BAEL-2569 Merge branch 'master' of https://github.com/eugenp/tutorials

algorithms-miscellaneous-1/README.md

@@ -17,3 +17,4 @@
 - [Java Two Pointer Technique](https://www.baeldung.com/java-two-pointer-technique)
 - [Permutations of an Array in Java](https://www.baeldung.com/java-array-permutations)
 - [Implementing Simple State Machines with Java Enums](https://www.baeldung.com/java-enum-simple-state-machine)
+- [Generate Combinations in Java](https://www.baeldung.com/java-combinations-algorithm)

algorithms-miscellaneous-2/src/main/java/com/baeldung/algorithms/relativelyprime/RelativelyPrime.java

@@ -0,0 +1,45 @@
+package com.baeldung.algorithms.relativelyprime;
+
+import java.math.BigInteger;
+
+class RelativelyPrime {
+
+    static boolean iterativeRelativelyPrime(int a, int b) {
+        return iterativeGCD(a, b) == 1;
+    }
+
+    static boolean recursiveRelativelyPrime(int a, int b) {
+        return recursiveGCD(a, b) == 1;
+    }
+
+    static boolean bigIntegerRelativelyPrime(int a, int b) {
+        return BigInteger.valueOf(a).gcd(BigInteger.valueOf(b)).equals(BigInteger.ONE);
+    }
+
+    private static int iterativeGCD(int a, int b) {
+        int tmp;
+        while (b != 0) {
+            if (a < b) {
+                tmp = a;
+                a = b;
+                b = tmp;
+            }
+            tmp = b;
+            b = a % b;
+            a = tmp;
+        }
+        return a;
+    }
+
+    private static int recursiveGCD(int a, int b) {
+        if (b == 0) {
+            return a;
+        }
+        if (a < b) {
+            return recursiveGCD(b, a);
+        }
+        return recursiveGCD(b, a % b);
+    }
+
+
+}

algorithms-miscellaneous-2/src/main/java/com/baeldung/algorithms/reversingtree/TreeNode.java

@@ -0,0 +1,42 @@
+package com.baeldung.algorithms.reversingtree;
+
+public class TreeNode {
+
+    private int value;
+    private TreeNode rightChild;
+    private TreeNode leftChild;
+
+    public int getValue() {
+        return value;
+    }
+
+    public void setValue(int value) {
+        this.value = value;
+    }
+
+    public TreeNode getRightChild() {
+        return rightChild;
+    }
+
+    public void setRightChild(TreeNode rightChild) {
+        this.rightChild = rightChild;
+    }
+
+    public TreeNode getLeftChild() {
+        return leftChild;
+    }
+
+    public void setLeftChild(TreeNode leftChild) {
+        this.leftChild = leftChild;
+    }
+
+    public TreeNode(int value, TreeNode rightChild, TreeNode leftChild) {
+        this.value = value;
+        this.rightChild = rightChild;
+        this.leftChild = leftChild;
+    }
+
+    public TreeNode(int value) {
+        this.value = value;
+    }
+}

algorithms-miscellaneous-2/src/main/java/com/baeldung/algorithms/reversingtree/TreeReverser.java

@@ -0,0 +1,68 @@
+package com.baeldung.algorithms.reversingtree;
+
+import java.util.LinkedList;
+
+public class TreeReverser {
+
+    public TreeNode createBinaryTree() {
+
+        TreeNode leaf1 = new TreeNode(3);
+        TreeNode leaf2 = new TreeNode(1);
+        TreeNode leaf3 = new TreeNode(9);
+        TreeNode leaf4 = new TreeNode(6);
+
+        TreeNode nodeLeft = new TreeNode(2, leaf1, leaf2);
+        TreeNode nodeRight = new TreeNode(7, leaf3, leaf4);
+
+        TreeNode root = new TreeNode(4, nodeRight, nodeLeft);
+
+        return root;
+    }
+
+    public void reverseRecursive(TreeNode treeNode) {
+        if (treeNode == null) {
+            return;
+        }
+
+        TreeNode temp = treeNode.getLeftChild();
+        treeNode.setLeftChild(treeNode.getRightChild());
+        treeNode.setRightChild(temp);
+
+        reverseRecursive(treeNode.getLeftChild());
+        reverseRecursive(treeNode.getRightChild());
+    }
+
+    public void reverseIterative(TreeNode treeNode) {
+        LinkedList<TreeNode> queue = new LinkedList<TreeNode>();
+
+        if (treeNode != null) {
+            queue.add(treeNode);
+        }
+
+        while (!queue.isEmpty()) {
+
+            TreeNode node = queue.poll();
+            if (node.getLeftChild() != null)
+                queue.add(node.getLeftChild());
+            if (node.getRightChild() != null)
+                queue.add(node.getRightChild());
+
+            TreeNode temp = node.getLeftChild();
+            node.setLeftChild(node.getRightChild());
+            node.setRightChild(temp);
+        }
+    }
+
+    public String toString(TreeNode root) {
+        if (root == null) {
+            return "";
+        }
+
+        StringBuffer buffer = new StringBuffer(String.valueOf(root.getValue())).append(" ");
+
+        buffer.append(toString(root.getLeftChild()));
+        buffer.append(toString(root.getRightChild()));
+
+        return buffer.toString();
+    }
+}

algorithms-miscellaneous-2/src/test/java/com/baeldung/algorithms/relativelyprime/RelativelyPrimeUnitTest.java

@@ -0,0 +1,51 @@
+package com.baeldung.algorithms.relativelyprime;
+
+import org.junit.Test;
+
+import static com.baeldung.algorithms.relativelyprime.RelativelyPrime.*;
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class RelativelyPrimeUnitTest {
+
+    @Test
+    public void givenNonRelativelyPrimeNumbers_whenCheckingIteratively_shouldReturnFalse() {
+
+        boolean result = iterativeRelativelyPrime(45, 35);
+        assertThat(result).isFalse();
+    }
+
+    @Test
+    public void givenRelativelyPrimeNumbers_whenCheckingIteratively_shouldReturnTrue() {
+
+        boolean result = iterativeRelativelyPrime(500, 501);
+        assertThat(result).isTrue();
+    }
+
+    @Test
+    public void givenNonRelativelyPrimeNumbers_whenCheckingRecursively_shouldReturnFalse() {
+
+        boolean result = recursiveRelativelyPrime(45, 35);
+        assertThat(result).isFalse();
+    }
+
+    @Test
+    public void givenRelativelyPrimeNumbers_whenCheckingRecursively_shouldReturnTrue() {
+
+        boolean result = recursiveRelativelyPrime(500, 501);
+        assertThat(result).isTrue();
+    }
+
+    @Test
+    public void givenNonRelativelyPrimeNumbers_whenCheckingUsingBigIntegers_shouldReturnFalse() {
+
+        boolean result = bigIntegerRelativelyPrime(45, 35);
+        assertThat(result).isFalse();
+    }
+
+    @Test
+    public void givenRelativelyPrimeNumbers_whenCheckingBigIntegers_shouldReturnTrue() {
+
+        boolean result = bigIntegerRelativelyPrime(500, 501);
+        assertThat(result).isTrue();
+    }
+}

algorithms-miscellaneous-2/src/test/java/com/baeldung/algorithms/reversingtree/TreeReverserUnitTest.java

@@ -0,0 +1,33 @@
+package com.baeldung.algorithms.reversingtree;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+public class TreeReverserUnitTest {
+
+    @Test
+    public void givenTreeWhenReversingRecursivelyThenReversed() {
+        TreeReverser reverser = new TreeReverser();
+
+        TreeNode treeNode = reverser.createBinaryTree();
+
+        reverser.reverseRecursive(treeNode);
+
+        assertEquals("4 7 9 6 2 3 1", reverser.toString(treeNode)
+            .trim());
+    }
+
+    @Test
+    public void givenTreeWhenReversingIterativelyThenReversed() {
+        TreeReverser reverser = new TreeReverser();
+
+        TreeNode treeNode = reverser.createBinaryTree();
+
+        reverser.reverseIterative(treeNode);
+
+        assertEquals("4 7 9 6 2 3 1", reverser.toString(treeNode)
+            .trim());
+    }
+
+}

apache-fop/README.md

@@ -3,7 +3,3 @@
 ## Core Java Cookbooks and Examples
 
 ### Relevant Articles: 
-- [Immutable ArrayList in Java](http://www.baeldung.com/java-immutable-list)
-- [Java - Reading a Large File Efficiently](http://www.baeldung.com/java-read-lines-large-file)
-- [Java InputStream to String](http://www.baeldung.com/convert-input-stream-to-string)
-

cloud-foundry-uaa/cf-uaa-config/uaa.yml

@@ -0,0 +1,68 @@
+issuer:
+  uri: http://localhost:8080/uaa
+
+spring_profiles: default,hsqldb
+  
+encryption:
+  active_key_label: CHANGE-THIS-KEY
+  encryption_keys:
+    - label: CHANGE-THIS-KEY
+      passphrase: CHANGEME
+
+login:
+  serviceProviderKey: |
+    -----BEGIN RSA PRIVATE KEY-----
+    MIICXQIBAAKBgQDHtC5gUXxBKpEqZTLkNvFwNGnNIkggNOwOQVNbpO0WVHIivig5
+    L39WqS9u0hnA+O7MCA/KlrAR4bXaeVVhwfUPYBKIpaaTWFQR5cTR1UFZJL/OF9vA
+    fpOwznoD66DDCnQVpbCjtDYWX+x6imxn8HCYxhMol6ZnTbSsFW6VZjFMjQIDAQAB
+    AoGAVOj2Yvuigi6wJD99AO2fgF64sYCm/BKkX3dFEw0vxTPIh58kiRP554Xt5ges
+    7ZCqL9QpqrChUikO4kJ+nB8Uq2AvaZHbpCEUmbip06IlgdA440o0r0CPo1mgNxGu
+    lhiWRN43Lruzfh9qKPhleg2dvyFGQxy5Gk6KW/t8IS4x4r0CQQD/dceBA+Ndj3Xp
+    ubHfxqNz4GTOxndc/AXAowPGpge2zpgIc7f50t8OHhG6XhsfJ0wyQEEvodDhZPYX
+    kKBnXNHzAkEAyCA76vAwuxqAd3MObhiebniAU3SnPf2u4fdL1EOm92dyFs1JxyyL
+    gu/DsjPjx6tRtn4YAalxCzmAMXFSb1qHfwJBAM3qx3z0gGKbUEWtPHcP7BNsrnWK
+    vw6By7VC8bk/ffpaP2yYspS66Le9fzbFwoDzMVVUO/dELVZyBnhqSRHoXQcCQQCe
+    A2WL8S5o7Vn19rC0GVgu3ZJlUrwiZEVLQdlrticFPXaFrn3Md82ICww3jmURaKHS
+    N+l4lnMda79eSp3OMmq9AkA0p79BvYsLshUJJnvbk76pCjR28PK4dV1gSDUEqQMB
+    qy45ptdwJLqLJCeNoR0JUcDNIRhOCuOPND7pcMtX6hI/
+    -----END RSA PRIVATE KEY-----
+  serviceProviderKeyPassword: password
+  serviceProviderCertificate: |
+    -----BEGIN CERTIFICATE-----
+    MIIDSTCCArKgAwIBAgIBADANBgkqhkiG9w0BAQQFADB8MQswCQYDVQQGEwJhdzEO
+    MAwGA1UECBMFYXJ1YmExDjAMBgNVBAoTBWFydWJhMQ4wDAYDVQQHEwVhcnViYTEO
+    MAwGA1UECxMFYXJ1YmExDjAMBgNVBAMTBWFydWJhMR0wGwYJKoZIhvcNAQkBFg5h
+    cnViYUBhcnViYS5hcjAeFw0xNTExMjAyMjI2MjdaFw0xNjExMTkyMjI2MjdaMHwx
+    CzAJBgNVBAYTAmF3MQ4wDAYDVQQIEwVhcnViYTEOMAwGA1UEChMFYXJ1YmExDjAM
+    BgNVBAcTBWFydWJhMQ4wDAYDVQQLEwVhcnViYTEOMAwGA1UEAxMFYXJ1YmExHTAb
+    BgkqhkiG9w0BCQEWDmFydWJhQGFydWJhLmFyMIGfMA0GCSqGSIb3DQEBAQUAA4GN
+    ADCBiQKBgQDHtC5gUXxBKpEqZTLkNvFwNGnNIkggNOwOQVNbpO0WVHIivig5L39W
+    qS9u0hnA+O7MCA/KlrAR4bXaeVVhwfUPYBKIpaaTWFQR5cTR1UFZJL/OF9vAfpOw
+    znoD66DDCnQVpbCjtDYWX+x6imxn8HCYxhMol6ZnTbSsFW6VZjFMjQIDAQABo4Ha
+    MIHXMB0GA1UdDgQWBBTx0lDzjH/iOBnOSQaSEWQLx1syGDCBpwYDVR0jBIGfMIGc
+    gBTx0lDzjH/iOBnOSQaSEWQLx1syGKGBgKR+MHwxCzAJBgNVBAYTAmF3MQ4wDAYD
+    VQQIEwVhcnViYTEOMAwGA1UEChMFYXJ1YmExDjAMBgNVBAcTBWFydWJhMQ4wDAYD
+    VQQLEwVhcnViYTEOMAwGA1UEAxMFYXJ1YmExHTAbBgkqhkiG9w0BCQEWDmFydWJh
+    QGFydWJhLmFyggEAMAwGA1UdEwQFMAMBAf8wDQYJKoZIhvcNAQEEBQADgYEAYvBJ
+    0HOZbbHClXmGUjGs+GS+xC1FO/am2suCSYqNB9dyMXfOWiJ1+TLJk+o/YZt8vuxC
+    KdcZYgl4l/L6PxJ982SRhc83ZW2dkAZI4M0/Ud3oePe84k8jm3A7EvH5wi5hvCkK
+    RpuRBwn3Ei+jCRouxTbzKPsuCVB+1sNyxMTXzf0=
+    -----END CERTIFICATE-----
+
+#The secret that an external login server will use to authenticate to the uaa using the id `login`
+LOGIN_SECRET: loginsecret
+
+jwt:
+  token:
+    signing-key: |
+      -----BEGIN RSA PRIVATE KEY-----
+      MIIEpAIBAAKCAQEAqUeygEfDGxI6c1VDQ6xIyUSLrP6iz1y97iHFbtXSxXaArL4a
+      ...
+      v6Mtt5LcRAAVP7pemunTdju4h8Q/noKYlVDVL30uLYUfKBL4UKfOBw==
+      -----END RSA PRIVATE KEY-----
+    verification-key: |
+      -----BEGIN PUBLIC KEY-----
+      MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAqUeygEfDGxI6c1VDQ6xI
+      ...
+      AwIDAQAB
+      -----END PUBLIC KEY-----

