Merge pull request #3 from eugenp/master

Update local repo

algorithms-miscellaneous-6/README.md

@@ -7,4 +7,5 @@
 - [Efficiently Merge Sorted Java Sequences](https://www.baeldung.com/java-merge-sorted-sequences)
 - [Introduction to Greedy Algorithms with Java](https://www.baeldung.com/java-greedy-algorithms)
 - [The Caesar Cipher in Java](https://www.baeldung.com/java-caesar-cipher)
+- [Implementing a 2048 Solver in Java](https://www.baeldung.com/2048-java-solver)
 - More articles: [[<-- prev]](/../algorithms-miscellaneous-5)

algorithms-miscellaneous-6/src/main/java/com/baeldung/algorithms/topkelements/BruteForceTopKElementsFinder.java

@@ -0,0 +1,26 @@
+package com.baeldung.algorithms.topkelements;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class BruteForceTopKElementsFinder implements TopKElementsFinder<Integer> {
+
+    public List<Integer> findTopK(List<Integer> input, int k) {
+        List<Integer> array = new ArrayList<>(input);
+        List<Integer> topKList = new ArrayList<>();
+
+        for (int i = 0; i < k; i++) {
+            int maxIndex = 0;
+
+            for (int j = 1; j < array.size(); j++) {
+                if (array.get(j) > array.get(maxIndex)) {
+                    maxIndex = j;
+                }
+            }
+
+            topKList.add(array.remove(maxIndex));
+        }
+
+        return topKList;
+    }
+}

algorithms-miscellaneous-6/src/main/java/com/baeldung/algorithms/topkelements/MaxHeapTopKElementsFinder.java

@@ -0,0 +1,26 @@
+package com.baeldung.algorithms.topkelements;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import java.util.PriorityQueue;
+
+public class MaxHeapTopKElementsFinder implements TopKElementsFinder<Integer> {
+
+    public List<Integer> findTopK(List<Integer> input, int k) {
+        PriorityQueue<Integer> maxHeap = new PriorityQueue<>();
+
+        input.forEach(number -> {
+            maxHeap.add(number);
+
+            if (maxHeap.size() > k) {
+                maxHeap.poll();
+            }
+        });
+
+        List<Integer> topKList = new ArrayList<>(maxHeap);
+        Collections.reverse(topKList);
+
+        return topKList;
+    }
+}

algorithms-miscellaneous-6/src/main/java/com/baeldung/algorithms/topkelements/TopKElementsFinder.java

@@ -0,0 +1,7 @@
+package com.baeldung.algorithms.topkelements;
+
+import java.util.List;
+
+public interface TopKElementsFinder<T extends Comparable<T>> {
+    List<T> findTopK(List<T> input, int k);
+}

algorithms-miscellaneous-6/src/main/java/com/baeldung/algorithms/topkelements/TreeSetTopKElementsFinder.java

@@ -0,0 +1,17 @@
+package com.baeldung.algorithms.topkelements;
+
+import java.util.Comparator;
+import java.util.List;
+import java.util.Set;
+import java.util.TreeSet;
+import java.util.stream.Collectors;
+
+public class TreeSetTopKElementsFinder implements TopKElementsFinder<Integer> {
+
+    public List<Integer> findTopK(List<Integer> input, int k) {
+        Set<Integer> sortedSet = new TreeSet<>(Comparator.reverseOrder());
+        sortedSet.addAll(input);
+
+        return sortedSet.stream().limit(k).collect(Collectors.toList());
+    }
+}

algorithms-miscellaneous-6/src/test/java/com/baeldung/algorithms/topkelements/TopKElementsFinderUnitTest.java

@@ -0,0 +1,46 @@
+package com.baeldung.algorithms.topkelements;
+
+import org.junit.Test;
+
+import java.util.Arrays;
+import java.util.List;
+
+import static org.assertj.core.api.Java6Assertions.assertThat;
+
+public class TopKElementsFinderUnitTest {
+    private final TopKElementsFinder<Integer> bruteForceFinder = new BruteForceTopKElementsFinder();
+    private final TopKElementsFinder<Integer> maxHeapFinder = new MaxHeapTopKElementsFinder();
+    private final TopKElementsFinder<Integer> treeSetFinder = new TreeSetTopKElementsFinder();
+
+    private final int k = 4;
+    private final List<Integer> distinctIntegers = Arrays.asList(1, 2, 3, 9, 7, 6, 12);
+    private final List<Integer> distinctIntegersTopK = Arrays.asList(9, 7, 6, 12);
+    private final List<Integer> nonDistinctIntegers = Arrays.asList(1, 2, 3, 3, 9, 9, 7, 6, 12);
+    private final List<Integer> nonDistinctIntegersTopK = Arrays.asList(9, 9, 7, 12);
+
+
+    @Test
+    public void givenArrayDistinctIntegers_whenBruteForceFindTopK_thenReturnKLargest() {
+        assertThat(bruteForceFinder.findTopK(distinctIntegers, k)).containsOnlyElementsOf(distinctIntegersTopK);
+    }
+
+    @Test
+    public void givenArrayDistinctIntegers_whenMaxHeapFindTopK_thenReturnKLargest() {
+        assertThat(maxHeapFinder.findTopK(distinctIntegers, k)).containsOnlyElementsOf(distinctIntegersTopK);
+    }
+
+    @Test
+    public void givenArrayDistinctIntegers_whenTreeSetFindTopK_thenReturnKLargest() {
+        assertThat(treeSetFinder.findTopK(distinctIntegers, k)).containsOnlyElementsOf(distinctIntegersTopK);
+    }
+
+    @Test
+    public void givenArrayNonDistinctIntegers_whenBruteForceFindTopK_thenReturnKLargest() {
+        assertThat(bruteForceFinder.findTopK(nonDistinctIntegers, k)).containsOnlyElementsOf(nonDistinctIntegersTopK);
+    }
+
+    @Test
+    public void givenArrayNonDistinctIntegers_whenMaxHeapFindTopK_thenReturnKLargest() {
+        assertThat(maxHeapFinder.findTopK(nonDistinctIntegers, k)).containsOnlyElementsOf(nonDistinctIntegersTopK);
+    }
+}

apache-shiro/pom.xml

@@ -39,10 +39,19 @@
             <artifactId>jcl-over-slf4j</artifactId>
             <scope>runtime</scope>
         </dependency>
+        <!-- spring-sec -->
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-web</artifactId>
+        </dependency>
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-security</artifactId>
+        </dependency>
     </dependencies>
 
     <properties>
-        <apache-shiro-core-version>1.4.0</apache-shiro-core-version>
+        <apache-shiro-core-version>1.5.3</apache-shiro-core-version>
         <log4j-version>1.2.17</log4j-version>
     </properties>
 

apache-shiro/src/main/java/com/baeldung/comparison/shiro/CustomRealm.java

@@ -0,0 +1,96 @@
+package com.baeldung.comparison.shiro;
+
+import java.sql.Connection;
+import java.sql.SQLException;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.Map;
+import java.util.Set;
+
+import org.apache.shiro.authc.AuthenticationException;
+import org.apache.shiro.authc.AuthenticationInfo;
+import org.apache.shiro.authc.AuthenticationToken;
+import org.apache.shiro.authc.SimpleAuthenticationInfo;
+import org.apache.shiro.authc.UnknownAccountException;
+import org.apache.shiro.authc.UsernamePasswordToken;
+import org.apache.shiro.authz.AuthorizationInfo;
+import org.apache.shiro.authz.SimpleAuthorizationInfo;
+import org.apache.shiro.realm.jdbc.JdbcRealm;
+import org.apache.shiro.subject.PrincipalCollection;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class CustomRealm extends JdbcRealm {
+    
+    private Logger logger = LoggerFactory.getLogger(CustomRealm.class);
+
+    private Map<String, String> credentials = new HashMap<>();
+    private Map<String, Set<String>> roles = new HashMap<>();
+    private Map<String, Set<String>> permissions = new HashMap<>();
+
+    {
+        credentials.put("Tom", "password");
+        credentials.put("Jerry", "password");
+
+        roles.put("Jerry", new HashSet<>(Arrays.asList("ADMIN")));
+        roles.put("Tom", new HashSet<>(Arrays.asList("USER")));
+
+        permissions.put("ADMIN", new HashSet<>(Arrays.asList("READ", "WRITE")));
+        permissions.put("USER", new HashSet<>(Arrays.asList("READ")));
+    }
+
+    @Override
+    protected AuthenticationInfo doGetAuthenticationInfo(AuthenticationToken token) throws AuthenticationException {
+
+        UsernamePasswordToken userToken = (UsernamePasswordToken) token;
+
+        if (userToken.getUsername() == null || userToken.getUsername()
+            .isEmpty() || !credentials.containsKey(userToken.getUsername())) {
+            throw new UnknownAccountException("User doesn't exist");
+        }
+
+        return new SimpleAuthenticationInfo(userToken.getUsername(), credentials.get(userToken.getUsername()), getName());
+    }
+
+    @Override
+    protected AuthorizationInfo doGetAuthorizationInfo(PrincipalCollection principals) {
+        Set<String> roles = new HashSet<>();
+        Set<String> permissions = new HashSet<>();
+
+        for (Object user : principals) {
+            try {
+                roles.addAll(getRoleNamesForUser(null, (String) user));
+                permissions.addAll(getPermissions(null, null, roles));
+            } catch (SQLException e) {
+                logger.error(e.getMessage());
+            }
+        }
+        SimpleAuthorizationInfo authInfo = new SimpleAuthorizationInfo(roles);
+        authInfo.setStringPermissions(permissions);
+        return authInfo;
+    }
+
+    @Override
+    protected Set<String> getRoleNamesForUser(Connection conn, String username) throws SQLException {
+        if (!roles.containsKey(username)) {
+            throw new SQLException("User doesn't exist");
+        }
+        return roles.get(username);
+    }
+
+    @Override
+    protected Set<String> getPermissions(Connection conn, String username, Collection<String> roles) throws SQLException {
+        Set<String> userPermissions = new HashSet<>();
+
+        for (String role : roles) {
+            if (!permissions.containsKey(role)) {
+                throw new SQLException("Role doesn't exist");
+            }
+            userPermissions.addAll(permissions.get(role));
+        }
+        return userPermissions;
+    }
+
+}

apache-shiro/src/main/java/com/baeldung/comparison/shiro/ShiroApplication.java

@@ -0,0 +1,33 @@
+package com.baeldung.comparison.shiro;
+
+import org.apache.shiro.realm.Realm;
+import org.apache.shiro.spring.web.config.DefaultShiroFilterChainDefinition;
+import org.apache.shiro.spring.web.config.ShiroFilterChainDefinition;
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+import org.springframework.boot.autoconfigure.security.servlet.SecurityAutoConfiguration;
+import org.springframework.context.annotation.Bean;
+
+@SpringBootApplication(exclude = SecurityAutoConfiguration.class)
+public class ShiroApplication {
+
+    public static void main(String... args) {
+        SpringApplication.run(ShiroApplication.class, args);
+    }
+
+    @Bean
+    public Realm customRealm() {
+        return new CustomRealm();
+    }
+
+    @Bean
+    public ShiroFilterChainDefinition shiroFilterChainDefinition() {
+        DefaultShiroFilterChainDefinition filter = new DefaultShiroFilterChainDefinition();
+
+        filter.addPathDefinition("/home", "authc");
+        filter.addPathDefinition("/**", "anon");
+
+        return filter;
+    }
+
+}

apache-shiro/src/main/java/com/baeldung/comparison/shiro/controllers/ShiroController.java

