Merge branch 'master' of https://github.com/eugenp/tutorials

algorithms-miscellaneous-3/README.md

@@ -13,6 +13,5 @@ This module contains articles about algorithms. Some classes of algorithms, e.g.
 - [Checking if a Java Graph has a Cycle](https://www.baeldung.com/java-graph-has-a-cycle)
 - [A Guide to the Folding Technique in Java](https://www.baeldung.com/folding-hashing-technique)
 - [Creating a Triangle with for Loops in Java](https://www.baeldung.com/java-print-triangle)
-- [Efficient Word Frequency Calculator in Java](https://www.baeldung.com/java-word-frequency)
 - [The K-Means Clustering Algorithm in Java](https://www.baeldung.com/java-k-means-clustering-algorithm)
 - More articles: [[<-- prev]](/algorithms-miscellaneous-2) [[next -->]](/algorithms-miscellaneous-4)

algorithms-miscellaneous-6/README.md

@@ -0,0 +1,4 @@
+### Relevant Articles:
+
+- [Boruvka’s Algorithm for Minimum Spanning Trees](https://www.baeldung.com/java-boruvka-algorithm)
+- [Gradient Descent in Java](https://www.baeldung.com/java-gradient-descent)

algorithms-sorting-2/README.md

@@ -1,3 +1,7 @@
 ### Relevant Articles:
 
+- [Sorting a String Alphabetically in Java](https://www.baeldung.com/java-sort-string-alphabetically)
+- [Sorting Strings by Contained Numbers in Java](https://www.baeldung.com/java-sort-strings-contained-numbers)
+- [How an In-Place Sorting Algorithm Works](https://www.baeldung.com/java-in-place-sorting)
 - [Partitioning and Sorting Arrays with Many Repeated Entries](https://www.baeldung.com/java-sorting-arrays-with-repeated-entries)
+- More articles: [[<-- prev]](/algorithms-sorting)

algorithms-sorting-2/src/main/java/com/baeldung/algorithms/bynumber/NaturalOrderComparators.java

@@ -1,4 +1,4 @@
-package com.baeldung.algorithms.sort.bynumber;
+package com.baeldung.algorithms.bynumber;
 
 import java.util.Comparator;
 

algorithms-sorting-2/src/test/java/com/baeldung/algorithms/bynumber/NaturalOrderComparatorsUnitTest.java

@@ -1,6 +1,5 @@
-package com.baeldung.algorithms.sort.bynumber;
+package com.baeldung.algorithms.bynumber;
 
-import com.baeldung.algorithms.sort.bynumber.NaturalOrderComparators;
 import org.junit.Test;
 
 import java.util.ArrayList;

algorithms-sorting/README.md

@@ -11,10 +11,7 @@ This module contains articles about sorting algorithms.
 - [Heap Sort in Java](https://www.baeldung.com/java-heap-sort)
 - [Shell Sort in Java](https://www.baeldung.com/java-shell-sort)
 - [Counting Sort in Java](https://www.baeldung.com/java-counting-sort)
-- [Sorting Strings by Contained Numbers in Java](https://www.baeldung.com/java-sort-strings-contained-numbers)
-- [How an In-Place Sorting Algorithm Works](https://www.baeldung.com/java-in-place-sorting)
 - [Selection Sort in Java](https://www.baeldung.com/java-selection-sort)
-- [Sorting Strings by Contained Numbers in Java](https://www.baeldung.com/java-sort-strings-contained-numbers)
 - [Radix Sort in Java](https://www.baeldung.com/java-radix-sort)
-- [Sorting a String Alphabetically in Java](https://www.baeldung.com/java-sort-string-alphabetically)
 - [Bucket Sort in Java](https://www.baeldung.com/java-bucket-sort)
+- More articles: [[next -->]](/algorithms-sorintg-2)

apache-olingo/olingo2/README.md

@@ -1,3 +0,0 @@
-### Relevant Articles:
-
-- [Intro to OData with Olingo](https://www.baeldung.com/olingo)

atomikos/README.md

@@ -0,0 +1,7 @@
+## Atomikos
+
+This module contains articles about Atomikos
+
+### Relevant Articles: 
+
+- [Guide Transactions Using Atomikos]()

atomikos/pom.xml

@@ -0,0 +1,119 @@
+<?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/maven-v4_0_0.xsd">
+	<modelVersion>4.0.0</modelVersion>
+	<artifactId>atomikos</artifactId>
+	<name>atomikos</name>
+
+	<parent>
+		<groupId>com.baeldung</groupId>
+		<artifactId>parent-modules</artifactId>
+		<version>1.0.0-SNAPSHOT</version>
+	</parent>
+
+	<dependencies>
+		<dependency>
+			<groupId>com.atomikos</groupId>
+			<artifactId>transactions-jdbc</artifactId>
+			<version>${atomikos-version}</version>
+		</dependency>
+		<dependency>
+			<groupId>com.atomikos</groupId>
+			<artifactId>transactions-jms</artifactId>
+			<version>${atomikos-version}</version>
+		</dependency>
+		<dependency>
+			<groupId>com.atomikos</groupId>
+			<artifactId>transactions-hibernate4</artifactId>
+			<version>${atomikos-version}</version>
+		</dependency>
+		<dependency>
+			<groupId>org.springframework</groupId>
+			<artifactId>spring-context</artifactId>
+			<version>${spring-version}</version>
+		</dependency>
+		<dependency>
+			<groupId>org.springframework</groupId>
+			<artifactId>spring-tx</artifactId>
+			<version>${spring-version}</version>
+		</dependency>
+		<dependency>
+			<groupId>org.springframework.data</groupId>
+			<artifactId>spring-data-jpa</artifactId>
+			<version>1.11.23.RELEASE</version>
+		</dependency>
+		<dependency>
+			<groupId>org.springframework</groupId>
+			<artifactId>spring-test</artifactId>
+			<version>${spring-version}</version>
+			<scope>test</scope>
+		</dependency>
+		<dependency>
+			<groupId>org.hibernate</groupId>
+			<artifactId>hibernate-entitymanager</artifactId>
+			<version>${hibernate.version}</version>
+			<scope>provided</scope>
+			<exclusions>
+				<exclusion>
+					<groupId>javax.transaction</groupId>
+					<artifactId>jta</artifactId>
+				</exclusion>
+			</exclusions>
+		</dependency>
+		<dependency>
+			<groupId>org.apache.activemq</groupId>
+			<artifactId>activemq-core</artifactId>
+			<version>5.7.0</version>
+		</dependency>
+		<dependency>
+			<groupId>org.apache.derby</groupId>
+			<artifactId>derby</artifactId>
+			<version>10.8.1.2</version>
+		</dependency>
+		<dependency>
+			<groupId>junit</groupId>
+			<artifactId>junit</artifactId>
+			<version>4.12</version>
+			<scope>test</scope>
+		</dependency>
+		<!-- the JTA API -->
+		<dependency>
+			<groupId>javax.transaction</groupId>
+			<artifactId>jta</artifactId>
+			<version>1.1</version>
+		</dependency>
+		<dependency>
+			<groupId>org.apache.geronimo.specs</groupId>
+			<artifactId>geronimo-jta_1.0.1B_spec</artifactId>
+			<version>1.0</version>
+		</dependency>
+		<dependency>
+			<groupId>javax.validation</groupId>
+			<artifactId>validation-api</artifactId>
+			<version>2.0.1.Final</version>
+		</dependency>
+		<dependency>
+			<groupId>org.hibernate.validator</groupId>
+			<artifactId>hibernate-validator</artifactId>
+			<version>6.1.2.Final</version>
+		</dependency>
+		<dependency>
+			<groupId>javax.el</groupId>
+			<artifactId>javax.el-api</artifactId>
+			<version>3.0.0</version>
+		</dependency>
+		<dependency>
+			<groupId>org.glassfish.web</groupId>
+			<artifactId>javax.el</artifactId>
+			<version>2.2.4</version>
+		</dependency>
+	</dependencies>
+
+	<properties>
+		<atomikos-version>5.0.6</atomikos-version>
+		<spring-version>5.1.6.RELEASE</spring-version>
+		<hibernate.version>5.4.3.Final</hibernate.version>
+	</properties>
+
+</project>

