java学习之路4-Socket

TCP

服务端

TCP的数据传送使用的是流，也就是通过DataInputStream，DataOutputStream来传递。
在服务器端，我们需要绑定监听端口，然后就可以获取该端口的输入流和输出流。
ServerSocket 是创建一个socket的服务，指定监听窗口。
然后用该对象能够返回一个Socket，通过这个Socket中的信息来通信

package Socket;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.net.*;
public class Server {

	public static void main(String[] args) {
		ServerSocket socket = null;
		Socket socket2 = null;
		try {
			//此处可以直接改为try-with-resoutce形式，避免使用finally语句关闭资源
			socket = new ServerSocket(8000);
			//创建一个ServerSocket对象，指定监听端口，与客户端程序保持一致
			System.out.println("Listening on port 8000");
			socket2 = socket.accept();
			//监听并等待接受连接：accept
			DataInputStream in = new DataInputStream(socket2.getInputStream());
			DataOutputStream out = new DataOutputStream(socket2.getOutputStream());
			//创建Data Input/Output 流
			double radius = in.readDouble();
			//从客户端接受圆的半径（通过DataInput流读取）
			double area = radius*radius*Math.PI;
			//计算圆的面积
			out.writeDouble(area);
			//把圆面积发给客户端
			System.out.println("Send Area:"+area+" to client");
			//输出提示信息
			// 加入while循环，使得服务器不断接收半径并且发送面积
			// 从客户端接受圆的半径
			//半径小于0，则退出循环
			//计算圆的面积
			//把面积发送给客户端
			//输出提示信息
			in.close();
			out.close();
			socket2.close();
			socket.close();
		} catch (Exception e) {
			e.printStackTrace();
		}finally {
		}
	}

}

在客户端，我们需要发送信息，就要指定IP地址和端口号。如果是本地的话就是’localhost’。

客户端

package Socket;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.net.DatagramSocket;
import java.net.Socket;
import java.net.SocketException;
import java.util.Scanner;

import unit09.*;
public class ClientSocket {
	public static void main(String[] args)
	{
		Socket socket = null;
		Scanner scanner = new Scanner(System.in);
		//创建一个Socket对象，连接到服务器，端口号，IP地址
		try {
            //创建一个Socket，里面指明发送的地址（地址包含IP地址和端口号）
			socket = new Socket("localhost", 8000);
            //创建一个Data Stream 输入流对象，从服务器读取数据
			DataInputStream in = new DataInputStream(socket.getInputStream());
            //创建一个data Stream 输出流对象，向服务器发送数据
			DataOutputStream out = new DataOutputStream(socket.getOutputStream());
            //提示并从键盘读入一个浮点数作为圆的半径
			double radius=scanner.nextDouble();
            //将半径发送给服务器，并且提示
			out.writeDouble(radius);
			System.out.println("Sent radius: "+radius+" to Server ");
			double area = in.readDouble();
            //从服务器读取圆面积，并且显示
			System.out.println("Receive area:"+area);
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}

UDP

UDP的连接是通过DatagramPacket来传递的，里面包含有传递需要的信息,字节数组，字节数组的长度以及IP地址和端口号等等

服务端

在服务端，我们需要创建一个DatagramSocket(int port)的实例，然后使用这个实例来发送Packet和接受Packet。
如果想要对接受到的信息做出回应，在接受到的Packet中，会包含该IP地址和端口号，可以通过SetAddress和SetPort来设置发送的地址，然后使用DatagramSocket来发送就好了。