@@ -0,0 +1,99 @@
+package com.baeldung.comparison.shiro.controllers;
+
+import javax.servlet.http.HttpServletRequest;
+
+import org.apache.shiro.SecurityUtils;
+import org.apache.shiro.authc.AuthenticationException;
+import org.apache.shiro.authc.UsernamePasswordToken;
+import org.apache.shiro.subject.Subject;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.springframework.stereotype.Controller;
+import org.springframework.ui.Model;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.PostMapping;
+import org.springframework.web.servlet.mvc.support.RedirectAttributes;
+
+import com.baeldung.comparison.shiro.models.UserCredentials;
+
+@Controller
+public class ShiroController {
+    
+    private Logger logger = LoggerFactory.getLogger(ShiroController.class);
+
+    @GetMapping("/")
+    public String getIndex() {
+        return "comparison/index";
+    }
+
+    @GetMapping("/login")
+    public String showLoginPage() {
+        return "comparison/login";
+    }
+
+    @PostMapping("/login")
+    public String doLogin(HttpServletRequest req, UserCredentials credentials, RedirectAttributes attr) {
+
+        Subject subject = SecurityUtils.getSubject();
+
+        if (!subject.isAuthenticated()) {
+            UsernamePasswordToken token = new UsernamePasswordToken(credentials.getUsername(), credentials.getPassword());
+            try {
+                subject.login(token);
+            } catch (AuthenticationException ae) {
+                logger.error(ae.getMessage());
+                attr.addFlashAttribute("error", "Invalid Credentials");
+                return "redirect:/login";
+            }
+        }
+        return "redirect:/home";
+    }
+
+    @GetMapping("/home")
+    public String getMeHome(Model model) {
+
+        addUserAttributes(model);
+
+        return "comparison/home";
+    }
+
+    @GetMapping("/admin")
+    public String adminOnly(Model model) {
+        addUserAttributes(model);
+
+        Subject currentUser = SecurityUtils.getSubject();
+        if (currentUser.hasRole("ADMIN")) {
+            model.addAttribute("adminContent", "only admin can view this");
+        }
+        return "comparison/home";
+    }
+
+    @PostMapping("/logout")
+    public String logout() {
+        Subject subject = SecurityUtils.getSubject();
+        subject.logout();
+        return "redirect:/";
+    }
+
+    private void addUserAttributes(Model model) {
+        Subject currentUser = SecurityUtils.getSubject();
+        String permission = "";
+
+        if (currentUser.hasRole("ADMIN")) {
+            model.addAttribute("role", "ADMIN");
+        } else if (currentUser.hasRole("USER")) {
+            model.addAttribute("role", "USER");
+        }
+
+        if (currentUser.isPermitted("READ")) {
+            permission = permission + " READ";
+        }
+
+        if (currentUser.isPermitted("WRITE")) {
+            permission = permission + " WRITE";
+        }
+        model.addAttribute("username", currentUser.getPrincipal());
+        model.addAttribute("permission", permission);
+    }
+
+}

apache-shiro/src/main/java/com/baeldung/comparison/shiro/models/UserCredentials.java

@@ -0,0 +1,28 @@
+package com.baeldung.comparison.shiro.models;
+
+public class UserCredentials {
+
+    private String username;
+    private String password;
+
+    public String getUsername() {
+        return username;
+    }
+
+    public void setUsername(String username) {
+        this.username = username;
+    }
+
+    public String getPassword() {
+        return password;
+    }
+
+    public void setPassword(String password) {
+        this.password = password;
+    }
+
+    @Override
+    public String toString() {
+        return "username = " + getUsername();
+    }
+}

apache-shiro/src/main/java/com/baeldung/comparison/springsecurity/Application.java

@@ -0,0 +1,19 @@
+package com.baeldung.comparison.springsecurity;
+
+import org.apache.shiro.spring.boot.autoconfigure.ShiroAnnotationProcessorAutoConfiguration;
+import org.apache.shiro.spring.boot.autoconfigure.ShiroAutoConfiguration;
+import org.apache.shiro.spring.config.web.autoconfigure.ShiroWebAutoConfiguration;
+import org.apache.shiro.spring.config.web.autoconfigure.ShiroWebFilterConfiguration;
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+
+@SpringBootApplication(exclude = {ShiroAutoConfiguration.class,
+        ShiroAnnotationProcessorAutoConfiguration.class,
+        ShiroWebAutoConfiguration.class,
+        ShiroWebFilterConfiguration.class})
+public class Application {
+
+    public static void main(String[] args) {
+        SpringApplication.run(Application.class, args);
+    }
+}

apache-shiro/src/main/java/com/baeldung/comparison/springsecurity/config/SecurityConfig.java

@@ -0,0 +1,45 @@
+package com.baeldung.comparison.springsecurity.config;
+
+import org.springframework.context.annotation.Bean;
+import org.springframework.security.config.annotation.authentication.builders.AuthenticationManagerBuilder;
+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;
+import org.springframework.security.crypto.bcrypt.BCryptPasswordEncoder;
+import org.springframework.security.crypto.password.PasswordEncoder;
+
+@EnableWebSecurity
+public class SecurityConfig extends WebSecurityConfigurerAdapter {
+
+    @Override
+    protected void configure(HttpSecurity http) throws Exception {
+        http.csrf().disable().authorizeRequests(authorize -> authorize.antMatchers("/index", "/login")
+            .permitAll()
+            .antMatchers("/home", "/logout")
+            .authenticated()
+            .antMatchers("/admin/**")
+            .hasRole("ADMIN"))
+            .formLogin(formLogin -> formLogin.loginPage("/login")
+                .failureUrl("/login-error"));
+    }
+
+    @Override
+    protected void configure(AuthenticationManagerBuilder auth) throws Exception {
+        auth.inMemoryAuthentication()
+            .withUser("Jerry")
+            .password(passwordEncoder().encode("password"))
+            .authorities("READ", "WRITE")
+            .roles("ADMIN")
+            .and()
+            .withUser("Tom")
+            .password(passwordEncoder().encode("password"))
+            .authorities("READ")
+            .roles("USER");
+    }
+
+    @Bean
+    public PasswordEncoder passwordEncoder() {
+        return new BCryptPasswordEncoder();
+    }
+
+}

apache-shiro/src/main/java/com/baeldung/comparison/springsecurity/web/SpringController.java

@@ -0,0 +1,79 @@
+package com.baeldung.comparison.springsecurity.web;
+
+import java.util.Collection;
+
+import javax.servlet.http.HttpServletRequest;
+
+import org.springframework.security.authentication.AnonymousAuthenticationToken;
+import org.springframework.security.core.Authentication;
+import org.springframework.security.core.GrantedAuthority;
+import org.springframework.security.core.context.SecurityContextHolder;
+import org.springframework.security.core.userdetails.User;
+import org.springframework.stereotype.Controller;
+import org.springframework.ui.Model;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.PostMapping;
+import org.springframework.web.bind.annotation.RequestMapping;
+
+@Controller
+public class SpringController {
+
+    @GetMapping("/")
+    public String getIndex() {
+        return "comparison/index";
+    }
+
+    @GetMapping("/login")
+    public String showLoginPage() {
+        return "comparison/login";
+    }
+
+    @RequestMapping("/login-error")
+    public String loginError(Model model) {
+        model.addAttribute("error", "Invalid Credentials");
+        return "comparison/login";
+    }
+
+    @PostMapping("/login")
+    public String doLogin(HttpServletRequest req) {
+        return "redirect:/home";
+    }
+
+    @GetMapping("/home")
+    public String showHomePage(HttpServletRequest req, Model model) {
+        addUserAttributes(model);
+        return "comparison/home";
+    }
+
+    @GetMapping("/admin")
+    public String adminOnly(HttpServletRequest req, Model model) {
+        addUserAttributes(model);
+        model.addAttribute("adminContent", "only admin can view this");
+        return "comparison/home";
+    }
+
+    private void addUserAttributes(Model model) {
+        Authentication auth = SecurityContextHolder.getContext()
+            .getAuthentication();
+        if (auth != null && !auth.getClass()
+            .equals(AnonymousAuthenticationToken.class)) {
+            User user = (User) auth.getPrincipal();
+            model.addAttribute("username", user.getUsername());
+
+            Collection<GrantedAuthority> authorities = user.getAuthorities();
+
+            for (GrantedAuthority authority : authorities) {
+                if (authority.getAuthority()
+                    .contains("USER")) {
+                    model.addAttribute("role", "USER");
+                    model.addAttribute("permission", "READ");
+                } else if (authority.getAuthority()
+                    .contains("ADMIN")) {
+                    model.addAttribute("role", "ADMIN");
+                    model.addAttribute("permission", "READ WRITE");
+                }
+            }
+        }
+    }
+
+}

apache-shiro/src/main/java/com/baeldung/intro/Main.java

@@ -1,4 +1,4 @@
-package com.baeldung;
+package com.baeldung.intro;
 
 import org.apache.shiro.SecurityUtils;
 import org.apache.shiro.authc.AuthenticationException;

apache-shiro/src/main/java/com/baeldung/intro/MyCustomRealm.java

@@ -1,4 +1,4 @@
-package com.baeldung;
+package com.baeldung.intro;
 
 import java.sql.Connection;
 import java.sql.SQLException;

apache-shiro/src/main/java/com/baeldung/intro/ShiroSpringApplication.java

@@ -1,4 +1,4 @@
-package com.baeldung;
+package com.baeldung.intro;
 
 import org.apache.shiro.realm.Realm;
 import org.apache.shiro.spring.web.config.DefaultShiroFilterChainDefinition;
@@ -7,12 +7,13 @@ import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 import org.springframework.boot.SpringApplication;
 import org.springframework.boot.autoconfigure.SpringBootApplication;
+import org.springframework.boot.autoconfigure.security.servlet.SecurityAutoConfiguration;
 import org.springframework.context.annotation.Bean;
 
 /**
  * Created by smatt on 21/08/2017.
  */
-@SpringBootApplication
+@SpringBootApplication(exclude = SecurityAutoConfiguration.class)
 public class ShiroSpringApplication {
 
     private static final transient Logger log = LoggerFactory.getLogger(ShiroSpringApplication.class);
@@ -29,7 +30,7 @@ public class ShiroSpringApplication {
 
 
     @Bean
-    public ShiroFilterChainDefinition shiroFilterChainDefinition() {
+    public ShiroFilterChainDefinition filterChainDefinition() {
         DefaultShiroFilterChainDefinition filter
           = new DefaultShiroFilterChainDefinition();
 

apache-shiro/src/main/java/com/baeldung/intro/controllers/ShiroSpringController.java

@@ -1,6 +1,5 @@
-package com.baeldung.controllers;
+package com.baeldung.intro.controllers;
 