atomikos/src/main/java/com/baeldung/atomikos/direct/Application.java

@@ -0,0 +1,53 @@
+package com.baeldung.atomikos.direct;
+
+import java.sql.Connection;
+import java.sql.Statement;
+import java.util.UUID;
+
+import javax.sql.DataSource;
+
+import com.atomikos.icatch.jta.UserTransactionImp;
+
+public class Application {
+
+    private DataSource inventoryDataSource;
+    private DataSource orderDataSource;
+
+    public Application(DataSource inventoryDataSource, DataSource orderDataSource) {
+        this.inventoryDataSource = inventoryDataSource;
+        this.orderDataSource = orderDataSource;
+    }
+
+    public void placeOrder(String productId, int amount) throws Exception {
+
+        UserTransactionImp utx = new UserTransactionImp();
+        String orderId = UUID.randomUUID()
+            .toString();
+        boolean rollback = false;
+        try {
+            utx.begin();
+            Connection inventoryConnection = inventoryDataSource.getConnection();
+            Connection orderConnection = orderDataSource.getConnection();
+            Statement s1 = inventoryConnection.createStatement();
+            String q1 = "update Inventory set balance = balance - " + amount + " where productId ='" + productId + "'";
+            s1.executeUpdate(q1);
+            s1.close();
+            Statement s2 = orderConnection.createStatement();
+            String q2 = "insert into Orders values ( '" + orderId + "', '" + productId + "', " + amount + " )";
+            s2.executeUpdate(q2);
+            s2.close();
+            inventoryConnection.close();
+            orderConnection.close();
+        } catch (Exception e) {
+            System.out.println(e.getMessage());
+            rollback = true;
+        } finally {
+            if (!rollback)
+                utx.commit();
+            else
+                utx.rollback();
+        }
+
+    }
+
+}

atomikos/src/main/java/com/baeldung/atomikos/spring/Application.java

@@ -0,0 +1,41 @@
+package com.baeldung.atomikos.spring;
+
+import java.sql.Connection;
+import java.sql.Statement;
+import java.util.UUID;
+
+import javax.sql.DataSource;
+
+import org.springframework.transaction.annotation.Transactional;
+
+public class Application {
+
+    private DataSource inventoryDataSource;
+    private DataSource orderDataSource;
+
+    public Application(DataSource inventoryDataSource, DataSource orderDataSource) {
+        this.inventoryDataSource = inventoryDataSource;
+        this.orderDataSource = orderDataSource;
+    }
+
+    @Transactional(rollbackFor = Exception.class)
+    public void placeOrder(String productId, int amount) throws Exception {
+
+        String orderId = UUID.randomUUID()
+            .toString();
+        Connection inventoryConnection = inventoryDataSource.getConnection();
+        Connection orderConnection = orderDataSource.getConnection();
+        Statement s1 = inventoryConnection.createStatement();
+        String q1 = "update Inventory set balance = balance - " + amount + " where productId ='" + productId + "'";
+        s1.executeUpdate(q1);
+        s1.close();
+        Statement s2 = orderConnection.createStatement();
+        String q2 = "insert into Orders values ( '" + orderId + "', '" + productId + "', " + amount + " )";
+        s2.executeUpdate(q2);
+        s2.close();
+        inventoryConnection.close();
+        orderConnection.close();
+
+    }
+
+}

atomikos/src/main/java/com/baeldung/atomikos/spring/config/Config.java

@@ -0,0 +1,68 @@
+package com.baeldung.atomikos.spring.config;
+
+import java.util.Properties;
+
+import javax.transaction.SystemException;
+
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.transaction.annotation.EnableTransactionManagement;
+import org.springframework.transaction.jta.JtaTransactionManager;
+
+import com.atomikos.icatch.jta.UserTransactionManager;
+import com.atomikos.jdbc.AtomikosDataSourceBean;
+import com.baeldung.atomikos.spring.Application;
+
+@Configuration
+@EnableTransactionManagement
+public class Config {
+
+    @Bean(initMethod = "init", destroyMethod = "close")
+    public AtomikosDataSourceBean inventoryDataSource() {
+        AtomikosDataSourceBean dataSource = new AtomikosDataSourceBean();
+        dataSource.setLocalTransactionMode(true);
+        dataSource.setUniqueResourceName("db1");
+        dataSource.setXaDataSourceClassName("org.apache.derby.jdbc.EmbeddedXADataSource");
+        Properties xaProperties = new Properties();
+        xaProperties.put("databaseName", "db1");
+        xaProperties.put("createDatabase", "create");
+        dataSource.setXaProperties(xaProperties);
+        dataSource.setPoolSize(10);
+        return dataSource;
+    }
+
+    @Bean(initMethod = "init", destroyMethod = "close")
+    public AtomikosDataSourceBean orderDataSource() {
+        AtomikosDataSourceBean dataSource = new AtomikosDataSourceBean();
+        dataSource.setLocalTransactionMode(true);
+        dataSource.setUniqueResourceName("db2");
+        dataSource.setXaDataSourceClassName("org.apache.derby.jdbc.EmbeddedXADataSource");
+        Properties xaProperties = new Properties();
+        xaProperties.put("databaseName", "db2");
+        xaProperties.put("createDatabase", "create");
+        dataSource.setXaProperties(xaProperties);
+        dataSource.setPoolSize(10);
+        return dataSource;
+    }
+
+    @Bean(initMethod = "init", destroyMethod = "close")
+    public UserTransactionManager userTransactionManager() throws SystemException {
+        UserTransactionManager userTransactionManager = new UserTransactionManager();
+        userTransactionManager.setTransactionTimeout(300);
+        userTransactionManager.setForceShutdown(true);
+        return userTransactionManager;
+    }
+
+    @Bean
+    public JtaTransactionManager jtaTransactionManager() throws SystemException {
+        JtaTransactionManager jtaTransactionManager = new JtaTransactionManager();
+        jtaTransactionManager.setTransactionManager(userTransactionManager());
+        jtaTransactionManager.setUserTransaction(userTransactionManager());
+        return jtaTransactionManager;
+    }
+
+    @Bean
+    public Application application() {
+        return new Application(inventoryDataSource(), orderDataSource());
+    }
+}

atomikos/src/main/java/com/baeldung/atomikos/spring/jpa/Application.java

@@ -0,0 +1,48 @@
+package com.baeldung.atomikos.spring.jpa;
+
+import java.util.Set;
+import java.util.UUID;
+
+import javax.validation.ConstraintViolation;
+import javax.validation.Validation;
+import javax.validation.Validator;
+import javax.validation.ValidatorFactory;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.transaction.annotation.Transactional;
+
+import com.baeldung.atomikos.spring.jpa.inventory.Inventory;
+import com.baeldung.atomikos.spring.jpa.inventory.InventoryRepository;
+import com.baeldung.atomikos.spring.jpa.order.Order;
+import com.baeldung.atomikos.spring.jpa.order.OrderRepository;
+
+public class Application {
+
+    @Autowired
+    private InventoryRepository inventoryRepository;
+
+    @Autowired
+    private OrderRepository orderRepository;
+
+    @Transactional(rollbackFor = Exception.class)
+    public void placeOrder(String productId, int amount) throws Exception {
+
+        String orderId = UUID.randomUUID()
+            .toString();
+        Inventory inventory = inventoryRepository.findOne(productId);
+        inventory.setBalance(inventory.getBalance() - amount);
+        inventoryRepository.save(inventory);
+        Order order = new Order();
+        order.setOrderId(orderId);
+        order.setProductId(productId);
+        order.setAmount(new Long(amount));
+        ValidatorFactory factory = Validation.buildDefaultValidatorFactory();
+        Validator validator = factory.getValidator();
+        Set<ConstraintViolation<Order>> violations = validator.validate(order);
+        if (violations.size() > 0)
+            throw new Exception("Invalid instance of an order.");
+        orderRepository.save(order);
+
+    }
+
+}

