;
 
 import java.util.UUID;
 
+import com.baeldung.axon.coreapi.exceptions.UnconfirmedOrderException;
 import org.axonframework.test.aggregate.AggregateTestFixture;
 import org.axonframework.test.aggregate.FixtureConfiguration;
 import org.junit.*;
@@ -41,12 +42,12 @@ public class OrderAggregateUnitTest {
     }
 
     @Test
-    public void givenOrderPlacedEvent_whenShipOrderCommand_thenShouldThrowIllegalStateException() {
+    public void givenOrderPlacedEvent_whenShipOrderCommand_thenShouldThrowUnconfirmedOrderException() {
         String orderId = UUID.randomUUID().toString();
         String product = "Deluxe Chair";
         fixture.given(new OrderPlacedEvent(orderId, product))
                .when(new ShipOrderCommand(orderId))
-               .expectException(IllegalStateException.class);
+               .expectException(UnconfirmedOrderException.class);
     }
 
     @Test

core-java-modules/core-java-12/README.md

@@ -1,3 +1,4 @@
-## Relevant articles:
+## Relevant Articles:
+
 
 - [String API Updates in Java 12](https://www.baeldung.com/java12-string-api)

core-java-modules/core-java-8/src/main/java/com/baeldung/java_8_features/groupingby/Tuple.java

@@ -0,0 +1,34 @@
+package com.baeldung.java_8_features.groupingby;
+
+public class Tuple {
+
+    private BlogPostType type;
+    private String author;
+    
+    public Tuple(BlogPostType type, String author) {
+        super();
+        this.type = type;
+        this.author = author;
+    }
+
+    public BlogPostType getType() {
+        return type;
+    }
+
+    public void setType(BlogPostType type) {
+        this.type = type;
+    }
+
+    public String getAuthor() {
+        return author;
+    }
+
+    public void setAuthor(String author) {
+        this.author = author;
+    }
+
+    @Override
+    public String toString() {
+        return "Tuple [type=" + type + ", author=" + author + ", getType()=" + getType() + ", getAuthor()=" + getAuthor() + ", getClass()=" + getClass() + ", hashCode()=" + hashCode() + ", toString()=" + super.toString() + "]";
+    }
+}

core-java-modules/core-java-arrays-2/.gitignore

@@ -0,0 +1,25 @@
+*.class
+
+0.*
+
+#folders#
+/target
+/neoDb*
+/data
+/src/main/webapp/WEB-INF/classes
+*/META-INF/*
+.resourceCache
+
+# Packaged files #
+*.jar
+*.war
+*.ear
+
+# Files generated by integration tests
+backup-pom.xml
+/bin/
+/temp
+
+#IntelliJ specific
+.idea/
+*.iml

core-java-modules/core-java-arrays-2/pom.xml

@@ -0,0 +1,50 @@
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <groupId>com.baeldung</groupId>
+    <artifactId>core-java-arrays-2</artifactId>
+    <version>0.1.0-SNAPSHOT</version>
+    <name>core-java-arrays-2</name>
+    <packaging>jar</packaging>
+
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-java</artifactId>
+        <version>0.0.1-SNAPSHOT</version>
+        <relativePath>../../parent-java</relativePath>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-lang3</artifactId>
+            <version>${commons-lang3.version}</version>
+        </dependency>
+        <!-- test scoped -->
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>${assertj-core.version}</version>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <finalName>core-java-arrays-2</finalName>
+        <resources>
+            <resource>
+                <directory>src/main/resources</directory>
+                <filtering>true</filtering>
+            </resource>
+        </resources>
+    </build>
+
+    <properties>
+
+        <!-- util -->
+        <commons-lang3.version>3.9</commons-lang3.version>
+        <!-- testing -->
+        <assertj-core.version>3.10.0</assertj-core.version>
+    </properties>
+
+</project>

core-java-modules/core-java-arrays-2/src/main/java/com/baeldung/array/looping/LoopDiagonally.java

@@ -0,0 +1,45 @@
+package com.baeldung.array.looping;
+
+public class LoopDiagonally {
+
+
+    public String loopDiagonally(String[][] twoDArray) {
+
+        int length = twoDArray.length;
+        int diagonalLines = (length + length) - 1;
+        int itemsInDiagonal = 0;
+        int midPoint = (diagonalLines / 2) + 1;
+        StringBuilder output = new StringBuilder();
+
+        for (int i = 1; i <= diagonalLines; i++) {
+
+            StringBuilder items = new StringBuilder();
+            int rowIndex;
+            int columnIndex;
+
+            if (i <= midPoint) {
+                itemsInDiagonal++;
+                for (int j = 0; j < itemsInDiagonal; j++) {
+                    rowIndex = (i - j) - 1;
+                    columnIndex = j;
+                    items.append(twoDArray[rowIndex][columnIndex]);
+                }
+            } else {
+                itemsInDiagonal--;
+                for (int j = 0; j < itemsInDiagonal; j++) {
+                    rowIndex = (length - 1) - j;
+                    columnIndex = (i - length) + j;
+                    items.append(twoDArray[rowIndex][columnIndex]);
+                }
+            }
+
+            if (i != diagonalLines) {
+                output.append(items).append(" ");
+            } else {
+                output.append(items);
+            }
+        }
+
+        return output.toString();
+    }
+}

core-java-modules/core-java-arrays-2/src/test/java/com/baeldung/array/looping/LoopDiagonallyUnitTest.java

@@ -0,0 +1,20 @@
+package com.baeldung.array.looping;
+
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+public class LoopDiagonallyUnitTest {
+
+    @Test
+    public void twoArrayIsLoopedDiagonallyAsExpected() {
+
+        LoopDiagonally loopDiagonally = new LoopDiagonally();
+        String[][] twoDArray = {{"a", "b", "c"},
+                                {"d", "e", "f"},
+                                {"g", "h", "i"}};
+
+        String output = loopDiagonally.loopDiagonally(twoDArray);
+        assertEquals("a db gec hf i", output);
+    }
+}

core-java-modules/core-java-arrays/src/main/java/com/baeldung/array/SortedArrayChecker.java

@@ -2,7 +2,10 @@ package com.baeldung.array;
 
 import com.baeldung.arraycopy.model.Employee;
 
+import java.util.Comparator;
+
 public class SortedArrayChecker {
+
     boolean isSorted(int[] array, int length) {
         if (array == null || length < 2)
             return true;
@@ -22,7 +25,7 @@ public class SortedArrayChecker {
         return true;
     }
 
-    boolean isSorted(String[] array, int length) {
+    boolean isSorted(Comparable[] array, int length) {
         if (array == null || length < 2)
             return true;
 
@@ -32,40 +35,31 @@ public class SortedArrayChecker {
         return isSorted(array, length - 1);
     }
 
-boolean isSorted(String[] array) {
+    boolean isSorted(Comparable[] array) {
         for (int i = 0; i < array.length - 1; ++i) {
             if (array[i].compareTo(array[i + 1]) > 0)
                 return false;
         }
 
         return true;
-}
+    }
 
-    boolean isSortedByName(Employee[] array) {
+    boolean isSorted(Object[] array, Comparator comparator) {
         for (int i = 0; i < array.length - 1; ++i) {
-            if (array[i].getName().compareTo(array[i + 1].getName()) > 0)
+            if (comparator.compare(array[i], (array[i + 1])) > 0)
                 return false;
         }
 
         return true;
     }
 
-boolean isSortedByAge(Employee[] array) {
+    boolean isSorted(Object[] array, Comparator comparator, int length) {
-    for (int i = 0; i < array.length - 1; ++i) {
-        if (array[i].getAge() > (array[i + 1].getAge()))
-            return false;
-    }
-
-    return true;
-}
-
-    boolean isSortedByAge(Employee[] array, int length) {
         if (array == null || length < 2)
             return true;
 
-        if (array[length - 2].getAge() > array[length - 1].getAge())
+        if (comparator.compare(array[length - 2], array[length - 1]) > 0)
             return false;
 
-        return isSortedByAge(array, length - 1);
+        return isSorted(array, comparator, length - 1);
     }
 }

core-java-modules/core-java-arrays/src/test/java/com/baeldung/array/SortedArrayCheckerUnitTest.java

@@ -4,32 +4,33 @@ import com.baeldung.arraycopy.model.Employee;
 import org.junit.Before;
 import org.junit.Test;
 
+import java.util.Comparator;
+
 import static org.assertj.core.api.Assertions.assertThat;
 
-class SortedArrayCheckerUnitTest {
+public class SortedArrayCheckerUnitTest {
-
     private static final int[] INTEGER_SORTED = {1, 3, 5, 7, 9};
     private static final int[] INTEGER_NOT_SORTED = {1, 3, 11, 7};
 
     private static final String[] STRING_SORTED = {"abc", "cde", "fgh"};
     private static final String[] STRING_NOT_SORTED = {"abc", "fgh", "cde", "ijk"};
 
-    private final Employee[] EMPLOYEES_SORTED_BY_NAME = {
+    private static final Employee[] EMPLOYEES_SORTED_BY_NAME = {
             new Employee(1, "Carlos", 26),
             new Employee(2, "Daniel", 31),
             new Employee(3, "Marta", 27)};
 
-    private final Employee[] EMPLOYEES_NOT_SORTED_BY_NAME = {
+    private static final Employee[] EMPLOYEES_NOT_SORTED_BY_NAME = {
             new Employee(1, "Daniel", 31),
             new Employee(2, "Carlos", 26),
             new Employee(3, "Marta", 27)};
 
-    private final Employee[] EMPLOYEES_SORTED_BY_AGE = {
+    private static final Employee[] EMPLOYEES_SORTED_BY_AGE = {
             new Employee(1, "Carlos", 26),
             new Employee(2, "Marta", 27),
             new Employee(3, "Daniel", 31)};
 
-    private final Employee[] EMPLOYEES_NOT_SORTED_BY_AGE = {
+    private static final Employee[] EMPLOYEES_NOT_SORTED_BY_AGE = {
             new Employee(1, "Marta", 27),
             new Employee(2, "Carlos", 26),
             new Employee(3, "Daniel", 31)};
@@ -61,13 +62,18 @@ class SortedArrayCheckerUnitTest {
 
     @Test
     public void givenEmployeeArray_thenReturnIfItIsSortedOrNot() {
-        assertThat(sortedArrayChecker.isSortedByName(EMPLOYEES_SORTED_BY_NAME)).isEqualTo(true);
+        assertThat(sortedArrayChecker.isSorted(EMPLOYEES_SORTED_BY_NAME, Comparator.comparing(Employee::getName))).isEqualTo(true);
-        assertThat(sortedArrayChecker.isSortedByName(EMPLOYEES_NOT_SORTED_BY_NAME)).isEqualTo(false);
+        assertThat(sortedArrayChecker.isSorted(EMPLOYEES_NOT_SORTED_BY_NAME, Comparator.comparing(Employee::getName))).isEqualTo(false);
 
-        assertThat(sortedArrayChecker.isSortedByAge(EMPLOYEES_SORTED_BY_AGE)).isEqualTo(true);
+        assertThat(sortedArrayChecker.isSorted(EMPLOYEES_SORTED_BY_AGE, Comparator.comparingInt(Employee::getAge))).isEqualTo(true);
-        assertThat(sortedArrayChecker.isSortedByAge(EMPLOYEES_NOT_SORTED_BY_AGE)).isEqualTo(false);
+        assertThat(sortedArrayChecker.isSorted(EMPLOYEES_NOT_SORTED_BY_AGE, Comparator.comparingInt(Employee::getAge))).isEqualTo(false);
 