-import com.baeldung.models.UserCredentials;
 import org.apache.shiro.SecurityUtils;
 import org.apache.shiro.authc.AuthenticationException;
 import org.apache.shiro.authc.UsernamePasswordToken;
@@ -13,6 +12,8 @@ import org.springframework.web.bind.annotation.RequestMapping;
 import org.springframework.web.bind.annotation.RequestMethod;
 import org.springframework.web.servlet.mvc.support.RedirectAttributes;
 
+import com.baeldung.intro.models.UserCredentials;
+
 import javax.servlet.http.HttpServletRequest;
 
 @Controller

apache-shiro/src/main/java/com/baeldung/intro/models/UserCredentials.java

@@ -1,4 +1,4 @@
-package com.baeldung.models;
+package com.baeldung.intro.models;
 
 public class UserCredentials {
 

apache-shiro/src/main/java/com/baeldung/permissions/custom/Main.java

@@ -1,4 +1,4 @@
-package com.baeldung.shiro.permissions.custom;
+package com.baeldung.permissions.custom;
 
 import org.apache.shiro.SecurityUtils;
 import org.apache.shiro.authc.AuthenticationException;

apache-shiro/src/main/java/com/baeldung/permissions/custom/PathPermission.java

@@ -1,4 +1,4 @@
-package com.baeldung.shiro.permissions.custom;
+package com.baeldung.permissions.custom;
 
 import org.apache.shiro.authz.Permission;
 

apache-shiro/src/main/java/com/baeldung/permissions/custom/PathPermissionResolver.java

@@ -1,4 +1,4 @@
-package com.baeldung.shiro.permissions.custom;
+package com.baeldung.permissions.custom;
 
 import org.apache.shiro.authz.Permission;
 import org.apache.shiro.authz.permission.PermissionResolver;

apache-shiro/src/main/resources/templates/comparison/home.ftl

@@ -0,0 +1,19 @@
+<html>
+<head>
+    <title>Home Page</title>
+</head>
+<body style="margin-left: 30px;">
+<h1>Welcome ${username}!</h1>
+<p><strong>Role</strong>: ${role}</p>
+<p><strong>Permissions</strong></p>
+<p>${permission}</p>
+<a href="/admin">Admin only</a>
+<#if adminContent??>
+  ${adminContent}
+</#if>
+<br>
+<form role="form" action="/logout" method="POST">
+   <input type="Submit" value="Logout" />
+</form>
+</body>
+</html>

apache-shiro/src/main/resources/templates/comparison/index.ftl

@@ -0,0 +1,10 @@
+<html>
+<head>
+    <title>Index</title>
+</head>
+<body>
+    <h1>Welcome Guest!</h1>
+    <br>
+    Go to the <a href="/home">secured page
+</body>
+</html>

apache-shiro/src/main/resources/templates/comparison/login.ftl

@@ -0,0 +1,25 @@
+<html>
+<head>
+    <title>Login</title>
+</head>
+<body style="margin-left: 30px;">
+<h3>Login</h3>
+<br>
+<form action="/login" method="post">
+    <#if (error?length > 0)??>
+        <p style="color:darkred;">${error}</p>
+    <#else>
+    </#if>
+
+    <label for="username">Username</label>
+    <br>
+    <input type="text" name="username">
+    <br><br>
+    <label for="password">Password</label>
+    <br>
+    <input type="password" name="password">
+    <br><br>
+    <input type="submit" value="Submit">
+</form>
+</body>
+</html>

apache-shiro/src/test/java/com/baeldung/comparison/shiro/SpringContextTest.java

@@ -0,0 +1,20 @@
+package com.baeldung.comparison.shiro;
+
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.test.context.junit.jupiter.SpringExtension;
+
+import com.baeldung.comparison.shiro.ShiroApplication;
+
+@ExtendWith(SpringExtension.class)
+@SpringBootTest(classes = { ShiroApplication.class })
+public class SpringContextTest {
+
+    @Test
+    public void whenSpringContextIsBootstrapped_thenNoExceptions() {
+
+    }
+
+}

apache-shiro/src/test/java/com/baeldung/comparison/springsecurity/SpringContextTest.java

@@ -0,0 +1,19 @@
+package com.baeldung.comparison.springsecurity;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.test.context.junit.jupiter.SpringExtension;
+
+import com.baeldung.comparison.springsecurity.Application;
+
+@ExtendWith(SpringExtension.class)
+@SpringBootTest(classes = { Application.class })
+public class SpringContextTest {
+
+    @Test
+    public void whenSpringContextIsBootstrapped_thenNoExceptions() {
+
+    }
+
+}

aws-app-sync/pom.xml

@@ -46,7 +46,4 @@
         </plugins>
     </build>
 
-    <properties>
-        <java.version>1.8</java.version>
-    </properties>
 </project>

core-groovy/README.md

@@ -13,4 +13,5 @@ This module contains articles about core Groovy concepts
 - [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)
 - [Convert String to Integer in Groovy](https://www.baeldung.com/groovy-convert-string-to-integer)
+- [Groovy Variable Scope](https://www.baeldung.com/groovy/variable-scope)
 - [[More -->]](/core-groovy-2)

core-java-modules/core-java-11/README.md

@@ -8,7 +8,7 @@ This module contains articles about Java 11 core features
 - [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)
+- [Exploring the New HTTP Client in Java](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)
 - [Guide to jlink](https://www.baeldung.com/jlink)
 - [Negate a Predicate Method Reference with Java 11](https://www.baeldung.com/java-negate-predicate-method-reference)

core-java-modules/core-java-9-jigsaw/src/simple-modules/main.app/com/baeldung/modules/main/MainApp.java

@@ -1,12 +1,15 @@
 package com.baeldung.modules.main;
 
+import com.baeldung.modules.hello.HelloInterface;
 import com.baeldung.modules.hello.HelloModules;
+import java.util.ServiceLoader;
 
 public class MainApp {
     public static void main(String[] args) {
         HelloModules.doSomething();
-
-        HelloModules module = new HelloModules();
-        module.sayHello();
+        
+        Iterable<HelloInterface> services = ServiceLoader.load(HelloInterface.class);
+        HelloInterface service = services.iterator().next();
+        service.sayHello();
     }
 }

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

@@ -13,3 +13,4 @@ This module contains articles about core Java features that have been introduced
 - [Java 9 Platform Logging API](https://www.baeldung.com/java-9-logging-api)
 - [Java 9 Reactive Streams](https://www.baeldung.com/java-9-reactive-streams)
 - [Multi-Release JAR Files with Maven](https://www.baeldung.com/maven-multi-release-jars)
+- [The Difference between RxJava API and the Java 9 Flow API](https://www.baeldung.com/rxjava-vs-java-flow-api)

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

@@ -9,3 +9,4 @@ This module contains articles about Java 9 core features
 - [Iterate Through a Range of Dates in Java](https://www.baeldung.com/java-iterate-date-range)
 - [Initialize a HashMap in Java](https://www.baeldung.com/java-initialize-hashmap)
 - [Immutable ArrayList in Java](https://www.baeldung.com/java-immutable-list)
+- [Easy Ways to Write a Java InputStream to an OutputStream](https://www.baeldung.com/java-inputstream-to-outputstream)

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

@@ -5,4 +5,4 @@ This module contains complete guides about arrays in Java
 ### Relevant Articles: 
 - [Arrays in Java: A Reference Guide](https://www.baeldung.com/java-arrays-guide)
 - [Guide to the java.util.Arrays Class](https://www.baeldung.com/java-util-arrays)
-- [What is [Ljava.lang.Object;?]](https://www.baeldung.com/java-tostring-array)
+- [What is \[Ljava.lang.Object;?](https://www.baeldung.com/java-tostring-array)

core-java-modules/core-java-collections-3/pom.xml

@@ -27,6 +27,11 @@
             <version>${assertj.version}</version>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-lang3</artifactId>
+            <version>3.10</version>
+        </dependency>
     </dependencies>
 
     <properties>

core-java-modules/core-java-collections-3/src/main/java/com/baeldung/collections/convertarrayprimitives/ConvertPrimitivesArrayToList.java

@@ -0,0 +1,47 @@
+package com.baeldung.collections.iterators;
+
+import java.util.List;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.stream.Collectors;
+import java.util.stream.IntStream;
+import com.google.common.primitives.Ints;
+import org.apache.commons.lang3.ArrayUtils;
+
+public class ConvertPrimitivesArrayToList {
+
+    public static void failConvert() {
+        int[] input = new int[]{1,2,3,4};
+        // List<Integer> inputAsList = Arrays.asList(input);
+    }
+
+    public static List<Integer> iterateConvert(int[] input) {
+        List<Integer> output = new ArrayList<Integer>();
+        for (int value : input) {
+            output.add(value);
+        }
+        return output;
+    }
+
+    public static List<Integer> streamConvert(int[] input) {
+        List<Integer> output = Arrays.stream(input).boxed().collect(Collectors.toList());
+        return output;
+    }
+
+    public static List<Integer> streamConvertIntStream(int[] input) {
+        List<Integer> output = IntStream.of(input).boxed().collect(Collectors.toList());
+        return output;
+    }
+
+    public static List<Integer> guavaConvert(int[] input) {
+        List<Integer> output = Ints.asList(input);
+        return output;
+    }
+
+    public static List<Integer> apacheCommonConvert(int[] input) {
+        Integer[] outputBoxed = ArrayUtils.toObject(input);
+        List<Integer> output = Arrays.asList(outputBoxed);
+        return output;
+    }
+
+}

core-java-modules/core-java-collections-3/src/test/java/com/baeldung/collections/convertarrayprimitives/ConvertPrimitivesArrayToListUnitTest.java

@@ -0,0 +1,38 @@
+package com.baeldung.collections.iterators;
+
+import java.util.List;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.stream.Collectors;
+import com.google.common.primitives.Ints;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+public class ConvertPrimitivesArrayToListUnitTest {
+
+    @Test
+    public void givenArrayWithPrimitives_whenIterativeConvert_thenArrayGetsConverted() {
+        assertEquals(Arrays.asList(1,2,3,4), ConvertPrimitivesArrayToList.iterateConvert(new int[]{1,2,3,4}));
+    }
+
+    @Test
+    public void givenArrayWithPrimitives_whenStreamConvert_thenArrayGetsConverted() {
+        assertEquals(Arrays.asList(1,2,3,4), ConvertPrimitivesArrayToList.streamConvert(new int[]{1,2,3,4}));
+    }
+
+    @Test
+    public void givenArrayWithPrimitives_whenIntStreamConvert_thenArrayGetsConverted() {
+        assertEquals(Arrays.asList(1,2,3,4), ConvertPrimitivesArrayToList.streamConvertIntStream(new int[]{1,2,3,4}));
+    }
+
+    @Test
+    public void givenArrayWithPrimitives_whenGuavaConvert_thenArrayGetsConverted() {
+        assertEquals(Arrays.asList(1,2,3,4), ConvertPrimitivesArrayToList.guavaConvert(new int[]{1,2,3,4}));
+    }
+
+    @Test
+    public void givenArrayWithPrimitives_whenApacheCommonConvert_thenArrayGetsConverted() {
+        assertEquals(Arrays.asList(1,2,3,4), ConvertPrimitivesArrayToList.apacheCommonConvert(new int[]{1,2,3,4}));
+    }
+}

core-java-modules/core-java-concurrency-advanced-3/README.md

@@ -15,4 +15,5 @@ This module contains articles about advanced topics about multithreading with co
 - [The ABA Problem in Concurrency](https://www.baeldung.com/cs/aba-concurrency)
 - [Introduction to Lock-Free Data Structures](https://www.baeldung.com/lock-free-programming)
 - [Introduction to Exchanger in Java](https://www.baeldung.com/java-exchanger)
+- [Why Not To Start A Thread In The Constructor?](https://www.baeldung.com/java-thread-constructor)
 - [[<-- previous]](/core-java-modules/core-java-concurrency-advanced-2)

core-java-modules/core-java-concurrency-basic-2/src/main/java/com/baeldung/concurrent/localvariables/LocalAndLambda.java

