network programming and reflection

src/main/java/com/examplehub/basics/network/SocketClient.java

@@ -8,29 +8,26 @@
 public class SocketClient {
   public static void main(String[] args) throws IOException {
     Socket clientSocket = new Socket("127.0.0.1", 6666);
-    try (InputStream inputStream = clientSocket.getInputStream()) {
-      try (OutputStream outputStream = clientSocket.getOutputStream()) {
-        handle(inputStream, outputStream);
-      }
+    try (InputStream inputStream = clientSocket.getInputStream(); OutputStream outputStream = clientSocket.getOutputStream()) {
+      handle(inputStream, outputStream);
     }
     clientSocket.close();
     System.out.println("disconnected.");
   }
 
   private static void handle(InputStream inputStream, OutputStream outputStream)
-      throws IOException {
+          throws IOException {
     var writer = new BufferedWriter(new OutputStreamWriter(outputStream, StandardCharsets.UTF_8));
     var reader = new BufferedReader(new InputStreamReader(inputStream, StandardCharsets.UTF_8));
     Scanner scanner = new Scanner(System.in);
     System.out.println("[server] " + reader.readLine());
     for (; ; ) {
-      System.out.print(">>> "); // 打印提示
-      String s = scanner.nextLine(); // 读取一行输入
+      System.out.print(">>> ");
+      String s = scanner.nextLine();
       writer.write(s + System.lineSeparator());
-      //      writer.newLine();
       writer.flush();
       String resp = reader.readLine();
-      System.out.println("<<< " + resp);
+      System.out.println("[server]: " + resp);
       if (resp.equals("bye")) {
         break;
       }

src/main/java/com/examplehub/basics/network/SocketServer.java

@@ -1,27 +1,30 @@
 package com.examplehub.basics.network;
 
+import com.examplehub.strings.ReverseString;
+import com.examplehub.utils.StringUtils;
+
 import java.io.*;
 import java.net.ServerSocket;
 import java.net.Socket;
 import java.nio.charset.StandardCharsets;
 
 public class SocketServer {
   static class ServerHandler implements Runnable {
-    private Socket socket;
+    private final Socket socket;
 
     public ServerHandler(Socket socket) {
       this.socket = socket;
     }
 
     public void run() {
-      try (InputStream inputStream = this.socket.getInputStream()) {
-        try (OutputStream outputStream = this.socket.getOutputStream()) {
-          handle(inputStream, outputStream);
-        }
+      try (InputStream inputStream = this.socket.getInputStream();
+           OutputStream outputStream = this.socket.getOutputStream()) {
+        handle(inputStream, outputStream);
       } catch (Exception e) {
         try {
           this.socket.close();
         } catch (IOException ex) {
+          ex.printStackTrace();
         }
         System.out.println("client disconnect");
       }
@@ -30,24 +33,27 @@ public void run() {
     private void handle(InputStream inputStream, OutputStream outputStream) throws IOException {
       var reader = new BufferedReader(new InputStreamReader(inputStream, StandardCharsets.UTF_8));
       var writer = new BufferedWriter(new OutputStreamWriter(outputStream, StandardCharsets.UTF_8));
-      writer.write("hello!\n");
+      writer.write("welcome connect service!\n");
       writer.flush();
       while (true) {
         String line = reader.readLine();
+        System.out.println("[client]: " + line);
         if (line.equals("bye")) {
           writer.write("bye\n");
           writer.flush();
           break;
         }
-        writer.write("ok: " + line + "\n");
+        writer.write("ok: " + ReverseString.reverse(line) + "\n");
         writer.flush();
       }
     }
   }
 
   public static void main(String[] args) throws IOException {
-    ServerSocket serverSocket = new ServerSocket(6666);
-    System.out.println("server is started!");
+    int port = 6666;
+    ServerSocket serverSocket = new ServerSocket(port);
+    System.out.print("server is started! listen on: ");
+    System.err.print(port);
     while (true) {
       Socket socket = serverSocket.accept();
       System.out.println("connected from " + socket.getRemoteSocketAddress());