-        assertThat(sortedArrayChecker.isSortedByAge(EMPLOYEES_SORTED_BY_AGE, EMPLOYEES_SORTED_BY_AGE.length)).isEqualTo(true);
+        assertThat(sortedArrayChecker
-        assertThat(sortedArrayChecker.isSortedByAge(EMPLOYEES_NOT_SORTED_BY_AGE, EMPLOYEES_NOT_SORTED_BY_AGE.length)).isEqualTo(false);
+                .isSorted(EMPLOYEES_SORTED_BY_AGE, Comparator.comparingInt(Employee::getAge), EMPLOYEES_SORTED_BY_AGE.length))
+                .isEqualTo(true);
+        assertThat(sortedArrayChecker
+                .isSorted(EMPLOYEES_NOT_SORTED_BY_AGE, Comparator.comparingInt(Employee::getAge), EMPLOYEES_NOT_SORTED_BY_AGE.length))
+                .isEqualTo(false);
     }
+
 }

core-java-modules/core-java-collections-array-list/src/test/java/org/baeldung/java/collections/CoreJavaCollectionsUnitTest.java

@@ -42,7 +42,7 @@ public class CoreJavaCollectionsUnitTest {
     @Test(expected = UnsupportedOperationException.class)
     public final void givenUsingGuavaBuilder_whenUnmodifiableListIsCreatedFromOriginal_thenNoLongerModifiable() {
         final List<String> list = new ArrayList<String>(Arrays.asList("one", "two", "three"));
-        final ImmutableList<Object> unmodifiableList = ImmutableList.builder().addAll(list).build();
+        final ImmutableList<String> unmodifiableList = ImmutableList.<String>builder().addAll(list).build();
         unmodifiableList.add("four");
     }
 

core-java-modules/core-java-exceptions/README.md

@@ -1,3 +1,3 @@
-## Relevant articles:
+## Relevant Articles:
 
 - [Will an Error Be Caught by Catch Block in Java?](https://www.baeldung.com/java-error-catch)

core-java-modules/core-java-lang-oop-2/src/main/java/com/baeldung/relationships/aggregation/Car.java

@@ -0,0 +1,9 @@
+package com.baeldung.relationships.aggregation;
+
+import java.util.List;
+
+public class Car {
+
+    private List<Wheel> wheels;
+    
+}

core-java-modules/core-java-lang-oop-2/src/main/java/com/baeldung/relationships/aggregation/CarWithStaticInnerWheel.java

@@ -0,0 +1,13 @@
+package com.baeldung.relationships.aggregation;
+
+import java.util.List;
+
+public class CarWithStaticInnerWheel {
+
+    private List<Wheel> wheels;
+
+    public static class Wheel {
+
+    }
+
+}

core-java-modules/core-java-lang-oop-2/src/main/java/com/baeldung/relationships/aggregation/Wheel.java

@@ -0,0 +1,7 @@
+package com.baeldung.relationships.aggregation;
+
+public class Wheel {
+
+    private Car car;
+    
+}

core-java-modules/core-java-lang-oop-2/src/main/java/com/baeldung/relationships/association/Child.java

@@ -0,0 +1,7 @@
+package com.baeldung.relationships.association;
+
+public class Child {
+
+    private Mother mother;
+
+}

core-java-modules/core-java-lang-oop-2/src/main/java/com/baeldung/relationships/association/Mother.java

@@ -0,0 +1,9 @@
+package com.baeldung.relationships.association;
+
+import java.util.List;
+
+public class Mother {
+
+    private List<Child> children;
+
+}

core-java-modules/core-java-lang-oop-2/src/main/java/com/baeldung/relationships/composition/Building.java

@@ -0,0 +1,18 @@
+package com.baeldung.relationships.composition;
+
+import java.util.List;
+
+public class Building {
+
+    private String address;
+    private List<Room> rooms;
+    
+    public class Room {
+        
+        public String getBuildingAddress() {
+            return Building.this.address;
+        }
+        
+    }
+    
+}

core-java-modules/core-java-lang-oop-2/src/main/java/com/baeldung/relationships/composition/BuildingWithDefinitionRoomInMethod.java

@@ -0,0 +1,28 @@
+package com.baeldung.relationships.composition;
+
+public class BuildingWithDefinitionRoomInMethod {
+
+    public Room createAnonymousRoom() {
+        return new Room() {
+            @Override
+            public void doInRoom() {}
+        };
+    }
+
+    public Room createInlineRoom() {
+        class InlineRoom implements Room {
+            @Override
+            public void doInRoom() {}
+        }
+        return new InlineRoom();
+    }
+    
+    public Room createLambdaRoom() {
+        return () -> {};
+    }
+
+    public interface Room {
+        void doInRoom();
+    }
+
+}

core-java-modules/core-java-lang-oop-2/src/main/java/com/baeldung/relationships/university/Department.java

@@ -0,0 +1,9 @@
+package com.baeldung.relationships.university;
+
+import java.util.List;
+
+public class Department {
+
+    private List<Professor> professors;
+
+}

core-java-modules/core-java-lang-oop-2/src/main/java/com/baeldung/relationships/university/Professor.java

@@ -0,0 +1,10 @@
+package com.baeldung.relationships.university;
+
+import java.util.List;
+
+public class Professor {
+
+    private List<Department> department;
+    private List<Professor> friends;
+    
+}

core-java-modules/core-java-lang-oop-2/src/main/java/com/baeldung/relationships/university/University.java

@@ -0,0 +1,9 @@
+package com.baeldung.relationships.university;
+
+import java.util.List;
+
+public class University {
+
+    private List<Department> department;
+    
+}

core-java-modules/core-java-lang-oop/src/main/java/com/baeldung/constructors/BankAccount.java

@@ -54,3 +54,15 @@ class BankAccountCopyConstructor extends BankAccount {
         this.balance = 0.0f;
     }
 }
+
+class BankAccountChainedConstructors extends BankAccount {
+    public BankAccountChainedConstructors(String name, LocalDateTime opened, double balance) {
+        this.name = name;
+        this.opened = opened;
+        this.balance = balance;
+    }
+
+    public BankAccountChainedConstructors(String name) {
+        this(name, LocalDateTime.now(), 0.0f);
+    }
+}

core-java-modules/core-java-lang-oop/src/test/java/com/baeldung/constructors/ConstructorUnitTest.java

@@ -1,15 +1,14 @@
 package com.baeldung.constructors;
 
-import com.baeldung.constructors.*;
+import com.google.common.collect.Comparators;
+import org.junit.Test;
 
-import java.util.logging.Logger;
 import java.time.LocalDateTime;
 import java.time.Month;
+import java.util.ArrayList;
+import java.util.logging.Logger;
 
-import org.junit.Test;
+import static org.assertj.core.api.Assertions.*;
-import static org.assertj.core.api.Assertions.assertThat;
-import static org.assertj.core.api.Assertions.assertThatCode;
-import static org.assertj.core.api.Assertions.assertThatThrownBy;
 
 public class ConstructorUnitTest {
     final static Logger LOGGER = Logger.getLogger(ConstructorUnitTest.class.getName());
@@ -17,7 +16,9 @@ public class ConstructorUnitTest {
     @Test
     public void givenNoExplicitContructor_whenUsed_thenFails() {
         BankAccount account = new BankAccount();
-        assertThatThrownBy(() -> { account.toString(); }).isInstanceOf(Exception.class);
+        assertThatThrownBy(() -> {
+            account.toString();
+        }).isInstanceOf(Exception.class);
     }
 
     @Test
@@ -50,4 +51,13 @@ public class ConstructorUnitTest {
 
         assertThat(newAccount.getBalance()).isEqualTo(0.0f);
     }
+
+    @Test
+    public void givenChainedConstructor_whenUsed_thenMaintainsLogic() {
+        BankAccountChainedConstructors account = new BankAccountChainedConstructors("Tim");
+        BankAccountChainedConstructors newAccount = new BankAccountChainedConstructors("Tim", LocalDateTime.now(), 0.0f);
+
+        assertThat(account.getName()).isEqualTo(newAccount.getName());
+        assertThat(account.getBalance()).isEqualTo(newAccount.getBalance());
+    }
 }

core-java-modules/core-java-lang/README.md

@@ -18,7 +18,6 @@
 - [A Guide to Inner Interfaces in Java](http://www.baeldung.com/java-inner-interfaces)
 - [Recursion In Java](http://www.baeldung.com/java-recursion)
 - [A Guide to the finalize Method in Java](http://www.baeldung.com/java-finalize)
-- [A Guide to Java Enums](http://www.baeldung.com/a-guide-to-java-enums)
 - [Infinite Loops in Java](http://www.baeldung.com/infinite-loops-java)
 - [Quick Guide to java.lang.System](http://www.baeldung.com/java-lang-system)
 - [Using Java Assertions](http://www.baeldung.com/java-assert)

core-java-modules/core-java-networking-2/.gitignore

@@ -0,0 +1,25 @@
+*.class
+
+0.*
+
+#folders#
+/target
+/neoDb*
+/data
+/src/main/webapp/WEB-INF/classes
+*/META-INF/*
+.resourceCache
+
+# Packaged files #
+*.jar
+*.war
+*.ear
+
+# Files generated by integration tests
+backup-pom.xml
+/bin/
+/temp
+
+#IntelliJ specific
+.idea/
+*.iml

core-java-modules/core-java-networking-2/pom.xml

@@ -0,0 +1,20 @@
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <artifactId>core-java-networking-2</artifactId>
+    <name>core-java-networking-2</name>
+    <packaging>jar</packaging>
+
+    <parent>
+        <groupId>com.baeldung.core-java-modules</groupId>
+        <artifactId>core-java-modules</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+    </parent>
+
+    <dependencies>
+    </dependencies>
+
+    <build>
+        <finalName>core-java-networking-2</finalName>
+    </build>	
+</project>

core-java-modules/core-java-networking-2/src/main/java/com/baeldung/url/UrlChecker.java

@@ -0,0 +1,25 @@
+package com.baeldung.url;
+
+import java.io.IOException;
+import java.net.HttpURLConnection;
+import java.net.URL;
+
+public class UrlChecker {
+
+    public int getResponseCodeForURL(String address) throws IOException {
+        return getResponseCodeForURLUsing(address, "GET");
+    }
+
+    public int getResponseCodeForURLUsingHead(String address) throws IOException {
+        return getResponseCodeForURLUsing(address, "HEAD");
+    }
+
+    private int getResponseCodeForURLUsing(String address, String method) throws IOException {
+        HttpURLConnection.setFollowRedirects(false); // Set follow redirects to false
+        final URL url = new URL(address);
+        HttpURLConnection huc = (HttpURLConnection) url.openConnection();
+        huc.setRequestMethod(method);
+        return huc.getResponseCode();
+    }
+
+}

core-java-modules/core-java-networking-2/src/test/java/com/baeldung/url/UrlCheckerUnitTest.java

@@ -0,0 +1,39 @@
+package com.baeldung.url;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.io.IOException;
+
+import org.junit.Test;
+
+public class UrlCheckerUnitTest {
+
+    @Test
+    public void givenValidUrl_WhenUsingHEAD_ThenReturn200() throws IOException {
+        UrlChecker tester = new UrlChecker();
+        int responseCode = tester.getResponseCodeForURLUsingHead("http://www.example.com");
+        assertEquals(200, responseCode);
+    }
+    
+    @Test
+    public void givenInvalidIUrl_WhenUsingHEAD_ThenReturn404() throws IOException {
+        UrlChecker tester = new UrlChecker();
+        int responseCode = tester.getResponseCodeForURLUsingHead("http://www.example.com/unkownurl");
+        assertEquals(404, responseCode);
+    }
+    
+    @Test
+    public void givenValidUrl_WhenUsingGET_ThenReturn200() throws IOException {
+        UrlChecker tester = new UrlChecker();
+        int responseCode = tester.getResponseCodeForURL("http://www.example.com");
+        assertEquals(200, responseCode);
+    }
+    
+    @Test
+    public void givenInvalidIUrl_WhenUsingGET_ThenReturn404() throws IOException {
+        UrlChecker tester = new UrlChecker();
+        int responseCode = tester.getResponseCodeForURL("http://www.example.com/unkownurl");
+        assertEquals(404, responseCode);
+    }
+    
+}

core-java-modules/core-java-os/src/main/java/com/baeldung/core/pwd/CurrentDirectoryFetcher.java