atomikos/src/main/java/com/baeldung/atomikos/spring/jpa/config/Config.java

@@ -0,0 +1,38 @@
+package com.baeldung.atomikos.spring.jpa.config;
+
+import javax.transaction.SystemException;
+
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.transaction.annotation.EnableTransactionManagement;
+import org.springframework.transaction.jta.JtaTransactionManager;
+
+import com.atomikos.icatch.jta.UserTransactionManager;
+import com.baeldung.atomikos.spring.jpa.Application;
+
+@Configuration
+@EnableTransactionManagement
+public class Config {
+
+    @Bean(initMethod = "init", destroyMethod = "close")
+    public UserTransactionManager userTransactionManager() throws SystemException {
+        UserTransactionManager userTransactionManager = new UserTransactionManager();
+        userTransactionManager.setTransactionTimeout(300);
+        userTransactionManager.setForceShutdown(true);
+        return userTransactionManager;
+    }
+
+    @Bean
+    public JtaTransactionManager transactionManager() throws SystemException {
+        JtaTransactionManager jtaTransactionManager = new JtaTransactionManager();
+        jtaTransactionManager.setTransactionManager(userTransactionManager());
+        jtaTransactionManager.setUserTransaction(userTransactionManager());
+        return jtaTransactionManager;
+    }
+
+    @Bean
+    public Application application() {
+        return new Application();
+    }
+
+}

atomikos/src/main/java/com/baeldung/atomikos/spring/jpa/inventory/Inventory.java

@@ -0,0 +1,31 @@
+package com.baeldung.atomikos.spring.jpa.inventory;
+
+import javax.persistence.Entity;
+import javax.persistence.Id;
+import javax.persistence.Table;
+
+@Entity
+@Table(name = "INVENTORY")
+public class Inventory {
+
+    @Id
+    private String productId;
+    private Long balance;
+
+    public String getProductId() {
+        return productId;
+    }
+
+    public void setProductId(String productId) {
+        this.productId = productId;
+    }
+
+    public Long getBalance() {
+        return balance;
+    }
+
+    public void setBalance(Long balance) {
+        this.balance = balance;
+    }
+
+}

atomikos/src/main/java/com/baeldung/atomikos/spring/jpa/inventory/InventoryConfig.java

@@ -0,0 +1,53 @@
+package com.baeldung.atomikos.spring.jpa.inventory;
+
+import java.util.Properties;
+
+import javax.persistence.EntityManagerFactory;
+
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.data.jpa.repository.config.EnableJpaRepositories;
+import org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean;
+import org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter;
+
+import com.atomikos.jdbc.AtomikosDataSourceBean;
+
+@Configuration
+@EnableJpaRepositories(basePackages = "com.baeldung.atomikos.spring.jpa.inventory", entityManagerFactoryRef = "inventoryEntityManager", transactionManagerRef = "transactionManager")
+public class InventoryConfig {
+
+    @Bean(initMethod = "init", destroyMethod = "close")
+    public AtomikosDataSourceBean inventoryDataSource() {
+        AtomikosDataSourceBean dataSource = new AtomikosDataSourceBean();
+        dataSource.setLocalTransactionMode(true);
+        dataSource.setUniqueResourceName("db1");
+        dataSource.setXaDataSourceClassName("org.apache.derby.jdbc.EmbeddedXADataSource");
+        Properties xaProperties = new Properties();
+        xaProperties.put("databaseName", "db1");
+        xaProperties.put("createDatabase", "create");
+        dataSource.setXaProperties(xaProperties);
+        dataSource.setPoolSize(10);
+        return dataSource;
+    }
+
+    @Bean
+    public EntityManagerFactory inventoryEntityManager() {
+        HibernateJpaVendorAdapter vendorAdapter = new HibernateJpaVendorAdapter();
+        LocalContainerEntityManagerFactoryBean factory = new LocalContainerEntityManagerFactoryBean();
+        factory.setJpaVendorAdapter(vendorAdapter);
+        factory.setPackagesToScan("com.baeldung.atomikos.spring.jpa.inventory");
+        factory.setDataSource(inventoryDataSource());
+        Properties jpaProperties = new Properties();
+        //jpaProperties.put("hibernate.show_sql", "true");
+        //jpaProperties.put("hibernate.format_sql", "true");
+        jpaProperties.put("hibernate.dialect", "org.hibernate.dialect.DerbyDialect");
+        jpaProperties.put("hibernate.current_session_context_class", "jta");
+        jpaProperties.put("javax.persistence.transactionType", "jta");
+        jpaProperties.put("hibernate.transaction.manager_lookup_class", "com.atomikos.icatch.jta.hibernate3.TransactionManagerLookup");
+        jpaProperties.put("hibernate.hbm2ddl.auto", "create-drop");
+        factory.setJpaProperties(jpaProperties);
+        factory.afterPropertiesSet();
+        return factory.getObject();
+    }
+
+}

atomikos/src/main/java/com/baeldung/atomikos/spring/jpa/inventory/InventoryRepository.java

@@ -0,0 +1,9 @@
+package com.baeldung.atomikos.spring.jpa.inventory;
+
+import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.stereotype.Repository;
+
+@Repository
+public interface InventoryRepository extends JpaRepository<Inventory, String> {
+
+}

atomikos/src/main/java/com/baeldung/atomikos/spring/jpa/order/Order.java

@@ -0,0 +1,42 @@
+package com.baeldung.atomikos.spring.jpa.order;
+
+import javax.persistence.Entity;
+import javax.persistence.Id;
+import javax.persistence.Table;
+import javax.validation.constraints.Max;
+
+@Entity
+@Table(name = "ORDERS")
+public class Order {
+
+    @Id
+    private String orderId;
+    private String productId;
+    @Max(5)
+    private Long amount;
+
+    public String getOrderId() {
+        return orderId;
+    }
+
+    public void setOrderId(String orderId) {
+        this.orderId = orderId;
+    }
+
+    public String getProductId() {
+        return productId;
+    }
+
+    public void setProductId(String productId) {
+        this.productId = productId;
+    }
+
+    public Long getAmount() {
+        return amount;
+    }
+
+    public void setAmount(Long amount) {
+        this.amount = amount;
+    }
+
+}