@@ -0,0 +1,10 @@
+package com.baeldung.concurrent.localvariables;
+
+public class LocalAndLambda {
+    public static void main(String... args) {
+        String text = "";
+        // Un-commenting the next line will break compilation, because text is no longer effectively final
+        // text = "675";
+        new Thread(() -> System.out.println(text)).start();
+    }
+}

core-java-modules/core-java-concurrency-basic-2/src/main/java/com/baeldung/concurrent/localvariables/LocalVariables.java

@@ -0,0 +1,20 @@
+package com.baeldung.concurrent.localvariables;
+
+import java.security.SecureRandom;
+
+public class LocalVariables implements Runnable {
+    private int field;
+
+    public static void main(String... args) {
+        LocalVariables target = new LocalVariables();
+        new Thread(target).start();
+        new Thread(target).start();
+    }
+
+    @Override
+    public void run() {
+        field = new SecureRandom().nextInt();
+        int local = new SecureRandom().nextInt();
+        System.out.println(field + " - " + local);
+    }
+}

core-java-modules/core-java-concurrency-collections-2/README.md

@@ -1,3 +1,5 @@
 ### Relevant Articles:
 
 - [Introduction to Lock Striping](https://www.baeldung.com/java-lock-stripping)
+- [Guide to the Java TransferQueue](http://www.baeldung.com/java-transfer-queue)
+- [[<-- Prev]](/core-java-modules/core-java-concurrency-collections)

core-java-modules/core-java-concurrency-collections-2/pom.xml

@@ -3,9 +3,16 @@
     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.concurrent.lock</groupId>
     <artifactId>core-java-concurrency-collections-2</artifactId>
-    <version>0.0.1-SNAPSHOT</version>
+    <version>0.1.0-SNAPSHOT</version>
+    <name>core-java-concurrency-collections-2</name>
+    <packaging>jar</packaging>
+    <parent>
+        <groupId>com.baeldung.core-java-modules</groupId>
+        <artifactId>core-java-modules</artifactId>
+        <version>0.0.1-SNAPSHOT</version>
+        <relativePath>../</relativePath>
+    </parent>
 
     <dependencies>
         <dependency>
@@ -30,19 +37,6 @@
             <scope>test</scope>
         </dependency>
     </dependencies>
-    <build>
-        <sourceDirectory>src</sourceDirectory>
-        <plugins>
-            <plugin>
-                <artifactId>maven-compiler-plugin</artifactId>
-                <version>3.8.0</version>
-                <configuration>
-                    <source>1.8</source>
-                    <target>1.8</target>
-                </configuration>
-            </plugin>
-        </plugins>
-    </build>
 
     <properties>
         <jmh.version>1.21</jmh.version>

core-java-modules/core-java-concurrency-collections-2/src/test/java/com/baeldung/concurrent/queue/ConcurrentLinkedQueueUnitTest.java

@@ -19,7 +19,7 @@ import org.junit.FixMethodOrder;
 import org.junit.Test;
 
 @FixMethodOrder
-public class TestConcurrentLinkedQueue {
+public class ConcurrentLinkedQueueUnitTest {
 
     @Test
     public void givenThereIsExistingCollection_WhenAddedIntoQueue_ThenShouldContainElements() {

core-java-modules/core-java-concurrency-collections-2/src/test/java/com/baeldung/concurrent/queue/LinkedBlockingQueueUnitTest.java

@@ -18,7 +18,7 @@ import org.junit.FixMethodOrder;
 import org.junit.Test;
 
 @FixMethodOrder
-public class TestLinkedBlockingQueue {
+public class LinkedBlockingQueueUnitTest {
 
     @Test
     public void givenThereIsExistingCollection_WhenAddedIntoQueue_ThenShouldContainElements() {

core-java-modules/core-java-concurrency-collections-2/src/test/java/com/baeldung/transferqueue/TransferQueueIntegrationTest.java

@@ -4,7 +4,11 @@ import org.junit.FixMethodOrder;
 import org.junit.Test;
 import org.junit.runners.MethodSorters;
 
-import java.util.concurrent.*;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.LinkedTransferQueue;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.TransferQueue;
 
 import static junit.framework.TestCase.assertEquals;
 

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

@@ -10,7 +10,7 @@ This module contains articles about concurrent Java collections
 - [Custom Thread Pools In Java 8 Parallel Streams](http://www.baeldung.com/java-8-parallel-streams-custom-threadpool)
 - [Guide to DelayQueue](http://www.baeldung.com/java-delay-queue)
 - [A Guide to Java SynchronousQueue](http://www.baeldung.com/java-synchronous-queue)
-- [Guide to the Java TransferQueue](http://www.baeldung.com/java-transfer-queue)
 - [Guide to the ConcurrentSkipListMap](http://www.baeldung.com/java-concurrent-skip-list-map)
 - [Guide to CopyOnWriteArrayList](http://www.baeldung.com/java-copy-on-write-arraylist)
 - [LinkedBlockingQueue vs ConcurrentLinkedQueue](https://www.baeldung.com/java-queue-linkedblocking-concurrentlinked)
+- [[Next -->]](/core-java-modules/core-java-concurrency-collections-2)

core-java-modules/core-java-date-operations-2/README.md

@@ -2,6 +2,7 @@
 This module contains articles about date operations in Java.
 
 ### Relevant Articles:
+
 - [Get the Current Date Prior to Java 8](https://www.baeldung.com/java-get-the-current-date-legacy)
 - [Skipping Weekends While Adding Days to LocalDate in Java 8](https://www.baeldung.com/java-localdate-add-days-skip-weekends)
 - [Checking If Two Java Dates Are on the Same Day](https://www.baeldung.com/java-check-two-dates-on-same-day)
@@ -9,4 +10,5 @@ This module contains articles about date operations in Java.
 - [How to Set the JVM Time Zone](https://www.baeldung.com/java-jvm-time-zone)
 - [How to determine day of week by passing specific date in Java?](https://www.baeldung.com/java-get-day-of-week)
 - [Finding Leap Years in Java](https://www.baeldung.com/java-leap-year)
+- [Getting the Week Number From Any Date](https://www.baeldung.com/java-get-week-number)
 - [[<-- Prev]](/core-java-modules/core-java-date-operations-1)

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

@@ -12,3 +12,4 @@ This module contains articles about core java exceptions
 - [Java – Try with Resources](https://www.baeldung.com/java-try-with-resources)
 - [Java Global Exception Handler](https://www.baeldung.com/java-global-exception-handler)
 - [How to Find an Exception’s Root Cause in Java](https://www.baeldung.com/java-exception-root-cause)
+- [Java IOException “Too many open files”](https://www.baeldung.com/java-too-many-open-files)

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

@@ -33,7 +33,6 @@
     <url>http://maven.apache.org</url>
 
     <properties>
-        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
         <commons.lang3.version>3.10</commons.lang3.version>
         <!-- testing -->
         <assertj-core.version>3.10.0</assertj-core.version>

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

@@ -13,4 +13,4 @@ This module contains articles about core Java input and output (IO)
 - [How to Copy a File with Java](https://www.baeldung.com/java-copy-file)
 - [Create a Directory in Java](https://www.baeldung.com/java-create-directory) 
 - [Java IO vs NIO](https://www.baeldung.com/java-io-vs-nio)
-- [[<-- Prev]](/core-java-modules/core-java-io)
+- [[<-- Prev]](/core-java-modules/core-java-io)[[More -->]](/core-java-modules/core-java-io-3)

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

@@ -0,0 +1,7 @@
+## Core Java IO
+
+This module contains articles about core Java input and output (IO)
+
+### Relevant Articles: 
+- [Java – Create a File](https://www.baeldung.com/java-how-to-create-a-file)
+- [[<-- Prev]](/core-java-modules/core-java-io-2)

core-java-modules/core-java-io-3/pom.xml

@@ -0,0 +1,86 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project
+    xmlns="http://maven.apache.org/POM/4.0.0"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <artifactId>core-java-io-3</artifactId>
+    <version>0.1.0-SNAPSHOT</version>
+    <name>core-java-io-3</name>
+    <packaging>jar</packaging>
+    <parent>
+        <groupId>com.baeldung.core-java-modules</groupId>
+        <artifactId>core-java-modules</artifactId>
+        <version>0.0.1-SNAPSHOT</version>
+        <relativePath>../</relativePath>
+    </parent>
+
+    <dependencies>
+        <!-- utils -->
+        <dependency>
+            <groupId>com.google.guava</groupId>
+            <artifactId>guava</artifactId>
+            <version>${guava.version}</version>
+        </dependency>
+        <!-- utils -->
+        <dependency>
+            <groupId>commons-io</groupId>
+            <artifactId>commons-io</artifactId>
+            <version>${commons-io.version}</version>
+        </dependency>
+        <!-- logging -->
+        <dependency>
+            <groupId>log4j</groupId>
+            <artifactId>log4j</artifactId>
+            <version>${log4j.version}</version>
+        </dependency>
+        <dependency> <!-- needed to bridge to slf4j for projects that use the log4j APIs directly -->
+            <groupId>org.slf4j</groupId>
+            <artifactId>log4j-over-slf4j</artifactId>
+            <version>${org.slf4j.version}</version>
+        </dependency>
+        <!-- test scoped -->
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>${assertj.version}</version>
+            <scope>test</scope>
+        </dependency>
+        <!-- https://mvnrepository.com/artifact/com.github.tomakehurst/wiremock -->
+        <dependency>
+            <groupId>com.github.tomakehurst</groupId>
+            <artifactId>wiremock</artifactId>
+            <version>${wiremock.version}</version>
+            <scope>test</scope>
+        </dependency>
+
+    </dependencies>
+
+    <build>
+        <finalName>core-java-io-3</finalName>
+        <resources>
+            <resource>
+                <directory>src/main/resources</directory>
+                <filtering>true</filtering>
+            </resource>
+        </resources>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-javadoc-plugin</artifactId>
+                <version>${maven-javadoc-plugin.version}</version>
+                <configuration>
+                    <source>${maven.compiler.source}</source>
+                    <target>${maven.compiler.target}</target>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+
+    <properties>
+        <assertj.version>3.6.1</assertj.version>
+        <maven-javadoc-plugin.version>3.0.0-M1</maven-javadoc-plugin.version>
+        <wiremock.version>2.26.3</wiremock.version>
+    </properties>
+
+</project>

core-java-modules/core-java-io-3/src/test/java/com/baeldung/createfile/CreateFileUnitTest.java