cloud-foundry-uaa/cf-uaa-oauth2-client/pom.xml

@@ -0,0 +1,43 @@
+<?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>
+    <parent>
+        <groupId>org.springframework.boot</groupId>
+        <artifactId>spring-boot-starter-parent</artifactId>
+        <version>2.1.3.RELEASE</version>
+        <relativePath/> <!-- lookup parent from repository -->
+    </parent>
+    <groupId>com.example</groupId>
+    <artifactId>cf-uaa-oauth2-client</artifactId>
+    <version>0.0.1-SNAPSHOT</version>
+    <name>uaa-client-webapp</name>
+    <description>Demo project for Spring Boot</description>
+
+    <properties>
+        <java.version>1.8</java.version>
+    </properties>
+
+    <dependencies>
+
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-web</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-oauth2-client</artifactId>
+        </dependency>
+
+    </dependencies>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.springframework.boot</groupId>
+                <artifactId>spring-boot-maven-plugin</artifactId>
+            </plugin>
+        </plugins>
+    </build>
+
+</project>

cloud-foundry-uaa/cf-uaa-oauth2-client/src/main/java/com/baeldung/cfuaa/oauth2/client/CFUAAOAuth2ClientApplication.java

@@ -0,0 +1,13 @@
+package com.baeldung.cfuaa.oauth2.client;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+
+@SpringBootApplication
+public class CFUAAOAuth2ClientApplication {
+
+	public static void main(String[] args) {
+		SpringApplication.run(CFUAAOAuth2ClientApplication.class, args);
+	}
+
+}

cloud-foundry-uaa/cf-uaa-oauth2-client/src/main/java/com/baeldung/cfuaa/oauth2/client/CFUAAOAuth2ClientController.java

@@ -0,0 +1,80 @@
+package com.baeldung.cfuaa.oauth2.client;
+
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.http.HttpEntity;
+import org.springframework.http.HttpHeaders;
+import org.springframework.http.HttpMethod;
+import org.springframework.http.ResponseEntity;
+import org.springframework.security.oauth2.client.OAuth2AuthorizedClient;
+import org.springframework.security.oauth2.client.OAuth2AuthorizedClientService;
+import org.springframework.security.oauth2.client.authentication.OAuth2AuthenticationToken;
+import org.springframework.security.oauth2.core.OAuth2AccessToken;
+import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.RestController;
+import org.springframework.web.client.HttpClientErrorException;
+import org.springframework.web.client.RestTemplate;
+
+@RestController
+public class CFUAAOAuth2ClientController {
+
+    @Value("${resource.server.url}")
+    private String remoteResourceServer;
+
+    private RestTemplate restTemplate;
+
+    private OAuth2AuthorizedClientService authorizedClientService;
+
+    public CFUAAOAuth2ClientController(OAuth2AuthorizedClientService authorizedClientService) {
+        this.authorizedClientService = authorizedClientService;
+        this.restTemplate = new RestTemplate();
+    }
+
+    @RequestMapping("/")
+    public String index(OAuth2AuthenticationToken authenticationToken) {
+        OAuth2AuthorizedClient oAuth2AuthorizedClient = this.authorizedClientService.loadAuthorizedClient(authenticationToken.getAuthorizedClientRegistrationId(), authenticationToken.getName());
+        OAuth2AccessToken oAuth2AccessToken = oAuth2AuthorizedClient.getAccessToken();
+
+        String response = "Hello, " + authenticationToken.getPrincipal().getName();
+        response += "</br></br>";
+        response += "Here is your accees token :</br>" + oAuth2AccessToken.getTokenValue();
+        response += "</br>";
+        response += "</br>You can use it to call these Resource Server APIs:";
+        response += "</br></br>";
+        response += "<a href='/read'>Call Resource Server Read API</a>";
+        response += "</br>";
+        response += "<a href='/write'>Call Resource Server Write API</a>";
+        return response;
+    }
+
+    @RequestMapping("/read")
+    public String read(OAuth2AuthenticationToken authenticationToken) {
+        String url = remoteResourceServer + "/read";
+        return callResourceServer(authenticationToken, url);
+    }
+
+    @RequestMapping("/write")
+    public String write(OAuth2AuthenticationToken authenticationToken) {
+        String url = remoteResourceServer + "/write";
+        return callResourceServer(authenticationToken, url);
+    }
+
+    private String callResourceServer(OAuth2AuthenticationToken authenticationToken, String url) {
+        OAuth2AuthorizedClient oAuth2AuthorizedClient = this.authorizedClientService.loadAuthorizedClient(authenticationToken.getAuthorizedClientRegistrationId(), authenticationToken.getName());
+        OAuth2AccessToken oAuth2AccessToken = oAuth2AuthorizedClient.getAccessToken();
+
+        HttpHeaders headers = new HttpHeaders();
+        headers.add("Authorization", "Bearer " + oAuth2AccessToken.getTokenValue());
+
+        HttpEntity<String> entity = new HttpEntity<>("parameters", headers);
+        ResponseEntity<String> responseEntity = null;
+
+        String response = null;
+        try {
+            responseEntity = restTemplate.exchange(url, HttpMethod.GET, entity, String.class);
+            response = responseEntity.getBody();
+        } catch (HttpClientErrorException e) {
+            response = e.getMessage();
+        }
+        return response;
+    }
+}

cloud-foundry-uaa/cf-uaa-oauth2-client/src/main/resources/application.properties

@@ -0,0 +1,11 @@
+server.port=8081
+
+resource.server.url=http://localhost:8082
+
+spring.security.oauth2.client.registration.uaa.client-name=Web App Client
+spring.security.oauth2.client.registration.uaa.client-id=webappclient
+spring.security.oauth2.client.registration.uaa.client-secret=webappclientsecret
+spring.security.oauth2.client.registration.uaa.scope=resource.read,resource.write,openid,profile
+
+spring.security.oauth2.client.provider.uaa.issuer-uri=http://localhost:8080/uaa/oauth/token
+

cloud-foundry-uaa/cf-uaa-oauth2-client/src/main/resources/templates/index.html

@@ -0,0 +1 @@
+tintin

cloud-foundry-uaa/cf-uaa-oauth2-resource-server/pom.xml

@@ -0,0 +1,43 @@
+<?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>
+    <parent>
+        <groupId>org.springframework.boot</groupId>
+        <artifactId>spring-boot-starter-parent</artifactId>
+        <version>2.1.3.RELEASE</version>
+        <relativePath/> <!-- lookup parent from repository -->
+    </parent>
+    <groupId>com.baeldung.cfuaa</groupId>
+    <artifactId>cf-uaa-oauth2-resource-server</artifactId>
+    <version>0.0.1-SNAPSHOT</version>
+    <name>cf-uaa-oauth2-resource-server</name>
+    <description>Demo project for Spring Boot</description>
+
+    <properties>
+        <java.version>1.8</java.version>
+    </properties>
+
+    <dependencies>
+
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-oauth2-resource-server</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-web</artifactId>
+        </dependency>
+
+    </dependencies>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.springframework.boot</groupId>
+                <artifactId>spring-boot-maven-plugin</artifactId>
+            </plugin>
+        </plugins>
+    </build>
+
+</project>

cloud-foundry-uaa/cf-uaa-oauth2-resource-server/src/main/java/com/baeldung/cfuaa/oauth2/resourceserver/CFUAAOAuth2ResourceServerApplication.java

@@ -0,0 +1,13 @@
+package com.baeldung.cfuaa.oauth2.resourceserver;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+
+@SpringBootApplication
+public class CFUAAOAuth2ResourceServerApplication {
+
+	public static void main(String[] args) {
+		SpringApplication.run(CFUAAOAuth2ResourceServerApplication.class, args);
+	}
+
+}

cloud-foundry-uaa/cf-uaa-oauth2-resource-server/src/main/java/com/baeldung/cfuaa/oauth2/resourceserver/CFUAAOAuth2ResourceServerRestController.java

@@ -0,0 +1,28 @@
+package com.baeldung.cfuaa.oauth2.resourceserver;
+
+import org.springframework.security.core.annotation.AuthenticationPrincipal;
+import org.springframework.security.oauth2.jwt.Jwt;
+import org.springframework.security.oauth2.server.resource.authentication.JwtAuthenticationToken;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.RestController;
+
+import java.security.Principal;
+
+@RestController
+public class CFUAAOAuth2ResourceServerRestController {
+
+    @GetMapping("/")
+    public String index(@AuthenticationPrincipal Jwt jwt) {
+        return String.format("Hello, %s!", jwt.getSubject());
+    }
+
+    @GetMapping("/read")
+    public String read(JwtAuthenticationToken jwtAuthenticationToken) {
+        return "Hello write: " + jwtAuthenticationToken.getTokenAttributes();
+    }
+
+    @GetMapping("/write")
+    public String write(Principal principal) {
+        return "Hello write: " + principal.getName();
+    }
+}

cloud-foundry-uaa/cf-uaa-oauth2-resource-server/src/main/java/com/baeldung/cfuaa/oauth2/resourceserver/CFUAAOAuth2ResourceServerSecurityConfiguration.java

@@ -0,0 +1,21 @@
+package com.baeldung.cfuaa.oauth2.resourceserver;
+
+import org.springframework.security.config.annotation.web.builders.HttpSecurity;
+import org.springframework.security.config.annotation.web.configuration.EnableWebSecurity;
+import org.springframework.security.config.annotation.web.configuration.WebSecurityConfigurerAdapter;
+
+@EnableWebSecurity
+public class CFUAAOAuth2ResourceServerSecurityConfiguration extends WebSecurityConfigurerAdapter {
+
+	@Override
+	protected void configure(HttpSecurity http) throws Exception {
+		http
+			.authorizeRequests()
+                .antMatchers("/read/**").hasAuthority("SCOPE_resource.read")
+                .antMatchers("/write/**").hasAuthority("SCOPE_resource.write")
+                .anyRequest().authenticated()
+				.and()
+			.oauth2ResourceServer()
+				.jwt();
+	}
+}

cloud-foundry-uaa/cf-uaa-oauth2-resource-server/src/main/resources/application.properties

