public class TCPServer {
  public static void main(String[] args){
      try{
        ServerSocket server=new ServerSocket();
        SocketAddress address=new InetSocketAddress(InetAddress.getLocalHost(),10001);
        server.bind(address);
        System.out.println("等待连接客户端...");
        Socket client = server.accept();
        System.out.println("connected with"+client.getRemoteSocketAddress());
        PrintWriter socketOut = new PrintWriter(client.getOutputStream());
        System.out.println("等待客户端的消息...");
        byte buf[] = new byte[1024];
        if ( client.getInputStream().read(buf) > 0 ) {
          System.out.println("收到的消息: " + new String(buf));
        }
        System.out.println("发送消息给客户端...");
        String sendStr = "服务器返回的信息";
        socketOut.write(sendStr);
        socketOut.flush();
        socketOut.close();
        client.close();
        server.close();
      }catch (IOException e) {
        System.out.println(e.getMessage());
        e.printStackTrace();
      }
  }
}

public class TCPClient {
  public static void main(String[] args){
    try{
      final Socket socket = new Socket();
      SocketAddress address = new InetSocketAddress(InetAddress.getLocalHost(), 10001);
      System.out.println("连接服务端 ...");
      socket.connect(address);
      PrintWriter socketOut = new PrintWriter(socket.getOutputStream());
      BufferedReader socketIn = new BufferedReader(
          new InputStreamReader(socket.getInputStream()) );
      String sendStr = "客户端发送的消息";
      System.out.println("发送消息给服务端 ...");
      socketOut.write(sendStr);
      socketOut.flush();
      System.out.println("等待服务端的消息 ...");
      String receiveStr = socketIn.readLine();
      System.out.println("收到的消息: " + receiveStr);      
      socketOut.close();
      socketIn.close();
      socket.close();
    }catch (IOException e) {
      System.out.println(e.getMessage());
      e.printStackTrace();
    }
  }
}

public class UDPServer {
  public static void main(String args[]) {
    DatagramSocket socket = null;
    DatagramPacket datapacket = null;
    InetSocketAddress address = null;
    try {
      address = new InetSocketAddress(InetAddress.getLocalHost(), 7778);
      socket = new DatagramSocket(address);
      // socket.bind(address);
      byte buf[] = new byte[1024];
      datapacket = new DatagramPacket(buf, buf.length);
      System.out.println("block for receive messages...");
      socket.receive(datapacket);
      buf = datapacket.getData();
      InetAddress addr = datapacket.getAddress();
      int port = datapacket.getPort();
      System.out.println("Message Content: " + new String(buf) );
      System.out.println("Receive From " + addr + ":" + port);      
      SocketAddress toAddress = datapacket.getSocketAddress();
      String sendStr = "I'm Server, this is the message for client.";
      buf = sendStr.getBytes();
      datapacket = new DatagramPacket(buf, buf.length);
      datapacket.setSocketAddress(toAddress);
      socket.send(datapacket);
      System.out.println("message sended");
     //释放资源 
      socket.close(); 
    } catch (UnknownHostException e) {
      e.printStackTrace();
    } catch (SocketException e) {
      e.printStackTrace();
    } catch (IOException e) {
      e.printStackTrace();
    }
  }
}

public class UDPClient {
  public static void main(String args[]) {
    try {
      DatagramSocket getSocket = new DatagramSocket();
      DatagramPacket datapacket = null;
      InetSocketAddress toAddress = new InetSocketAddress(InetAddress.getLocalHost(), 7778);   
      String sendStr = "I'm client, this is the message for server.";
      byte buf[] = sendStr.getBytes();
      datapacket = new DatagramPacket(buf, buf.length);
      datapacket.setSocketAddress(toAddress);
      getSocket.send(datapacket);
      System.out.println("message sended");
      System.out.println("block for receive messages...");
      getSocket.receive(datapacket);
      buf = datapacket.getData();
      System.out.println("Message Content: " + new String(buf));
      getSocket.close(); 
    } catch (SocketException e) {
      e.printStackTrace();
    } catch (UnknownHostException e) {
      e.printStackTrace();
    } catch (IOException e) {
      e.printStackTrace();
    }
  }
}