@@ -0,0 +1,50 @@
+package com.baeldung.createfile;
+
+import org.apache.commons.io.FileUtils;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import java.io.File;
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+public class CreateFileUnitTest {
+
+    private final String FILE_NAME = "src/test/resources/fileToCreate.txt";
+
+    @AfterEach
+    @BeforeEach
+    public void cleanUpFiles() {
+        File targetFile = new File(FILE_NAME);
+        targetFile.delete();
+    }
+
+    @Test
+    public void givenUsingNio_whenCreatingFile_thenCorrect() throws IOException {
+        Path newFilePath = Paths.get(FILE_NAME);
+        Files.createFile(newFilePath);
+    }
+
+    @Test
+    public void givenUsingFile_whenCreatingFile_thenCorrect() throws IOException {
+        File newFile = new File(FILE_NAME);
+        boolean success = newFile.createNewFile();
+        assertTrue(success);
+    }
+
+    @Test
+    public void givenUsingGuava_whenCreatingFile_thenCorrect() throws IOException {
+        com.google.common.io.Files.touch(new File(FILE_NAME));
+    }
+
+    @Test
+    public void givenUsingCommonsIo_whenCreatingFile_thenCorrect() throws IOException {
+        FileUtils.touch(new File(FILE_NAME));
+    }
+
+}

core-java-modules/core-java-io-3/src/test/java/com/baeldung/emptiness/DirectoryEmptinessUnitTest.java

@@ -0,0 +1,63 @@
+package com.baeldung.emptiness;
+
+import org.junit.Test;
+
+import java.io.File;
+import java.io.IOException;
+import java.nio.file.DirectoryStream;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.util.stream.Stream;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class DirectoryEmptinessUnitTest {
+
+    @Test
+    public void givenPath_whenInvalid_thenReturnsFalse() throws IOException {
+        assertThat(isEmpty(Paths.get("invalid-addr"))).isFalse();
+    }
+
+    @Test
+    public void givenPath_whenNotDirectory_thenReturnsFalse() throws IOException {
+        Path aFile = Paths.get(getClass().getResource("/notDir.txt").getPath());
+        assertThat(isEmpty(aFile)).isFalse();
+    }
+
+    @Test
+    public void givenPath_whenNotEmptyDir_thenReturnsFalse() throws IOException {
+        Path currentDir = new File("").toPath().toAbsolutePath();
+        assertThat(isEmpty(currentDir)).isFalse();
+    }
+
+    @Test
+    public void givenPath_whenIsEmpty_thenReturnsTrue() throws Exception {
+        Path path = Files.createTempDirectory("baeldung-empty");
+        assertThat(isEmpty(path)).isTrue();
+    }
+
+    private static boolean isEmpty(Path path) throws IOException {
+        if (Files.isDirectory(path)) {
+            try (DirectoryStream<Path> directory = Files.newDirectoryStream(path)) {
+                return !directory.iterator().hasNext();
+            }
+        }
+
+        return false;
+    }
+
+    private static boolean isEmpty2(Path path) throws IOException {
+        if (Files.isDirectory(path)) {
+            try (Stream<Path> entries = Files.list(path)) {
+                return !entries.findFirst().isPresent();
+            }
+        }
+
+        return false;
+    }
+
+    private static boolean isEmptyInefficient(Path path) {
+        return path.toFile().listFiles().length == 0;
+    }
+}

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

@@ -7,7 +7,6 @@ This module contains articles about core Java input/output(IO) APIs.
 - [A Guide to the Java FileReader Class](https://www.baeldung.com/java-filereader)
 - [The Java File Class](https://www.baeldung.com/java-io-file)
 - [Java FileWriter](https://www.baeldung.com/java-filewriter)
-- [Differences Between the Java WatchService API and the Apache Commons IO Monitor Library](https://www.baeldung.com/java-watchservice-vs-apache-commons-io-monitor-library)
 - [Comparing getPath(), getAbsolutePath(), and getCanonicalPath() in Java](https://www.baeldung.com/java-path)
 - [Quick Use of FilenameFilter](https://www.baeldung.com/java-filename-filter)
 - [Guide to BufferedReader](https://www.baeldung.com/java-buffered-reader)

core-java-modules/core-java-io-conversions-2/README.md

@@ -6,4 +6,6 @@ This module contains articles about core Java input/output(IO) conversions.
 - [Java InputStream to String](https://www.baeldung.com/convert-input-stream-to-string)
 - [Java – Write an InputStream to a File](https://www.baeldung.com/convert-input-stream-to-a-file)
 - [Converting a BufferedReader to a JSONObject](https://www.baeldung.com/java-bufferedreader-to-jsonobject)
+- [Reading a CSV File into an Array](https://www.baeldung.com/java-csv-file-array)
+- [How to Write to a CSV File in Java](https://www.baeldung.com/java-csv)
 - More articles: [[<-- prev]](/core-java-modules/core-java-io-conversions)

core-java-modules/core-java-io-conversions-2/pom.xml

@@ -26,6 +26,12 @@
             <artifactId>json</artifactId>
             <version>${json.version}</version>
         </dependency>
+        <dependency>
+            <groupId>com.opencsv</groupId>
+            <artifactId>opencsv</artifactId>
+            <version>${opencsv.version}</version>
+            <scope>test</scope>
+        </dependency>
     </dependencies>
 
     <build>
@@ -40,6 +46,7 @@
 
     <properties>
         <json.version>20200518</json.version>
+        <opencsv.version>4.1</opencsv.version>
     </properties>
 
 </project>

core-java-modules/core-java-io-conversions-2/src/test/java/com/baeldung/csv/ReadCSVInArrayUnitTest.java

@@ -1,20 +1,11 @@
 package com.baeldung.csv;
 
-import java.io.BufferedReader;
-import java.io.File;
-import java.io.FileNotFoundException;
-import java.io.FileReader;
-import java.io.IOException;
-import java.util.ArrayList;
-import java.util.Arrays;
-import java.util.Collections;
-import java.util.List;
-import java.util.Scanner;
-
+import com.opencsv.CSVReader;
 import org.junit.Assert;
 import org.junit.Test;
 
-import com.opencsv.CSVReader;
+import java.io.*;
+import java.util.*;
 
 public class ReadCSVInArrayUnitTest {
     public static final String COMMA_DELIMITER = ",";

core-java-modules/core-java-io-conversions-2/src/test/java/com/baeldung/csv/WriteCsvFileExampleUnitTest.java

@@ -1,7 +1,9 @@
 package com.baeldung.csv;
 
-import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertTrue;
+import org.junit.Before;
+import org.junit.Test;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 import java.io.File;
 import java.io.FileNotFoundException;
@@ -10,10 +12,8 @@ import java.io.PrintWriter;
 import java.util.ArrayList;
 import java.util.List;
 
-import org.junit.Before;
-import org.junit.Test;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
 
 public class WriteCsvFileExampleUnitTest {
     private static final Logger LOG = LoggerFactory.getLogger(WriteCsvFileExampleUnitTest.class);

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

@@ -8,10 +8,9 @@ This module contains articles about core Java input and output (IO)
 - [Java – Directory Size](https://www.baeldung.com/java-folder-size)
 - [File Size in Java](https://www.baeldung.com/java-file-size)
 - [Zipping and Unzipping in Java](https://www.baeldung.com/java-compress-and-uncompress)
-- [Reading a CSV File into an Array](https://www.baeldung.com/java-csv-file-array)
 - [How to Get the File Extension of a File in Java](https://www.baeldung.com/java-file-extension)
 - [Getting a File’s Mime Type in Java](https://www.baeldung.com/java-file-mime-type)
-- [How to Write to a CSV File in Java](https://www.baeldung.com/java-csv)
 - [How to Avoid the Java FileNotFoundException When Loading Resources](https://www.baeldung.com/java-classpath-resource-cannot-be-opened)
 - [Create a Directory in Java](https://www.baeldung.com/java-create-directory)
+- [Java – Rename or Move a File](https://www.baeldung.com/java-how-to-rename-or-move-a-file)
 - [[More -->]](/core-java-modules/core-java-io-2)

core-java-modules/core-java-io/pom.xml

@@ -29,12 +29,6 @@
             <version>${hsqldb.version}</version>
             <scope>runtime</scope>
         </dependency>
-        <dependency>
-            <groupId>com.opencsv</groupId>
-            <artifactId>opencsv</artifactId>
-            <version>${opencsv.version}</version>
-            <scope>test</scope>
-        </dependency>
         <!-- Mime Type Resolution Libraries -->
         <dependency>
             <groupId>org.apache.tika</groupId>
@@ -142,8 +136,6 @@
     </profiles>
 
     <properties>
-        <!-- util -->
-        <opencsv.version>4.1</opencsv.version>
         <!-- testing -->
         <assertj.version>3.6.1</assertj.version>
         <!-- maven plugins -->

core-java-modules/core-java-io/src/test/java/com/baeldung/rename/RenameFileUnitTest.java

@@ -0,0 +1,64 @@
+package com.baeldung.rename;
+
+import org.apache.commons.io.FileUtils;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import java.io.File;
+import java.io.IOException;
+import java.nio.file.FileSystemException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+
+public class RenameFileUnitTest {
+
+    private final String FILE_TO_MOVE = "src/test/resources/originalFileToMove.txt";
+    private final String TARGET_FILE = "src/test/resources/targetFileToMove.txt";
+
+    @BeforeEach
+    public void createFileToMove() throws IOException {
+        File fileToMove = new File(FILE_TO_MOVE);
+        fileToMove.createNewFile();
+    }
+
+    @AfterEach
+    public void cleanUpFiles() {
+        File targetFile = new File(TARGET_FILE);
+        targetFile.delete();
+    }
+
+    @Test
+    public void givenUsingNio_whenMovingFile_thenCorrect() throws IOException {
+        Path fileToMovePath = Paths.get(FILE_TO_MOVE);
+        Path targetPath = Paths.get(TARGET_FILE);
+        Files.move(fileToMovePath, targetPath);
+    }
+
+    @Test
+    public void givenUsingFileClass_whenMovingFile_thenCorrect() throws IOException {
+        File fileToMove = new File(FILE_TO_MOVE);
+        boolean isMoved = fileToMove.renameTo(new File(TARGET_FILE));
+        if (!isMoved) {
+            throw new FileSystemException(TARGET_FILE);
+        }
+    }
+
+    @Test
+    public void givenUsingGuava_whenMovingFile_thenCorrect()
+            throws IOException {
+        File fileToMove = new File(FILE_TO_MOVE);
+        File targetFile = new File(TARGET_FILE);
+
+        com.google.common.io.Files.move(fileToMove, targetFile);
+    }
+
+    @Test
+    public void givenUsingApache_whenMovingFile_thenCorrect() throws IOException {
+        FileUtils.moveFile(
+                FileUtils.getFile(FILE_TO_MOVE),
+                FileUtils.getFile(TARGET_FILE));
+    }
+
+}

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

@@ -2,4 +2,11 @@
 
 This module contains articles about working with the Java Virtual Machine (JVM).
 