@@ -0,0 +1,3 @@
+server.port=8082
+
+spring.security.oauth2.resourceserver.jwt.issuer-uri=http://localhost:8080/uaa/oauth/token

core-groovy/README.md

@@ -8,3 +8,6 @@
 - [Types of Strings in Groovy](https://www.baeldung.com/groovy-strings)
 - [A Quick Guide to Iterating a Map in Groovy](https://www.baeldung.com/groovy-map-iterating)
 - [An Introduction to Traits in Groovy](https://www.baeldung.com/groovy-traits)
+- [Lists in Groovy](https://www.baeldung.com/groovy-lists)
+- [Converting a String to a Date in Groovy](https://www.baeldung.com/groovy-string-to-date)
+- [Guide to I/O in Groovy](https://www.baeldung.com/groovy-io)

core-groovy/src/main/groovy/com/baeldung/Person.groovy

@@ -0,0 +1,37 @@
+package com.baeldung
+
+class Person {
+    private String firstname
+    private String lastname
+    private Integer age
+
+    Person(String firstname, String lastname, Integer age) {
+        this.firstname = firstname
+        this.lastname = lastname
+        this.age = age
+    }
+
+    String getFirstname() {
+        return firstname
+    }
+
+    void setFirstname(String firstname) {
+        this.firstname = firstname
+    }
+
+    String getLastname() {
+        return lastname
+    }
+
+    void setLastname(String lastname) {
+        this.lastname = lastname
+    }
+
+    Integer getAge() {
+        return age
+    }
+
+    void setAge(Integer age) {
+        this.age = age
+    }
+}

core-groovy/src/main/groovy/com/baeldung/closures/Closures.groovy

@@ -0,0 +1,87 @@
+package com.baeldung.closures
+
+class Closures {
+    
+    def printWelcome = {
+        println "Welcome to Closures!"
+    }
+    
+    def print = { name ->
+        println name
+    }
+    
+    def formatToLowerCase(name) {
+        return name.toLowerCase()
+    }
+    def formatToLowerCaseClosure = { name ->
+        return name.toLowerCase()
+    }
+    
+    def count=0
+    
+    def increaseCount = {
+        count++
+    }
+    
+    def greet = {
+        return "Hello! ${it}"
+    }
+   
+    def multiply = { x, y ->
+        return x*y
+    }
+    
+    def calculate = {int x, int y, String operation ->
+        
+        //log closure
+        def log = {
+            println "Performing $it"
+        }
+        
+        def result = 0    
+        switch(operation) {
+            case "ADD":
+                log("Addition")
+                result = x+y
+                break
+            case "SUB":
+                log("Subtraction")
+                result = x-y
+                break
+            case "MUL":
+                log("Multiplication")
+                result = x*y
+                break
+            case "DIV":
+                log("Division")
+                result = x/y
+                break
+        }
+        return result
+    }
+    
+    def addAll = { int... args ->
+        return args.sum()
+    }
+    
+    def volume(Closure areaCalculator, int... dimensions) {
+        if(dimensions.size() == 3) {
+            
+            //consider dimension[0] = length, dimension[1] = breadth, dimension[2] = height
+            //for cube and cuboid
+            return areaCalculator(dimensions[0], dimensions[1]) * dimensions[2]
+        } else if(dimensions.size() == 2) {
+            
+            //consider dimension[0] = radius, dimension[1] = height
+            //for cylinder and cone
+            return areaCalculator(dimensions[0]) * dimensions[1]
+        } else if(dimensions.size() == 1) {
+            
+            //consider dimension[0] = radius
+            //for sphere
+            return areaCalculator(dimensions[0]) * dimensions[0]
+        }
+        
+    }
+     
+}

core-groovy/src/main/groovy/com/baeldung/closures/Employee.groovy

@@ -0,0 +1,6 @@
+package com.baeldung.closures
+
+class Employee {
+    
+    String fullName
+}

core-groovy/src/test/groovy/com/baeldung/closures/ClosuresUnitTest.groovy

@@ -0,0 +1,80 @@
+package com.baeldung.closures
+
+import spock.lang.Specification
+
+class ClosuresUnitTest extends GroovyTestCase {
+
+    Closures closures = new Closures()
+    
+    void testDeclaration() {
+        
+        closures.print("Hello! Closure")
+        closures.formatToLowerCaseClosure("Hello! Closure")
+        
+        closures.print.call("Hello! Closure")
+        closures.formatToLowerCaseClosure.call("Hello! Closure")
+        
+    }
+    
+    void testClosureVsMethods() {   
+        assert closures.formatToLowerCase("TONY STARK") == closures.formatToLowerCaseClosure("Tony STark")
+    }
+    
+    void testParameters() {
+        //implicit parameter
+        assert closures.greet("Alex") == "Hello! Alex"
+        
+        //multiple parameters
+        assert closures.multiply(2, 4) == 8
+        
+        assert closures.calculate(12, 4, "ADD") == 16
+        assert closures.calculate(12, 4, "SUB") == 8
+        assert closures.calculate(43, 8, "DIV") == 5.375
+                
+        //varags
+        assert closures.addAll(12, 10, 14) == 36
+       
+    }
+    
+    void testClosureAsAnArgument() {
+        assert closures.volume({ l, b -> return l*b }, 12, 6, 10) == 720
+        
+        assert closures.volume({ radius -> return Math.PI*radius*radius/3 }, 5, 10) == Math.PI * 250/3
+    }
+    
+    void testGStringsLazyEvaluation() {
+        def name = "Samwell"
+        def welcomeMsg = "Welcome! $name"
+        
+        assert welcomeMsg == "Welcome! Samwell"
+        
+        // changing the name does not affect original interpolated value
+        name = "Tarly"
+        assert welcomeMsg != "Welcome! Tarly"
+        
+        def fullName = "Tarly Samson"
+        def greetStr = "Hello! ${-> fullName}"
+        
+        assert greetStr == "Hello! Tarly Samson"
+
+        // this time changing the variable affects the interpolated String's value
+        fullName = "Jon Smith"
+        assert greetStr == "Hello! Jon Smith"
+    }
+    
+    void testClosureInLists() {
+        def list = [10, 11, 12, 13, 14, true, false, "BUNTHER"]
+        list.each {
+            println it
+        }
+        
+        assert [13, 14] == list.findAll{ it instanceof Integer && it >= 13}
+    }
+    
+    void testClosureInMaps() {
+        def map = [1:10, 2:30, 4:5]
+        
+        assert [10, 60, 20] == map.collect{it.key * it.value}
+    }
+    
+}

core-groovy/src/test/groovy/com/baeldung/lists/ListTest.groovy

@@ -129,13 +129,13 @@ class ListTest{
         assertTrue(filterList.findAll{it > 3} == [4, 5, 6, 76])
 
         assertTrue(filterList.findAll{ it instanceof Number} == [2, 1, 3, 4, 5, 6, 76])
-        
+
         assertTrue(filterList.grep( Number )== [2, 1, 3, 4, 5, 6, 76])
-        
+
         assertTrue(filterList.grep{ it> 6 }== [76])
 
         def conditionList = [2, 1, 3, 4, 5, 6, 76]
-        
+
         assertFalse(conditionList.every{ it < 6})
 
         assertTrue(conditionList.any{ it%2 == 0})
@@ -165,7 +165,7 @@ class ListTest{
 
         def strList = ["na", "ppp", "as"]
         assertTrue(strList.max() == "ppp")
-        
+
         Comparator minc = {a,b -> a == b? 0: a < b? -1 : 1}
         def numberList = [3, 2, 0, 7]
         assertTrue(numberList.min(minc) == 0)

core-groovy/src/test/groovy/com/baeldung/lists/ListUnitTest.groovy

@@ -0,0 +1,58 @@
+package com.baeldung.lists
+
+import com.baeldung.Person
+import org.junit.Test
+
+import static org.junit.Assert.*
+
+class ListUnitTest {
+
+    private final personList = [
+      new Person("Regina", "Fitzpatrick", 25),
+      new Person("Abagail", "Ballard", 26),
+      new Person("Lucian", "Walter", 30),
+    ]
+
+    @Test
+    void whenListContainsElement_thenCheckReturnsTrue() {
+        def list = ['a', 'b', 'c']
+
+        assertTrue(list.indexOf('a') > -1)
+        assertTrue(list.contains('a'))
+    }
+
+    @Test
+    void whenListContainsElement_thenCheckWithMembershipOperatorReturnsTrue() {
+        def list = ['a', 'b', 'c']
+
+        assertTrue('a' in list)
+    }
+
+    @Test
+    void givenListOfPerson_whenUsingStreamMatching_thenShouldEvaluateList() {
+        assertTrue(personList.stream().anyMatch {it.age > 20})
+        assertFalse(personList.stream().allMatch {it.age < 30})
+    }
+
+    @Test
+    void givenListOfPerson_whenUsingCollectionMatching_thenShouldEvaluateList() {
+        assertTrue(personList.any {it.age > 20})
+        assertFalse(personList.every {it.age < 30})
+    }
+
+    @Test
+    void givenListOfPerson_whenUsingStreamFind_thenShouldReturnMatchingElements() {
+        assertTrue(personList.stream().filter {it.age > 20}.findAny().isPresent())
+        assertFalse(personList.stream().filter {it.age > 30}.findAny().isPresent())
+        assertTrue(personList.stream().filter {it.age > 20}.findAll().size() == 3)
+        assertTrue(personList.stream().filter {it.age > 30}.findAll().isEmpty())
+    }
+
+    @Test
+    void givenListOfPerson_whenUsingCollectionFind_thenShouldReturnMatchingElements() {
+        assertNotNull(personList.find {it.age > 20})
+        assertNull(personList.find {it.age > 30})
+        assertTrue(personList.findAll {it.age > 20}.size() == 3)
+        assertTrue(personList.findAll {it.age > 30}.isEmpty())
+    }
+}

core-groovy/src/test/groovy/com/baeldung/map/MapUnitTest.groovy

@@ -1,10 +1,18 @@
 package com.baeldung.map
 
-import static org.junit.Assert.*
+import com.baeldung.Person
 import org.junit.Test
 
+import static org.junit.Assert.*
+
 class MapUnitTest {
 
+    private final personMap = [
+      Regina : new Person("Regina", "Fitzpatrick", 25),
+      Abagail: new Person("Abagail", "Ballard", 26),
+      Lucian : new Person("Lucian", "Walter", 30)
+    ]
+
     @Test
     void whenUsingEach_thenMapIsIterated() {
         def map = [
@@ -63,7 +71,7 @@ class MapUnitTest {
             'FF6347' : 'Tomato',
             'FF4500' : 'Orange Red'
         ]
-        
+
         map.eachWithIndex { key, val, index ->
             def indent = ((index == 0 || index % 2 == 0) ? "   " : "")
             println "$indent Hex Code: $key = Color Name: $val"
@@ -82,4 +90,65 @@ class MapUnitTest {
             println "Hex Code: $entry.key = Color Name: $entry.value"
         }
     }
+
+    @Test
+    void whenMapContainsKeyElement_thenCheckReturnsTrue() {
+        def map = [a: 'd', b: 'e', c: 'f']
+
+        assertTrue(map.containsKey('a'))
+        assertFalse(map.containsKey('e'))
+        assertTrue(map.containsValue('e'))
+    }
+
+    @Test
+    void whenMapContainsKeyElement_thenCheckByMembershipReturnsTrue() {
+        def map = [a: 'd', b: 'e', c: 'f']
+
+        assertTrue('a' in map)
+        assertFalse('f' in map)
+    }
+
+    @Test
+    void whenMapContainsFalseBooleanValues_thenCheckReturnsFalse() {
+        def map = [a: true, b: false, c: null]
+
+        assertTrue(map.containsKey('b'))
+        assertTrue('a' in map)
+        assertFalse('b' in map)
+        assertFalse('c' in map)
+    }
+
+    @Test
+    void givenMapOfPerson_whenUsingStreamMatching_thenShouldEvaluateMap() {
+        assertTrue(personMap.keySet().stream().anyMatch {it == "Regina"})
+        assertFalse(personMap.keySet().stream().allMatch {it == "Albert"})
+        assertFalse(personMap.values().stream().allMatch {it.age < 30})
+        assertTrue(personMap.entrySet().stream().anyMatch {it.key == "Abagail" && it.value.lastname == "Ballard"})
+    }
+
+    @Test
+    void givenMapOfPerson_whenUsingCollectionMatching_thenShouldEvaluateMap() {
+        assertTrue(personMap.keySet().any {it == "Regina"})
+        assertFalse(personMap.keySet().every {it == "Albert"})
+        assertFalse(personMap.values().every {it.age < 30})
+        assertTrue(personMap.any {firstname, person -> firstname == "Abagail" && person.lastname == "Ballard"})
+    }
+
+    @Test
+    void givenMapOfPerson_whenUsingCollectionFind_thenShouldReturnElements() {
+        assertNotNull(personMap.find {it.key == "Abagail" && it.value.lastname == "Ballard"})
+        assertTrue(personMap.findAll {it.value.age > 20}.size() == 3)
+    }
+
+    @Test
+    void givenMapOfPerson_whenUsingStreamFind_thenShouldReturnElements() {
+        assertTrue(
+          personMap.entrySet().stream()
+            .filter {it.key == "Abagail" && it.value.lastname == "Ballard"}
+            .findAny().isPresent())
+        assertTrue(
+          personMap.entrySet().stream()
+            .filter {it.value.age > 20}
+            .findAll().size() == 3)
+    }
 }