package Socket;
import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.util.Arrays;
import java.util.Date;
public class Demo09P7S {
  public static void main(String[] args) throws IOException {
    // The byte array for sending and receiving datagram packets
    byte[] buf = new byte[1024];
    byte[] sendbuf = new byte[1024];
    // Create a packet for receiving data with DatagramPacket(buffer, length)
      DatagramPacket recvPacket = null;
    // Create a packet for sending data with DatagramPacket
      DatagramPacket sendPacket = null;
    // Create a server socket with DatagramSocket(port)
      DatagramSocket socket = new DatagramSocket(8000);
    // Print information about server started
    System.out.println("Server started on port 8000, " + new Date());
    while (true) { 
      // Initialize buffer for each iteration with Arrays.fill()
      Arrays.fill(buf, (byte)0);
      Arrays.fill(sendbuf,(byte)0);
      // Assign data to the received packet
      recvPacket = new DatagramPacket(buf, buf.length);
      // Receive radius from the client socket in a packet, call receive()
       socket.receive(recvPacket);
      // Print the client hostname and port number with DatagramPacket.getAddress/getPort
       sendPacket = new DatagramPacket(sendbuf, sendbuf.length);
       sendPacket.setAddress(recvPacket.getAddress());
       sendPacket.setPort(recvPacket.getPort());
      System.out.println("Received packet from ");
      // use Double.parseDouble to transfer byte[] to double
      double radius = Double.parseDouble(new String(buf));
      System.out.println("Radius: " + radius);
      // Compute area
      double area = radius * radius * Math.PI;
      System.out.println("Area is " + area + '\n');
      // Send area to the client in a packet, with DatagramPacket.setAddress/setPort/setData/send
      sendbuf = Double.valueOf(area).toString().getBytes();

      // TODO 鍙戦�佺殑鏁扮粍鍙兘瓒呰繃涓�涓狣ouble澶у皬锛屾鏌ユ敹绔槸鍚︽纭帴鏀�

      // Assign data to the packet sending to client with setData
      sendPacket.setData(sendbuf);
      // send the packet
      socket.send(sendPacket);
      System.out.println("Area sent.");
    } // end while
  } // end main
}

客户端

客户端的DatagramSocket不需要指明端口号，因为需要发送的时候，JVM会随机一个可用的端口号来使用。
只需要把发送的信息封装到packet中就好了

package Socket;

import java.io.*;
import java.net.*;
import java.util.*;
public class Demo09P7C {
  public static void main(String[] args) {
    // The byte array for sending and receiving datagram packets
    byte[] buf = new byte[1024];
    // Server InetAddress
    InetAddress server = null;
    // The packet sent to the server
    DatagramPacket sendpacket = null;
    // The packet received from the server
    DatagramPacket recvpacket = null;

    // get a DatagramSocket socket
    try (DatagramSocket socket = new DatagramSocket()){
      // get the Server address with InetAddress.getByName
    	server=InetAddress.getByName("10.128.227.70");
      // Create a send packet with DatagramPacket(buffer, length, InetAddress, port)
      // Or create DatagramPacket with buffer and length, with server address/port set later
      // Create a receive packet with DatagramPacket(buffer, length)
      recvpacket= new DatagramPacket(buf, buf.length);
      // Initialize buffer for each iteration with Arrays.fill
      Arrays.fill(buf, (byte)0);

      // 输入圆的半径 with Scanner
      System.out.println("Please input radius : ");
      Scanner scanner = new Scanner(System.in);
      double r = scanner.nextDouble();
      // Transfer double number to byte[] with Double.valueOf() and String.getBytes()
      buf=Double.valueOf(r).toString().getBytes();
      // assign the byte[] buf to packet with DatagramPacket.setData
      sendpacket = new DatagramPacket(buf, buf.length,server,8000);
      // send the packet with DatagramSocket.send(DatagramPacket)
      int cnt = 0;
      while(cnt<1000)socket.send(sendpacket);
      // receive area from the server in a packet with DatagramSocket.receive(DatagramPacket)   
      buf = new byte[1024];
      Arrays.fill(buf, (byte) 0);
      recvpacket = new DatagramPacket(buf, buf.length);
      socket.receive(recvpacket);
      // Transfer byte[] to double with Double.parseDouble and String(byte[])
      double area=Double.parseDouble(new String(buf));
      // Display radius and area.
      System.out.println("Radius is " + r + "\n");
      System.out.println("Area received from the server is " + area
          + '\n');
      scanner.close();
    } catch (IOException ex) {
      ex.printStackTrace();
    } 
  }
}