-### Relevant Articles: 
+### Relevant Articles: 
+
+- [Memory Layout of Objects in Java](https://www.baeldung.com/java-memory-layout)
+- [Measuring Object Sizes in the JVM](https://www.baeldung.com/jvm-measuring-object-sizes)
+- [Adding Shutdown Hooks for JVM Applications](https://www.baeldung.com/jvm-shutdown-hooks)
+- [boolean and boolean[] Memory Layout in the JVM](https://www.baeldung.com/jvm-boolean-memory-layout)
+- [Where Is the Array Length Stored in JVM?](https://www.baeldung.com/java-jvm-array-length)
+- More articles: [[<-- prev]](/core-java-modules/core-java-jvm)

core-java-modules/core-java-jvm-2/src/test/java/com/baeldung/memaddress/MemoryAddressUnitTest.java

@@ -0,0 +1,24 @@
+package com.baeldung.memaddress;
+
+import org.junit.Test;
+import org.openjdk.jol.vm.VM;
+
+public class MemoryAddressUnitTest {
+
+    @Test
+    public void printTheMemoryAddress() {
+        String answer = "42";
+
+        System.out.println("The memory address is " + VM.current().addressOf(answer));
+    }
+
+    @Test
+    public void identityHashCodeAndMemoryAddress() {
+        Object obj = new Object();
+
+        System.out.println("Memory address: " + VM.current().addressOf(obj));
+        System.out.println("hashCode: " + obj.hashCode());
+        System.out.println("hashCode: " + System.identityHashCode(obj));
+        System.out.println("toString: " + obj);
+    }
+}

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

@@ -11,8 +11,7 @@ This module contains articles about working with the Java Virtual Machine (JVM).
 - [A Guide to System.exit()](https://www.baeldung.com/java-system-exit)
 - [Guide to System.gc()](https://www.baeldung.com/java-system-gc)
 - [Runtime.getRuntime().halt() vs System.exit() in Java](https://www.baeldung.com/java-runtime-halt-vs-system-exit)
-- [Adding Shutdown Hooks for JVM Applications](https://www.baeldung.com/jvm-shutdown-hooks)
 - [How to Get the Size of an Object in Java](http://www.baeldung.com/java-size-of-object)
 - [What Causes java.lang.OutOfMemoryError: unable to create new native thread](https://www.baeldung.com/java-outofmemoryerror-unable-to-create-new-native-thread)
 - [View Bytecode of a Class File in Java](https://www.baeldung.com/java-class-view-bytecode)
-- [boolean and boolean[] Memory Layout in the JVM](https://www.baeldung.com/jvm-boolean-memory-layout)
+- More articles: [[next -->]](/core-java-modules/core-java-jvm-2)

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

@@ -13,4 +13,4 @@ This module contains articles about core features in the Java language
 - [Comparing Long Values in Java](https://www.baeldung.com/java-compare-long-values)
 - [Comparing Objects in Java](https://www.baeldung.com/java-comparing-objects)
 - [Casting int to Enum in Java](https://www.baeldung.com/java-cast-int-to-enum)
-- [[<-- Prev]](/core-java-modules/core-java-lang)
+[[ <-- Prev]](/core-java-modules/core-java-lang)[[Next --> ]](/core-java-modules/core-java-lang-3)

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

@@ -2,5 +2,5 @@
 
 This module contains articles about core features in the Java language
 
-### Relevant Articles: 
+- [Class.isInstance vs Class.isAssignableFrom](https://www.baeldung.com/java-isinstance-isassignablefrom)
 - [[<-- Prev]](/core-java-modules/core-java-lang-2)

core-java-modules/core-java-lang-3/pom.xml

@@ -8,6 +8,7 @@
     <version>0.1.0-SNAPSHOT</version>
     <name>core-java-lang-3</name>
     <packaging>jar</packaging>
+
     <parent>
         <groupId>com.baeldung.core-java-modules</groupId>
         <artifactId>core-java-modules</artifactId>
@@ -16,7 +17,12 @@
     </parent>
 
     <dependencies>
-        
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>${assertj.version}</version>
+            <scope>test</scope>
+        </dependency>
     </dependencies>
 
     <build>
@@ -30,7 +36,7 @@
     </build>
 
     <properties>
-        
+        <assertj.version>3.12.2</assertj.version>
     </properties>
-
-</project>
+      
+</project>

core-java-modules/core-java-lang-3/src/main/java/com/baeldung/staticvariables/StaticVariableDemo.java

@@ -0,0 +1,23 @@
+package com.baeldung.staticvariables;
+
+public class StaticVariableDemo {
+    public static int i;
+    public static int j = 20;
+    public static int z;
+
+    static {
+        z = 30;
+        a = 40;
+    }
+
+    public static int a = 50;
+
+    public static final int b = 100;
+
+    public StaticVariableDemo() {
+    }
+
+    static class Nested {
+        public static String nestedClassStaticVariable = "test";
+    }
+}

core-java-modules/core-java-lang-3/src/test/java/com/baeldung/staticvariables/StaticVariableUnitTest.java

@@ -0,0 +1,113 @@
+package com.baeldung.staticvariables;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.lang.reflect.Field;
+
+import org.junit.jupiter.api.Test;
+
+public class StaticVariableUnitTest {
+
+    @Test
+    public void initializeStaticVariable_checkAssignedValues() {
+
+        try {
+            Class<?> staticVariableDemo = this.getClass()
+                .getClassLoader()
+                .loadClass("com.baeldung.staticvariables.StaticVariableDemo");
+
+            Field field1 = staticVariableDemo.getField("i");
+
+            assertThat(field1.getInt(staticVariableDemo)).isEqualTo(0);
+
+            Field field2 = staticVariableDemo.getField("j");
+
+            assertThat(field2.getInt(staticVariableDemo)).isEqualTo(20);
+
+        } catch (ClassNotFoundException | NoSuchFieldException | SecurityException e) {
+            e.printStackTrace();
+        } catch (IllegalArgumentException e) {
+            e.printStackTrace();
+        } catch (IllegalAccessException e) {
+            e.printStackTrace();
+        }
+
+    }
+
+    @Test
+    public void initializeStaticVariable_checkStaticBlock() {
+
+        try {
+            Class<?> staticVariableDemo = this.getClass()
+                .getClassLoader()
+                .loadClass("com.baeldung.staticvariables.StaticVariableDemo");
+
+            Field field1 = staticVariableDemo.getField("z");
+
+            assertThat(field1.getInt(staticVariableDemo)).isEqualTo(30);
+
+            Field field2 = staticVariableDemo.getField("a");
+
+            assertThat(field2.getInt(staticVariableDemo)).isEqualTo(50);
+
+        } catch (ClassNotFoundException | NoSuchFieldException | SecurityException e) {
+            e.printStackTrace();
+        } catch (IllegalArgumentException e) {
+            e.printStackTrace();
+        } catch (IllegalAccessException e) {
+            e.printStackTrace();
+        }
+
+    }
+
+    @Test
+    public void initializeStaticVariable_checkFinalValues() {
+
+        try {
+            Class<?> staticVariableDemo = this.getClass()
+                .getClassLoader()
+                .loadClass("com.baeldung.staticvariables.StaticVariableDemo");
+
+            Field field1 = staticVariableDemo.getField("b");
+
+            assertThat(field1.getInt(staticVariableDemo)).isEqualTo(100);
+
+        } catch (ClassNotFoundException | NoSuchFieldException | SecurityException e) {
+            e.printStackTrace();
+        } catch (IllegalArgumentException e) {
+            e.printStackTrace();
+        } catch (IllegalAccessException e) {
+            e.printStackTrace();
+        }
+
+    }
+
+    @Test
+    public void initializeStaticVariable_checkInnerClassValues() {
+
+        try {
+            Class<?> staticVariableDemo = this.getClass()
+                .getClassLoader()
+                .loadClass("com.baeldung.staticvariables.StaticVariableDemo");
+
+            Class<?>[] nestedClasses = staticVariableDemo.getClasses();
+
+            for (Class<?> nestedClass : nestedClasses) {
+                if (nestedClass.getName()
+                    .equals("Nested")) {
+
+                    Field field1 = nestedClass.getField("nestedClassStaticVariable");
+                    assertThat(field1.get(nestedClass)).isEqualTo("test");
+                }
+            }
+
+        } catch (ClassNotFoundException | NoSuchFieldException | SecurityException e) {
+            e.printStackTrace();
+        } catch (IllegalArgumentException e) {
+            e.printStackTrace();
+        } catch (IllegalAccessException e) {
+            e.printStackTrace();
+        }
+
+    }
+}

core-java-modules/core-java-lang-3/src/test/java/com/baeldung/stringtoboolean/StringToBooleanUnitTest.java

@@ -0,0 +1,30 @@
+package com.baeldung.stringtoboolean;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.Test;
+
+public class StringToBooleanUnitTest {
+    
+    @Test
+    public void givenStringTrue_whenUsingParseBoolean_thenTrue() {
+        assertThat(Boolean.parseBoolean("true")).isTrue();
+    }
+
+    @Test
+    public void givenStringTrue_whenUsingValueOf_thenTrue() {
+        assertThat(Boolean.valueOf("true")).isTrue();
+    }
+
+    @Test
+    public void givenStringTrue_whenUsingGetBoolean_thenFalse() {
+        assertThat(Boolean.getBoolean("true")).isFalse();
+    }
+
+    @Test
+    public void givenSystemProperty_whenUsingGetBoolean_thenTrue() {
+        System.setProperty("CODING_IS_FUN", "true");
+        
+        assertThat(Boolean.getBoolean("CODING_IS_FUN")).isTrue();
+    }
+}

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

@@ -3,7 +3,9 @@
 This module contains articles about methods in Java
 
 ### Relevant Articles: 
+
 - [Methods in Java](https://www.baeldung.com/java-methods)
 - [Method Overloading and Overriding in Java](https://www.baeldung.com/java-method-overload-override)
 - [Java equals() and hashCode() Contracts](https://www.baeldung.com/java-equals-hashcode-contracts)
 - [Guide to hashCode() in Java](https://www.baeldung.com/java-hashcode)
+- [The Covariant Return Type in Java](https://www.baeldung.com/java-covariant-return-type)

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

@@ -13,4 +13,5 @@ This module contains articles about core features in the Java language
 - [Retrieving a Class Name in Java](https://www.baeldung.com/java-class-name)
 - [The Java continue and break Keywords](https://www.baeldung.com/java-continue-and-break)
 - [Infinite Loops in Java](https://www.baeldung.com/infinite-loops-java)
-- [[More --> ]](/core-java-modules/core-java-lang-2)
+
+[[Next --> ]](/core-java-modules/core-java-lang-2)

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

@@ -12,4 +12,5 @@ This module contains articles about networking in Java
 - [Authentication with HttpUrlConnection](https://www.baeldung.com/java-http-url-connection)
 - [Download a File from an URL in Java](https://www.baeldung.com/java-download-file)
 - [Handling java.net.ConnectException](https://www.baeldung.com/java-net-connectexception)
+- [Getting MAC addresses in Java](https://www.baeldung.com/java-mac-address)
 - [[<-- Prev]](/core-java-modules/core-java-networking)

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

@@ -0,0 +1,3 @@
+### Relevant Articles:
+
+- [Reading the Value of ‘private’ Fields from a Different Class in Java](https://www.baeldung.com/java-reflection-read-private-field-value)

core-java-modules/core-java-reflection/README.MD

@@ -8,5 +8,4 @@
 - [Changing Annotation Parameters At Runtime](http://www.baeldung.com/java-reflection-change-annotation-params)
 - [Dynamic Proxies in Java](http://www.baeldung.com/java-dynamic-proxies)
 - [What Causes java.lang.reflect.InvocationTargetException?](https://www.baeldung.com/java-lang-reflect-invocationtargetexception)
-- [How to Find all Getters Returning Null](http://www.baeldung.com/java-getters-returning-null)
 - [How to Get a Name of a Method Being Executed?](http://www.baeldung.com/java-name-of-executing-method)