atomikos/src/main/java/com/baeldung/atomikos/spring/jpa/order/OrderConfig.java

@@ -0,0 +1,53 @@
+package com.baeldung.atomikos.spring.jpa.order;
+
+import java.util.Properties;
+
+import javax.persistence.EntityManagerFactory;
+
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.data.jpa.repository.config.EnableJpaRepositories;
+import org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean;
+import org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter;
+
+import com.atomikos.jdbc.AtomikosDataSourceBean;
+
+@Configuration
+@EnableJpaRepositories(basePackages = "com.baeldung.atomikos.spring.jpa.order", entityManagerFactoryRef = "orderEntityManager", transactionManagerRef = "transactionManager")
+public class OrderConfig {
+
+    @Bean(initMethod = "init", destroyMethod = "close")
+    public AtomikosDataSourceBean orderDataSource() {
+        AtomikosDataSourceBean dataSource = new AtomikosDataSourceBean();
+        dataSource.setLocalTransactionMode(true);
+        dataSource.setUniqueResourceName("db2");
+        dataSource.setXaDataSourceClassName("org.apache.derby.jdbc.EmbeddedXADataSource");
+        Properties xaProperties = new Properties();
+        xaProperties.put("databaseName", "db2");
+        xaProperties.put("createDatabase", "create");
+        dataSource.setXaProperties(xaProperties);
+        dataSource.setPoolSize(10);
+        return dataSource;
+    }
+
+    @Bean
+    public EntityManagerFactory orderEntityManager() {
+        HibernateJpaVendorAdapter vendorAdapter = new HibernateJpaVendorAdapter();
+        LocalContainerEntityManagerFactoryBean factory = new LocalContainerEntityManagerFactoryBean();
+        factory.setJpaVendorAdapter(vendorAdapter);
+        factory.setPackagesToScan("com.baeldung.atomikos.spring.jpa.order");
+        factory.setDataSource(orderDataSource());
+        Properties jpaProperties = new Properties();
+        //jpaProperties.put("hibernate.show_sql", "true");
+        //jpaProperties.put("hibernate.format_sql", "true");
+        jpaProperties.put("hibernate.dialect", "org.hibernate.dialect.DerbyDialect");
+        jpaProperties.put("hibernate.current_session_context_class", "jta");
+        jpaProperties.put("javax.persistence.transactionType", "jta");
+        jpaProperties.put("hibernate.transaction.manager_lookup_class", "com.atomikos.icatch.jta.hibernate3.TransactionManagerLookup");
+        jpaProperties.put("hibernate.hbm2ddl.auto", "create-drop");
+        factory.setJpaProperties(jpaProperties);
+        factory.afterPropertiesSet();
+        return factory.getObject();
+    }
+
+}

atomikos/src/main/java/com/baeldung/atomikos/spring/jpa/order/OrderRepository.java

@@ -0,0 +1,9 @@
+package com.baeldung.atomikos.spring.jpa.order;
+
+import org.springframework.data.jpa.repository.JpaRepository;
+import org.springframework.stereotype.Repository;
+
+@Repository
+public interface OrderRepository extends JpaRepository<Order, String> {
+
+}

atomikos/src/main/resources/schema.sql

@@ -0,0 +1,10 @@
+CREATE TABLE INVENTORY (
+    productId VARCHAR PRIMARY KEY,
+    balance INT
+);
+
+CREATE TABLE ORDERS (
+    orderId VARCHAR PRIMARY KEY,
+    productId VARCHAR,
+    amount INT NOT NULL CHECK (amount <= 5)
+);

atomikos/src/main/resources/transactions.properties

@@ -0,0 +1 @@
+com.atomikos.icatch.file=logs

atomikos/src/test/java/com/baeldung/atomikos/direct/ApplicationUnitTest.java

@@ -0,0 +1,118 @@
+package com.baeldung.atomikos.direct;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.sql.Connection;
+import java.sql.ResultSet;
+import java.sql.SQLException;
+import java.sql.Statement;
+import java.util.Properties;
+import java.util.UUID;
+
+import javax.sql.DataSource;
+
+import org.junit.BeforeClass;
+import org.junit.Ignore;
+import org.junit.Test;
+
+import com.atomikos.icatch.jta.UserTransactionImp;
+import com.atomikos.jdbc.AtomikosDataSourceBean;
+
+public class ApplicationUnitTest {
+
+    private static DataSource inventoryDataSource;
+    private static DataSource orderDataSource;
+
+    private static String productId = UUID.randomUUID()
+        .toString();
+
+    @Test
+    @Ignore
+    public void testPlaceOrderSuccess() throws Exception {
+        int amount = 1;
+        long initialBalance = getBalance(inventoryDataSource, productId);
+        Application application = new Application(inventoryDataSource, orderDataSource);
+        application.placeOrder(productId, amount);
+        long finalBalance = getBalance(inventoryDataSource, productId);
+        assertEquals(initialBalance - amount, finalBalance);
+    }
+
+    @Test
+    @Ignore
+    public void testPlaceOrderFailure() throws Exception {
+        int amount = 10;
+        long initialBalance = getBalance(inventoryDataSource, productId);
+        Application application = new Application(inventoryDataSource, orderDataSource);
+        application.placeOrder(productId, amount);
+        long finalBalance = getBalance(inventoryDataSource, productId);
+        assertEquals(initialBalance, finalBalance);
+    }
+
+    @BeforeClass
+    public static void setUp() throws SQLException {
+
+        inventoryDataSource = getDataSource("db1");
+        orderDataSource = getDataSource("db2");
+        Connection inventoryConnection = inventoryDataSource.getConnection();
+        Connection orderConnection = orderDataSource.getConnection();
+        String createInventoryTable = "create table Inventory ( " + " productId VARCHAR ( 100 ) PRIMARY KEY, balance INT )";
+        String createInventoryRow = "insert into Inventory values ( '" + productId + "', 10000 )";
+        Statement s1 = inventoryConnection.createStatement();
+        try {
+            s1.executeUpdate(createInventoryTable);
+        } catch (Exception e) {
+            System.out.println("Inventory table exists");
+        }
+        try {
+            s1.executeUpdate(createInventoryRow);
+        } catch (Exception e) {
+            System.out.println("Product row exists");
+        }
+        s1.close();
+        String createOrderTable = "create table Orders ( orderId VARCHAR ( 100 ) PRIMARY KEY, productId VARCHAR ( 100 ), amount INT NOT NULL CHECK (amount <= 5) )";
+        Statement s2 = orderConnection.createStatement();
+        try {
+            s2.executeUpdate(createOrderTable);
+        } catch (Exception e) {
+            System.out.println("Orders table exists");
+        }
+        s2.close();
+        inventoryConnection.close();
+        orderConnection.close();
+    }
+
+    private static DataSource getDataSource(String db) {
+
+        DataSource ds;
+        AtomikosDataSourceBean ads = new AtomikosDataSourceBean();
+        ads.setXaDataSourceClassName("org.apache.derby.jdbc.EmbeddedXADataSource");
+        Properties properties = new Properties();
+        properties.put("databaseName", db);
+        properties.put("createDatabase", "create");
+        ads.setXaProperties(properties);
+        ads.setUniqueResourceName(db);
+        ads.setPoolSize(10); // optional
+        ads.setBorrowConnectionTimeout(10); // optional
+        ds = ads;
+        return ds;
+
+    }
+
+    private static long getBalance(DataSource inventoryDataSource, String productId) throws Exception {
+
+        UserTransactionImp utx = new UserTransactionImp();
+        utx.begin();
+        Connection inventoryConnection = inventoryDataSource.getConnection();
+        Statement s1 = inventoryConnection.createStatement();
+        String q1 = "select balance from Inventory where productId='" + productId + "'";
+        ResultSet rs1 = s1.executeQuery(q1);
+        if (rs1 == null || !rs1.next())
+            throw new Exception("Product not found: " + productId);
+        long balance = rs1.getLong(1);
+        inventoryConnection.close();
+        utx.commit();
+        return balance;
+
+    }
+
+}