@@ -0,0 +1,40 @@
+package com.baeldung.core.pwd;
+
+import java.io.File;
+import java.nio.file.FileSystems;
+import java.nio.file.Paths;
+
+public final class CurrentDirectoryFetcher {
+
+    public static void main(String[] args) {
+        System.out.printf("Current Directory Using Java System API: %s%n", currentDirectoryUsingSystemProperties());
+
+        System.out.printf("Current Directory Using Java IO File API: %s%n", currentDirectoryUsingFile());
+
+        System.out.printf("Current Directory Using Java NIO FileSystems API: %s%n", currentDirectoryUsingFileSystems());
+
+        System.out.printf("Current Directory Using Java NIO Paths API: %s%n", currentDirectoryUsingPaths());
+    }
+
+    public static String currentDirectoryUsingSystemProperties() {
+        return System.getProperty("user.dir");
+    }
+
+    public static String currentDirectoryUsingPaths() {
+        return Paths.get("")
+            .toAbsolutePath()
+            .toString();
+    }
+
+    public static String currentDirectoryUsingFileSystems() {
+        return FileSystems.getDefault()
+            .getPath("")
+            .toAbsolutePath()
+            .toString();
+    }
+
+    public static String currentDirectoryUsingFile() {
+        return new File("").getAbsolutePath();
+    }
+
+}

core-java-modules/core-java-os/src/test/java/com/baeldung/core/pwd/CurrentDirectoryFetcherTest.java

@@ -0,0 +1,34 @@
+package com.baeldung.core.pwd;
+
+import static org.junit.Assert.assertTrue;
+
+import org.junit.Test;
+
+public class CurrentDirectoryFetcherTest {
+
+    private static final String CURRENT_DIR = "core-java-os";
+
+    @Test
+    public void whenUsingSystemProperties_thenReturnCurrentDirectory() {
+        assertTrue(CurrentDirectoryFetcher.currentDirectoryUsingSystemProperties()
+            .endsWith(CURRENT_DIR));
+    }
+
+    @Test
+    public void whenUsingJavaNioPaths_thenReturnCurrentDirectory() {
+        assertTrue(CurrentDirectoryFetcher.currentDirectoryUsingPaths()
+            .endsWith(CURRENT_DIR));
+    }
+
+    @Test
+    public void whenUsingJavaNioFileSystems_thenReturnCurrentDirectory() {
+        assertTrue(CurrentDirectoryFetcher.currentDirectoryUsingFileSystems()
+            .endsWith(CURRENT_DIR));
+    }
+
+    @Test
+    public void whenUsingJavaIoFile_thenReturnCurrentDirectory() {
+        assertTrue(CurrentDirectoryFetcher.currentDirectoryUsingFile()
+            .endsWith(CURRENT_DIR));
+    }
+}

core-java-modules/core-java-security/src/main/java/com/baeldung/sasl/ClientCallbackHandler.java

@@ -0,0 +1,29 @@
+package com.baeldung.sasl;
+
+import java.io.IOException;
+
+import javax.security.auth.callback.Callback;
+import javax.security.auth.callback.CallbackHandler;
+import javax.security.auth.callback.NameCallback;
+import javax.security.auth.callback.PasswordCallback;
+import javax.security.auth.callback.UnsupportedCallbackException;
+import javax.security.sasl.RealmCallback;
+
+public class ClientCallbackHandler implements CallbackHandler {
+
+    @Override
+    public void handle(Callback[] cbs) throws IOException, UnsupportedCallbackException {
+        for (Callback cb : cbs) {
+            if (cb instanceof NameCallback) {
+                NameCallback nc = (NameCallback) cb;
+                nc.setName("username");
+            } else if (cb instanceof PasswordCallback) {
+                PasswordCallback pc = (PasswordCallback) cb;
+                pc.setPassword("password".toCharArray());
+            } else if (cb instanceof RealmCallback) {
+                RealmCallback rc = (RealmCallback) cb;
+                rc.setText("myServer");
+            }
+        }
+    }
+}

core-java-modules/core-java-security/src/main/java/com/baeldung/sasl/ServerCallbackHandler.java

@@ -0,0 +1,34 @@
+package com.baeldung.sasl;
+
+import java.io.IOException;
+
+import javax.security.auth.callback.Callback;
+import javax.security.auth.callback.CallbackHandler;
+import javax.security.auth.callback.NameCallback;
+import javax.security.auth.callback.PasswordCallback;
+import javax.security.auth.callback.UnsupportedCallbackException;
+import javax.security.sasl.AuthorizeCallback;
+import javax.security.sasl.RealmCallback;
+
+public class ServerCallbackHandler implements CallbackHandler {
+
+    @Override
+    public void handle(Callback[] cbs) throws IOException, UnsupportedCallbackException {
+        for (Callback cb : cbs) {
+            if (cb instanceof AuthorizeCallback) {
+                AuthorizeCallback ac = (AuthorizeCallback) cb;
+                ac.setAuthorized(true);
+            } else if (cb instanceof NameCallback) {
+                NameCallback nc = (NameCallback) cb;
+                nc.setName("username");
+
+            } else if (cb instanceof PasswordCallback) {
+                PasswordCallback pc = (PasswordCallback) cb;
+                pc.setPassword("password".toCharArray());
+            } else if (cb instanceof RealmCallback) {
+                RealmCallback rc = (RealmCallback) cb;
+                rc.setText("myServer");
+            }
+        }
+    }
+}

core-java-modules/core-java-security/src/test/java/com/baeldung/sasl/SaslUnitTest.java

@@ -0,0 +1,76 @@
+package com.baeldung.sasl;
+
+import static org.junit.Assert.assertTrue;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.nio.charset.StandardCharsets;
+import java.util.HashMap;
+import java.util.Map;
+
+import javax.security.sasl.Sasl;
+import javax.security.sasl.SaslClient;
+import javax.security.sasl.SaslException;
+import javax.security.sasl.SaslServer;
+
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+
+public class SaslUnitTest {
+
+    private static final String MECHANISM = "DIGEST-MD5";
+    private static final String SERVER_NAME = "myServer";
+    private static final String PROTOCOL = "myProtocol";
+    private static final String AUTHORIZATION_ID = null;
+    private static final String QOP_LEVEL = "auth-conf";
+
+    private SaslServer saslServer;
+    private SaslClient saslClient;
+
+    @Before
+    public void setUp() throws SaslException {
+
+        ServerCallbackHandler serverHandler = new ServerCallbackHandler();
+        ClientCallbackHandler clientHandler = new ClientCallbackHandler();
+
+        Map<String, String> props = new HashMap<>();
+        props.put(Sasl.QOP, QOP_LEVEL);
+
+        saslServer = Sasl.createSaslServer(MECHANISM, PROTOCOL, SERVER_NAME, props, serverHandler);
+        saslClient = Sasl.createSaslClient(new String[] { MECHANISM }, AUTHORIZATION_ID, PROTOCOL, SERVER_NAME, props, clientHandler);
+
+    }
+
+    @Test
+    public void givenHandlers_whenStarted_thenAutenticationWorks() throws SaslException {
+
+        byte[] challenge;
+        byte[] response;
+
+        challenge = saslServer.evaluateResponse(new byte[0]);
+        response = saslClient.evaluateChallenge(challenge);
+
+        challenge = saslServer.evaluateResponse(response);
+        response = saslClient.evaluateChallenge(challenge);
+
+        assertTrue(saslServer.isComplete());
+        assertTrue(saslClient.isComplete());
+
+        String qop = (String) saslClient.getNegotiatedProperty(Sasl.QOP);
+        assertEquals("auth-conf", qop);
+
+        byte[] outgoing = "Baeldung".getBytes();
+        byte[] secureOutgoing = saslClient.wrap(outgoing, 0, outgoing.length);
+
+        byte[] secureIncoming = secureOutgoing;
+        byte[] incoming = saslServer.unwrap(secureIncoming, 0, secureIncoming.length);
+        assertEquals("Baeldung", new String(incoming, StandardCharsets.UTF_8));
+    }
+
+    @After
+    public void tearDown() throws SaslException {
+        saslClient.dispose();
+        saslServer.dispose();
+    }
+
+}

core-java-modules/core-java/README.md

@@ -37,7 +37,6 @@
 - [Common Java Exceptions](http://www.baeldung.com/java-common-exceptions)
 - [Throw Exception in Optional in Java 8](https://www.baeldung.com/java-optional-throw-exception)
 - [Merging java.util.Properties Objects](https://www.baeldung.com/java-merging-properties)
-- [Merging java.util.Properties Objects](https://www.baeldung.com/java-merging-properties)
 - [Java – Try with Resources](https://www.baeldung.com/java-try-with-resources)
 - [Abstract Classes in Java](https://www.baeldung.com/java-abstract-class)
 - [Guide to Character Encoding](https://www.baeldung.com/java-char-encoding)

core-java-modules/multimodulemavenproject/README.md

@@ -0,0 +1,3 @@
+## Relevant Articles
+
+- [Multi-Module Maven Application with Java Modules](https://www.baeldung.com/maven-multi-module-project-java-jpms)

core-java-modules/pom.xml

@@ -17,6 +17,7 @@
         <module>pre-jpms</module>
         <module>core-java-exceptions</module>
         <module>core-java-optional</module>
+        <module>core-java-networking-2</module>
     </modules>
     
 </project>

custom-pmd/src/main/java/org/baeldung/pmd/UnitTestNamingConventionRule.java

@@ -22,6 +22,10 @@ public class UnitTestNamingConventionRule extends AbstractJavaRule {
         String className = node.getImage();
         Objects.requireNonNull(className);
 
