TCP

1.服务器绑定端口号启动服务器欢迎socket。

2. 等待客户端发送请求。

3.等到客户端发送请求之后，服务器与客户端重新建立一个socket，但是客户端的目标端口不变。

java代码如下

客户端

客户端代码图解

import java.io.*;
import java.net.*;
class TCPClient {
    public static void main(String argv[]) throws Exception
    {
        String sentence;
        String modifiedSentence;
        BufferedReader inFromUser = new BufferedReader(
                new InputStreamReader(System.in));
        //开一个socket
        Socket clientSocket = new Socket("localhost", 6789);
        DataOutputStream outToServer = new DataOutputStream(
                clientSocket.getOutputStream());
        BufferedReader inFromServer =
                new BufferedReader(new InputStreamReader(
                        clientSocket.getInputStream()));
        sentence = inFromUser.readLine();
        //发送请求
        outToServer.writeBytes(sentence + '\n');
        //接受响应
        modifiedSentence = inFromServer.readLine();
        System.out.println("FROM SERVER: " +
            modifiedSentence);
        //关闭客户端
        clientSocket.close();
    }
}

服务端 

import java.io.*;
import java.net.*;
class TCPServer {

    public static void main(String argv[]) throws Exception
    {
        String clientSentence;
        String capitalizedSentence;
        //开一个socket用做于欢迎socket
        ServerSocket welcomeSocket = new ServerSocket
                (6789);
        while(true) {
            //接受客户端的请求
            Socket connectionSocket = welcomeSocket.
                    accept();
            BufferedReader inFromClient =
                    new BufferedReader(new InputStreamReader(
                            connectionSocket.getInputStream()));
            DataOutputStream outToClient =
                    new DataOutputStream(
                            connectionSocket.getOutputStream());
            //从客户端接受到信息
            clientSentence = inFromClient.readLine();
            //改变客户端发送的信息
            capitalizedSentence =
                    clientSentence.toUpperCase() + '\n';
            //发回给客户端
            outToClient.writeBytes(capitalizedSentence);
        }
    }
}

UDP 

1.udp的客户端可以比udp的服务端先开启

2.服务器绑定端口 

java代码如下：

客户端 

import java.io.*;
import java.net.*;
class UDPClient {
    public static void main(String args[]) throws Exception
    {
        BufferedReader inFromUser =
                new BufferedReader(new InputStreamReader
                        (System.in));
        //为客户端进程创建了一个门，但没有在两个进程之间创建管道
        DatagramSocket clientSocket = new DatagramSocket();
        //调用DNS查找
        InetAddress IPAddress =
                InetAddress.getByName("localhost");
        byte[] sendData = new byte[1024];
        byte[] receiveData = new byte[1024];
        String sentence = inFromUser.readLine();
        sendData = sentence.getBytes();
        //与TCP发送流不同，udp是打一个包发过去，这个就是udp的包
        //这一行构造数据包sendPacket，客户机将通过套接字将其弹出到网络中。
        // 这个包包括包中包含的数据、sendData、该数据的长度、服务器的IP地址和应用程序的端口号(我们将其设置为9876)。
        DatagramPacket sendPacket =
                new DatagramPacket(sendData, sendData.length,
                        IPAddress, 9876);
        clientSocket.send(sendPacket);
        //接受服务器响应包
        DatagramPacket receivePacket =
                new DatagramPacket(receiveData,
                        receiveData.length);
        clientSocket.receive(receivePacket);
        //将回复的包中的数据拿出来
        String modifiedSentence =
                new String(receivePacket.getData());
        System.out.println("FROM SERVER:" +
            modifiedSentence);
        //关闭客户端，释放资源
        clientSocket.close();
    }
}

 服务器

import java.io.*;
import java.net.*;
public class UDPServer {
    public static void main(String args[]) throws Exception
    {
        DatagramSocket serverSocket = new
                DatagramSocket(9876);
        byte[] receiveData = new byte[1024];
        byte[] sendData = new byte[1024];
        while(true)
        {
            //接受客户端发来的请求
            DatagramPacket receivePacket =
                    new DatagramPacket(receiveData,
                            receiveData.length);
            serverSocket.receive(receivePacket);
            //将客户端的请求的信息转为字符数组
            String sentence = new String(
                    receivePacket.getData());
            //从请求里拿到客户端IP地址
            InetAddress IPAddress =
                    receivePacket.getAddress();
            //拿到客户端端口
            int port = receivePacket.getPort();
            String capitalizedSentence =
                    sentence.toUpperCase();
            sendData = capitalizedSentence.getBytes();
            //将要返回的响应打包，里面需要客户端的IP地址，客户端端口
            DatagramPacket sendPacket =
                    new DatagramPacket(sendData,
                            sendData.length, IPAddress, port);
            //服务器发送响应包
            serverSocket.send(sendPacket);
        }
    }
}