atomikos/src/test/java/com/baeldung/atomikos/spring/ApplicationUnitTest.java

@@ -0,0 +1,108 @@
+package com.baeldung.atomikos.spring;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.sql.Connection;
+import java.sql.ResultSet;
+import java.sql.SQLException;
+import java.sql.Statement;
+import java.util.UUID;
+
+import javax.sql.DataSource;
+
+import org.junit.Before;
+import org.junit.Ignore;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.test.context.ContextConfiguration;
+import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
+
+import com.baeldung.atomikos.spring.config.Config;
+
+@RunWith(SpringJUnit4ClassRunner.class)
+@ContextConfiguration(classes = { Config.class })
+public class ApplicationUnitTest {
+
+    private static String productId = UUID.randomUUID()
+        .toString();
+
+    @Autowired
+    Application application;
+
+    @Autowired
+    DataSource inventoryDataSource;
+
+    @Autowired
+    DataSource orderDataSource;
+
+    @Test
+    @Ignore
+    public void testPlaceOrderSuccess() throws Exception {
+        int amount = 1;
+        long initialBalance = getBalance(inventoryDataSource, productId);
+        application.placeOrder(productId, amount);
+        long finalBalance = getBalance(inventoryDataSource, productId);
+        assertEquals(initialBalance - amount, finalBalance);
+    }
+
+    @Test
+    @Ignore
+    public void testPlaceOrderFailure() throws Exception {
+        int amount = 10;
+        long initialBalance = getBalance(inventoryDataSource, productId);
+        try {
+            application.placeOrder(productId, amount);
+        } catch (Exception e) {
+            System.out.println(e.getMessage());
+        }
+        long finalBalance = getBalance(inventoryDataSource, productId);
+        assertEquals(initialBalance, finalBalance);
+    }
+
+    @Before
+    public void setUp() throws SQLException {
+
+        Connection inventoryConnection = inventoryDataSource.getConnection();
+        Connection orderConnection = orderDataSource.getConnection();
+        String createInventoryTable = "create table Inventory ( " + " productId VARCHAR ( 100 ) PRIMARY KEY, balance INT )";
+        String createInventoryRow = "insert into Inventory values ( '" + productId + "', 10000 )";
+        Statement s1 = inventoryConnection.createStatement();
+        try {
+            s1.executeUpdate(createInventoryTable);
+        } catch (Exception e) {
+            System.out.println("Inventory table exists");
+        }
+        try {
+            s1.executeUpdate(createInventoryRow);
+        } catch (Exception e) {
+            System.out.println("Product row exists");
+        }
+        s1.close();
+        String createOrderTable = "create table Orders ( orderId VARCHAR ( 100 ) PRIMARY KEY, productId VARCHAR ( 100 ), amount INT NOT NULL CHECK (amount <= 5) )";
+        Statement s2 = orderConnection.createStatement();
+        try {
+            s2.executeUpdate(createOrderTable);
+        } catch (Exception e) {
+            System.out.println("Orders table exists");
+        }
+        s2.close();
+        inventoryConnection.close();
+        orderConnection.close();
+    }
+
+    private static long getBalance(DataSource inventoryDataSource, String productId) throws Exception {
+
+        Connection inventoryConnection = inventoryDataSource.getConnection();
+        Statement s1 = inventoryConnection.createStatement();
+        String q1 = "select balance from Inventory where productId='" + productId + "'";
+        ResultSet rs1 = s1.executeQuery(q1);
+        if (rs1 == null || !rs1.next())
+            throw new Exception("Product not found: " + productId);
+        long balance = rs1.getLong(1);
+        inventoryConnection.close();
+        return balance;
+
+    }
+
+}

atomikos/src/test/java/com/baeldung/atomikos/spring/jpa/ApplicationUnitTest.java

@@ -0,0 +1,80 @@
+package com.baeldung.atomikos.spring.jpa;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.sql.SQLException;
+import java.util.UUID;
+
+import org.junit.Before;
+import org.junit.Ignore;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.test.context.ContextConfiguration;
+import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
+
+import com.baeldung.atomikos.spring.jpa.config.Config;
+import com.baeldung.atomikos.spring.jpa.inventory.Inventory;
+import com.baeldung.atomikos.spring.jpa.inventory.InventoryConfig;
+import com.baeldung.atomikos.spring.jpa.inventory.InventoryRepository;
+import com.baeldung.atomikos.spring.jpa.order.OrderConfig;
+import com.baeldung.atomikos.spring.jpa.order.OrderRepository;
+
+@RunWith(SpringJUnit4ClassRunner.class)
+@ContextConfiguration(classes = { Config.class, InventoryConfig.class, OrderConfig.class })
+public class ApplicationUnitTest {
+
+    private static String productId = UUID.randomUUID()
+        .toString();
+
+    @Autowired
+    Application application;
+
+    @Autowired
+    InventoryRepository inventoryRepository;
+
+    @Autowired
+    OrderRepository orderRepository;
+
+    @Test
+    @Ignore
+    public void testPlaceOrderSuccess() throws Exception {
+        int amount = 1;
+        long initialBalance = getBalance(inventoryRepository, productId);
+        application.placeOrder(productId, amount);
+        long finalBalance = getBalance(inventoryRepository, productId);
+        assertEquals(initialBalance - amount, finalBalance);
+    }
+
+    @Test
+    @Ignore
+    public void testPlaceOrderFailure() throws Exception {
+        int amount = 10;
+        long initialBalance = getBalance(inventoryRepository, productId);
+        try {
+            application.placeOrder(productId, amount);
+        } catch (Exception e) {
+            System.out.println(e.getMessage());
+        }
+        long finalBalance = getBalance(inventoryRepository, productId);
+        assertEquals(initialBalance, finalBalance);
+    }
+
+    @Before
+    public void setUp() throws SQLException {
+
+        Inventory inventory = new Inventory();
+        inventory.setProductId(productId);
+        inventory.setBalance(new Long(10000));
+        inventoryRepository.save(inventory);
+
+    }
+
+    private static long getBalance(InventoryRepository inventoryRepository, String productId) throws Exception {
+
+        return inventoryRepository.findOne(productId)
+            .getBalance();
+
+    }
+
+}

atomikos/src/test/resources/logback.xml

@@ -0,0 +1,13 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<configuration>
+    <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
+        <encoder>
+            <pattern>%d{HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n
+            </pattern>
+        </encoder>
+    </appender>
+
+    <root level="INFO">
+        <appender-ref ref="STDOUT" />
+    </root>
+</configuration>

atomikos/src/test/resources/transactions.properties

@@ -0,0 +1 @@
+com.atomikos.icatch.file=logs

cas/README.md

@@ -1,7 +1,18 @@
 ## CAS
 
-This module contains articles about the Central Authentication Service (CAS)
+This module contains articles about the Central Authentication Service (CAS).
+
+The module consists of 2 submodules:
+1. `cas-server` - it requires JDK11 and uses the Gradle War Overlay style to ease setup and deployment. To  start the server, simply run:
+
+`./gradlew run
+  -Dorg.gradle.java.home=$JAVA11_HOME
+  -Pargs="-Dcas.standalone.configurationDirectory=/cas-server/src/main/resources/etc/cas/config"`
+
+The server starts at https://localhost:8443. `casuser`/`Mellon` are the username and password for logging in.
+
+2. `cas-secured-app` - A Maven based Springboot Application
 
 ### Relevant Articles: 
 
-- [CAS SSO With Spring Security](baeldung.com/spring-security-cas-sso)
+- [CAS SSO With Spring Security](https://www.baeldung.com/spring-security-cas-sso)