+        if (className.endsWith("SpringContextTest")) {
+            return data;
+        }
+        
         if (className.endsWith("Tests")
                 || (className.endsWith("Test") && allowedEndings.stream().noneMatch(className::endsWith))) {
             addViolation(data, node);

data-structures/src/main/java/com/baeldung/graph/Graph.java

@@ -0,0 +1,72 @@
+package com.baeldung.graph;
+
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Stack;
+
+public class Graph {
+
+    private Map<Integer, List<Integer>> adjVertices;
+
+    public Graph() {
+        this.adjVertices = new HashMap<Integer, List<Integer>>();
+    }
+
+    public void addVertex(int vertex) {
+        adjVertices.putIfAbsent(vertex, new ArrayList<>());
+    }
+
+    public void addEdge(int src, int dest) {
+        adjVertices.get(src).add(dest);
+    }
+
+    public void dfsWithoutRecursion(int start) {
+        Stack<Integer> stack = new Stack<Integer>();
+        boolean[] isVisited = new boolean[adjVertices.size()];
+        stack.push(start);
+        while (!stack.isEmpty()) {
+            int current = stack.pop();
+            isVisited[current] = true;
+            System.out.print(" " + current);
+            for (int dest : adjVertices.get(current)) {
+                if (!isVisited[dest])
+                    stack.push(dest);
+            }
+        }
+    }
+
+    public void dfs(int start) {
+        boolean[] isVisited = new boolean[adjVertices.size()];
+        dfsRecursive(start, isVisited);
+    }
+
+    private void dfsRecursive(int current, boolean[] isVisited) {
+        isVisited[current] = true;
+        System.out.print(" " + current);
+        for (int dest : adjVertices.get(current)) {
+            if (!isVisited[dest])
+                dfsRecursive(dest, isVisited);
+        }
+    }
+
+    public void topologicalSort(int start) {
+        Stack<Integer> result = new Stack<Integer>();
+        boolean[] isVisited = new boolean[adjVertices.size()];
+        topologicalSortRecursive(start, isVisited, result);
+        while (!result.isEmpty()) {
+            System.out.print(" " + result.pop());
+        }
+    }
+
+    private void topologicalSortRecursive(int current, boolean[] isVisited, Stack<Integer> result) {
+        isVisited[current] = true;
+        for (int dest : adjVertices.get(current)) {
+            if (!isVisited[dest])
+                topologicalSortRecursive(dest, isVisited, result);
+        }
+        result.push(current);
+    }
+
+}

data-structures/src/main/java/com/baeldung/tree/BinaryTree.java

@@ -2,6 +2,7 @@ package com.baeldung.tree;
 
 import java.util.LinkedList;
 import java.util.Queue;
+import java.util.Stack;
 
 public class BinaryTree {
 
@@ -147,6 +148,68 @@ public class BinaryTree {
         }
     }
 
+    
+    public void traverseInOrderWithoutRecursion() {
+        Stack<Node> stack = new Stack<Node>();
+        Node current = root;
+        stack.push(root);
+        while(! stack.isEmpty()) {
+            while(current.left != null) {
+                current = current.left;                
+                stack.push(current);                
+            }
+            current = stack.pop();
+            System.out.print(" " + current.value);
+            if(current.right != null) {
+                current = current.right;                
+                stack.push(current);
+            }
+        }
+    }
+    
+    public void traversePreOrderWithoutRecursion() {
+        Stack<Node> stack = new Stack<Node>();
+        Node current = root;
+        stack.push(root);
+        while(! stack.isEmpty()) {
+            current = stack.pop();
+            System.out.print(" " + current.value);
+            
+            if(current.right != null)
+                stack.push(current.right);
+                
+            if(current.left != null)
+                stack.push(current.left);
+        }        
+    }
+    
+    public void traversePostOrderWithoutRecursion() {
+        Stack<Node> stack = new Stack<Node>();
+        Node prev = root;
+        Node current = root;
+        stack.push(root);
+
+        while (!stack.isEmpty()) {
+            current = stack.peek();
+            boolean hasChild = (current.left != null || current.right != null);
+            boolean isPrevLastChild = (prev == current.right || (prev == current.left && current.right == null));
+
+            if (!hasChild || isPrevLastChild) {
+                current = stack.pop();
+                System.out.print(" " + current.value);
+                prev = current;
+            } else {
+                if (current.right != null) {
+                    stack.push(current.right);
+                }
+                if (current.left != null) {
+                    stack.push(current.left);
+                }
+            }
+        }   
+    }    
+    
+    
     class Node {
         int value;
         Node left;

data-structures/src/test/java/com/baeldung/graph/GraphUnitTest.java

@@ -0,0 +1,37 @@
+package com.baeldung.graph;
+
+import org.junit.Test;
+
+public class GraphUnitTest {
+
+    @Test
+    public void givenDirectedGraph_whenDFS_thenPrintAllValues() {
+        Graph graph = createDirectedGraph();
+        graph.dfs(0);
+        System.out.println();
+        graph.dfsWithoutRecursion(0);
+    }
+
+    @Test
+    public void givenDirectedGraph_whenGetTopologicalSort_thenPrintValuesSorted() {
+        Graph graph = createDirectedGraph();
+        graph.topologicalSort(0);
+    }
+
+    private Graph createDirectedGraph() {
+        Graph graph = new Graph();
+        graph.addVertex(0);
+        graph.addVertex(1);
+        graph.addVertex(2);
+        graph.addVertex(3);
+        graph.addVertex(4);
+        graph.addVertex(5);
+        graph.addEdge(0, 1);
+        graph.addEdge(0, 2);
+        graph.addEdge(1, 3);
+        graph.addEdge(2, 3);
+        graph.addEdge(3, 4);
+        graph.addEdge(4, 5);
+        return graph;
+    }
+}

data-structures/src/test/java/com/baeldung/tree/BinaryTreeUnitTest.java

@@ -87,6 +87,8 @@ public class BinaryTreeUnitTest {
         BinaryTree bt = createBinaryTree();
 
         bt.traverseInOrder(bt.root);
+        System.out.println();
+        bt.traverseInOrderWithoutRecursion();
     }
 
     @Test
@@ -95,6 +97,8 @@ public class BinaryTreeUnitTest {
         BinaryTree bt = createBinaryTree();
 
         bt.traversePreOrder(bt.root);
+        System.out.println();
+        bt.traversePreOrderWithoutRecursion();
     }
 
     @Test
@@ -103,6 +107,8 @@ public class BinaryTreeUnitTest {
         BinaryTree bt = createBinaryTree();
 
         bt.traversePostOrder(bt.root);
+        System.out.println();
+        bt.traversePostOrderWithoutRecursion();
     }
 
     @Test

jackson-simple/src/test/java/com/baeldung/jackson/test/JacksonSerializationIgnoreUnitTest.java

@@ -165,7 +165,7 @@ public class JacksonSerializationIgnoreUnitTest {
     }
 
     @Test
-    public final void givenIgnoringNullFieldsOnClass_whenWritingObjectWithNullField_thenFieldIsIgnored() throws JsonProcessingException {
+    public final void givenNullsIgnoredOnClass_whenWritingObjectWithNullField_thenIgnored() throws JsonProcessingException {
         final ObjectMapper mapper = new ObjectMapper();
         final MyDtoIgnoreNull dtoObject = new MyDtoIgnoreNull();
 
@@ -178,7 +178,7 @@ public class JacksonSerializationIgnoreUnitTest {
     }
 
     @Test
-    public final void givenIgnoringNullFieldsGlobally_whenWritingObjectWithNullField_thenIgnored() throws JsonProcessingException {
+    public final void givenNullsIgnoredGlobally_whenWritingObjectWithNullField_thenIgnored() throws JsonProcessingException {
         final ObjectMapper mapper = new ObjectMapper();
         mapper.setSerializationInclusion(Include.NON_NULL);
         final MyDto dtoObject = new MyDto();

java-numbers-2/src/main/java/com/baeldung/binarynumbers/BinaryNumbers.java

@@ -0,0 +1,148 @@
+package com.baeldung.binarynumbers;
+
+public class BinaryNumbers {
+
+    /**
+     * This method takes a decimal number and convert it into a binary number.
+     * example:- input:10, output:1010
+     *
+     * @param decimalNumber
+     * @return binary number
+     */
+    public Integer convertDecimalToBinary(Integer decimalNumber) {
+
+        if (decimalNumber == 0) {
+            return decimalNumber;
+        }
+
+        StringBuilder binaryNumber = new StringBuilder();
+
+        while (decimalNumber > 0) {
+
+            int remainder = decimalNumber % 2;
+            int result = decimalNumber / 2;
+
+            binaryNumber.append(remainder);
+            decimalNumber = result;
+        }
+
+        binaryNumber = binaryNumber.reverse();
+
+        return Integer.valueOf(binaryNumber.toString());
+    }
+
+    /**
+     * This method takes a binary number and convert it into a decimal number.
+     * example:- input:101, output:5
+     *
+     * @param binary number
+     * @return decimal Number
+     */
+    public Integer convertBinaryToDecimal(Integer binaryNumber) {
+
+        Integer result = 0;
+        Integer base = 1;
+
+        while (binaryNumber > 0) {
+
+            int lastDigit = binaryNumber % 10;
+            binaryNumber = binaryNumber / 10;
+
+            result += lastDigit * base;
+
+            base = base * 2;
+        }
+        return result;
+    }
+
+    /**
+     * This method accepts two binary numbers and returns sum of input numbers.
+     * Example:- firstNum: 101, secondNum: 100, output: 1001
+     *
+     * @param firstNum
+     * @param secondNum
+     * @return addition of input numbers
+     */
+    public Integer addBinaryNumber(Integer firstNum, Integer secondNum) {
+
+        StringBuilder output = new StringBuilder();
+
+        int carry = 0;
+        int temp;
+
+        while (firstNum != 0 || secondNum != 0) {
+
+            temp = (firstNum % 10 + secondNum % 10 + carry) % 2;
+            output.append(temp);
+
+            carry = (firstNum % 10 + secondNum % 10 + carry) / 2;
+
+            firstNum = firstNum / 10;
+            secondNum = secondNum / 10;
+        }
+
+        if (carry != 0) {
+            output.append(carry);
+        }
+
+        return Integer.valueOf(output.reverse()
+            .toString());
+    }
+
+    /**
+    * This method takes two binary number as input and subtract second number from the first number.
+    * example:- firstNum: 1000, secondNum: 11, output: 101
+    * @param firstNum
+    * @param secondNum
+    * @return Result of subtraction of secondNum from first
+    */
+    public Integer substractBinaryNumber(Integer firstNum, Integer secondNum) {
+
+        int onesComplement = Integer.valueOf(getOnesComplement(secondNum));
+
+        StringBuilder output = new StringBuilder();
+
+        int carry = 0;
+        int temp;
+
+        while (firstNum != 0 || onesComplement != 0) {
+
+            temp = (firstNum % 10 + onesComplement % 10 + carry) % 2;
+            output.append(temp);
+
+            carry = (firstNum % 10 + onesComplement % 10 + carry) / 2;
+
+            firstNum = firstNum / 10;
+            onesComplement = onesComplement / 10;
+        }
+
+        String additionOfFirstNumAndOnesComplement = output.reverse()
+            .toString();
+
+        if (carry == 1) {
+            return addBinaryNumber(Integer.valueOf(additionOfFirstNumAndOnesComplement), carry);
+        } else {
+            return getOnesComplement(Integer.valueOf(additionOfFirstNumAndOnesComplement));
+        }
+
+    }
+
+    public Integer getOnesComplement(Integer num) {
+
+        StringBuilder onesComplement = new StringBuilder();
+
+        while (num > 0) {
+            int lastDigit = num % 10;
+            if (lastDigit == 0) {
+                onesComplement.append(1);
+            } else {
+                onesComplement.append(0);
+            }
+            num = num / 10;
+        }
+
+        return Integer.valueOf(onesComplement.reverse()
+            .toString());
+    }
+
+}

java-numbers-2/src/test/java/com/baeldung/binarynumbers/BinaryNumbersUnitTest.java