src/main/java/com/examplehub/basics/network/UDPClient.java

@@ -0,0 +1,21 @@
+package com.examplehub.basics.network;
+
+import java.io.IOException;
+import java.net.DatagramPacket;
+import java.net.DatagramSocket;
+import java.net.InetAddress;
+import java.nio.charset.StandardCharsets;
+
+public class UDPClient {
+  public static void main(String[] args) throws IOException {
+    DatagramSocket datagramSocket = new DatagramSocket();
+    byte[] buffer = "123".getBytes(StandardCharsets.UTF_8);
+    DatagramPacket datagramPacket = new DatagramPacket(buffer, buffer.length, InetAddress.getLocalHost(), 6666);
+    datagramSocket.send(datagramPacket);
+
+    byte[] bytes = new byte[1024];
+    DatagramPacket dp = new DatagramPacket(bytes, bytes.length);
+    datagramSocket.receive(dp);
+    System.out.println("[server]: " + new String(bytes, 0, dp.getLength()));
+  }
+}

src/main/java/com/examplehub/basics/network/UDPServer.java

@@ -0,0 +1,27 @@
+package com.examplehub.basics.network;
+
+import com.examplehub.strings.ReverseString;
+
+import java.io.IOException;
+import java.net.DatagramPacket;
+import java.net.DatagramSocket;
+import java.nio.charset.StandardCharsets;
+
+public class UDPServer {
+  public static void main(String[] args) throws IOException {
+    int port = 6666;
+    try(DatagramSocket datagramSocket = new DatagramSocket(port)) {
+      System.out.println("server started! listen on: " + port);
+      byte[] buffer = new byte[1024];
+      DatagramPacket datagramPacket = new DatagramPacket(buffer, buffer.length);
+      datagramSocket.receive(datagramPacket);
+      System.out.println("[client]: " + new String(buffer, 0, datagramPacket.getLength()));
+
+      byte[] bytes = ReverseString.reverse(new String(buffer, 0, datagramPacket.getLength()))
+              .getBytes(StandardCharsets.UTF_8);
+      System.out.println(new String(bytes));
+      DatagramPacket dp = new DatagramPacket(bytes, bytes.length, datagramPacket.getAddress(), datagramPacket.getPort());
+      datagramSocket.send(dp);
+    }
+  }
+}

src/test/java/com/examplehub/basics/reflection/CreateObjFromClassTest.java

@@ -4,11 +4,93 @@
 
 import org.junit.jupiter.api.Test;
 
+import java.lang.reflect.Constructor;
+import java.lang.reflect.InvocationTargetException;
+
+class User {
+  private  String username;
+  private  int age;
+
+  public User() {
+  }
+
+  public User(String username, int age) {
+    this.username = username;
+    this.age = age;
+  }
+
+  public void setAge(int age) {
+    this.age = age;
+  }
+
+  public void setUsername(String username) {
+    this.username = username;
+  }
+
+  @Override
+  public String toString() {
+    return "User{" +
+            "username='" + username + '\'' +
+            ", age=" + age +
+            '}';
+  }
+}
 class CreateObjFromClassTest {
   @Test
-  void testCreateObj() throws InstantiationException, IllegalAccessException {
-    Class cls = String.class;
-    String str = (String) cls.newInstance();
+  void testCreateObjUsingNewInstance() throws InstantiationException, IllegalAccessException {
+    Class<String> cls = String.class;
+    String str = cls.newInstance();
     assertTrue(str.isEmpty());
   }
+
+  @Test
+  void testCreateCustomObject() throws InstantiationException, IllegalAccessException, ClassNotFoundException {
+
+    Class<?> userClass = User.class;
+    User user = (User) userClass.newInstance();
+    user.setUsername("admin");
+    user.setAge(25);
+    assertEquals("User{username='admin', age=25}", user.toString());
+  }
+
+  @Test
+  void testCreateCustomObjectUsingConstructor() throws ClassNotFoundException, NoSuchMethodException, InvocationTargetException, InstantiationException, IllegalAccessException {
+    Class<?> userClass = Class.forName("com.examplehub.basics.reflection.User");
+    Constructor<?> constructor = userClass.getConstructor();
+    assertEquals("public com.examplehub.basics.reflection.User()", constructor.toString());
+    User user = (User) constructor.newInstance();
+    user.setUsername("duyuanchao");
+    user.setAge(25);
+    assertEquals("User{username='duyuanchao', age=25}", user.toString());
+  }
+
+  @Test
+  void testCreateCustomObjectUsingConstructorWithArgs() throws ClassNotFoundException, NoSuchMethodException, InvocationTargetException, InstantiationException, IllegalAccessException {
+    Class<?> userClass = Class.forName("com.examplehub.basics.reflection.User");
+    Constructor<?> constructor = userClass.getConstructor(String.class, int.class);
+    assertEquals("public com.examplehub.basics.reflection.User(java.lang.String,int)", constructor.toString());
+    User user = (User) constructor.newInstance("duyuanchao", 26);
+    assertEquals("User{username='duyuanchao', age=26}", user.toString());
+  }
+
+  @Test
+  void testGetAllConstructors() throws ClassNotFoundException {
+    Class<?> userClass = Class.forName("com.examplehub.basics.reflection.User");
+    Constructor<?>[] constructors = userClass.getConstructors();
+    for (Constructor<?> constructor : constructors) {
+      assertEquals(1, constructor.getModifiers());
+      assertEquals("com.examplehub.basics.reflection.User", constructor.getName());
+      Class<?>[] classes = constructor.getParameterTypes();
+      int count = 0;
+      for (Class<?> cls : classes) {
+        if (count == 0) {
+          assertEquals("java.lang.String", cls.getName());
+        }
+        if (count == 1) {
+          assertEquals("int", cls.getName());
+        }
+        count++;
+      }
+    }
+  }
 }