core-groovy/src/test/groovy/com/baeldung/set/SetUnitTest.groovy

@@ -0,0 +1,16 @@
+package com.baeldung.set
+
+import org.junit.Test
+
+import static org.junit.Assert.assertTrue
+
+class SetUnitTest {
+
+    @Test
+    void whenSetContainsElement_thenCheckReturnsTrue() {
+        def set = ['a', 'b', 'c'] as Set
+
+        assertTrue(set.contains('a'))
+        assertTrue('a' in set)
+    }
+}

core-java-11/README.md

@@ -4,3 +4,5 @@
 - [Java 11 Local Variable Syntax for Lambda Parameters](https://www.baeldung.com/java-var-lambda-params)
 - [Java 11 String API Additions](https://www.baeldung.com/java-11-string-api)
 - [Java 11 Nest Based Access Control](https://www.baeldung.com/java-nest-based-access-control)
+- [Exploring the New HTTP Client in Java 9 and 11](https://www.baeldung.com/java-9-http-client)
+- [An Introduction to Epsilon GC: A No-Op Experimental Garbage Collector](https://www.baeldung.com/jvm-epsilon-gc-garbage-collector)

core-java-11/src/modules/jlinkModule/com/baeldung/jlink/HelloWorld.java

@@ -0,0 +1,12 @@
+package com.baeldung.jlink;
+
+import java.util.logging.Logger;
+
+public class HelloWorld {
+
+    private static final Logger LOG = Logger.getLogger(HelloWorld.class.getName());
+
+    public static void main(String[] args) {
+        LOG.info("Hello World!");
+    }
+}

core-java-11/src/modules/jlinkModule/module-info.java

@@ -0,0 +1,3 @@
+module jlinkModule {
+    requires java.logging;
+}

core-java-12/pom.xml

@@ -0,0 +1,48 @@
+<?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>
+    <groupId>com.baeldung</groupId>
+    <artifactId>core-java-12</artifactId>
+    <version>0.1.0-SNAPSHOT</version>
+    <name>core-java-12</name>
+    <packaging>jar</packaging>
+    <url>http://maven.apache.org</url>
+
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-modules</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>${assertj.version}</version>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <version>${maven-compiler-plugin.version}</version>
+                <configuration>
+                    <source>${maven.compiler.source.version}</source>
+                    <target>${maven.compiler.target.version}</target>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+
+    <properties>
+        <maven.compiler.source.version>12</maven.compiler.source.version>
+        <maven.compiler.target.version>12</maven.compiler.target.version>
+        <assertj.version>3.6.1</assertj.version>
+    </properties>
+
+</project>

core-java-12/src/test/java/com/baeldung/collectors/CollectorsUnitTest.java

@@ -0,0 +1,71 @@
+package com.baeldung.collectors;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.Objects;
+
+import org.junit.Test;
+
+import static java.util.stream.Collectors.maxBy;
+import static java.util.stream.Collectors.minBy;
+import static java.util.stream.Collectors.teeing;
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Unit tests for collectors additions in Java 12.
+ */
+public class CollectorsUnitTest {
+
+    @Test
+    public void whenTeeing_ItShouldCombineTheResultsAsExpected() {
+        List<Integer> numbers = Arrays.asList(42, 4, 2, 24);
+        Range range = numbers.stream()
+            .collect(teeing(minBy(Integer::compareTo), maxBy(Integer::compareTo), (min, max) -> new Range(min.orElse(null), max.orElse(null))));
+
+        assertThat(range).isEqualTo(new Range(2, 42));
+    }
+
+    /**
+     * Represents a closed range of numbers between {@link #min} and
+     * {@link #max}, both inclusive.
+     */
+    private static class Range {
+
+        private final Integer min;
+
+        private final Integer max;
+
+        Range(Integer min, Integer max) {
+            this.min = min;
+            this.max = max;
+        }
+
+        Integer getMin() {
+            return min;
+        }
+
+        Integer getMax() {
+            return max;
+        }
+
+        @Override
+        public boolean equals(Object o) {
+            if (this == o)
+                return true;
+            if (o == null || getClass() != o.getClass())
+                return false;
+            Range range = (Range) o;
+            return Objects.equals(getMin(), range.getMin()) && Objects.equals(getMax(), range.getMax());
+        }
+
+        @Override
+        public int hashCode() {
+            return Objects.hash(getMin(), getMax());
+        }
+
+        @Override
+        public String toString() {
+            return "Range{" + "min=" + min + ", max=" + max + '}';
+        }
+    }
+}

core-java-8/src/test/java/com/baeldung/java8/Java8SortUnitTest.java

@@ -124,11 +124,44 @@ public class Java8SortUnitTest {
 
     @Test
     public final void givenStreamCustomOrdering_whenSortingEntitiesByName_thenCorrectlySorted() {
-        
         final List<Human> humans = Lists.newArrayList(new Human("Sarah", 10), new Human("Jack", 12));
         final Comparator<Human> nameComparator = (h1, h2) -> h1.getName().compareTo(h2.getName());
         
         final List<Human> sortedHumans = humans.stream().sorted(nameComparator).collect(Collectors.toList());
         Assert.assertThat(sortedHumans.get(0), equalTo(new Human("Jack", 12)));
     }
+
+    @Test
+    public final void givenStreamComparatorOrdering_whenSortingEntitiesByName_thenCorrectlySorted() {
+        final List<Human> humans = Lists.newArrayList(new Human("Sarah", 10), new Human("Jack", 12));
+
+        final List<Human> sortedHumans = humans.stream().sorted(Comparator.comparing(Human::getName)).collect(Collectors.toList());
+        Assert.assertThat(sortedHumans.get(0), equalTo(new Human("Jack", 12)));
+    }
+
+    @Test
+    public final void givenStreamNaturalOrdering_whenSortingEntitiesByNameReversed_thenCorrectlySorted() {
+        final List<String> letters = Lists.newArrayList("B", "A", "C");
+
+        final List<String> reverseSortedLetters = letters.stream().sorted(Comparator.reverseOrder()).collect(Collectors.toList());
+        Assert.assertThat(reverseSortedLetters.get(0), equalTo("C"));
+    }
+
+    @Test
+    public final void givenStreamCustomOrdering_whenSortingEntitiesByNameReversed_thenCorrectlySorted() {
+        final List<Human> humans = Lists.newArrayList(new Human("Sarah", 10), new Human("Jack", 12));
+        final Comparator<Human> reverseNameComparator = (h1, h2) -> h2.getName().compareTo(h1.getName());
+
+        final List<Human> reverseSortedHumans = humans.stream().sorted(reverseNameComparator).collect(Collectors.toList());
+        Assert.assertThat(reverseSortedHumans.get(0), equalTo(new Human("Sarah", 10)));
+    }
+
+    @Test
+    public final void givenStreamComparatorOrdering_whenSortingEntitiesByNameReversed_thenCorrectlySorted() {
+        final List<Human> humans = Lists.newArrayList(new Human("Sarah", 10), new Human("Jack", 12));
+
+        final List<Human> reverseSortedHumans = humans.stream().sorted(Comparator.comparing(Human::getName, Comparator.reverseOrder())).collect(Collectors.toList());
+        Assert.assertThat(reverseSortedHumans.get(0), equalTo(new Human("Sarah", 10)));
+    }
+
 }

core-java-8/src/test/java/com/baeldung/java8/optional/OptionalChainingUnitTest.java

@@ -0,0 +1,110 @@
+package com.baeldung.java8.optional;
+
+import org.junit.Before;
+import org.junit.Test;
+
+import java.util.Optional;
+import java.util.function.Supplier;
+import java.util.stream.Stream;
+
+import static org.junit.Assert.*;
+
+public class OptionalChainingUnitTest {
+
+    private boolean getEmptyEvaluated;
+    private boolean getHelloEvaluated;
+    private boolean getByeEvaluated;
+
+    @Before
+    public void setUp() {
+        getEmptyEvaluated = false;
+        getHelloEvaluated = false;
+        getByeEvaluated = false;
+    }
+
+    @Test
+    public void givenThreeOptionals_whenChaining_thenFirstNonEmptyIsReturned() {
+        Optional<String> found = Stream.of(getEmpty(), getHello(), getBye())
+                .filter(Optional::isPresent)
+                .map(Optional::get)
+                .findFirst();
+
+        assertEquals(getHello(), found);
+    }
+
+    @Test
+    public void givenTwoEmptyOptionals_whenChaining_thenEmptyOptionalIsReturned() {
+        Optional<String> found = Stream.of(getEmpty(), getEmpty())
+                .filter(Optional::isPresent)
+                .map(Optional::get)
+                .findFirst();
+
+        assertFalse(found.isPresent());
+    }
+
+    @Test
+    public void givenTwoEmptyOptionals_whenChaining_thenDefaultIsReturned() {
+        String found = Stream.<Supplier<Optional<String>>>of(
+                () -> createOptional("empty"),
+                () -> createOptional("empty")
+        )
+                .map(Supplier::get)
+                .filter(Optional::isPresent)
+                .map(Optional::get)
+                .findFirst()
+                .orElseGet(() -> "default");
+
+        assertEquals("default", found);
+    }
+
+    @Test
+    public void givenThreeOptionals_whenChaining_thenFirstNonEmptyIsReturnedAndRestNotEvaluated() {
+        Optional<String> found = Stream.<Supplier<Optional<String>>>of(this::getEmpty, this::getHello, this::getBye)
+                .map(Supplier::get)
+                .filter(Optional::isPresent)
+                .map(Optional::get)
+                .findFirst();
+
+        assertTrue(this.getEmptyEvaluated);
+        assertTrue(this.getHelloEvaluated);
+        assertFalse(this.getByeEvaluated);
+        assertEquals(getHello(), found);
+    }
+
+    @Test
+    public void givenTwoOptionalsReturnedByOneArgMethod_whenChaining_thenFirstNonEmptyIsReturned() {
+        Optional<String> found = Stream.<Supplier<Optional<String>>>of(
+                () -> createOptional("empty"),
+                () -> createOptional("hello")
+        )
+                .map(Supplier::get)
+                .filter(Optional::isPresent)
+                .map(Optional::get)
+                .findFirst();
+
+        assertEquals(createOptional("hello"), found);
+    }
+
+    private Optional<String> getEmpty() {
+        this.getEmptyEvaluated = true;
+        return Optional.empty();
+    }
+
+    private Optional<String> getHello() {
+        this.getHelloEvaluated = true;
+        return Optional.of("hello");
+    }
+
+    private Optional<String> getBye() {
+        this.getByeEvaluated = true;
+        return Optional.of("bye");
+    }
+
+    private Optional<String> createOptional(String input) {
+        if (input == null || input == "" || input == "empty") {
+            return Optional.empty();
+        }
+
+        return Optional.of(input);
+    }
+}

core-java-9/README.md

@@ -9,7 +9,6 @@
 - [Java 9 Convenience Factory Methods for Collections](http://www.baeldung.com/java-9-collections-factory-methods) 
 - [New Stream Collectors in Java 9](http://www.baeldung.com/java9-stream-collectors)
 - [Java 9 CompletableFuture API Improvements](http://www.baeldung.com/java-9-completablefuture)
-- [Java 9 Process API Improvements](http://www.baeldung.com/java-9-process-api)
 - [Introduction to Java 9 StackWalking API](http://www.baeldung.com/java-9-stackwalking-api)
 - [Introduction to Project Jigsaw](http://www.baeldung.com/project-jigsaw-java-modularity)
 - [Java 9 Optional API Additions](http://www.baeldung.com/java-9-optional)
@@ -25,7 +24,9 @@
 - [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)
 - [Java 9 Platform Logging API](https://www.baeldung.com/java-9-logging-api)
-- [Guide to java.lang.Process API](https://www.baeldung.com/java-process-api)
 - [Immutable Set in Java](https://www.baeldung.com/java-immutable-set)
 - [Multi-Release Jar Files](https://www.baeldung.com/java-multi-release-jar)
 - [Ahead of Time Compilation (AoT)](https://www.baeldung.com/ahead-of-time-compilation)
+- [Java 9 Process API Improvements](https://www.baeldung.com/java-9-process-api)
+- [Guide to java.lang.Process API](https://www.baeldung.com/java-process-api)
+

core-java-collections-list/README.md

@@ -30,3 +30,4 @@
 - [Determine If All Elements Are the Same in a Java List](https://www.baeldung.com/java-list-all-equal)
 - [List of Primitive Integer Values in Java](https://www.baeldung.com/java-list-primitive-int)
 - [Performance Comparison of Primitive Lists in Java](https://www.baeldung.com/java-list-primitive-performance)
+- [Filtering a Java Collection by a List](https://www.baeldung.com/java-filter-collection-by-list)