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

@@ -3,6 +3,7 @@
 ## Core Java 8 Cookbooks and Examples
 
 ### Relevant Articles: 
+
 - [An Overview of Regular Expressions Performance in Java](https://www.baeldung.com/java-regex-performance)
 - [A Guide To Java Regular Expressions API](http://www.baeldung.com/regular-expressions-java)
 - [Guide to Escaping Characters in Java RegExps](http://www.baeldung.com/java-regexp-escape-char)
@@ -11,3 +12,4 @@
 - [How to Use Regular Expressions to Replace Tokens in Strings](https://www.baeldung.com/java-regex-token-replacement)
 - [Regular Expressions \s and \s+ in Java](https://www.baeldung.com/java-regex-s-splus)
 - [Validate Phone Numbers With Java Regex](https://www.baeldung.com/java-regex-validate-phone-numbers)
+- [How to Count the Number of Matches for a Regex?](https://www.baeldung.com/java-count-regex-matches)

core-java-modules/core-java-security-2/src/main/java/com/baeldung/pem/JavaSecurityPemUtils.java

@@ -0,0 +1,48 @@
+package com.baeldung.pem;
+
+import org.apache.commons.codec.binary.Base64;
+
+import java.io.File;
+import java.io.IOException;
+import java.nio.charset.Charset;
+import java.nio.file.Files;
+import java.security.GeneralSecurityException;
+import java.security.KeyFactory;
+import java.security.interfaces.RSAPrivateKey;
+import java.security.interfaces.RSAPublicKey;
+import java.security.spec.PKCS8EncodedKeySpec;
+import java.security.spec.X509EncodedKeySpec;
+
+public class JavaSecurityPemUtils {
+
+    public static RSAPrivateKey readPKCS8PrivateKey(File file) throws GeneralSecurityException, IOException {
+        String key = new String(Files.readAllBytes(file.toPath()), Charset.defaultCharset());
+
+        String privateKeyPEM = key
+                .replace("-----BEGIN PRIVATE KEY-----", "")
+                .replaceAll(System.lineSeparator(), "")
+                .replace("-----END PRIVATE KEY-----", "");
+
+        byte[] encoded = Base64.decodeBase64(privateKeyPEM);
+
+        KeyFactory keyFactory = KeyFactory.getInstance("RSA");
+        PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(encoded);
+        return (RSAPrivateKey) keyFactory.generatePrivate(keySpec);
+    }
+
+    public static RSAPublicKey readX509PublicKey(File file) throws GeneralSecurityException, IOException {
+        String key = new String(Files.readAllBytes(file.toPath()), Charset.defaultCharset());
+
+        String publicKeyPEM = key
+                .replace("-----BEGIN PUBLIC KEY-----", "")
+                .replaceAll(System.lineSeparator(), "")
+                .replace("-----END PUBLIC KEY-----", "");
+
+        byte[] encoded = Base64.decodeBase64(publicKeyPEM);
+
+        KeyFactory keyFactory = KeyFactory.getInstance("RSA");
+        X509EncodedKeySpec keySpec = new X509EncodedKeySpec(encoded);
+        return (RSAPublicKey) keyFactory.generatePublic(keySpec);
+    }
+
+}

core-java-modules/core-java-security-2/src/main/resources/pem/private-key-pkcs8.pem

@@ -0,0 +1,28 @@
+-----BEGIN PRIVATE KEY-----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+-----END PRIVATE KEY-----

core-java-modules/core-java-security-2/src/main/resources/pem/public-key.pem

@@ -0,0 +1,9 @@
+-----BEGIN PUBLIC KEY-----
+MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAsjtGIk8SxD+OEiBpP2/T
+JUAF0upwuKGMk6wH8Rwov88VvzJrVm2NCticTk5FUg+UG5r8JArrV4tJPRHQyvqK
+wF4NiksuvOjv3HyIf4oaOhZjT8hDne1Bfv+cFqZJ61Gk0MjANh/T5q9vxER/7TdU
+NHKpoRV+NVlKN5bEU/NQ5FQjVXicfswxh6Y6fl2PIFqT2CfjD+FkBPU1iT9qyJYH
+A38IRvwNtcitFgCeZwdGPoxiPPh1WHY8VxpUVBv/2JsUtrB/rAIbGqZoxAIWvijJ
+Pe9o1TY3VlOzk9ASZ1AeatvOir+iDVJ5OpKmLnzc46QgGPUsjIyo6Sje9dxpGtoG
+QQIDAQAB
+-----END PUBLIC KEY-----

core-java-modules/core-java-security-2/src/test/java/com/baeldung/pem/JavaSecurityPemUtilsUnitTest.java

@@ -0,0 +1,33 @@
+package com.baeldung.pem;
+
+
+import org.junit.jupiter.api.Test;
+
+import java.io.File;
+import java.security.interfaces.RSAPrivateKey;
+import java.security.interfaces.RSAPublicKey;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class JavaSecurityPemUtilsUnitTest {
+
+    @Test
+    public void whenReadPublicKeyFromPEMFile_thenSuccess() throws Exception {
+        File pemFile = new File(JavaSecurityPemUtilsUnitTest.class.getResource("/pem/public-key.pem").getFile());
+
+        RSAPublicKey publicKey = JavaSecurityPemUtils.readX509PublicKey(pemFile);
+
+        assertEquals("X.509", publicKey.getFormat());
+        assertEquals("RSA", publicKey.getAlgorithm());
+    }
+
+    @Test
+    public void whenReadPrivateKeyFromPEMFile_thenSuccess() throws Exception {
+        File pemFile = new File(JavaSecurityPemUtilsUnitTest.class.getResource("/pem/private-key-pkcs8.pem").getFile());
+
+        RSAPrivateKey privateKey = JavaSecurityPemUtils.readPKCS8PrivateKey(pemFile);
+
+        assertEquals("PKCS#8", privateKey.getFormat());
+        assertEquals("RSA", privateKey.getAlgorithm());
+    }
+}

core-java-modules/core-java-string-operations-3/README.md

@@ -0,0 +1,3 @@
+### Relevant Articles:
+
+- [Version Comparison in Java](https://www.baeldung.com/java-comparing-versions)

core-java-modules/core-java-string-operations-3/pom.xml

@@ -0,0 +1,61 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project
+    xmlns="http://maven.apache.org/POM/4.0.0"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <artifactId>core-java-string-operations-3</artifactId>
+    <version>0.1.0-SNAPSHOT</version>
+    <name>core-java-string-operations-3</name>
+    <packaging>jar</packaging>
+    <parent>
+        <groupId>com.baeldung.core-java-modules</groupId>
+        <artifactId>core-java-modules</artifactId>
+        <version>0.0.1-SNAPSHOT</version>
+        <relativePath>../</relativePath>
+    </parent>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>${assertj.version}</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.apache.maven</groupId>
+            <artifactId>maven-artifact</artifactId>
+            <version>${maven-artifact.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>org.gradle</groupId>
+            <artifactId>gradle-core</artifactId>
+            <version>${gradle-core.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>com.fasterxml.jackson.core</groupId>
+            <artifactId>jackson-core</artifactId>
+            <version>${jackson-core.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>com.vdurmont</groupId>
+            <artifactId>semver4j</artifactId>
+            <version>${semver4j.version}</version>
+        </dependency>
+    </dependencies>
+
+    <properties>
+        <assertj.version>3.6.1</assertj.version>
+        <maven-artifact.version>3.6.3</maven-artifact.version>
+        <gradle-core.version>6.1.1</gradle-core.version>
+        <jackson-core.version>2.11.1</jackson-core.version>
+        <semver4j.version>3.1.0</semver4j.version>
+    </properties>
+
+	<repositories>
+	      <repository>
+	          <id>gradle-repo</id>
+	          <url>https://repo.gradle.org/gradle/libs-releases-local/</url>
+	      </repository>
+	</repositories>
+</project>

core-java-modules/core-java-string-operations-3/src/main/java/com/baeldung/versioncomparison/VersionCompare.java

@@ -0,0 +1,25 @@
+package com.baeldung.versioncomparison;
+
+public class VersionCompare {
+
+    public static int compareVersions(String version1, String version2) {
+        int comparisonResult = 0;
+        
+        String[] version1Splits = version1.split("\\.");
+        String[] version2Splits = version2.split("\\.");
+
+        int maxLengthOfVersionSplits = Math.max(version1Splits.length, version2Splits.length);
+        for (int i = 0; i < maxLengthOfVersionSplits; i++){
+            Integer v1 = i < version1Splits.length ? Integer.parseInt(version1Splits[i]) : 0;
+            Integer v2 = i < version2Splits.length ? Integer.parseInt(version2Splits[i]) : 0;
+            int compare = v1.compareTo(v2);
+            if (compare != 0) {
+                comparisonResult = compare;
+                break;
+            }
+        }
+
+        return comparisonResult;
+    }
+
+}

core-java-modules/core-java-string-operations-3/src/test/java/com/baeldung/versioncomparison/VersionComparisonUnitTest.java

