Socket 编程—单个客户端

        Socket编程就是根据服务器/客户端模型，在Socket API的基础上开发的网络计算机和进程间相互通信的应用。 

        1.服务端绑定一个端口号，并在此端口监听客户端的连接，线程会block直到有客户连接请求，读取请求信息，然后处理并返回。 

        2.客户端和指定的服务器的指定端口建立连接，发送请求信息，并等待返回信息。 

服务端：

package com.bijian.study01;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;

public class MyServer {
    
    ServerSocket server;
    Socket client;
    BufferedReader in;
    PrintWriter out;

    public MyServer() {
        
        try {
            // Instantiate a ServerSocket with specified port
            server = new ServerSocket(4451);

            // Listen on the port to receive the connection request
            client = server.accept();

            // Construct a reader to get the information from the client
            in = new BufferedReader(new InputStreamReader(client.getInputStream()));

            // Construct a writer to respond to the client
            out = new PrintWriter(client.getOutputStream());

            // Continually to retrieve the message from the client
            while (true) {
                String input = in.readLine();

                System.out.println(input);
                out.println("has received: " + input);
                out.flush();

                if (input.equals("end"))
                    break;
            }
        } catch (IOException ex) {
            ex.printStackTrace();
        } finally {
            // Release the resources - omitted
        }
    }

    public static void main(String[] args) {
        new MyServer();
    }
}

客户端：

package com.bijian.study01;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.InetAddress;
import java.net.Socket;
import java.net.UnknownHostException;

public class MyClient {

    Socket connection;
    BufferedReader in;
    PrintWriter out;
    BufferedReader reader;

    public MyClient() {

        try {
            // Establish a connection to the Socket server
            connection = new Socket(InetAddress.getLocalHost(), 4451);

            // Construct a reader to get the response from the server
            in = new BufferedReader(new InputStreamReader(connection.getInputStream()));

            // Construct a writer to send messages to the server
            out = new PrintWriter(connection.getOutputStream());

            // Construct a reader to accept the user input
            reader = new BufferedReader(new InputStreamReader(System.in));

            // Continuously send out the messages to the server and receive the response 
            while (true) {
                String str = reader.readLine();
                out.println(str);
                out.flush();
                System.out.println("sent out: " + str);

                if (str.equals("end"))
                    break;

                System.out.println(in.readLine());
            }
        } catch (UnknownHostException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            // Release the resources - omitted
        }
    }

    public static void main(String[] args) {
        new MyClient();
    }
}

        测试运行结果：

客户端：

hello
sent out: hello
has received: hello
today
sent out: today
has received: today
bye
sent out: bye
has received: bye
end
sent out: end

服务端：

hello
today
bye
end

其中： 

1.out = new PrintWriter(connection.getOutputStream()); 使用系统默认的编码格式。

       如果默认编码不符合要求，使用OutputStreamWriter指定： 

out = new PrintWriter(new OutputStreamWriter(connection.getOutputStream(), "utf-8")); 

2.可以把手动flush改成自动的： 

out = new PrintWriter(connection.getOutputStream(), true); 

        这样，当println, printf, format方法调用时，将缓存输出到底层流并清空缓存。 

3.必须首先开启服务端，否则客户端建立连接的时候会报java.net.ConnectException: Connection refused: connect

 

文章来源：http://czj4451.iteye.com/blog/1465239