@@ -0,0 +1,73 @@
+package com.baeldung.binarynumbers;
+
+import static org.junit.Assert.assertEquals;
+
+import org.junit.Test;
+
+public class BinaryNumbersUnitTest {
+
+    private BinaryNumbers binaryNumbers = new BinaryNumbers();
+
+    @Test
+    public void given_decimalNumber_then_returnBinaryNumber() {
+        assertEquals(Integer.valueOf(1000), binaryNumbers.convertDecimalToBinary(8));
+        assertEquals(Integer.valueOf(10100), binaryNumbers.convertDecimalToBinary(20));
+    }
+
+    @Test
+    public void given_decimalNumber_then_convertToBinaryNumber() {
+        assertEquals("1000", Integer.toBinaryString(8));
+        assertEquals("10100", Integer.toBinaryString(20));
+    }
+
+    @Test
+    public void given_binaryNumber_then_ConvertToDecimalNumber() {
+        assertEquals(8, Integer.parseInt("1000", 2));
+        assertEquals(20, Integer.parseInt("10100", 2));
+    }
+
+    @Test
+    public void given_binaryNumber_then_returnDecimalNumber() {
+        assertEquals(Integer.valueOf(8), binaryNumbers.convertBinaryToDecimal(1000));
+        assertEquals(Integer.valueOf(20), binaryNumbers.convertBinaryToDecimal(10100));
+    }
+
+    @Test
+    public void given_twoBinaryNumber_then_returnAddition() {
+        // adding 4 and 10
+        assertEquals(Integer.valueOf(1110), binaryNumbers.addBinaryNumber(100, 1010));
+
+        // adding 26 and 14
+        assertEquals(Integer.valueOf(101000), binaryNumbers.addBinaryNumber(11010, 1110));
+    }
+
+    @Test
+    public void given_twoBinaryNumber_then_returnSubtraction() {
+        // subtracting 16 from 25
+        assertEquals(Integer.valueOf(1001), binaryNumbers.substractBinaryNumber(11001, 10000));
+
+        // subtracting 29 from 16, the output here is negative
+        assertEquals(Integer.valueOf(1101), binaryNumbers.substractBinaryNumber(10000, 11101));
+    }
+
+    @Test
+    public void given_binaryLiteral_thenReturnDecimalValue() {
+
+        byte five = 0b101;
+        assertEquals((byte) 5, five);
+
+        short three = 0b11;
+        assertEquals((short) 3, three);
+
+        int nine = 0B1001;
+        assertEquals(9, nine);
+
+        long twentyNine = 0B11101;
+        assertEquals(29, twentyNine);
+
+        int minusThirtySeven = -0B100101;
+        assertEquals(-37, minusThirtySeven);
+
+    }
+
+}

java-strings-2/src/test/java/com/baeldung/string/changecase/ToLowerCaseUnitTest.java

@@ -0,0 +1,29 @@
+package com.baeldung.string.changecase;
+
+import static org.junit.Assert.assertEquals;
+
+import java.util.Locale;
+
+import org.junit.Test;
+
+public class ToLowerCaseUnitTest {
+
+    private static final Locale TURKISH = new Locale("tr");
+    private String name = "John Doe";
+    private String foreignUppercase = "\u0049";
+
+    @Test
+    public void givenMixedCaseString_WhenToLowerCase_ThenResultIsLowerCase() {
+        assertEquals("john doe", name.toLowerCase());
+    }
+
+    @Test
+    public void givenForeignString_WhenToLowerCaseWithoutLocale_ThenResultIsLowerCase() {
+        assertEquals("\u0069", foreignUppercase.toLowerCase());
+    }
+
+    @Test
+    public void givenForeignString_WhenToLowerCaseWithLocale_ThenResultIsLowerCase() {
+        assertEquals("\u0131", foreignUppercase.toLowerCase(TURKISH));
+    }
+}

java-strings-2/src/test/java/com/baeldung/string/changecase/ToUpperCaseUnitTest.java

@@ -0,0 +1,29 @@
+package com.baeldung.string.changecase;
+
+import static org.junit.Assert.assertEquals;
+
+import java.util.Locale;
+
+import org.junit.Test;
+
+public class ToUpperCaseUnitTest {
+
+    private static final Locale TURKISH = new Locale("tr");
+    private String name = "John Doe";
+    private String foreignLowercase = "\u0069";
+
+    @Test
+    public void givenMixedCaseString_WhenToUpperCase_ThenResultIsUpperCase() {
+        assertEquals("JOHN DOE", name.toUpperCase());
+    }
+
+    @Test
+    public void givenForeignString_WhenToUpperCaseWithoutLocale_ThenResultIsUpperCase() {
+        assertEquals("\u0049", foreignLowercase.toUpperCase());
+    }
+
+    @Test
+    public void givenForeignString_WhenToUpperCaseWithLocale_ThenResultIsUpperCase() {
+        assertEquals("\u0130", foreignLowercase.toUpperCase(TURKISH));
+    }
+}

java-strings-2/src/test/java/com/baeldung/string/multiline/MultiLineStringUnitTest.java

@@ -1,4 +1,4 @@
-package com.baeldung.string;
+package com.baeldung.string.multiline;
 
 import org.junit.Test;
 import static org.junit.Assert.assertEquals;

java-strings-2/src/test/java/com/baeldung/string/todouble/StringToDoubleConversionUnitTest.java

@@ -0,0 +1,56 @@
+package com.baeldung.string.todouble;
+
+import static org.junit.Assert.assertEquals;
+
+import java.text.DecimalFormat;
+import java.text.ParseException;
+
+import org.junit.Test;
+
+public class StringToDoubleConversionUnitTest {
+
+    @Test
+    public void givenValidString_WhenParseDouble_ThenResultIsPrimitiveDouble() {
+        assertEquals(1.23, Double.parseDouble("1.23"), 0.000001);
+    }
+    
+    @Test(expected = NullPointerException.class)
+    public void givenNullString_WhenParseDouble_ThenNullPointerExceptionIsThrown() {
+        Double.parseDouble(null);
+    }
+    
+    @Test(expected = NumberFormatException.class)
+    public void givenInalidString_WhenParseDouble_ThenNumberFormatExceptionIsThrown() {
+        Double.parseDouble("&");
+    }
+    
+    @Test
+    public void givenValidString_WhenValueOf_ThenResultIsPrimitiveDouble() {
+        assertEquals(1.23, Double.valueOf("1.23"), 0.000001);
+    }
+    
+    @Test(expected = NullPointerException.class)
+    public void givenNullString_WhenValueOf_ThenNullPointerExceptionIsThrown() {
+        Double.valueOf(null);
+    }
+    
+    @Test(expected = NumberFormatException.class)
+    public void givenInalidString_WhenValueOf_ThenNumberFormatExceptionIsThrown() {
+        Double.valueOf("&");
+    }
+    
+    @Test
+    public void givenValidString_WhenDecimalFormat_ThenResultIsValidDouble() throws ParseException {
+        assertEquals(1.23, new DecimalFormat("#").parse("1.23").doubleValue(), 0.000001);
+    }
+    
+    @Test(expected = NullPointerException.class)
+    public void givenNullString_WhenDecimalFormat_ThenNullPointerExceptionIsThrown() throws ParseException {
+        new DecimalFormat("#").parse(null);
+    }
+    
+    @Test(expected = ParseException.class)
+    public void givenInvalidString_WhenDecimalFormat_ThenParseExceptionIsThrown() throws ParseException {
+        new DecimalFormat("#").parse("&");
+    }
+}

javaxval/src/main/java/org/baeldung/javabeanconstraints/bigdecimal/Invoice.java

@@ -0,0 +1,19 @@
+package org.baeldung.javabeanconstraints.bigdecimal;
+
+import java.math.BigDecimal;
+
+import javax.validation.constraints.DecimalMin;
+import javax.validation.constraints.Digits;
+
+public class Invoice {
+	
+	@DecimalMin(value = "0.0", inclusive = false)
+	@Digits(integer=3, fraction=2)
+    private BigDecimal price;
+    private String description;
+    
+	public Invoice(BigDecimal price, String description) {
+		this.price = price;
+		this.description = description;
+	}
+}

javaxval/src/test/java/org/baeldung/javabeanconstraints/bigdecimal/InvoiceUnitTest.java

@@ -0,0 +1,62 @@
+package org.baeldung.javabeanconstraints.bigdecimal;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.math.BigDecimal;
+import java.util.Set;
+
+import javax.validation.ConstraintViolation;
+import javax.validation.Validation;
+import javax.validation.Validator;
+
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+public class InvoiceUnitTest {
+	
+	private static Validator validator;
+
+    @BeforeClass
+    public static void setupValidatorInstance() {
+        validator = Validation.buildDefaultValidatorFactory().getValidator();
+    }
+    
+    @Test
+    public void whenPriceIntegerDigitLessThanThreeWithDecimalValue_thenShouldGiveConstraintViolations() {
+    	Invoice invoice = new Invoice(new BigDecimal(10.21), "Book purchased");
+        Set<ConstraintViolation<Invoice>> violations = validator.validate(invoice);
+        assertThat(violations.size()).isEqualTo(1);
+        violations.forEach(action-> assertThat(action.getMessage()).isEqualTo("numeric value out of bounds (<3 digits>.<2 digits> expected)"));
+    }
+    
+    @Test
+    public void whenPriceIntegerDigitLessThanThreeWithIntegerValue_thenShouldNotGiveConstraintViolations() {
+    	Invoice invoice = new Invoice(new BigDecimal(10), "Book purchased");
+        Set<ConstraintViolation<Invoice>> violations = validator.validate(invoice);
+        assertThat(violations.size()).isEqualTo(0);
+    }
+    
+    @Test
+    public void whenPriceIntegerDigitGreaterThanThree_thenShouldGiveConstraintViolations() {
+    	Invoice invoice = new Invoice(new BigDecimal(1021.21), "Book purchased");
+        Set<ConstraintViolation<Invoice>> violations = validator.validate(invoice);
+        assertThat(violations.size()).isEqualTo(1);
+        violations.forEach(action-> assertThat(action.getMessage()).isEqualTo("numeric value out of bounds (<3 digits>.<2 digits> expected)"));
+    }
+    
+    @Test
+    public void whenPriceIsZero_thenShouldGiveConstraintViolations() {
+    	Invoice invoice = new Invoice(new BigDecimal(000.00), "Book purchased");
+        Set<ConstraintViolation<Invoice>> violations = validator.validate(invoice);
+        assertThat(violations.size()).isEqualTo(1);
+        violations.forEach(action-> assertThat(action.getMessage()).isEqualTo("must be greater than 0.0"));
+    }
+    
+    @Test
+    public void whenPriceIsGreaterThanZero_thenShouldNotGiveConstraintViolations() {
+    	Invoice invoice = new Invoice(new BigDecimal(100.50), "Book purchased");
+        Set<ConstraintViolation<Invoice>> violations = validator.validate(invoice);
+        assertThat(violations.size()).isEqualTo(0);
+    }
+
+}

jhipster/README.md

@@ -1,6 +0,0 @@
-## Relevant articles:
-
-- [JHipster with a Microservice Architecture](http://www.baeldung.com/jhipster-microservices)
-- [Intro to JHipster](http://www.baeldung.com/jhipster)
-- [Building a Basic UAA-Secured JHipster Microservice](https://www.baeldung.com/jhipster-uaa-secured-micro-service)
-- [Creating New Roles and Authorities in JHipster](https://www.baeldung.com/jhipster-new-roles)

jhipster/jhipster-microservice/README.md

@@ -0,0 +1,3 @@
+## Relevant Articles
+
+- [JHipster with a Microservice Architecture](https://www.baeldung.com/jhipster-microservices)

jhipster/jhipster-monolithic/README.md

@@ -1,4 +1,6 @@
-### Relevant articles
+## Relevant Articles
+
+- [Intro to JHipster](https://www.baeldung.com/jhipster)
 
 
 # baeldung

jhipster/jhipster-uaa/README.md

@@ -0,0 +1,3 @@
+## Relevant Articles
+
+- [Building a Basic UAA-Secured JHipster Microservice](https://www.baeldung.com/jhipster-uaa-secured-micro-service)

libraries-io/README.md

@@ -0,0 +1,5 @@
+
+### Relevant Articles: 
+
+- [Transferring a File Through SFTP in Java](https://www.baeldung.com/java-file-sftp)
+

libraries-io/pom.xml

@@ -0,0 +1,40 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <artifactId>libraries-io</artifactId>
+    <name>libraries-io</name>
+
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-modules</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+    </parent>
+
+    <dependencies>
+        <!-- sftp file transfer -->
+        <dependency>
+            <groupId>com.jcraft</groupId>
+            <artifactId>jsch</artifactId>
+            <version>${jsch.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>com.hierynomus</groupId>
+            <artifactId>sshj</artifactId>
+            <version>${sshj.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-vfs2</artifactId>
+            <version>${vfs.version}</version>
+        </dependency>
+    </dependencies>
+
+    <properties>
+        <!-- sftp -->
+        <jsch.version>0.1.55</jsch.version>
+        <sshj.version>0.27.0</sshj.version>
+        <vfs.version>2.4</vfs.version>
+    </properties>
+</project>

libraries-io/src/main/resources/input.txt

@@ -0,0 +1 @@
+This is a sample text content

libraries-io/src/test/java/org/baeldung/java/io/remote/SftpFileTransferLiveTest.java