core-java-collections/README.md

@@ -33,3 +33,4 @@
 - [Differences Between HashMap and Hashtable](https://www.baeldung.com/hashmap-hashtable-differences)
 - [Java ArrayList vs Vector](https://www.baeldung.com/java-arraylist-vs-vector)
 - [Defining a Char Stack in Java](https://www.baeldung.com/java-char-stack)
+- [Time Comparison of Arrays.sort(Object[]) and Arrays.sort(int[])](https://www.baeldung.com/arrays-sortobject-vs-sortint)

core-java-concurrency-advanced/README.md

@@ -21,4 +21,5 @@
 - [Java CyclicBarrier vs CountDownLatch](https://www.baeldung.com/java-cyclicbarrier-countdownlatch)
 - [Guide to the Fork/Join Framework in Java](http://www.baeldung.com/java-fork-join)
 - [A Guide to ThreadLocalRandom in Java](http://www.baeldung.com/java-thread-local-random)
-- [The Thread.join() Method in Java](http://www.baeldung.com/java-thread-join)
+- [The Thread.join() Method in Java](http://www.baeldung.com/java-thread-join)
+- [Passing Parameters to Java Threads](https://www.baeldung.com/java-thread-parameters)

core-java-concurrency-basic/README.md

@@ -16,3 +16,4 @@
 - [Life Cycle of a Thread in Java](http://www.baeldung.com/java-thread-lifecycle)
 - [Runnable vs. Callable in Java](http://www.baeldung.com/java-runnable-callable)
 - [What is Thread-Safety and How to Achieve it](https://www.baeldung.com/java-thread-safety)
+- [How to Start a Thread in Java](https://www.baeldung.com/java-start-thread)

core-java-io/README.md

@@ -30,7 +30,6 @@
 - [Download a File From an URL in Java](http://www.baeldung.com/java-download-file)
 - [Create a Symbolic Link with Java](http://www.baeldung.com/java-symlink)
 - [Quick Use of FilenameFilter](http://www.baeldung.com/java-filename-filter)
-- [Initialize a HashMap in Java](https://www.baeldung.com/java-initialize-hashmap)
 - [Read a File into an ArrayList](https://www.baeldung.com/java-file-to-arraylist)
 - [Guide to Java OutputStream](https://www.baeldung.com/java-outputstream)
 - [Reading a CSV File into an Array](https://www.baeldung.com/java-csv-file-array)
@@ -40,3 +39,4 @@
 - [Create a Directory in Java](https://www.baeldung.com/java-create-directory)
 - [How to Write to a CSV File in Java](https://www.baeldung.com/java-csv)
 - [List Files in a Directory in Java](https://www.baeldung.com/java-list-directory-files)
+- [Java InputStream to Byte Array and ByteBuffer](https://www.baeldung.com/convert-input-stream-to-array-of-bytes)

core-java-jvm/README.md

@@ -0,0 +1,6 @@
+=========
+
+## Core Java JVM Cookbooks and Examples
+
+### Relevant Articles: 
+- [Method Inlining in the JVM](http://www.baeldung.com/method-inlining-in-the-jvm/)

core-java-jvm/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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <groupId>com.baeldung</groupId>
+    <artifactId>core-java-jvm</artifactId>
+    <version>0.1.0-SNAPSHOT</version>
+    <packaging>jar</packaging>
+    <name>core-java-jvm</name>
+
+    <parent>
+        <groupId>com.baeldung</groupId>
+        <artifactId>parent-modules</artifactId>
+        <version>1.0.0-SNAPSHOT</version>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>junit</groupId>
+            <artifactId>junit</artifactId>
+            <version>${junit.version}</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-lang3</artifactId>
+            <version>${commons-lang3.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>${assertj.version}</version>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+    <properties>
+        <commons-lang3.version>3.5</commons-lang3.version>
+        <assertj.version>3.6.1</assertj.version>
+    </properties>
+</project>

core-java-jvm/src/main/java/com/baeldung/inlining/ConsecutiveNumbersSum.java

@@ -0,0 +1,19 @@
+package com.baeldung.inlining;
+
+public class ConsecutiveNumbersSum {
+
+    private long totalSum;
+    private int totalNumbers;
+
+    public ConsecutiveNumbersSum(int totalNumbers) {
+        this.totalNumbers = totalNumbers;
+    }
+
+    public long getTotalSum() {
+        totalSum = 0;
+        for (int i = 1; i <= totalNumbers; i++) {
+            totalSum += i;
+        }
+        return totalSum;
+    }
+}

core-java-jvm/src/main/java/com/baeldung/inlining/InliningExample.java

@@ -0,0 +1,16 @@
+package com.baeldung.inlining;
+
+public class InliningExample {
+
+    public static final int NUMBERS_OF_ITERATIONS = 15000;
+
+    public static void main(String[] args) {
+        for (int i = 1; i < NUMBERS_OF_ITERATIONS; i++) {
+            calculateSum(i);
+        }
+    }
+
+    private static long calculateSum(int n) {
+        return new ConsecutiveNumbersSum(n).getTotalSum();
+    }
+}

core-java-jvm/src/test/java/com/baeldung/inlining/ConsecutiveNumbersSumUnitTest.java

@@ -0,0 +1,22 @@
+package com.baeldung.inlining;
+
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+public class ConsecutiveNumbersSumUnitTest {
+
+    private static final int TOTAL_NUMBERS = 10;
+
+    @Test
+    public void givenTotalIntegersNumber_whenSumCalculated_thenEquals() {
+        ConsecutiveNumbersSum consecutiveNumbersSum = new ConsecutiveNumbersSum(TOTAL_NUMBERS);
+        long expectedSum = calculateExpectedSum(TOTAL_NUMBERS);
+
+        assertEquals(expectedSum, consecutiveNumbersSum.getTotalSum());
+    }
+
+    private long calculateExpectedSum(int totalNumbers) {
+        return totalNumbers * (totalNumbers + 1) / 2;
+    }
+}

core-java-lang-oop/README.md

@@ -5,7 +5,6 @@
 ### Relevant Articles: 
 - [Guide to hashCode() in Java](http://www.baeldung.com/java-hashcode)
 - [A Guide to the Static Keyword in Java](http://www.baeldung.com/java-static)
-- [A Guide to Java Initialization](http://www.baeldung.com/java-initialization)
 - [Polymorphism in Java](http://www.baeldung.com/java-polymorphism)
 - [Method Overloading and Overriding in Java](http://www.baeldung.com/java-method-overload-override)
 - [How to Make a Deep Copy of an Object in Java](http://www.baeldung.com/java-deep-copy)

core-java-lang-syntax/src/main/java/com/baeldung/enums/README.md

@@ -1,2 +0,0 @@
-### Relevant Articles:
-- [A Guide to Java Enums](http://www.baeldung.com/a-guide-to-java-enums)

core-java-lang-syntax/src/main/java/com/baeldung/generics/Generics.java

@@ -1,5 +1,6 @@
 package com.baeldung.generics;
 
+import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
 import java.util.function.Function;
@@ -28,4 +29,10 @@ public class Generics {
         buildings.forEach(Building::paint);
     }
 
+    public static List<Integer> createList(int a) {
+        List<Integer> list = new ArrayList<>();
+        list.add(a);
+        return list;
+    }
+
 }

core-java-lang-syntax/src/test/java/com/baeldung/generics/GenericsUnitTest.java

@@ -6,6 +6,7 @@ import java.util.ArrayList;
 import java.util.List;
 
 import static org.hamcrest.CoreMatchers.hasItems;
+import static org.hamcrest.CoreMatchers.is;
 import static org.hamcrest.MatcherAssert.assertThat;
 import static org.junit.Assert.fail;
 
@@ -66,4 +67,12 @@ public class GenericsUnitTest {
         }
     }
 
+    @Test
+    public void givenAnInt_whenAddedToAGenericIntegerList_thenAListItemCanBeAssignedToAnInt() {
+        int number = 7;
+        List<Integer> list = Generics.createList(number);
+        int otherNumber = list.get(0);
+        assertThat(otherNumber, is(number));
+    }
+
 }

core-java-networking/src/main/java/com/baeldung/socket/read/Client.java

@@ -0,0 +1,29 @@
+package com.baeldung.socket.read;
+
+import java.net.*;
+import java.nio.charset.StandardCharsets;
+import java.io.*; 
+
+public class Client {
+    
+    public void runClient(String ip, int port) {
+        try {
+            Socket socket = new Socket(ip, port);
+            System.out.println("Connected to server ...");
+            DataInputStream in = new DataInputStream(System.in);
+            DataOutputStream out = new DataOutputStream(socket.getOutputStream());
+            
+            char type = 's'; // s for string
+            int length = 29;
+            String data = "This is a string of length 29";
+            byte[] dataInBytes = data.getBytes(StandardCharsets.UTF_8);         
+            //Sending data in TLV format        
+            out.writeChar(type);
+            out.writeInt(length);
+            out.write(dataInBytes);
+        } catch (IOException e) {
+            e.printStackTrace();
+        }
+    }
+
+}

core-java-networking/src/main/java/com/baeldung/socket/read/Server.java

@@ -0,0 +1,49 @@
+package com.baeldung.socket.read;
+
+import java.net.*;
+import java.nio.charset.StandardCharsets;
+import java.io.*; 
+
+public class Server {
+    
+    public void runServer(int port) {
+        //Start the server and wait for connection
+        try {
+            ServerSocket server = new ServerSocket(port);
+            System.out.println("Server Started. Waiting for connection ...");
+            Socket socket = server.accept();
+            System.out.println("Got connection from client.");
+            //Get input stream from socket variable and convert the same to DataInputStream
+            DataInputStream in = new DataInputStream(new BufferedInputStream(socket.getInputStream()));
+            //Read type and length of data
+            char dataType = in.readChar();
+            int length = in.readInt();
+            System.out.println("Type : "+dataType);
+            System.out.println("Lenght :"+length);
+            if(dataType == 's') {
+                //Read String data in bytes
+                byte[] messageByte = new byte[length];
+                boolean end = false;
+                StringBuilder dataString = new StringBuilder(length);
+                int totalBytesRead = 0;
+                //We need to run while loop, to read all data in that stream
+                while(!end) {
+                    int currentBytesRead = in.read(messageByte);
+                    totalBytesRead = currentBytesRead + totalBytesRead;
+                    if(totalBytesRead <= length) {
+                        dataString.append(new String(messageByte,0,currentBytesRead,StandardCharsets.UTF_8));
+                    } else {
+                        dataString.append(new String(messageByte,0,length - totalBytesRead + currentBytesRead,StandardCharsets.UTF_8));
+                    }
+                    if(dataString.length()>=length) {
+                        end = true;
+                    }
+                }
+                System.out.println("Read "+length+" bytes of message from client. Message = "+dataString);
+            }
+        } catch (Exception e) {
+            e.printStackTrace();
+        }
+    }
+
+}

core-java-networking/src/test/java/com/baeldung/socket/read/SocketReadAllDataLiveTest.java