cas/cas-server/README.md

@@ -1,146 +0,0 @@
-CAS Overlay Template [![Build Status](https://travis-ci.org/apereo/cas-overlay-template.svg?branch=master)](https://travis-ci.org/apereo/cas-overlay-template)
-=======================
-
-Generic CAS WAR overlay to exercise the latest versions of CAS. This overlay could be freely used as a starting template for local CAS war overlays.
-
-# Versions
-
-- CAS `6.1.x`
-- JDK `11`
-
-# Overview
-
-To build the project, use:
-
-```bash
-# Use --refresh-dependencies to force-update SNAPSHOT versions
-./gradlew[.bat] clean build
-```
-
-To see what commands are available to the build script, run:
-
-```bash
-./gradlew[.bat] tasks
-```
-
-To launch into the CAS command-line shell:
-
-```bash
-./gradlew[.bat] downloadShell runShell
-```
-
-To fetch and overlay a CAS resource or view, use:
-
-```bash
-./gradlew[.bat] getResource -PresourceName=[resource-name]
-```
-
-To list all available CAS views and templates:
-
-```bash
-./gradlew[.bat] listTemplateViews
-```
-
-To unzip and explode the CAS web application file and the internal resources jar:
-
-```bash
-./gradlew[.bat] explodeWar
-```
-
-# Configuration
-
-- The `etc` directory contains the configuration files and directories that need to be copied to `/etc/cas/config`.
-
-```bash
-./gradlew[.bat] copyCasConfiguration
-```
-
-- The specifics of the build are controlled using the `gradle.properties` file.
-
-## Adding Modules
-
-CAS modules may be specified under the `dependencies` block of the [Gradle build script](build.gradle):
-
-```gradle
-dependencies {
-    compile "org.apereo.cas:cas-server-some-module:${project.casVersion}"
-    ...
-}
-```
-
-To collect the list of all project modules and dependencies:
-
-```bash
-./gradlew[.bat] allDependencies
-```
-
-### Clear Gradle Cache
-
-If you need to, on Linux/Unix systems, you can delete all the existing artifacts (artifacts and metadata) Gradle has downloaded using:
-
-```bash
-# Only do this when absolutely necessary
-rm -rf $HOME/.gradle/caches/
-```
-
-Same strategy applies to Windows too, provided you switch `$HOME` to its equivalent in the above command.
-
-# Deployment
-
-- Create a keystore file `thekeystore` under `/etc/cas`. Use the password `changeit` for both the keystore and the key/certificate entries. This can either be done using the JDK's `keytool` utility or via the following command:
-
-```bash
-./gradlew[.bat] createKeystore
-```
-
-- Ensure the keystore is loaded up with keys and certificates of the server.
-
-On a successful deployment via the following methods, CAS will be available at:
-
-* `https://cas.server.name:8443/cas`
-
-## Executable WAR
-
-Run the CAS web application as an executable WAR:
-
-```bash
-./gradlew[.bat] run
-```
-
-Debug the CAS web application as an executable WAR:
-
-```bash
-./gradlew[.bat] debug
-```
-
-Run the CAS web application as a *standalone* executable WAR:
-
-```bash
-./gradlew[.bat] clean executable
-```
-
-## External
-
-Deploy the binary web application file `cas.war` after a successful build to a servlet container of choice.
-
-## Docker
-
-The following strategies outline how to build and deploy CAS Docker images.
-
-### Jib
-
-The overlay embraces the [Jib Gradle Plugin](https://github.com/GoogleContainerTools/jib) to provide easy-to-use out-of-the-box tooling for building CAS docker images. Jib is an open-source Java containerizer from Google that lets Java developers build containers using the tools they know. It is a container image builder that handles all the steps of packaging your application into a container image. It does not require you to write a Dockerfile or have Docker installed, and it is directly integrated into the overlay.
-
-```bash
-./gradlew build jibDockerBuild
-```
-
-### Dockerfile
-
-You can also use the native Docker tooling and the provided `Dockerfile` to build and run CAS.
-
-```bash
-chmod +x *.sh
-./docker-build.sh
-./docker-run.sh
-```

core-groovy-2/determine-datatype/pom.xml

@@ -0,0 +1,40 @@
+<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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <groupId>com.baeldung.groovy</groupId>
+    <artifactId>determine-datatype</artifactId>
+    <version>0.0.1-SNAPSHOT</version>
+    <build>
+        <sourceDirectory>src</sourceDirectory>
+        <plugins>
+            <plugin>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <version>3.8.0</version>
+                <configuration>
+                    <source>1.8</source>
+                    <target>1.8</target>
+                </configuration>
+            </plugin>
+            <plugin>
+                <groupId>org.codehaus.gmaven</groupId>
+                <artifactId>groovy-maven-plugin</artifactId>
+                <dependencies>
+                    <dependency>
+                        <groupId>org.codehaus.groovy</groupId>
+                        <artifactId>groovy-all</artifactId>
+                        <version>2.0.6</version>
+                    </dependency>
+                </dependencies>
+            </plugin>
+        </plugins>
+    </build>
+    <dependencies>
+        <!-- https://mvnrepository.com/artifact/org.junit/junit5-engine -->
+        <dependency>
+            <groupId>org.junit</groupId>
+            <artifactId>junit5-engine</artifactId>
+            <version>5.0.0-ALPHA</version>
+        </dependency>
+    </dependencies>
+</project>

core-groovy-2/determine-datatype/src/com/baeldung/groovy/determine/datatype/Person.groovy

@@ -0,0 +1,14 @@
+package com.baeldung.groovy.determine.datatype
+
+class Person {
+    
+    private int ageAsInt
+    private Double ageAsDouble
+    private String ageAsString
+    
+    Person() {}
+    Person(int ageAsInt) { this.ageAsInt =  ageAsInt}
+    Person(Double ageAsDouble) { this.ageAsDouble =  ageAsDouble}
+    Person(String ageAsString) { this.ageAsString =  ageAsString}    
+}
+class Student extends Person {}

core-groovy-2/determine-datatype/src/com/baeldung/groovy/determine/datatype/PersonTest.groovy

@@ -0,0 +1,55 @@
+package com.baeldung.groovy.determine.datatype;
+
+import org.junit.Assert
+import org.junit.Test;
+
+public class PersonTest {
+    
+    @Test
+    public void givenWhenParameterTypeIsInteger_thenReturnTrue() {
+        Person personObj = new Person(10)
+        Assert.assertTrue(personObj.ageAsInt instanceof Integer);
+    }
+    
+    @Test
+    public void givenWhenParameterTypeIsDouble_thenReturnTrue() {
+        Person personObj = new Person(10.0)
+        Assert.assertTrue((personObj.ageAsDouble).getClass() == Double)
+    }
+    
+    @Test
+    public void givenWhenParameterTypeIsString_thenReturnTrue() {
+        Person personObj = new Person("10 years")
+        Assert.assertTrue(personObj.ageAsString.class == String)
+    }
+    
+    @Test
+    public void givenClassName_WhenParameterIsInteger_thenReturnTrue() {
+        Assert.assertTrue(Person.class.getDeclaredField('ageAsInt').type == int.class)
+    }
+    
+    @Test
+    public void givenWhenObjectIsInstanceOfType_thenReturnTrue() {
+        Person personObj = new Person()
+        Assert.assertTrue(personObj instanceof Person)
+    }
+
+    @Test
+    public void givenWhenInstanceIsOfSubtype_thenReturnTrue() {
+        Student studentObj = new Student()
+        Assert.assertTrue(studentObj in Person)
+    }
+    
+    @Test
+    public void givenGroovyList_WhenFindClassName_thenReturnTrue() {
+      def ageList = ['ageAsString','ageAsDouble', 10]   
+      Assert.assertTrue(ageList.class == ArrayList)     
+      Assert.assertTrue(ageList.getClass() == ArrayList)
+    }
+    
+    @Test
+    public void givenGrooyMap_WhenFindClassName_thenReturnTrue() {
+      def ageMap = [ageAsString: '10 years', ageAsDouble: 10.0]
+      Assert.assertFalse(ageMap.class == LinkedHashMap)
+    }
+}