@@ -0,0 +1,106 @@
+package org.baeldung.java.io.remote;
+
+import java.io.IOException;
+
+import org.apache.commons.vfs2.FileObject;
+import org.apache.commons.vfs2.FileSystemManager;
+import org.apache.commons.vfs2.Selectors;
+import org.apache.commons.vfs2.VFS;
+import org.junit.Test;
+
+import com.jcraft.jsch.ChannelSftp;
+import com.jcraft.jsch.JSch;
+import com.jcraft.jsch.JSchException;
+import com.jcraft.jsch.Session;
+import com.jcraft.jsch.SftpException;
+
+import net.schmizz.sshj.SSHClient;
+import net.schmizz.sshj.sftp.SFTPClient;
+import net.schmizz.sshj.transport.verification.PromiscuousVerifier;
+
+public class SftpFileTransferLiveTest {
+
+    private String remoteHost = "HOST_NAME_HERE";
+    private String username = "USERNAME_HERE";
+    private String password = "PASSWORD_HERE";
+    private String localFile = "src/main/resources/input.txt";
+    private String remoteFile = "welcome.txt";
+    private String localDir = "src/main/resources/";
+    private String remoteDir = "remote_sftp_test/";
+    private String knownHostsFileLoc = "/Users/USERNAME/known_hosts_sample";
+
+    @Test
+    public void whenUploadFileUsingJsch_thenSuccess() throws JSchException, SftpException {
+        ChannelSftp channelSftp = setupJsch();
+        channelSftp.connect();
+        channelSftp.put(localFile, remoteDir + "jschFile.txt");
+        channelSftp.exit();
+    }
+
+    @Test
+    public void whenDownloadFileUsingJsch_thenSuccess() throws JSchException, SftpException {
+        ChannelSftp channelSftp = setupJsch();
+        channelSftp.connect();
+        channelSftp.get(remoteFile, localDir + "jschFile.txt");
+        channelSftp.exit();
+    }
+
+    @Test
+    public void whenUploadFileUsingSshj_thenSuccess() throws IOException {
+        SSHClient sshClient = setupSshj();
+        SFTPClient sftpClient = sshClient.newSFTPClient();
+        sftpClient.put(localFile, remoteDir + "sshjFile.txt");
+        sftpClient.close();
+        sshClient.disconnect();
+    }
+
+    @Test
+    public void whenDownloadFileUsingSshj_thenSuccess() throws IOException {
+        SSHClient sshClient = setupSshj();
+        SFTPClient sftpClient = sshClient.newSFTPClient();
+        sftpClient.get(remoteFile, localDir + "sshjFile.txt");
+        sftpClient.close();
+        sshClient.disconnect();
+    }
+
+    @Test
+    public void whenUploadFileUsingApacheVfs_thenSuccess() throws IOException {
+        FileSystemManager manager = VFS.getManager();
+        FileObject local = manager.resolveFile(System.getProperty("user.dir") + "/" + localFile);
+        FileObject remote = manager.resolveFile("sftp://" + username + ":" + password + "@" + remoteHost + "/" + remoteDir + "vfsFile.txt");
+        remote.copyFrom(local, Selectors.SELECT_SELF);
+        local.close();
+        remote.close();
+    }
+
+    @Test
+    public void whenDownloadFileUsingApacheVfs_thenSuccess() throws IOException {
+        FileSystemManager manager = VFS.getManager();
+        FileObject local = manager.resolveFile(System.getProperty("user.dir") + "/" + localDir + "vfsFile.txt");
+        FileObject remote = manager.resolveFile("sftp://" + username + ":" + password + "@" + remoteHost + "/" + remoteFile);
+        local.copyFrom(remote, Selectors.SELECT_SELF);
+        local.close();
+        remote.close();
+    }
+
+    // ====== ssh-keyscan -H -t rsa remoteHost >> known_hosts_sample
+
+    private ChannelSftp setupJsch() throws JSchException {
+        JSch jsch = new JSch();
+        jsch.setKnownHosts(knownHostsFileLoc);
+        Session jschSession = jsch.getSession(username, remoteHost);
+        jschSession.setPassword(password);
+        //jschSession.setConfig("StrictHostKeyChecking", "no");
+        jschSession.connect();
+        return (ChannelSftp) jschSession.openChannel("sftp");
+    }
+
+    private SSHClient setupSshj() throws IOException {
+        SSHClient client = new SSHClient();
+        client.addHostKeyVerifier(new PromiscuousVerifier());
+        client.connect(remoteHost);
+        client.authPassword(username, password);
+        return client;
+    }
+
+}

libraries/README.md

@@ -42,7 +42,6 @@
 - [Introduction to Akka Actors in Java](http://www.baeldung.com/akka-actors-java)
 - [Introduction to Smooks](http://www.baeldung.com/smooks)
 - [A Guide to Infinispan in Java](http://www.baeldung.com/infinispan)
-- [Introduction to OpenCSV](http://www.baeldung.com/opencsv)
 - [A Guide to Unirest](http://www.baeldung.com/unirest)
 - [Introduction to Akka Actors in Java](http://www.baeldung.com/akka-actors-java)
 - [A Guide to Byte Buddy](http://www.baeldung.com/byte-buddy)

lombok/src/main/java/com/baeldung/lombok/getter/GetterLazy.java

@@ -13,9 +13,9 @@ public class GetterLazy {
     private static final String DELIMETER = ",";
 
     @Getter(lazy = true)
-    private final Map<String, Long> transactions = readTxnsFromFile();
+    private final Map<String, Long> transactions = getTransactions();
 
-    private Map<String, Long> readTxnsFromFile() {
+    private Map<String, Long> getTransactions() {
 
         final Map<String, Long> cache = new HashMap<>();
         List<String> txnRows = readTxnListFromFile();

lombok/src/main/java/com/baeldung/lombok/intro/Utility.java

@@ -0,0 +1,26 @@
+package com.baeldung.lombok.intro;
+
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.InputStreamReader;
+import java.util.stream.Collectors;
+
+import lombok.SneakyThrows;
+import lombok.Synchronized;
+
+public class Utility {
+
+    @SneakyThrows
+    public String resourceAsString() throws IOException {
+        try (InputStream is = this.getClass().getResourceAsStream("sure_in_my_jar.txt")) {
+            BufferedReader br = new BufferedReader(new InputStreamReader(is, "UTF-8"));
+            return br.lines().collect(Collectors.joining("\n"));
+        } 
+    }
+
+    @Synchronized
+    public void putValueInCache(String key, String value) {
+        System.out.println("Thread safe here with key : [" + key + "] and value[" + value + "]");
+    }
+}

lombok/src/main/resources/sure_in_my_jar.txt

@@ -0,0 +1 @@
+Hello

oauth2-framework-impl/oauth2-authorization-server/src/main/java/com/baeldung/oauth2/authorization/server/api/AuthorizationEndpoint.java

@@ -121,8 +121,8 @@ public class AuthorizationEndpoint {
         String redirectUri = originalParams.getFirst("resolved_redirect_uri");
         StringBuilder sb = new StringBuilder(redirectUri);
 
-        String approbationStatus = params.getFirst("approbation_status");
+        String approvalStatus = params.getFirst("approval_status");
-        if ("NO".equals(approbationStatus)) {
+        if ("NO".equals(approvalStatus)) {
             URI location = UriBuilder.fromUri(sb.toString())
                     .queryParam("error", "User doesn't approved the request.")
                     .queryParam("error_description", "User doesn't approved the request.")

oauth2-framework-impl/oauth2-authorization-server/src/main/java/com/baeldung/oauth2/authorization/server/api/TokenEndpoint.java

@@ -15,15 +15,14 @@ import javax.ws.rs.core.HttpHeaders;
 import javax.ws.rs.core.MediaType;
 import javax.ws.rs.core.MultivaluedMap;
 import javax.ws.rs.core.Response;
+import java.util.Arrays;
 import java.util.Base64;
-import java.util.Collections;
 import java.util.List;
-import java.util.Objects;
 
 @Path("token")
 public class TokenEndpoint {
 
-    List<String> supportedGrantTypes = Collections.singletonList("authorization_code");
+    List<String> supportedGrantTypes = Arrays.asList("authorization_code", "refresh_token");
 
     @Inject
     private AppDataRepository appDataRepository;
@@ -39,36 +38,36 @@ public class TokenEndpoint {
 
         //Check grant_type params
         String grantType = params.getFirst("grant_type");
-        Objects.requireNonNull(grantType, "grant_type params is required");
+        if (grantType == null || grantType.isEmpty())
-        if (!supportedGrantTypes.contains(grantType)) {
+            return responseError("Invalid_request", "grant_type is required", Response.Status.BAD_REQUEST);
-            JsonObject error = Json.createObjectBuilder()
-                    .add("error", "unsupported_grant_type")
-                    .add("error_description", "grant type should be one of :" + supportedGrantTypes)
-                    .build();
-            return Response.status(Response.Status.BAD_REQUEST)
-                    .entity(error).build();
 
+        if (!supportedGrantTypes.contains(grantType)) {
+            return responseError("unsupported_grant_type", "grant_type should be one of :" + supportedGrantTypes, Response.Status.BAD_REQUEST);
         }
 
         //Client Authentication
         String[] clientCredentials = extract(authHeader);
+        if (clientCredentials.length != 2) {
+            return responseError("Invalid_request", "Bad Credentials client_id/client_secret", Response.Status.BAD_REQUEST);
+        }
         String clientId = clientCredentials[0];
-        String clientSecret = clientCredentials[1];
         Client client = appDataRepository.getClient(clientId);
-        if (client == null || clientSecret == null || !clientSecret.equals(client.getClientSecret())) {
+        if (client == null) {
-            JsonObject error = Json.createObjectBuilder()
+            return responseError("Invalid_request", "Invalid client_id", Response.Status.BAD_REQUEST);
-                    .add("error", "invalid_client")
+        }
-                    .build();
+        String clientSecret = clientCredentials[1];
-            return Response.status(Response.Status.UNAUTHORIZED)
+        if (!clientSecret.equals(client.getClientSecret())) {
-                    .entity(error).build();
+            return responseError("Invalid_request", "Invalid client_secret", Response.Status.UNAUTHORIZED);
         }
 
         AuthorizationGrantTypeHandler authorizationGrantTypeHandler = authorizationGrantTypeHandlers.select(NamedLiteral.of(grantType)).get();
         JsonObject tokenResponse = null;
         try {
             tokenResponse = authorizationGrantTypeHandler.createAccessToken(clientId, params);
+        } catch (WebApplicationException e) {
+            return e.getResponse();
         } catch (Exception e) {
-            e.printStackTrace();
+            return responseError("Invalid_request", "Can't get token", Response.Status.INTERNAL_SERVER_ERROR);
         }
 
         return Response.ok(tokenResponse)
@@ -81,6 +80,15 @@ public class TokenEndpoint {
         if (authHeader != null && authHeader.startsWith("Basic ")) {
             return new String(Base64.getDecoder().decode(authHeader.substring(6))).split(":");
         }
-        return null;
+        return new String[]{};
+    }
+
+    private Response responseError(String error, String errorDescription, Response.Status status) {
+        JsonObject errorResponse = Json.createObjectBuilder()
+                .add("error", error)
+                .add("error_description", errorDescription)
+                .build();
+        return Response.status(status)
+                .entity(errorResponse).build();
     }
 }

oauth2-framework-impl/oauth2-authorization-server/src/main/java/com/baeldung/oauth2/authorization/server/handler/AbstractGrantTypeHandler.java