@@ -0,0 +1,37 @@
+package com.baeldung.socket.read;
+
+import java.util.concurrent.TimeUnit;
+import org.junit.jupiter.api.Test;
+
+public class SocketReadAllDataLiveTest {
+    
+    @Test
+    public void givenServerAndClient_whenClientSendsAndServerReceivesData_thenCorrect() {
+        //Run server in new thread
+        Runnable runnable1 = () -> { runServer(); };
+        Thread thread1 = new Thread(runnable1);
+        thread1.start();
+        //Wait for 10 seconds 
+        try {
+            TimeUnit.SECONDS.sleep(10);
+        } catch (InterruptedException e) {
+            e.printStackTrace();
+        }
+        //Run client in a new thread
+        Runnable runnable2 = () -> { runClient(); };
+        Thread thread2 = new Thread(runnable2);
+        thread2.start();
+    }
+    
+    public static void runServer() {
+        //Run Server
+        Server server = new Server();
+        server.runServer(5555);
+    }
+    
+    public static void runClient() {
+        //Run Client
+        Client client = new Client();
+        client.runClient("127.0.0.1", 5555);
+    }
+}

core-java-os/.gitignore

@@ -0,0 +1,26 @@
+*.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
+*.txt
+backup-pom.xml
+/bin/
+/temp
+
+#IntelliJ specific
+.idea/
+*.iml

core-java-os/README.md

@@ -0,0 +1,10 @@
+=========
+
+This module uses Java 9, so make sure to have the JDK 9 installed to run it.
+
+## 
+### Relevant Articles: 
+- [Java 9 Process API Improvements](http://www.baeldung.com/java-9-process-api)
+- [Guide to java.lang.Process API](https://www.baeldung.com/java-process-api)
+- [Guide to java.lang.ProcessBuilder API](https://www.baeldung.com/java-lang-processbuilder-api)
+

core-java-os/pom.xml

@@ -0,0 +1,82 @@
+<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-os</artifactId>
+    <version>0.1.0-SNAPSHOT</version>
+    <name>core-java-os</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-collections4</artifactId>
+            <version>${commons-collections4.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>commons-io</groupId>
+            <artifactId>commons-io</artifactId>
+            <version>${commons-io.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-lang3</artifactId>
+            <version>${commons-lang3.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>log4j</groupId>
+            <artifactId>log4j</artifactId>
+            <version>${log4j.version}</version>
+        </dependency>
+        <!-- test scoped -->
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>${assertj.version}</version>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <finalName>core-java-os</finalName>
+        <resources>
+            <resource>
+                <directory>src/main/resources</directory>
+                <filtering>true</filtering>
+            </resource>
+        </resources>
+
+        <plugins>
+         <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <version>${maven-compiler-plugin.version}</version>
+                <configuration>
+                    <source>${maven.compiler.source}</source>
+                    <target>${maven.compiler.target}</target>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+
+    <properties>
+        <!-- util -->
+        <commons-lang3.version>3.5</commons-lang3.version>
+        <commons-collections4.version>4.1</commons-collections4.version>
+        <collections-generic.version>4.01</collections-generic.version>
+    
+        <!-- testing -->
+        <assertj.version>3.6.1</assertj.version>
+        <asspectj.version>1.8.9</asspectj.version>
+        <maven.compiler.source>1.9</maven.compiler.source>
+        <maven.compiler.target>1.9</maven.compiler.target>
+        <guava.version>25.1-jre</guava.version>
+    </properties>
+</project>

core-java-os/src/main/java/com/baeldung/java9/process/ProcessCompilationError.java

@@ -3,5 +3,5 @@ package com.baeldung.java9.process;
 public class ProcessCompilationError {
     //This method has been written to generate error to display 
     //how process errorStream() can consume error
-    public static void();
+    //public static void();
 }

core-java-os/src/main/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>

core-java-os/src/test/java/com/baeldung/java9/process/ProcessAPIEnhancementsUnitTest.java

@@ -18,13 +18,13 @@ import org.slf4j.LoggerFactory;
 
 public class ProcessAPIEnhancementsUnitTest {
 
-    Logger log = LoggerFactory.getLogger(ProcessAPIEnhancementsTest.class);
+    Logger log = LoggerFactory.getLogger(ProcessAPIEnhancementsUnitTest.class);
 
     @Test
     public void givenCurrentProcess_whenInvokeGetInfo_thenSuccess() throws IOException {
         ProcessHandle processHandle = ProcessHandle.current();
         ProcessHandle.Info processInfo = processHandle.info();
-        assertNotNull(processHandle.getPid());
+        assertNotNull(processHandle.pid());
         assertEquals(false, processInfo.arguments()
           .isPresent());
         assertEquals(true, processInfo.command()
@@ -51,7 +51,7 @@ public class ProcessAPIEnhancementsUnitTest {
           .start();
         ProcessHandle processHandle = process.toHandle();
         ProcessHandle.Info processInfo = processHandle.info();
-        assertNotNull(processHandle.getPid());
+        assertNotNull(processHandle.pid());
         assertEquals(false, processInfo.arguments()
           .isPresent());
         assertEquals(true, processInfo.command()
@@ -72,7 +72,7 @@ public class ProcessAPIEnhancementsUnitTest {
         Stream<ProcessHandle> liveProcesses = ProcessHandle.allProcesses();
         liveProcesses.filter(ProcessHandle::isAlive)
             .forEach(ph -> {
-                assertNotNull(ph.getPid());
+                assertNotNull(ph.pid());
                 assertEquals(true, ph.info()
                   .command()
                   .isPresent());
@@ -102,12 +102,12 @@ public class ProcessAPIEnhancementsUnitTest {
         Stream<ProcessHandle> children = ProcessHandle.current()
           .children();
         children.filter(ProcessHandle::isAlive)
-          .forEach(ph -> log.info("PID: {}, Cmd: {}", ph.getPid(), ph.info()
+          .forEach(ph -> log.info("PID: {}, Cmd: {}", ph.pid(), ph.info()
             .command()));
         Stream<ProcessHandle> descendants = ProcessHandle.current()
           .descendants();
         descendants.filter(ProcessHandle::isAlive)
-          .forEach(ph -> log.info("PID: {}, Cmd: {}", ph.getPid(), ph.info()
+          .forEach(ph -> log.info("PID: {}, Cmd: {}", ph.pid(), ph.info()
             .command()));
     }
 
@@ -121,12 +121,12 @@ public class ProcessAPIEnhancementsUnitTest {
           .start();
         ProcessHandle processHandle = process.toHandle();
 
-        log.info("PID: {} has started", processHandle.getPid());
+        log.info("PID: {} has started", processHandle.pid());
         CompletableFuture<ProcessHandle> onProcessExit = processHandle.onExit();
         onProcessExit.get();
         assertEquals(false, processHandle.isAlive());
         onProcessExit.thenAccept(ph -> {
-            log.info("PID: {} has stopped", ph.getPid());
+            log.info("PID: {} has stopped", ph.pid());
         });
     }
 

core-java-os/src/test/java/com/baeldung/java9/process/ProcessApiUnitTest.java

@@ -30,7 +30,7 @@ public class ProcessApiUnitTest {
     @Test
     public void processInfoExample() throws NoSuchAlgorithmException {
         ProcessHandle self = ProcessHandle.current();
-        long PID = self.getPid();
+        long PID = self.pid();
         ProcessHandle.Info procInfo = self.info();
         Optional<String[]> args = procInfo.arguments();
         Optional<String> cmd = procInfo.commandLine();
@@ -45,7 +45,7 @@ public class ProcessApiUnitTest {
 
         Stream<ProcessHandle> allProc = ProcessHandle.current().children();
         allProc.forEach(p -> {
-            System.out.println("Proc " + p.getPid());
+            System.out.println("Proc " + p.pid());
         });
 
     }
@@ -54,7 +54,7 @@ public class ProcessApiUnitTest {
     public void createAndDestroyProcess() throws IOException, InterruptedException {
         int numberOfChildProcesses = 5;
         for (int i = 0; i < numberOfChildProcesses; i++) {
-            createNewJVM(ServiceMain.class, i).getPid();
+            createNewJVM(ServiceMain.class, i).pid();
         }
 
         Stream<ProcessHandle> childProc = ProcessHandle.current().children();
@@ -62,10 +62,10 @@ public class ProcessApiUnitTest {
 
         childProc = ProcessHandle.current().children();
         childProc.forEach(processHandle -> {
-            assertTrue("Process " + processHandle.getPid() + " should be alive!", processHandle.isAlive());
+            assertTrue("Process " + processHandle.pid() + " should be alive!", processHandle.isAlive());
             CompletableFuture<ProcessHandle> onProcExit = processHandle.onExit();
             onProcExit.thenAccept(procHandle -> {
-                System.out.println("Process with PID " + procHandle.getPid() + " has stopped");
+                System.out.println("Process with PID " + procHandle.pid() + " has stopped");
             });
         });
 
@@ -73,14 +73,14 @@ public class ProcessApiUnitTest {
 
         childProc = ProcessHandle.current().children();
         childProc.forEach(procHandle -> {
-            assertTrue("Could not kill process " + procHandle.getPid(), procHandle.destroy());
+            assertTrue("Could not kill process " + procHandle.pid(), procHandle.destroy());
         });
 
         Thread.sleep(5000);
 
         childProc = ProcessHandle.current().children();
         childProc.forEach(procHandle -> {
-            assertFalse("Process " + procHandle.getPid() + " should not be alive!", procHandle.isAlive());
+            assertFalse("Process " + procHandle.pid() + " should not be alive!", procHandle.isAlive());
         });
 
     }

core-java-os/src/test/java/com/baeldung/java9/process/ProcessUnderstandingUnitTest.java

@@ -14,7 +14,7 @@ import java.lang.Integer;
 
 import org.junit.jupiter.api.Test;
 
-class ProcessUnderstandingTest {
+class ProcessUnderstandingUnitTest {
 
     @Test
     public void givenSourceProgram_whenExecutedFromAnotherProgram_thenSourceProgramOutput3() throws IOException {

core-java-os/src/test/resources/.gitignore

@@ -0,0 +1,13 @@
+*.class
+
+#folders#
+/target
+/neoDb*
+/data
+/src/main/webapp/WEB-INF/classes
+*/META-INF/*
+
+# Packaged files #
+*.jar
+*.war
+*.ear

core-java/README.md

@@ -29,7 +29,6 @@
 - [What is the serialVersionUID?](http://www.baeldung.com/java-serial-version-uid)
 - [A Guide to the ResourceBundle](http://www.baeldung.com/java-resourcebundle)
 - [Class Loaders in Java](http://www.baeldung.com/java-classloaders)
-- [Double-Checked Locking with Singleton](http://www.baeldung.com/java-singleton-double-checked-locking)
 - [Guide to Java Clock Class](http://www.baeldung.com/java-clock)
 - [Importance of Main Manifest Attribute in a Self-Executing JAR](http://www.baeldung.com/java-jar-executable-manifest-main-class)
 - [Java Global Exception Handler](http://www.baeldung.com/java-global-exception-handler)
@@ -51,3 +50,4 @@
 - [Finding Leap Years in Java](https://www.baeldung.com/java-leap-year)
 - [Java Bitwise Operators](https://www.baeldung.com/java-bitwise-operators)
 - [Guide to Creating and Running a Jar File in Java](https://www.baeldung.com/java-create-jar)
+- [Making a JSON POST Request With HttpURLConnection](https://www.baeldung.com/httpurlconnection-post)

core-kotlin-2/README.md

@@ -2,3 +2,5 @@
 
 - [Void Type in Kotlin](https://www.baeldung.com/kotlin-void-type)
 - [How to use Kotlin Range Expressions](https://www.baeldung.com/kotlin-ranges)
+- [Split a List into Parts in Kotlin](https://www.baeldung.com/kotlin-split-list-into-parts)
+- [String Comparison in Kotlin](https://www.baeldung.com/kotlin-string-comparison)

core-kotlin-2/pom.xml

@@ -13,4 +13,66 @@
         <relativePath>../parent-kotlin</relativePath>
     </parent>
 
-</project>
+    <dependencies>
+        <dependency>
+            <groupId>org.jetbrains.kotlin</groupId>
+            <artifactId>kotlin-stdlib-jdk8</artifactId>
+            <version>${kotlin.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.junit.platform</groupId>
+            <artifactId>junit-platform-runner</artifactId>
+            <version>${junit.platform.version}</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>${assertj.version}</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.jetbrains.kotlin</groupId>
+            <artifactId>kotlin-test</artifactId>
+            <version>${kotlin.version}</version>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.jetbrains.kotlin</groupId>
+                <artifactId>kotlin-maven-plugin</artifactId>
+                <version>${kotlin.version}</version>
+                <executions>
+                    <execution>
+                        <id>compile</id>
+                        <phase>compile</phase>
+                        <goals>
+                            <goal>compile</goal>
+                        </goals>
+                    </execution>
+                    <execution>
+                        <id>test-compile</id>
+                        <phase>test-compile</phase>
+                        <goals>
+                            <goal>test-compile</goal>
+                        </goals>
+                    </execution>
+                </executions>
+                <configuration>
+                    <jvmTarget>1.8</jvmTarget>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+
+    <properties>
+        <kotlin.version>1.2.71</kotlin.version>
+        <junit.platform.version>1.1.1</junit.platform.version>
+        <junit.vintage.version>5.2.0</junit.vintage.version>
+        <assertj.version>3.10.0</assertj.version>
+    </properties>
+
+</project>

core-kotlin-2/src/main/kotlin/com/baeldung/annotations/Annotations.kt

@@ -0,0 +1,7 @@
+package com.baeldung.annotations
+
+@Target(AnnotationTarget.FIELD)
+annotation class Positive
+
+@Target(AnnotationTarget.FIELD)
+annotation class AllowedNames(val names: Array<String>)

core-kotlin-2/src/main/kotlin/com/baeldung/annotations/Item.kt

@@ -0,0 +1,3 @@
+package com.baeldung.annotations
+
+class Item(@Positive val amount: Float, @AllowedNames(["Alice", "Bob"]) val name: String)

core-kotlin-2/src/main/kotlin/com/baeldung/annotations/Main.kt

@@ -0,0 +1,7 @@
+package com.baeldung.annotations
+
+fun main(args: Array<String>) {
+    val item = Item(amount = 1.0f, name = "Bob")
+    val validator = Validator()
+    println("Is instance valid? ${validator.isValid(item)}")
+}