core-groovy/src/test/groovy/com/baeldung/stringtoint/ConvertStringToInt.groovy

@@ -0,0 +1,110 @@
+package com.baeldung.stringtoint
+
+import org.junit.Test
+
+import java.text.DecimalFormat
+
+import static org.junit.Assert.assertEquals
+import static org.junit.Assert.assertNull
+
+class ConvertStringToInt {
+
+    @Test
+    void givenString_whenUsingAsInteger_thenConvertToInteger() {
+        def stringNum = "123"
+        def invalidString = "123a"
+        Integer expectedInteger = 123
+        Integer integerNum = stringNum as Integer
+        def intNum = invalidString?.isInteger() ? invalidString as Integer : null
+
+        assertNull(null, intNum)
+        assertEquals(integerNum, expectedInteger)
+    }
+
+    @Test
+    void givenString_whenUsingAsInt_thenConvertToInt() {
+        def stringNum = "123"
+        int expectedInt = 123
+        int intNum = stringNum as int
+
+        assertEquals(intNum, expectedInt)
+    }
+
+    @Test
+    void givenString_whenUsingToInteger_thenConvertToInteger() {
+        def stringNum = "123"
+        int expectedInt = 123
+        int intNum = stringNum.toInteger()
+
+        assertEquals(intNum, expectedInt)
+    }
+
+    @Test
+    void givenString_whenUsingParseInt_thenConvertToInteger() {
+        def stringNum = "123"
+        int expectedInt = 123
+        int intNum = Integer.parseInt(stringNum)
+
+        assertEquals(intNum, expectedInt)
+    }
+
+    @Test
+    void givenString_whenUsingValueOf_thenConvertToInteger() {
+        def stringNum = "123"
+        int expectedInt = 123
+        int intNum = Integer.valueOf(stringNum)
+
+        assertEquals(intNum, expectedInt)
+    }
+
+    @Test
+    void givenString_whenUsingIntValue_thenConvertToInteger() {
+        def stringNum = "123"
+        int expectedInt = 123
+        int intNum = new Integer(stringNum).intValue()
+
+        assertEquals(intNum, expectedInt)
+    }
+
+    @Test
+    void givenString_whenUsingNewInteger_thenConvertToInteger() {
+        def stringNum = "123"
+        int expectedInt = 123
+        int intNum = new Integer(stringNum)
+
+        assertEquals(intNum, expectedInt)
+    }
+
+    @Test
+    void givenString_whenUsingDecimalFormat_thenConvertToInteger() {
+        def stringNum = "123"
+        int expectedInt = 123
+        DecimalFormat decimalFormat = new DecimalFormat("#")
+        int intNum = decimalFormat.parse(stringNum).intValue()
+
+        assertEquals(intNum, expectedInt)
+    }
+
+    @Test(expected = NumberFormatException.class)
+    void givenInvalidString_whenUsingAs_thenThrowNumberFormatException() {
+        def invalidString = "123a"
+        invalidString as Integer
+    }
+
+    @Test(expected = NullPointerException.class)
+    void givenNullString_whenUsingToInteger_thenThrowNullPointerException() {
+        def invalidString = null
+        invalidString.toInteger()
+    }
+
+    @Test
+    void givenString_whenUsingIsInteger_thenCheckIfCorrectValue() {
+        def invalidString = "123a"
+        def validString = "123"
+        def invalidNum = invalidString?.isInteger() ? invalidString as Integer : false
+        def correctNum = validString?.isInteger() ? validString as Integer : false
+
+        assertEquals(false, invalidNum)
+        assertEquals(123, correctNum)
+    }
+}

core-java-modules/core-java-14/README.md

@@ -7,3 +7,4 @@ This module contains articles about Java 14.
 - [Guide to the @Serial Annotation in Java 14](https://www.baeldung.com/java-14-serial-annotation)
 - [Java Text Blocks](https://www.baeldung.com/java-text-blocks)
 - [Pattern Matching for instanceof in Java 14](https://www.baeldung.com/java-pattern-matching-instanceof)
+- [Helpful NullPointerExceptions in Java 14](https://www.baeldung.com/java-14-nullpointerexception)

core-java-modules/core-java-14/src/main/java/com/baeldung/java14/helpfulnullpointerexceptions/HelpfulNullPointerException.java

@@ -0,0 +1,56 @@
+package com.baeldung.java14.helpfulnullpointerexceptions;
+
+public class HelpfulNullPointerException {
+
+    public static void main(String[] args) {
+        Employee employee = null;
+        employee.getName();
+    }
+
+    public String getEmployeeEmailAddress(Employee employee) {
+        String emailAddress = employee.getPersonalDetails().getEmailAddress().toLowerCase();
+        return emailAddress;
+    }
+
+    static class Employee {
+        String name;
+        PersonalDetails personalDetails;
+
+        public String getName() {
+            return name;
+        }
+
+        public void setName(String name) {
+            this.name = name;
+        }
+
+        public PersonalDetails getPersonalDetails() {
+            return personalDetails;
+        }
+
+        public void setPersonalDetails(PersonalDetails personalDetails) {
+            this.personalDetails = personalDetails;
+        }
+    }
+
+    static class PersonalDetails {
+        String emailAddress;
+        String phone;
+
+        public String getEmailAddress() {
+            return emailAddress;
+        }
+
+        public void setEmailAddress(String emailAddress) {
+            this.emailAddress = emailAddress;
+        }
+
+        public String getPhone() {
+            return phone;
+        }
+
+        public void setPhone(String phone) {
+            this.phone = phone;
+        }
+    }
+}

core-java-modules/core-java-14/src/test/java/com/baeldung/java14/helpfulnullpointerexceptions/HelpfulNullPointerExceptionUnitTest.java

@@ -0,0 +1,37 @@
+package com.baeldung.java14.helpfulnullpointerexceptions;
+
+import org.junit.Test;
+
+import static com.baeldung.java14.helpfulnullpointerexceptions.HelpfulNullPointerException.Employee;
+import static com.baeldung.java14.helpfulnullpointerexceptions.HelpfulNullPointerException.PersonalDetails;
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class HelpfulNullPointerExceptionUnitTest {
+
+    @Test (expected = NullPointerException.class)
+    public void givenAnEmptyPersonalDetails_whenEmailAddressIsAccessed_thenThrowNPE() {
+        var helpfulNPE = new HelpfulNullPointerException();
+
+        var employee = new Employee();
+        employee.setName("Eduard");
+        employee.setPersonalDetails(new PersonalDetails());
+        helpfulNPE.getEmployeeEmailAddress(employee);
+    }
+
+    @Test
+    public void givenCompletePersonalDetails_whenEmailAddressIsAccessed_thenSuccess() {
+        var helpfulNPE = new HelpfulNullPointerException();
+        var emailAddress = "eduard@gmx.com";
+
+        var employee = new Employee();
+        employee.setName("Eduard");
+
+        var personalDetails = new PersonalDetails();
+        personalDetails.setEmailAddress(emailAddress.toUpperCase());
+        personalDetails.setPhone("1234");
+        employee.setPersonalDetails(personalDetails);
+
+        assertThat(helpfulNPE.getEmployeeEmailAddress(employee)).isEqualTo(emailAddress);
+    }
+
+}

core-java-modules/core-java-8-2/README.md

@@ -4,7 +4,6 @@ This module contains articles about Java 8 core features
 
 ### Relevant Articles: 
 
-- [How to Delay Code Execution in Java](https://www.baeldung.com/java-delay-code-execution)
 - [Run a Java Application from the Command Line](https://www.baeldung.com/java-run-jar-with-arguments)
 - [Java 8 Stream skip() vs limit()](https://www.baeldung.com/java-stream-skip-vs-limit)
 - [Guide to Java BiFunction Interface](https://www.baeldung.com/java-bifunction-interface)

core-java-modules/core-java-8-datetime-2/README.md

@@ -0,0 +1,5 @@
+### Relevant Articles:
+
+- [Generating Random Dates in Java](https://www.baeldung.com/java-random-dates)
+- [Creating a LocalDate with Values in Java](https://www.baeldung.com/java-creating-localdate-with-values)
+- [[<-- Prev]](/core-java-modules/core-java-datetime-java8-1)

core-java-modules/core-java-8-datetime-2/pom.xml

@@ -4,9 +4,9 @@
     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-datetime-java8</artifactId>
+    <artifactId>core-java-8-datetime</artifactId>
     <version>${project.parent.version}</version>
-    <name>core-java-datetime-java8</name>
+    <name>core-java-8-datetime</name>
     <packaging>jar</packaging>
 
     <parent>
@@ -64,8 +64,8 @@
     </build>
 
     <properties>
-        <maven.compiler.source>1.9</maven.compiler.source>
-        <maven.compiler.target>1.9</maven.compiler.target>
+        <maven.compiler.source>1.8</maven.compiler.source>
+        <maven.compiler.target>1.8</maven.compiler.target>
         <joda-time.version>2.10</joda-time.version>
         <!-- testing -->
         <assertj.version>3.6.1</assertj.version>

core-java-modules/core-java-8-datetime-2/src/test/java/com/baeldung/localdate/LocalDateExampleUnitTest.java