src/test/java/com/examplehub/basics/reflection/GetClassExampleTest.java

@@ -4,18 +4,48 @@
 
 import org.junit.jupiter.api.Test;
 
+import java.time.Month;
+
 class GetClassExampleTest {
+
+  @Test
+  void testVoid() {
+    Class<Void> c = void.class;
+    assertEquals("void", c.getName());
+    assertEquals("void", c.getSimpleName());
+    assertEquals("java.lang", c.getPackageName());
+    assertEquals("void", c.toString());
+  }
+
   @Test
   void testGetClass() throws ClassNotFoundException {
-    Class cls = String.class;
-    Class cls2 = "hello".getClass();
-    Class cls3 = Class.forName("java.lang.String");
-    assertTrue(cls == cls2 && cls == cls3);
+    Class<String> cls = String.class;
+    Class<?> cls2 = "hello".getClass();
+    Class<?> cls3 = Class.forName("java.lang.String");
+    assertSame(cls, cls2);
+    assertSame(cls, cls3);
+  }
+
+  @Test
+  void testGetClassByTYPE() {
+    Class<?> c = Integer.TYPE;
+    assertEquals("int", c.getName());
+    assertEquals("int", c.getSimpleName());
+    assertEquals("java.lang", c.getPackageName());
+    assertEquals("int", c.toString());
+    assertTrue(c.isPrimitive());
+  }
+
+  @Test
+  void testGetClassByClassloader() throws ClassNotFoundException {
+    ClassLoader classLoader = GetClassExample.class.getClassLoader();
+    Class<?> cls = classLoader.loadClass("java.lang.String");
+    assertEquals("java.lang.String", cls.getName());
   }
 
   @Test
   void testStringClass() {
-    Class cls = "".getClass();
+    Class<?> cls = "".getClass();
     assertEquals("java.lang.String", cls.getName());
     assertEquals("String", cls.getSimpleName());
     assertEquals("java.lang", cls.getPackageName());
@@ -27,7 +57,7 @@ void testStringClass() {
 
   @Test
   void testInterface() {
-    Class cls = Runnable.class;
+    Class<Runnable> cls = Runnable.class;
     assertEquals("java.lang.Runnable", cls.getName());
     assertEquals("Runnable", cls.getSimpleName());
     assertEquals("java.lang", cls.getPackageName());
@@ -39,7 +69,7 @@ void testInterface() {
 
   @Test
   void testMonth() {
-    Class cls = java.time.Month.class;
+    Class<Month> cls = java.time.Month.class;
     assertEquals("java.time.Month", cls.getName());
     assertEquals("Month", cls.getSimpleName());
     assertEquals("java.time", cls.getPackageName());
@@ -51,7 +81,7 @@ void testMonth() {
 
   @Test
   void testStringArray() {
-    Class cls = String[].class;
+    Class<String[]> cls = String[].class;
     assertEquals("[Ljava.lang.String;", cls.getName());
     assertEquals("String[]", cls.getSimpleName());
     assertEquals("java.lang", cls.getPackageName());
@@ -63,7 +93,7 @@ void testStringArray() {
 
   @Test
   void testPrimitive() {
-    Class cls = int.class;
+    Class<?> cls = int.class;
     assertEquals("int", cls.getName());
     assertEquals("int", cls.getSimpleName());
     assertEquals("java.lang", cls.getPackageName());