core-kotlin-2/src/main/kotlin/com/baeldung/annotations/Validator.kt

@@ -0,0 +1,38 @@
+package com.baeldung.annotations
+
+/**
+ * Naive annotation-based validator.
+ * @author A.Shcherbakov
+ */
+class Validator() {
+
+    /**
+     * Return true if every item's property annotated with @Positive is positive and if
+     * every item's property annotated with @AllowedNames has a value specified in that annotation.
+     */
+    fun isValid(item: Item): Boolean {
+        val fields = item::class.java.declaredFields
+        for (field in fields) {
+            field.isAccessible = true
+            for (annotation in field.annotations) {
+                val value = field.get(item)
+                if (field.isAnnotationPresent(Positive::class.java)) {
+                    val amount = value as Float
+                    if (amount < 0) {
+                        return false
+                    }
+                }
+                if (field.isAnnotationPresent(AllowedNames::class.java)) {
+                    val allowedNames = field.getAnnotation(AllowedNames::class.java)?.names
+                    val name = value as String
+                    allowedNames?.let {
+                        if (!it.contains(name)) {
+                            return false
+                        }
+                    }
+                }
+            }
+        }
+        return true
+    }
+}

core-kotlin-2/src/main/kotlin/com/baeldung/range/CharRange.kt

@@ -0,0 +1,13 @@
+package com.baeldung.range
+
+fun main(args: Array<String>) {
+
+    for (ch in 'a'..'f') {
+        print(ch)
+    }
+    println()
+
+    for (ch in 'f' downTo 'a') {
+        print(ch)
+    }
+}

core-kotlin-2/src/main/kotlin/com/baeldung/range/Color.kt

@@ -0,0 +1,21 @@
+package com.baeldung.range
+
+enum class Color(val rgb: Int) {
+    BLUE(0x0000FF),
+    GREEN(0x008000),
+    RED(0xFF0000),
+    MAGENTA(0xFF00FF),
+    YELLOW(0xFFFF00);
+}
+
+fun main(args: Array<String>) {
+
+    println(Color.values().toList());
+    val red = Color.RED
+    val yellow = Color.YELLOW
+    val range = red..yellow
+
+    println(range.contains(Color.MAGENTA))
+    println(range.contains(Color.BLUE))
+    println(range.contains(Color.GREEN))
+}

core-kotlin-2/src/main/kotlin/com/baeldung/range/CustomColor.kt

@@ -0,0 +1,56 @@
+package com.baeldung.range
+
+import java.lang.IllegalStateException
+
+class CustomColor(val rgb: Int): Comparable<CustomColor> {
+
+    override fun compareTo(other: CustomColor): Int {
+        return this.rgb.compareTo(other.rgb)
+    }
+
+    operator fun rangeTo(that: CustomColor) = ColorRange(this,that)
+
+    operator fun inc(): CustomColor {
+        return CustomColor(rgb + 1)
+    }
+
+    init {
+        if(rgb < 0x000000 || rgb > 0xFFFFFF){
+            throw IllegalStateException("RGB must be between 0 and 16777215")
+        }
+    }
+
+    override fun toString(): String {
+        return "CustomColor(rgb=$rgb)"
+    }
+}
+class ColorRange(override val start: CustomColor,
+                override val endInclusive: CustomColor) : ClosedRange<CustomColor>, Iterable<CustomColor>{
+
+    override fun iterator(): Iterator<CustomColor> {
+        return ColorIterator(start, endInclusive)
+    }
+}
+
+class ColorIterator(val start: CustomColor, val endInclusive: CustomColor) : Iterator<CustomColor> {
+
+    var initValue = start
+
+    override fun hasNext(): Boolean {
+        return initValue <= endInclusive
+    }
+
+    override fun next(): CustomColor {
+        return initValue++
+    }
+}
+
+fun main(args: Array<String>) {
+    val a = CustomColor(0xABCDEF)
+    val b = CustomColor(-1)
+    val c = CustomColor(0xABCDFF)
+
+    for(color in a..c){
+        println(color)
+    }
+}

core-kotlin-2/src/main/kotlin/com/baeldung/range/Filter.kt

@@ -0,0 +1,18 @@
+package com.baeldung.range
+
+fun main(args: Array<String>) {
+    val r = 1..10
+
+    //Apply filter
+    val f = r.filter { it -> it % 2 == 0 }
+    println(f)
+
+    //Map
+    val m = r.map { it -> it * it }
+    println(m)
+
+    //Reduce
+    val rdc = r.reduce { a, b -> a + b }
+    println(rdc)
+
+}

core-kotlin-2/src/main/kotlin/com/baeldung/range/FirstLast.kt

@@ -0,0 +1,8 @@
+package com.baeldung.range
+
+fun main(args: Array<String>) {
+
+    println((1..9).first)
+    println((1..9 step 2).step)
+    println((3..9).reversed().last)
+}

core-kotlin-2/src/main/kotlin/com/baeldung/range/OtherRangeFunctions.kt

@@ -0,0 +1,14 @@
+package com.baeldung.range
+
+fun main(args: Array<String>) {
+
+    val r = 1..20
+    println(r.min())
+    println(r.max())
+    println(r.sum())
+    println(r.average())
+    println(r.count())
+
+    val repeated = listOf(1, 1, 2, 4, 4, 6, 10)
+    println(repeated.distinct())
+}

core-kotlin-2/src/main/kotlin/com/baeldung/range/Range.kt

@@ -0,0 +1,28 @@
+package com.baeldung.range
+
+fun main(args: Array<String>) {
+
+    for (i in 1..9) {
+        print(i)
+    }
+    println()
+
+    for (i in 9 downTo 1) {
+        print(i)
+    }
+    println()
+
+    for (i in 1.rangeTo(9)) {
+        print(i)
+    }
+    println()
+
+    for (i in 9.downTo(1)) {
+        print(i)
+    }
+    println()
+
+    for (i in 1 until 9) {
+        print(i)
+    }
+}

core-kotlin-2/src/main/kotlin/com/baeldung/range/ReverseRange.kt

@@ -0,0 +1,14 @@
+package com.baeldung.range
+
+fun main(args: Array<String>) {
+
+    (1..9).reversed().forEach {
+        print(it)
+    }
+
+    println()
+
+    (1..9).reversed().step(3).forEach {
+        print(it)
+    }
+}

core-kotlin-2/src/main/kotlin/com/baeldung/range/Step.kt

@@ -0,0 +1,15 @@
+package com.baeldung.range
+
+fun main(args: Array<String>) {
+
+    for(i in 1..9 step 2){
+        print(i)
+    }
+
+    println()
+
+    for (i in 9 downTo 1 step 2){
+        print(i)
+    }
+
+}

core-kotlin-2/src/main/kotlin/com/baeldung/range/UntilRange.kt

@@ -0,0 +1,8 @@
+package com.baeldung.range
+
+fun main(args: Array<String>) {
+
+    for (i in 1 until 9) {
+        print(i)
+    }
+}

core-kotlin-2/src/main/kotlin/com/baeldung/scope/ScopeFunctions.kt

@@ -0,0 +1,25 @@
+package com.baeldung.scope
+
+data class Student(var studentId: String = "", var name: String = "", var surname: String = "") {
+}
+
+data class Teacher(var teacherId: Int = 0, var name: String = "", var surname: String = "") {
+    fun setId(anId: Int): Teacher = apply { teacherId = anId }
+    fun setName(aName: String): Teacher = apply { name = aName }
+    fun setSurname(aSurname: String): Teacher = apply { surname = aSurname }
+}
+
+data class Headers(val headerInfo: String)
+
+data class Response(val headers: Headers)
+
+data class RestClient(val url: String) {
+    fun getResponse() = Response(Headers("some header info"))
+}
+
+data class BankAccount(val id: Int) {
+    fun checkAuthorization(username: String) = Unit
+    fun addPayee(payee: String) = Unit
+    fun makePayment(paymentDetails: String) = Unit
+
+}

core-kotlin-2/src/test/kotlin/com/baeldung/annotations/ValidationTest.kt

@@ -0,0 +1,41 @@
+package com.baeldung.annotations
+
+import org.junit.Test
+import kotlin.test.assertTrue
+import kotlin.test.assertFalse
+
+class ValidationTest {
+
+    @Test
+    fun whenAmountIsOneAndNameIsAlice_thenTrue() {
+        assertTrue(Validator().isValid(Item(1f, "Alice")))
+    }
+
+    @Test
+    fun whenAmountIsOneAndNameIsBob_thenTrue() {
+        assertTrue(Validator().isValid(Item(1f, "Bob")))
+    }
+
+
+    @Test
+    fun whenAmountIsMinusOneAndNameIsAlice_thenFalse() {
+        assertFalse(Validator().isValid(Item(-1f, "Alice")))
+    }
+
+    @Test
+    fun whenAmountIsMinusOneAndNameIsBob_thenFalse() {
+        assertFalse(Validator().isValid(Item(-1f, "Bob")))
+    }
+
+    @Test
+    fun whenAmountIsOneAndNameIsTom_thenFalse() {
+        assertFalse(Validator().isValid(Item(1f, "Tom")))
+    }
+
+    @Test
+    fun whenAmountIsMinusOneAndNameIsTom_thenFalse() {
+        assertFalse(Validator().isValid(Item(-1f, "Tom")))
+    }
+
+
+}

core-kotlin-2/src/test/kotlin/com/baeldung/range/CharRangeTest.kt

@@ -0,0 +1,17 @@
+package com.baeldung.range
+
+import org.junit.Test
+import kotlin.test.assertEquals
+
+class CharRangeTest {
+
+    @Test
+    fun testCharRange() {
+        assertEquals(listOf('a', 'b', 'c'), ('a'..'c').toList())
+    }
+
+    @Test
+    fun testCharDownRange() {
+        assertEquals(listOf('c', 'b', 'a'), ('c'.downTo('a')).toList())
+    }
+}

core-kotlin-2/src/test/kotlin/com/baeldung/range/ColorTest.kt

@@ -0,0 +1,20 @@
+package com.baeldung.range
+
+import org.junit.Test
+import kotlin.test.assertFalse
+import kotlin.test.assertTrue
+
+class ColorTest {
+
+    @Test
+    fun testEnumRange() {
+
+        println(Color.values().toList());
+        val red = Color.RED
+        val yellow = Color.YELLOW
+        val range = red..yellow
+
+        assertTrue { range.contains(Color.MAGENTA) }
+        assertFalse { range.contains(Color.BLUE) }
+    }
+}

core-kotlin-2/src/test/kotlin/com/baeldung/range/CustomColorTest.kt

@@ -0,0 +1,41 @@
+package com.baeldung.range
+
+import org.junit.Test
+import java.lang.IllegalStateException
+import kotlin.test.assertFailsWith
+import kotlin.test.assertTrue
+
+class CustomColorTest {
+
+    @Test
+    fun testInvalidConstructor(){
+        assertFailsWith(IllegalStateException::class){
+            CustomColor(-1)
+        }
+    }
+
+    @Test
+    fun assertHas10Colors(){
+        assertTrue {
+            val a = CustomColor(1)
+            val b = CustomColor(10)
+            val range = a..b
+            for(cc in range){
+                println(cc)
+            }
+            range.toList().size == 10
+        }
+    }
+
+    @Test
+    fun assertContains0xCCCCCC(){
+        assertTrue {
+            val a = CustomColor(0xBBBBBB)
+            val b = CustomColor(0xDDDDDD)
+            val range = a..b
+            range.contains(CustomColor(0xCCCCCC))
+        }
+    }
+
+}
+

core-kotlin-2/src/test/kotlin/com/baeldung/range/FilterTest.kt

@@ -0,0 +1,24 @@
+package com.baeldung.range
+
+import org.junit.Test
+import kotlin.test.assertEquals
+
+class FilterTest {
+
+    val r = 1..10
+
+    @Test
+    fun filterTest() {
+        assertEquals(listOf(2, 4, 6, 8, 10), r.filter { it -> it % 2 == 0 }.toList())
+    }
+
+    @Test
+    fun mapTest() {
+        assertEquals(listOf(1, 4, 9, 16, 25, 36, 49, 64, 81, 100), r.map { it -> it * it }.toList())
+    }
+
+    @Test
+    fun reduceTest() {
+        assertEquals(55, r.reduce { a, b -> a + b })
+    }
+}

core-kotlin-2/src/test/kotlin/com/baeldung/range/FirstLastTest.kt

@@ -0,0 +1,22 @@
+package com.baeldung.range
+
+import org.junit.Test
+import kotlin.test.assertEquals
+
+class FirstLastTest {
+
+    @Test
+    fun testFirst() {
+        assertEquals(1, (1..9).first)
+    }
+
+    @Test
+    fun testLast() {
+        assertEquals(9, (1..9).last)
+    }
+
+    @Test
+    fun testStep() {
+        assertEquals(2, (1..9 step 2).step)
+    }
+}