@@ -11,31 +11,31 @@ public class LocalDateExampleUnitTest {
 
     @Test
     public void givenValues_whenUsingOfMethod_thenLocalDate() {
-        assertEquals("2020-01-08", date.getCustomDateOne(2020, 1, 8));
+        assertEquals("2020-01-08", date.getCustomDateOne(2020, 1, 8).toString());
     }
 
     @Test
     public void givenValuesWithMonthEnum_whenUsingOfMethod_thenLocalDate() {
-        assertEquals("2020-01-08", date.getCustomDateTwo(2020, Month.JANUARY, 8));
+        assertEquals("2020-01-08", date.getCustomDateTwo(2020, Month.JANUARY, 8).toString());
     }
 
     @Test
     public void givenValues_whenUsingEpochDay_thenLocalDate() {
-        assertEquals("2020-01-08", date.getDateFromEpochDay(18269));
+        assertEquals("2020-01-08", date.getDateFromEpochDay(18269).toString());
     }
 
     @Test
     public void givenValues_whenUsingYearDay_thenLocalDate() {
-        assertEquals("2020-01-08", date.getDateFromYearAndDayOfYear(2020, 8));
+        assertEquals("2020-01-08", date.getDateFromYearAndDayOfYear(2020, 8).toString());
     }
 
     @Test
     public void givenValues_whenUsingParse_thenLocalDate() {
-        assertEquals("2020-01-08", date.getDateFromString("2020-01-08"));
+        assertEquals("2020-01-08", date.getDateFromString("2020-01-08").toString());
     }
 
     @Test
     public void givenValuesWithFormatter_whenUsingParse_thenLocalDate() {
-        assertEquals("2020-01-08", date.getDateFromStringAndFormatter("8-Jan-2020", "d-MMM-yyyy"));
+        assertEquals("2020-01-08", date.getDateFromStringAndFormatter("8-Jan-2020", "d-MMM-yyyy").toString());
     }
 }

core-java-modules/core-java-8-datetime/README.md

@@ -13,4 +13,4 @@ This module contains articles about the Date and Time API introduced with Java 8
 - [How to Get the Start and the End of a Day using Java](http://www.baeldung.com/java-day-start-end)
 - [Set the Time Zone of a Date in Java](https://www.baeldung.com/java-set-date-time-zone)
 - [Comparing Dates in Java](https://www.baeldung.com/java-comparing-dates)
-- [Generating Random Dates in Java](https://www.baeldung.com/java-random-dates)
+- [[Next -->]](/core-java-modules/core-java-datetime-java8-2)

core-java-modules/core-java-8-datetime/pom.xml

@@ -4,9 +4,9 @@
     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-datetime-java8</artifactId>
+    <artifactId>core-java-8-datetime</artifactId>
     <version>${project.parent.version}</version>
-    <name>core-java-datetime-java8</name>
+    <name>core-java-8-datetime</name>
     <packaging>jar</packaging>
 
     <parent>
@@ -64,8 +64,8 @@
     </build>
 
     <properties>
-        <maven.compiler.source>1.9</maven.compiler.source>
-        <maven.compiler.target>1.9</maven.compiler.target>
+        <maven.compiler.source>1.8</maven.compiler.source>
+        <maven.compiler.target>1.8</maven.compiler.target>
         <joda-time.version>2.10</joda-time.version>
         <!-- testing -->
         <assertj.version>3.6.1</assertj.version>

core-java-modules/core-java-9/README.md

@@ -8,5 +8,4 @@ This module contains articles about Java 9 core features
 - [Introduction to Chronicle Queue](https://www.baeldung.com/java-chronicle-queue)
 - [Iterate Through a Range of Dates in Java](https://www.baeldung.com/java-iterate-date-range)
 - [Initialize a HashMap in Java](https://www.baeldung.com/java-initialize-hashmap)
-- [Immutable Set in Java](https://www.baeldung.com/java-immutable-set)
 - [Immutable ArrayList in Java](https://www.baeldung.com/java-immutable-list)

core-java-modules/core-java-arrays-2/README.md

@@ -1,17 +0,0 @@
-## Core Java Arrays (Part 2)
-
-This module contains articles about Java arrays
-
-## Relevant Articles
-
-- [Extending an Array’s Length](https://www.baeldung.com/java-array-add-element-at-the-end)
-- [Looping Diagonally Through a 2d Java Array](https://www.baeldung.com/java-loop-diagonal-array)
-- [Converting Between Stream and Array in Java](https://www.baeldung.com/java-stream-to-array)
-- [Convert a Float to a Byte Array in Java](https://www.baeldung.com/java-convert-float-to-byte-array)
-- [Array Operations in Java](https://www.baeldung.com/java-common-array-operations)
-- [Intersection Between two Integer Arrays](https://www.baeldung.com/java-array-intersection)
-- [Removing an Element from an Array in Java](https://www.baeldung.com/java-array-remove-element)
-- [Removing the First Element of an Array](https://www.baeldung.com/java-array-remove-first-element)
-- [Adding an Element to a Java Array vs an ArrayList](https://www.baeldung.com/java-add-element-to-array-vs-list)
-- [Arrays.sort vs Arrays.parallelSort](https://www.baeldung.com/java-arrays-sort-vs-parallelsort)
-- [[<-- Prev]](/core-java-modules/core-java-arrays)

core-java-modules/core-java-arrays-3/README.md

@@ -1,3 +0,0 @@
-### Relevant Articles:
-
-- [Arrays.deepEquals](https://www.baeldung.com/java-arrays-deepequals)

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

@@ -0,0 +1,7 @@
+## Core Java Arrays - Conversions
+
+This module contains articles about arrays conversion in Java
+
+## Relevant Articles
+- [Convert a Float to a Byte Array in Java](https://www.baeldung.com/java-convert-float-to-byte-array)
+- [Converting Between Stream and Array in Java](https://www.baeldung.com/java-stream-to-array)

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

@@ -0,0 +1,27 @@
+<?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">
+    <parent>
+        <artifactId>core-java-modules</artifactId>
+        <groupId>com.baeldung.core-java-modules</groupId>
+        <version>1.0.0-SNAPSHOT</version>
+    </parent>
+    <modelVersion>4.0.0</modelVersion>
+
+    <artifactId>core-java-arrays-convert</artifactId>
+    <name>core-java-arrays-convert</name>
+    <packaging>jar</packaging>
+
+    <dependencies>
+        <dependency>
+            <groupId>com.google.guava</groupId>
+            <artifactId>guava</artifactId>
+            <version>${guava.version}</version>
+        </dependency>
+    </dependencies>
+
+    <properties>
+        <guava.version>28.2-jre</guava.version>
+    </properties>
+</project>

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

@@ -0,0 +1,7 @@
+## Core Java Arrays - Guides
+
+This module contains complete guides about arrays in Java
+
+### Relevant Articles: 
+- [Arrays in Java: A Reference Guide](https://www.baeldung.com/java-arrays-guide)
+- [Guide to the java.util.Arrays Class](https://www.baeldung.com/java-util-arrays)

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

@@ -0,0 +1,32 @@
+<?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">
+    <parent>
+        <artifactId>core-java-modules</artifactId>
+        <groupId>com.baeldung.core-java-modules</groupId>
+        <version>1.0.0-SNAPSHOT</version>
+    </parent>
+    <modelVersion>4.0.0</modelVersion>
+
+    <artifactId>core-java-arrays-guides</artifactId>
+    <name>core-java-arrays-guides</name>
+    <packaging>jar</packaging>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.openjdk.jmh</groupId>
+            <artifactId>jmh-core</artifactId>
+            <version>${jmh.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.openjdk.jmh</groupId>
+            <artifactId>jmh-generator-annprocess</artifactId>
+            <version>${jmh.version}</version>
+        </dependency>
+    </dependencies>
+
+    <properties>
+        <jmh.version>1.19</jmh.version>
+    </properties>
+</project>