@@ -0,0 +1,136 @@
+package com.baeldung.versioncomparison;
+
+import org.junit.Test;
+
+import com.fasterxml.jackson.core.Version;
+import com.vdurmont.semver4j.Semver;
+import com.vdurmont.semver4j.Semver.VersionDiff;
+
+import org.apache.maven.artifact.versioning.ComparableVersion;
+import org.gradle.util.VersionNumber;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+public class VersionComparisonUnitTest {
+    
+    @Test
+    public void givenVersionStrings_whenUsingMavenArtifact_thenCompareVersions() {
+        ComparableVersion version1_1 = new ComparableVersion("1.1");
+        ComparableVersion version1_2 = new ComparableVersion("1.2");
+        ComparableVersion version1_3 = new ComparableVersion("1.3");
+
+        assertTrue(version1_1.compareTo(version1_2) < 0);
+        assertTrue(version1_3.compareTo(version1_2) > 0);
+        
+        ComparableVersion version1_1_0 = new ComparableVersion("1.1.0"); 
+        assertEquals(0, version1_1.compareTo(version1_1_0));
+
+        ComparableVersion version1_1_alpha = new ComparableVersion("1.1-alpha");
+        assertTrue(version1_1.compareTo(version1_1_alpha) > 0);
+        
+        ComparableVersion version1_1_beta = new ComparableVersion("1.1-beta");
+        ComparableVersion version1_1_milestone = new ComparableVersion("1.1-milestone");
+        ComparableVersion version1_1_rc = new ComparableVersion("1.1-rc");
+        ComparableVersion version1_1_snapshot = new ComparableVersion("1.1-snapshot");
+        
+        assertTrue(version1_1_alpha.compareTo(version1_1_beta) < 0);
+        assertTrue(version1_1_beta.compareTo(version1_1_milestone) < 0);
+        assertTrue(version1_1_rc.compareTo(version1_1_snapshot) < 0);
+        assertTrue(version1_1_snapshot.compareTo(version1_1) < 0);        
+        
+        ComparableVersion version1_1_c = new ComparableVersion("1.1-c");
+        ComparableVersion version1_1_z = new ComparableVersion("1.1-z");
+        ComparableVersion version1_1_1 = new ComparableVersion("1.1.1");
+        
+        assertTrue(version1_1_c.compareTo(version1_1_z) < 0);
+        assertTrue(version1_1_z.compareTo(version1_1_1) < 0);
+    }
+    
+    @Test
+    public void givenVersionStrings_whenUsingGradle_thenCompareVersions() {
+        VersionNumber version1_1 = VersionNumber.parse("1.1");
+        VersionNumber version1_2 = VersionNumber.parse("1.2");
+        VersionNumber version1_3 = VersionNumber.parse("1.3");
+
+        assertTrue(version1_1.compareTo(version1_2) < 0);
+        assertTrue(version1_3.compareTo(version1_2) > 0);
+        
+        VersionNumber version1_1_0 = VersionNumber.parse("1.1.0");
+        assertEquals(0, version1_1.compareTo(version1_1_0));
+        
+        VersionNumber version1_1_1_1_alpha = VersionNumber.parse("1.1.1.1-alpha");
+        assertTrue(version1_1.compareTo(version1_1_1_1_alpha) < 0);
+        
+        VersionNumber version1_1_beta = VersionNumber.parse("1.1.0.0-beta"); 
+        assertTrue(version1_1_beta.compareTo(version1_1_1_1_alpha) < 0);
+
+        VersionNumber version1_1_1_snapshot = VersionNumber.parse("1.1.1-snapshot");
+        assertTrue(version1_1_1_1_alpha.compareTo(version1_1_1_snapshot) < 0);
+    }
+    
+    @Test
+    public void givenVersionStrings_whenUsingJackson_thenCompareVersions() {
+        Version version1_1 = new Version(1, 1, 0, null, null, null);
+        Version version1_2 = new Version(1, 2, 0, null, null, null);
+        Version version1_3 = new Version(1, 3, 0, null, null, null);
+        
+        assertTrue(version1_1.compareTo(version1_2) < 0);
+        assertTrue(version1_3.compareTo(version1_2) > 0);
+        
+        Version version1_1_1 = new Version(1, 1, 1, null, null, null);
+        assertTrue(version1_1.compareTo(version1_1_1) < 0);
+        
+        Version version1_1_maven = new Version(1, 1, 0, null, "org.apache.maven", null);
+        Version version1_1_gradle = new Version(1, 1, 0, null, "org.gradle", null);
+        assertTrue(version1_1_maven.compareTo(version1_1_gradle) < 0);
+        
+        Version version1_1_snapshot = new Version(1, 1, 0, "snapshot", null, null);
+        assertEquals(0, version1_1.compareTo(version1_1_snapshot));
+        
+        assertTrue(version1_1_snapshot.isSnapshot());
+    }
+    
+    @Test
+    public void givenVersionStrings_whenUsingSemver_thenCompareVersions() {
+        Semver version1_1 = new Semver("1.1.0");
+        Semver version1_2 = new Semver("1.2.0");
+        Semver version1_3 = new Semver("1.3.0");
+
+        assertTrue(version1_1.compareTo(version1_2) < 0);
+        assertTrue(version1_3.compareTo(version1_2) > 0);
+        
+        Semver version1_1_alpha = new Semver("1.1.0-alpha");
+        assertTrue(version1_1.isGreaterThan(version1_1_alpha));
+        
+        Semver version1_1_beta = new Semver("1.1.0-beta");
+        Semver version1_1_milestone = new Semver("1.1.0-milestone");
+        Semver version1_1_rc = new Semver("1.1.0-rc");
+        Semver version1_1_snapshot = new Semver("1.1.0-snapshot");
+        
+        assertTrue(version1_1_alpha.isLowerThan(version1_1_beta));
+        assertTrue(version1_1_beta.compareTo(version1_1_milestone) < 0);
+        assertTrue(version1_1_rc.compareTo(version1_1_snapshot) < 0);
+        assertTrue(version1_1_snapshot.compareTo(version1_1) < 0);        
+        
+        assertTrue(version1_1.isEqualTo("1.1.0"));
+        
+        assertEquals(VersionDiff.MAJOR, version1_1.diff("2.1.0"));
+        assertEquals(VersionDiff.MINOR, version1_1.diff("1.2.3"));
+        assertEquals(VersionDiff.PATCH, version1_1.diff("1.1.1"));
+        
+        assertTrue(version1_1.isStable());
+        assertFalse(version1_1_alpha.isStable());
+    }
+
+    @Test
+    public void givenVersionStrings_whenUsingCustomVersionCompare_thenCompareVersions() {
+        assertTrue(VersionCompare.compareVersions("1.0.1", "1.1.2") < 0);
+        assertTrue(VersionCompare.compareVersions("1.0.1", "1.10") < 0);
+        assertTrue(VersionCompare.compareVersions("1.1.2", "1.0.1") > 0);
+        assertTrue(VersionCompare.compareVersions("1.1.2", "1.2") < 0); 
+        assertEquals(0, VersionCompare.compareVersions("1.3.0", "1.3")); 
+    }
+    
+}

core-java-modules/pom.xml

@@ -72,6 +72,7 @@
 
         <module>core-java-io</module>
         <module>core-java-io-2</module>
+        <module>core-java-io-3</module>
         <module>core-java-io-apis</module>
         <module>core-java-io-conversions</module>
         <module>core-java-io-conversions-2</module>
@@ -85,6 +86,7 @@
         <module>core-java-lambdas</module>
         <module>core-java-lang</module>
         <module>core-java-lang-2</module>
+        <module>core-java-lang-3</module>
         <module>core-java-lang-math</module>
         <module>core-java-lang-math-2</module>
         <module>core-java-lang-oop-constructors</module>
@@ -125,6 +127,7 @@
         <module>core-java-string-conversions-2</module>
         <module>core-java-string-operations</module>
         <module>core-java-string-operations-2</module>
+        <module>core-java-string-operations-3</module>
         <module>core-java-strings</module>
         <module>core-java-sun</module>
 

core-kotlin-modules/core-kotlin-collections/src/main/kotlin/com/baeldung/index/IndexedIteration.kt

@@ -0,0 +1,33 @@
+package com.baeldung.index
+
+fun main() {
+
+    // Index only
+    val colors = listOf("Red", "Green", "Blue")
+    for (i in colors.indices) {
+        println(colors[i])
+    }
+
+    val colorArray = arrayOf("Red", "Green", "Blue")
+    for (i in colorArray.indices) {
+        println(colorArray[i])
+    }
+
+    (0 until colors.size).forEach { println(colors[it]) }
+    for (i in 0 until colors.size) {
+        println(colors[i])
+    }
+
+    // Index and Value
+    colors.forEachIndexed { i, v -> println("The value for index $i is $v") }
+    for (indexedValue in colors.withIndex()) {
+        println("The value for index ${indexedValue.index} is ${indexedValue.value}")
+    }
+
+    for ((i, v) in colors.withIndex()) {
+        println("The value for index $i is $v")
+    }
+
+    colors.filterIndexed { i, _ -> i % 2 == 0 }
+    colors.filterIndexed { _, v -> v == "RED" }
+}

core-kotlin-modules/core-kotlin-lang-2/README.md

@@ -7,7 +7,6 @@ This module contains articles about core features in the Kotlin language.
 - [Infix Functions in Kotlin](https://www.baeldung.com/kotlin-infix-functions)
 - [Lambda Expressions in Kotlin](https://www.baeldung.com/kotlin-lambda-expressions)
 - [Creating Java static final Equivalents in Kotlin](https://www.baeldung.com/kotlin-java-static-final)
-- [Initializing Arrays in Kotlin](https://www.baeldung.com/kotlin-initialize-array)
 - [Lazy Initialization in Kotlin](https://www.baeldung.com/kotlin-lazy-initialization)
 - [Comprehensive Guide to Null Safety in Kotlin](https://www.baeldung.com/kotlin-null-safety)
 - [Kotlin Scope Functions](https://www.baeldung.com/kotlin-scope-functions)

core-kotlin-modules/core-kotlin-lang-2/src/test/kotlin/com/baeldung/arrayinitialization/ArrayInitializationTest.kt

@@ -1,49 +0,0 @@
-package com.baeldung.arrayinitialization
-
-import org.junit.Test
-import kotlin.test.assertEquals
-
-class ArrayInitializationTest {
-
-    @Test
-    fun givenArrayOfStrings_thenValuesPopulated() {
-        val strings = arrayOf("January", "February", "March")
-
-        assertEquals(3, strings.size)
-        assertEquals("March", strings[2])
-    }
-
-    @Test
-    fun givenArrayOfIntegers_thenValuesPopulated() {
-        val integers = intArrayOf(1, 2, 3, 4)
-
-        assertEquals(4, integers.size)
-        assertEquals(1, integers[0])
-    }
-
-    @Test
-    fun givenArrayOfNulls_whenPopulated_thenValuesPresent() {
-        val array = arrayOfNulls<Number>(5)
-
-        for (i in array.indices) {
-            array[i] = i * i
-        }
-
-        assertEquals(16, array[4])
-    }
-
-    @Test
-    fun whenGeneratorUsed_thenValuesPresent() {
-        val generatedArray = IntArray(10) { i -> i * i }
-
-        assertEquals(81, generatedArray[9])
-    }
-
-    @Test
-    fun whenStringGenerated_thenValuesPresent() {
-        val generatedStringArray = Array(10) { i -> "Number of index: $i"  }
-
-        assertEquals("Number of index: 0", generatedStringArray[0])
-    }
-
-}

core-kotlin-modules/core-kotlin-lang-oop-2/src/main/kotlin/com/baeldung/anonymous/Anonymous.kt

@@ -0,0 +1,41 @@
+package com.baeldung.anonymous
+
+import java.io.Serializable
+import java.nio.channels.Channel
+
+fun main() {
+    val channel = object : Channel {
+        override fun isOpen() = false
+
+        override fun close() {
+        }
+    }
+
+    val maxEntries = 10
+    val lruCache = object : LinkedHashMap<String, Int>(10, 0.75f) {
+
+        override fun removeEldestEntry(eldest: MutableMap.MutableEntry<String, Int>?): Boolean {
+            return size > maxEntries
+        }
+    }
+
+    val map = object : LinkedHashMap<String, Int>() {
+        // omitted
+    }
+
+    val serializableChannel = object : Channel, Serializable {
+        override fun isOpen(): Boolean {
+            TODO("Not yet implemented")
+        }
+
+        override fun close() {
+            TODO("Not yet implemented")
+        }
+    }
+
+    val obj = object {
+        val question = "answer"
+        val answer = 42
+    }
+    println("The ${obj.question} is ${obj.answer}")
+}

data-structures/README.md

@@ -11,3 +11,4 @@ This module contains articles about data structures in Java
 - [Introduction to Big Queue](https://www.baeldung.com/java-big-queue)
 - [Guide to AVL Trees in Java](https://www.baeldung.com/java-avl-trees)
 - [Graphs in Java](https://www.baeldung.com/java-graphs)
+- [Implementing a Ring Buffer in Java](https://www.baeldung.com/java-ring-buffer)