core-kotlin-2/src/test/kotlin/com/baeldung/range/OtherRangeFunctionsTest.kt

@@ -0,0 +1,40 @@
+package com.baeldung.range
+
+import org.junit.Test
+import kotlin.test.assertEquals
+
+class OtherRangeFunctionsTest {
+
+    val r = 1..20
+    val repeated = listOf(1, 1, 2, 4, 4, 6, 10)
+
+    @Test
+    fun testMin() {
+        assertEquals(1, r.min())
+    }
+
+    @Test
+    fun testMax() {
+        assertEquals(20, r.max())
+    }
+
+    @Test
+    fun testSum() {
+        assertEquals(210, r.sum())
+    }
+
+    @Test
+    fun testAverage() {
+        assertEquals(10.5, r.average())
+    }
+
+    @Test
+    fun testCount() {
+        assertEquals(20, r.count())
+    }
+
+    @Test
+    fun testDistinct() {
+        assertEquals(listOf(1, 2, 4, 6, 10), repeated.distinct())
+    }
+}

core-kotlin-2/src/test/kotlin/com/baeldung/range/RangeTest.kt

@@ -0,0 +1,22 @@
+package com.baeldung.range
+
+import org.junit.Test
+import kotlin.test.assertEquals
+
+class RangeTest {
+
+    @Test
+    fun testRange() {
+        assertEquals(listOf(1,2,3), (1.rangeTo(3).toList()))
+    }
+
+    @Test
+    fun testDownTo(){
+        assertEquals(listOf(3,2,1), (3.downTo(1).toList()))
+    }
+
+    @Test
+    fun testUntil(){
+        assertEquals(listOf(1,2), (1.until(3).toList()))
+    }
+}

core-kotlin-2/src/test/kotlin/com/baeldung/range/ReverseRangeTest.kt

@@ -0,0 +1,12 @@
+package com.baeldung.range
+
+import org.junit.Test
+import kotlin.test.assertEquals
+
+class ReverseRangeTest {
+
+    @Test
+    fun reversedTest() {
+        assertEquals(listOf(9, 6, 3), (1..9).reversed().step(3).toList())
+    }
+}

core-kotlin-2/src/test/kotlin/com/baeldung/range/StepTest.kt

@@ -0,0 +1,17 @@
+package com.baeldung.range
+
+import org.junit.Test
+import kotlin.test.assertEquals
+
+class StepTest {
+
+    @Test
+    fun testStep() {
+        assertEquals(listOf(1, 3, 5, 7, 9), (1..9 step 2).toList())
+    }
+
+    @Test
+    fun testStepDown() {
+        assertEquals(listOf(9, 7, 5, 3, 1), (9 downTo 1 step 2).toList())
+    }
+}

core-kotlin-2/src/test/kotlin/com/baeldung/range/UntilRangeTest.kt

@@ -0,0 +1,12 @@
+package com.baeldung.range
+
+import org.junit.Test
+import kotlin.test.assertEquals
+
+class UntilRangeTest {
+
+    @Test
+    fun testUntil() {
+        assertEquals(listOf(1, 2, 3, 4), (1 until 5).toList())
+    }
+}

core-kotlin-2/src/test/kotlin/com/baeldung/scope/ScopeFunctionsUnitTest.kt

@@ -0,0 +1,143 @@
+package com.baeldung.scope
+
+import org.junit.Test
+import kotlin.test.assertTrue
+
+
+class ScopeFunctionsUnitTest {
+
+    class Logger {
+
+        var called : Boolean = false
+
+        fun info(message: String) {
+            called = true
+        }
+
+        fun wasCalled() = called
+    }
+
+    @Test
+    fun shouldTransformWhenLetFunctionUsed() {
+        val stringBuider = StringBuilder()
+        val numberOfCharacters = stringBuider.let {
+            it.append("This is a transformation function.")
+            it.append("It takes a StringBuilder instance and returns the number of characters in the generated String")
+            it.length
+        }
+
+        assertTrue {
+            numberOfCharacters == 128
+        }
+    }
+
+    @Test
+    fun shouldHandleNullabilityWhenLetFunctionUsed() {
+
+        val message: String? = "hello there!"
+        val charactersInMessage = message?.let {
+            "At this point is safe to reference the variable. Let's print the message: $it"
+        } ?: "default value"
+
+        assertTrue {
+            charactersInMessage.equals("At this point is safe to reference the variable. Let's print the message: hello there!")
+        }
+
+        val aNullMessage = null
+        val thisIsNull = aNullMessage?.let {
+            "At this point it would be safe to reference the variable. But it will not really happen because it is null. Let's reference: $it"
+        } ?: "default value"
+
+        assertTrue {
+            thisIsNull.equals("default value")
+        }
+    }
+
+    @Test
+    fun shouldInitializeObjectWhenUsingApply() {
+        val aStudent = Student().apply {
+            studentId = "1234567"
+            name = "Mary"
+            surname = "Smith"
+        }
+
+        assertTrue {
+            aStudent.name.equals("Mary")
+        }
+    }
+
+    @Test
+    fun shouldAllowBuilderStyleObjectDesignWhenApplyUsedInClassMethods() {
+        val teacher = Teacher()
+            .setId(1000)
+            .setName("Martha")
+            .setSurname("Spector")
+
+        assertTrue {
+            teacher.surname.equals("Spector")
+        }
+    }
+
+    @Test
+    fun shouldAllowSideEffectWhenUsingAlso() {
+        val restClient = RestClient("http://www.someurl.com")
+
+        val logger = Logger()
+
+        val headers = restClient
+            .getResponse()
+            .also { logger.info(it.toString()) }
+            .headers
+
+        assertTrue {
+            logger.wasCalled() && headers.headerInfo.equals("some header info")
+        }
+
+    }
+
+    @Test
+    fun shouldInitializeFieldWhenAlsoUsed() {
+        val aStudent = Student().also { it.name = "John"}
+
+        assertTrue {
+            aStudent.name.equals("John")
+        }
+    }
+
+    @Test
+    fun shouldLogicallyGroupObjectCallsWhenUsingWith() {
+        val bankAccount = BankAccount(1000)
+        with (bankAccount) {
+            checkAuthorization("someone")
+            addPayee("some payee")
+            makePayment("payment information")
+        }
+    }
+
+    @Test
+    fun shouldConvertObjectWhenRunUsed() {
+        val stringBuider = StringBuilder()
+        val numberOfCharacters = stringBuider.run {
+            append("This is a transformation function.")
+            append("It takes a StringBuilder instance and returns the number of characters in the generated String")
+            length
+        }
+
+        assertTrue {
+            numberOfCharacters == 128
+        }
+    }
+
+    @Test
+    fun shouldHandleNullabilityWhenRunIsUsed() {
+        val message: String? = "hello there!"
+        val charactersInMessage = message?.run {
+            "At this point is safe to reference the variable. Let's print the message: $this"
+        } ?: "default value"
+
+        assertTrue {
+            charactersInMessage.equals("At this point is safe to reference the variable. Let's print the message: hello there!")
+        }
+    }
+
+}

core-kotlin-2/src/test/kotlin/com/baeldung/splitting/SplittingTest.kt

@@ -0,0 +1,99 @@
+package com.baeldung.lambda
+
+import org.junit.jupiter.api.Test
+import kotlin.test.assertEquals
+
+class SplittingTest {
+    private val evenList = listOf(0, "a", 1, "b", 2, "c");
+
+    private val unevenList = listOf(0, "a", 1, "b", 2, "c", 3);
+
+    private fun verifyList(resultList: List<List<Any>>) {
+        assertEquals("[[0, a], [1, b], [2, c]]", resultList.toString())
+    }
+
+    private fun verifyPartialList(resultList: List<List<Any>>) {
+        assertEquals("[[0, a], [1, b], [2, c], [3]]", resultList.toString())
+    }
+
+    @Test
+    fun whenChunked_thenListIsSplit() {
+        val resultList = evenList.chunked(2)
+        verifyList(resultList)
+    }
+
+    @Test
+    fun whenUnevenChunked_thenListIsSplit() {
+        val resultList = unevenList.chunked(2)
+        verifyPartialList(resultList)
+    }
+
+    @Test
+    fun whenWindowed_thenListIsSplit() {
+        val resultList = evenList.windowed(2, 2)
+        verifyList(resultList)
+    }
+
+    @Test
+    fun whenUnevenPartialWindowed_thenListIsSplit() {
+        val resultList = unevenList.windowed(2, 2, partialWindows = true)
+        verifyPartialList(resultList)
+    }
+
+    @Test
+    fun whenUnevenWindowed_thenListIsSplit() {
+        val resultList = unevenList.windowed(2, 2, partialWindows = false)
+        verifyList(resultList)
+    }
+
+    @Test
+    fun whenGroupByWithAscendingNumbers_thenListIsSplit() {
+        val numberList = listOf(1, 2, 3, 4, 5, 6);
+        val resultList = numberList.groupBy { (it + 1) / 2 }
+        assertEquals("[[1, 2], [3, 4], [5, 6]]", resultList.values.toString())
+        assertEquals("[1, 2, 3]", resultList.keys.toString())
+    }
+
+    @Test
+    fun whenGroupByWithAscendingNumbersUneven_thenListIsSplit() {
+        val numberList = listOf(1, 2, 3, 4, 5, 6, 7);
+        val resultList = numberList.groupBy { (it + 1) / 2 }.values
+        assertEquals("[[1, 2], [3, 4], [5, 6], [7]]", resultList.toString())
+    }
+
+    @Test
+    fun whenGroupByWithRandomNumbers_thenListIsSplitInWrongWay() {
+        val numberList = listOf(1, 3, 8, 20, 23, 30);
+        val resultList = numberList.groupBy { (it + 1) / 2 }
+        assertEquals("[[1], [3], [8], [20], [23], [30]]", resultList.values.toString())
+        assertEquals("[1, 2, 4, 10, 12, 15]", resultList.keys.toString())
+    }
+
+    @Test
+    fun whenWithIndexGroupBy_thenListIsSplit() {
+        val resultList = evenList.withIndex()
+                .groupBy { it.index / 2 }
+                .map { it.value.map { it.value } }
+        verifyList(resultList)
+    }
+
+    @Test
+    fun whenWithIndexGroupByUneven_thenListIsSplit() {
+        val resultList = unevenList.withIndex()
+                .groupBy { it.index / 2 }
+                .map { it.value.map { it.value } }
+        verifyPartialList(resultList)
+    }
+
+    @Test
+    fun whenFoldIndexed_thenListIsSplit() {
+        val resultList = evenList.foldIndexed(ArrayList<ArrayList<Any>>(evenList.size / 2)) { index, acc, item ->
+            if (index % 2 == 0) {
+                acc.add(ArrayList(2))
+            }
+            acc.last().add(item)
+            acc
+        }
+        verifyList(resultList)
+    }
+}

core-kotlin/README.md

@@ -54,3 +54,5 @@
 - [Nested forEach in Kotlin](https://www.baeldung.com/kotlin-nested-foreach)
 - [Building DSLs in Kotlin](https://www.baeldung.com/kotlin-dsl)
 - [Static Methods Behavior in Kotlin](https://www.baeldung.com/kotlin-static-methods)
+- [Inline Functions in Kotlin](https://www.baeldung.com/kotlin-inline-functions)
+- [Delegation Pattern in Kotlin](https://www.baeldung.com/kotlin-delegation-pattern)

core-kotlin/src/main/kotlin/com/baeldung/forEach/forEach.kt

@@ -5,6 +5,15 @@ class Country(val name : String, val cities : List<City>)
 
 class City(val name : String, val streets : List<String>)
 
+fun City.getStreetsWithCityName() : List<String> {
+    return streets.map { "$name, $it" }.toList()
+}
+
+fun Country.getCitiesWithCountryName() : List<String> {
+    return cities.flatMap { it.getStreetsWithCityName() }
+            .map { "$name, $it" }
+}
+
 class World {
 
     private val streetsOfAmsterdam = listOf("Herengracht", "Prinsengracht")
@@ -45,6 +54,19 @@ class World {
             }
         }
     }
+
+    fun allStreetsFlatMap() {
+
+        countries.flatMap { it.cities}
+                .flatMap { it.streets}
+                .forEach { println(it) }
+    }
+
+    fun allFlatMapTable() {
+
+        countries.flatMap { it.getCitiesWithCountryName() }
+                .forEach { println(it) }
+    }
 }
 
 fun main(args : Array<String>) {
@@ -56,6 +78,10 @@ fun main(args : Array<String>) {
     world.allNested()
 
     world.allTable()
+
+    world.allStreetsFlatMap()
+
+    world.allFlatMapTable()
 }