@@ -0,0 +1,87 @@
+package com.baeldung.oauth2.authorization.server.handler;
+
+import com.baeldung.oauth2.authorization.server.PEMKeyUtils;
+import com.nimbusds.jose.*;
+import com.nimbusds.jose.crypto.RSASSASigner;
+import com.nimbusds.jose.crypto.RSASSAVerifier;
+import com.nimbusds.jose.jwk.JWK;
+import com.nimbusds.jose.jwk.RSAKey;
+import com.nimbusds.jwt.JWTClaimsSet;
+import com.nimbusds.jwt.SignedJWT;
+import org.eclipse.microprofile.config.Config;
+
+import javax.inject.Inject;
+import java.time.Instant;
+import java.time.temporal.ChronoUnit;
+import java.util.Arrays;
+import java.util.Date;
+import java.util.UUID;
+
+public abstract class AbstractGrantTypeHandler implements AuthorizationGrantTypeHandler {
+
+    //Always RSA 256, but could be parametrized
+    protected JWSHeader jwsHeader = new JWSHeader.Builder(JWSAlgorithm.RS256).type(JOSEObjectType.JWT).build();
+
+    @Inject
+    protected Config config;
+
+    //30 min
+    protected Long expiresInMin = 30L;
+
+    protected JWSVerifier getJWSVerifier() throws Exception {
+        String verificationkey = config.getValue("verificationkey", String.class);
+        String pemEncodedRSAPublicKey = PEMKeyUtils.readKeyAsString(verificationkey);
+        RSAKey rsaPublicKey = (RSAKey) JWK.parseFromPEMEncodedObjects(pemEncodedRSAPublicKey);
+        return new RSASSAVerifier(rsaPublicKey);
+    }
+
+    protected JWSSigner getJwsSigner() throws Exception {
+        String signingkey = config.getValue("signingkey", String.class);
+        String pemEncodedRSAPrivateKey = PEMKeyUtils.readKeyAsString(signingkey);
+        RSAKey rsaKey = (RSAKey) JWK.parseFromPEMEncodedObjects(pemEncodedRSAPrivateKey);
+        return new RSASSASigner(rsaKey.toRSAPrivateKey());
+    }
+
+    protected String getAccessToken(String clientId, String subject, String approvedScope) throws Exception {
+        //4. Signing
+        JWSSigner jwsSigner = getJwsSigner();
+
+        Instant now = Instant.now();
+        //Long expiresInMin = 30L;
+        Date expirationTime = Date.from(now.plus(expiresInMin, ChronoUnit.MINUTES));
+
+        //3. JWT Payload or claims
+        JWTClaimsSet jwtClaims = new JWTClaimsSet.Builder()
+                .issuer("http://localhost:9080")
+                .subject(subject)
+                .claim("upn", subject)
+                .claim("client_id", clientId)
+                .audience("http://localhost:9280")
+                .claim("scope", approvedScope)
+                .claim("groups", Arrays.asList(approvedScope.split(" ")))
+                .expirationTime(expirationTime) // expires in 30 minutes
+                .notBeforeTime(Date.from(now))
+                .issueTime(Date.from(now))
+                .jwtID(UUID.randomUUID().toString())
+                .build();
+        SignedJWT signedJWT = new SignedJWT(jwsHeader, jwtClaims);
+        signedJWT.sign(jwsSigner);
+        return signedJWT.serialize();
+    }
+
+    protected String getRefreshToken(String clientId, String subject, String approvedScope) throws Exception {
+        JWSSigner jwsSigner = getJwsSigner();
+        Instant now = Instant.now();
+        //6.Build refresh token
+        JWTClaimsSet refreshTokenClaims = new JWTClaimsSet.Builder()
+                .subject(subject)
+                .claim("client_id", clientId)
+                .claim("scope", approvedScope)
+                //refresh token for 1 day.
+                .expirationTime(Date.from(now.plus(1, ChronoUnit.DAYS)))
+                .build();
+        SignedJWT signedRefreshToken = new SignedJWT(jwsHeader, refreshTokenClaims);
+        signedRefreshToken.sign(jwsSigner);
+        return signedRefreshToken.serialize();
+    }
+}

oauth2-framework-impl/oauth2-authorization-server/src/main/java/com/baeldung/oauth2/authorization/server/handler/AuthorizationCodeGrantTypeHandler.java

@@ -1,18 +1,7 @@
 package com.baeldung.oauth2.authorization.server.handler;
 
-import com.baeldung.oauth2.authorization.server.PEMKeyUtils;
 import com.baeldung.oauth2.authorization.server.model.AuthorizationCode;
-import com.nimbusds.jose.JOSEObjectType;
-import com.nimbusds.jose.JWSAlgorithm;
-import com.nimbusds.jose.JWSHeader;
-import com.nimbusds.jose.crypto.RSASSASigner;
-import com.nimbusds.jose.jwk.JWK;
-import com.nimbusds.jose.jwk.RSAKey;
-import com.nimbusds.jwt.JWTClaimsSet;
-import com.nimbusds.jwt.SignedJWT;
-import org.eclipse.microprofile.config.Config;
 
-import javax.inject.Inject;
 import javax.inject.Named;
 import javax.json.Json;
 import javax.json.JsonObject;
@@ -20,22 +9,14 @@ import javax.persistence.EntityManager;
 import javax.persistence.PersistenceContext;
 import javax.ws.rs.WebApplicationException;
 import javax.ws.rs.core.MultivaluedMap;
-import java.time.Instant;
 import java.time.LocalDateTime;
-import java.time.temporal.ChronoUnit;
-import java.util.Arrays;
-import java.util.Date;
-import java.util.UUID;
 
 @Named("authorization_code")
-public class AuthorizationCodeGrantTypeHandler implements AuthorizationGrantTypeHandler {
+public class AuthorizationCodeGrantTypeHandler extends AbstractGrantTypeHandler {
 
     @PersistenceContext
     private EntityManager entityManager;
 
-    @Inject
-    private Config config;
-
     @Override
     public JsonObject createAccessToken(String clientId, MultivaluedMap<String, String> params) throws Exception {
         //1. code is required
@@ -58,42 +39,16 @@ public class AuthorizationCodeGrantTypeHandler implements AuthorizationGrantType
             throw new WebApplicationException("invalid_grant");
         }
 
-        //JWT Header
-        JWSHeader jwsHeader = new JWSHeader.Builder(JWSAlgorithm.RS256).type(JOSEObjectType.JWT).build();
-
-        Instant now = Instant.now();
-        Long expiresInMin = 30L;
-        Date expiresIn = Date.from(now.plus(expiresInMin, ChronoUnit.MINUTES));
-
         //3. JWT Payload or claims
-        JWTClaimsSet jwtClaims = new JWTClaimsSet.Builder()
+        String accessToken = getAccessToken(clientId, authorizationCode.getUserId(), authorizationCode.getApprovedScopes());
-                .issuer("http://localhost:9080")
+        String refreshToken = getRefreshToken(clientId, authorizationCode.getUserId(), authorizationCode.getApprovedScopes());
-                .subject(authorizationCode.getUserId())
-                .claim("upn", authorizationCode.getUserId())
-                .audience("http://localhost:9280")
-                .claim("scope", authorizationCode.getApprovedScopes())
-                .claim("groups", Arrays.asList(authorizationCode.getApprovedScopes().split(" ")))
-                .expirationTime(expiresIn) // expires in 30 minutes
-                .notBeforeTime(Date.from(now))
-                .issueTime(Date.from(now))
-                .jwtID(UUID.randomUUID().toString())
-                .build();
-        SignedJWT signedJWT = new SignedJWT(jwsHeader, jwtClaims);
-
-        //4. Signing
-        String signingkey = config.getValue("signingkey", String.class);
-        String pemEncodedRSAPrivateKey = PEMKeyUtils.readKeyAsString(signingkey);
-        RSAKey rsaKey = (RSAKey) JWK.parseFromPEMEncodedObjects(pemEncodedRSAPrivateKey);
-        signedJWT.sign(new RSASSASigner(rsaKey.toRSAPrivateKey()));
-
-        //5. Finally the JWT access token
-        String accessToken = signedJWT.serialize();
 
         return Json.createObjectBuilder()
                 .add("token_type", "Bearer")
                 .add("access_token", accessToken)
                 .add("expires_in", expiresInMin * 60)
                 .add("scope", authorizationCode.getApprovedScopes())
+                .add("refresh_token", refreshToken)
                 .build();
     }
 }

oauth2-framework-impl/oauth2-authorization-server/src/main/java/com/baeldung/oauth2/authorization/server/handler/RefreshTokenGrantTypeHandler.java

@@ -0,0 +1,72 @@
+package com.baeldung.oauth2.authorization.server.handler;
+
+import com.nimbusds.jose.JWSVerifier;
+import com.nimbusds.jwt.SignedJWT;
+
+import javax.inject.Named;
+import javax.json.Json;
+import javax.json.JsonObject;
+import javax.ws.rs.WebApplicationException;
+import javax.ws.rs.core.MultivaluedMap;
+import javax.ws.rs.core.Response;
+import java.util.Arrays;
+import java.util.Date;
+import java.util.HashSet;
+import java.util.Set;
+
+@Named("refresh_token")
+public class RefreshTokenGrantTypeHandler extends AbstractGrantTypeHandler {
+
+    @Override
+    public JsonObject createAccessToken(String clientId, MultivaluedMap<String, String> params) throws Exception {
+        String refreshToken = params.getFirst("refresh_token");
+        if (refreshToken == null || "".equals(refreshToken)) {
+            throw new WebApplicationException("invalid_grant");
+        }
+
+        //Decode refresh token
+        SignedJWT signedRefreshToken = SignedJWT.parse(refreshToken);
+        JWSVerifier verifier = getJWSVerifier();
+
+        if (!signedRefreshToken.verify(verifier)) {
+            throw new WebApplicationException("Invalid refresh token.");
+        }
+        if (!(new Date().before(signedRefreshToken.getJWTClaimsSet().getExpirationTime()))) {
+            throw new WebApplicationException("Refresh token expired.");
+        }
+        String refreshTokenClientId = signedRefreshToken.getJWTClaimsSet().getStringClaim("client_id");
+        if (!clientId.equals(refreshTokenClientId)) {
+            throw new WebApplicationException("Invalid client_id.");
+        }
+
+        //At this point, the refresh token is valid and not yet expired
+        //So create a new access token from it.
+        String subject = signedRefreshToken.getJWTClaimsSet().getSubject();
+        String approvedScopes = signedRefreshToken.getJWTClaimsSet().getStringClaim("scope");
+
+        String requestedScopes = params.getFirst("scope");
+        if (requestedScopes != null && !requestedScopes.isEmpty()) {
+            Set<String> rScopes = new HashSet(Arrays.asList(requestedScopes.split(" ")));
+            Set<String> aScopes = new HashSet(Arrays.asList(approvedScopes.split(" ")));
+            if (!aScopes.containsAll(rScopes)) {
+                JsonObject error = Json.createObjectBuilder()
+                        .add("error", "Invalid_request")
+                        .add("error_description", "Requested scopes should be a subset of the original scopes.")
+                        .build();
+                Response response = Response.status(Response.Status.BAD_REQUEST).entity(error).build();
+                throw new WebApplicationException(response);
+            }
+        } else {
+            requestedScopes = approvedScopes;
+        }
+
+        String accessToken = getAccessToken(clientId, subject, requestedScopes);
+        return Json.createObjectBuilder()
+                .add("token_type", "Bearer")
+                .add("access_token", accessToken)
+                .add("expires_in", expiresInMin * 60)
+                .add("scope", requestedScopes)
+                .add("refresh_token", refreshToken)
+                .build();
+    }
+}

oauth2-framework-impl/oauth2-authorization-server/src/main/webapp/authorize.jsp

@@ -41,8 +41,8 @@
 
             <tr>
                 <td colspan="2">
-                    <input type="submit" name="approbation_status" value="YES"/>
+                    <input type="submit" name="approval_status" value="YES"/>
-                    <input type="submit" name="approbation_status" value="NO"/>
+                    <input type="submit" name="approval_status" value="NO"/>
                 </td>
             </tr>
         </table>

oauth2-framework-impl/oauth2-client/src/main/java/com/baeldung/oauth2/client/AbstractServlet.java

@@ -0,0 +1,23 @@
+package com.baeldung.oauth2.client;
+
+import javax.servlet.RequestDispatcher;
+import javax.servlet.ServletException;
+import javax.servlet.http.HttpServlet;
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+import java.io.IOException;
+import java.util.Base64;
+
+public abstract class AbstractServlet extends HttpServlet {
+
+    protected void dispatch(String location, HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
+        RequestDispatcher requestDispatcher = request.getRequestDispatcher(location);
+        requestDispatcher.forward(request, response);
+    }
+
+    protected String getAuthorizationHeaderValue(String clientId, String clientSecret) {
+        String token = clientId + ":" + clientSecret;
+        String encodedString = Base64.getEncoder().encodeToString(token.getBytes());
+        return "Basic " + encodedString;
+    }
+}

oauth2-framework-impl/oauth2-client/src/main/java/com/baeldung/oauth2/client/CallbackServlet.java

@@ -4,10 +4,8 @@ import org.eclipse.microprofile.config.Config;
 
 import javax.inject.Inject;
 import javax.json.JsonObject;
-import javax.servlet.RequestDispatcher;
 import javax.servlet.ServletException;
 import javax.servlet.annotation.WebServlet;
-import javax.servlet.http.HttpServlet;
 import javax.servlet.http.HttpServletRequest;
 import javax.servlet.http.HttpServletResponse;
 import javax.ws.rs.client.Client;
@@ -18,10 +16,9 @@ import javax.ws.rs.core.Form;
 import javax.ws.rs.core.HttpHeaders;
 import javax.ws.rs.core.MediaType;
 import java.io.IOException;
-import java.util.Base64;
 
 @WebServlet(urlPatterns = "/callback")
-public class CallbackServlet extends HttpServlet {
+public class CallbackServlet extends AbstractServlet {
 
     @Inject
     private Config config;
@@ -29,6 +26,9 @@ public class CallbackServlet extends HttpServlet {
     @Override
     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
 
+        String clientId = config.getValue("client.clientId", String.class);
+        String clientSecret = config.getValue("client.clientSecret", String.class);
+
         //Error:
         String error = request.getParameter("error");
         if (error != null) {
@@ -53,24 +53,15 @@ public class CallbackServlet extends HttpServlet {
         form.param("code", code);
         form.param("redirect_uri", config.getValue("client.redirectUri", String.class));
 
+        try {
             JsonObject tokenResponse = target.request(MediaType.APPLICATION_JSON_TYPE)
-                .header(HttpHeaders.AUTHORIZATION, getAuthorizationHeaderValue())
+                    .header(HttpHeaders.AUTHORIZATION, getAuthorizationHeaderValue(clientId, clientSecret))
                     .post(Entity.entity(form, MediaType.APPLICATION_FORM_URLENCODED_TYPE), JsonObject.class);
-
             request.getSession().setAttribute("tokenResponse", tokenResponse);
+        } catch (Exception ex) {
+            System.out.println(ex.getMessage());
+            request.setAttribute("error", ex.getMessage());
+        }
         dispatch("/", request, response);
     }
-
-    private void dispatch(String location, HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
-        RequestDispatcher requestDispatcher = request.getRequestDispatcher(location);
-        requestDispatcher.forward(request, response);
-    }
-
-    private String getAuthorizationHeaderValue() {
-        String clientId = config.getValue("client.clientId", String.class);
-        String clientSecret = config.getValue("client.clientSecret", String.class);
-        String token = clientId + ":" + clientSecret;
-        String encodedString = Base64.getEncoder().encodeToString(token.getBytes());
-        return "Basic " + encodedString;
-    }
 }

oauth2-framework-impl/oauth2-client/src/main/java/com/baeldung/oauth2/client/RefreshTokenServlet.java

@@ -0,0 +1,57 @@
+package com.baeldung.oauth2.client;
+
+import org.eclipse.microprofile.config.Config;
+
+import javax.inject.Inject;
+import javax.json.JsonObject;
+import javax.servlet.ServletException;
+import javax.servlet.annotation.WebServlet;
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+import javax.ws.rs.client.Client;
+import javax.ws.rs.client.ClientBuilder;
+import javax.ws.rs.client.Entity;
+import javax.ws.rs.client.WebTarget;
+import javax.ws.rs.core.Form;
+import javax.ws.rs.core.HttpHeaders;
+import javax.ws.rs.core.MediaType;
+import javax.ws.rs.core.Response;
+import java.io.IOException;
+
+@WebServlet(urlPatterns = "/refreshtoken")
+public class RefreshTokenServlet extends AbstractServlet {
+
+    @Inject
+    private Config config;
+
+    @Override
+    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
+
+        String clientId = config.getValue("client.clientId", String.class);
+        String clientSecret = config.getValue("client.clientSecret", String.class);
+
+        JsonObject actualTokenResponse = (JsonObject) request.getSession().getAttribute("tokenResponse");
+        Client client = ClientBuilder.newClient();
+        WebTarget target = client.target(config.getValue("provider.tokenUri", String.class));
+
+        Form form = new Form();
+        form.param("grant_type", "refresh_token");
+        form.param("refresh_token", actualTokenResponse.getString("refresh_token"));
+
+        String scope = request.getParameter("scope");
+        if (scope != null && !scope.isEmpty()) {
+            form.param("scope", scope);
+        }
+
+        Response jaxrsResponse = target.request(MediaType.APPLICATION_JSON_TYPE)
+                .header(HttpHeaders.AUTHORIZATION, getAuthorizationHeaderValue(clientId, clientSecret))
+                .post(Entity.entity(form, MediaType.APPLICATION_FORM_URLENCODED_TYPE), Response.class);
+        JsonObject tokenResponse = jaxrsResponse.readEntity(JsonObject.class);
+        if (jaxrsResponse.getStatus() == 200) {
+            request.getSession().setAttribute("tokenResponse", tokenResponse);
+        } else {
+            request.setAttribute("error", tokenResponse.getString("error_description", "error!"));
+        }
+        dispatch("/", request, response);
+    }
+}

oauth2-framework-impl/oauth2-client/src/main/webapp/index.jsp

@@ -10,6 +10,7 @@
         body {
             margin: 0px;
         }
+
         input[type=text], input[type=password] {
             width: 75%;
             padding: 4px 0px;
@@ -17,6 +18,7 @@
             border: 1px solid #502bcc;
             box-sizing: border-box;
         }
+
         .container-error {
             padding: 16px;
             border: 1px solid #cc102a;
@@ -25,6 +27,7 @@
             margin-left: 25px;
             margin-bottom: 25px;
         }
+
         .container {
             padding: 16px;
             border: 1px solid #130ecc;
@@ -81,8 +84,20 @@
         <li>access_token: ${tokenResponse.getString("access_token")}</li>
         <li>scope: ${tokenResponse.getString("scope")}</li>
         <li>Expires in (s): ${tokenResponse.getInt("expires_in")}</li>
+        <li>refresh_token: ${tokenResponse.getString("refresh_token")}</li>
     </ul>
 </div>
+
+<div class="container">
+    <span><h4>Refresh Token</h4></span>
+    <hr>
+    <ul>
+        <li><a href="refreshtoken">Refresh token (original scope)</a></li>
+        <li><a href="refreshtoken?scope=resource.read">Refresh token (scope: resource.read)</a></li>
+        <li><a href="refreshtoken?scope=resource.write">Refresh token (scope: resource.write)</a></li>
+    </ul>
+</div>
+
 <div class="container">
     <span><h4>OAuth2 Resource Server Call</h4></span>
     <hr>
@@ -90,7 +105,6 @@
         <li><a href="downstream?action=read">Read Protected Resource</a></li>
         <li><a href="downstream?action=write">Write Protected Resource</a></li>
     </ul>
-
 </div>
 
 </body>

parent-boot-performance/README.md

@@ -1 +0,0 @@
-This is a parent module for projects that want to take advantage of the latest Spring Boot improvements/features.

parent-boot-performance/pom.xml

@@ -1,92 +0,0 @@
-<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
-    <modelVersion>4.0.0</modelVersion>
-    <artifactId>parent-boot-performance</artifactId>
-    <version>0.0.1-SNAPSHOT</version>
-    <name>parent-boot-performance</name>
-    <packaging>pom</packaging>
-    <description>Parent for all modules that want to take advantage of the latest Spring Boot improvements/features. Current version: 2.2</description>
-
-    <parent>
-        <groupId>com.baeldung</groupId>
-        <artifactId>parent-modules</artifactId>
-        <version>1.0.0-SNAPSHOT</version>
-    </parent>
-
-    <dependencyManagement>
-        <dependencies>
-            <dependency>
-                <groupId>org.springframework.boot</groupId>
-                <artifactId>spring-boot-dependencies</artifactId>
-                <version>${spring-boot.version}</version>
-                <type>pom</type>
-                <scope>import</scope>
-            </dependency>
-        </dependencies>
-    </dependencyManagement>
-	
-    <dependencies>
-        <dependency>
-            <groupId>io.rest-assured</groupId>
-            <artifactId>rest-assured</artifactId>
-            </dependency>
-        <dependency>
-            <groupId>org.springframework.boot</groupId>
-            <artifactId>spring-boot-starter-test</artifactId>
-            <scope>test</scope>
-        </dependency>
-    </dependencies>
-
-    <build>
-        <pluginManagement>
-            <plugins>
-                <plugin>
-                    <groupId>org.springframework.boot</groupId>
-                    <artifactId>spring-boot-maven-plugin</artifactId>
-                    <version>${spring-boot.version}</version>
-                    <configuration>
-                        <mainClass>${start-class}</mainClass>
-                        <!-- this is necessary as we're not using the Boot parent -->
-                    </configuration>
-                </plugin>
-            </plugins>
-        </pluginManagement>
-    </build>
-    
-    <repositories>
-        <repository>
-            <id>spring-milestones</id>
-            <name>Spring Milestones</name>
-            <url>https://repo.spring.io/milestone</url>
-        </repository>
-    </repositories>
-    
-    <profiles>
-        <profile>
-            <id>thin-jar</id>
-            <build>
-                <plugins>
-                    <plugin>
-                        <groupId>org.springframework.boot</groupId>
-                        <artifactId>spring-boot-maven-plugin</artifactId>
-                        <dependencies>
-                            <!-- The following enables the "thin jar" deployment option. -->
-                            <dependency>
-                                <groupId>org.springframework.boot.experimental</groupId>
-                                <artifactId>spring-boot-thin-layout</artifactId>
-                                <version>${thin.version}</version>
-                            </dependency>
-                        </dependencies>
-                    </plugin>
-                </plugins>
-            </build>
-        </profile>
-    </profiles>
-
-    <properties>
-        <rest-assured.version>3.1.0</rest-assured.version>
-        <!-- plugins -->
-        <thin.version>1.0.21.RELEASE</thin.version>
-        <spring-boot.version>2.2.0.M3</spring-boot.version>
-    </properties>
-</project>