Java编写客户/服务器程序

超、凢脫俗 2021-09-15 08:00 303阅读 0赞

传输层向应用层提供了套接字Socket接口，Socket封装了下层的数据传输细节，应用层的程序通过Socket来建立与远程主机的连接，以及进行数据传输。

站在应用层的角度，两个进程之间的一次通信过程从建立连接开始，接着交换数据，到断开连接结束。套接字可看做是通信线路两端的收发器，进程通过套接字来收发数据。如下图：

> > ![20180427131001932][]

> > > > > > **套接字可看做是通信连接两端的收发器 **

**java中有3中套接字类型：**

**        1、java.net.Socket**

**        2、java.net.ServerSocket**

**        3、java.net.DatagramSocket**。

其中Socket和ServerSocket类建立在TCP协议基础上，DatagramSocket类建立在UDP协议基础上。Java网络程序都采用客户/服务器通信模式。

**以EchoServer和EchoClient为例，介绍如何使用ServerSocket和Socket来编写服务器程序和客户程序。**

**1、创建EchoServer：**

**    ![20180427131832350][]**

服务器与客户利用ServerSocket和Socket来通信

![2018042713501267][]

**  EchoServer.java**

>     import java.io.BufferedReader;
>     import java.io.IOException;
>     import java.io.InputStream;
>     import java.io.InputStreamReader;
>     import java.io.OutputStream;
>     import java.io.PrintWriter;
>     import java.net.Socket;
>     import java.net.UnknownHostException;
>     
>     public class EchoClient {
>     
>     	public static void main(String[] args) throws IOException {
>     		new EchoClient1().talk();
>     
>     	}
>     }
>     
>     class EchoClient1{
>     	private String host="localhost";
>     	private int port=8001;
>     	private Socket socket;
>     	
>     	public EchoClient1() throws UnknownHostException, IOException{
>     		socket=new Socket(host, port);
>     	}
>     	
>     	private PrintWriter getWriter(Socket socket)throws IOException{
>     		OutputStream socketOut=socket.getOutputStream();
>     		return new PrintWriter(socketOut,true);
>     	}
>     	
>     	private BufferedReader getReader(Socket socket) throws IOException{
>     		InputStream socketIn=socket.getInputStream();
>     		return new BufferedReader(new InputStreamReader(socketIn));
>     	}
>     	
>     	public void talk() throws IOException{
>     		try {
>     			BufferedReader br=getReader(socket);
>     			PrintWriter pw=getWriter(socket);
>     			BufferedReader localReader=new BufferedReader(new InputStreamReader(System.in));
>     			String msg=null;
>     			while((msg=localReader.readLine())!=null){
>     				pw.println(msg);
>     				System.out.println(br.readLine());
>     				
>     				if(msg.equals("bye")){
>     					break;
>     				}
>     			}
>     		} catch (IOException e) {
>     			e.printStackTrace();
>     		}finally{
>     			try {
>     				socket.close();
>     			} catch (IOException e) {
>     				e.printStackTrace();
>     			}
>     		}
>     	}
>     }

EchoServer类最主要的方法为service()方法，它不断等待客户的连接请求，当serviceSocket.accept()方法返回一个Socket对象中得到输出流和输入流，并且分别为PrintWriter和BufferedReader来装饰它们。然后不断调用BufferedReader的readLine()方法读取客户发来的字符串XXX,在调用PriterWriter的println()方法向客户返回字符串echo：XXX。当客户发来的字符串为“bye”时，就会结束语客户的通信，调用socket.close()方法断开连接。

**2、创建EchoClient**

> **![20180427152610145][]**  
>

**    EchoClient.java**

>     import java.io.BufferedReader;
>     import java.io.IOException;
>     import java.io.InputStream;
>     import java.io.InputStreamReader;
>     import java.io.OutputStream;
>     import java.io.PrintWriter;
>     import java.net.ServerSocket;
>     import java.net.Socket;
>     
>     public class EchoServer {
>     
>     	public static void main(String[] args) throws IOException {
>     		new EchoServer1().service();
>     	}
>     }
>     
>     class EchoServer1{
>     	private int port=8001;
>     	private ServerSocket serverSocket;
>     	
>     	public EchoServer1() throws IOException{
>     		serverSocket=new ServerSocket(port);
>     		System.out.println("服务器启动");
>     	}
>     	
>     	public String echo(String msg){
>     		return "echo:"+msg;
>     	}
>     	
>     	private PrintWriter getWriter(Socket socket) throws IOException{
>     		OutputStream socketOut=socket.getOutputStream();
>     		return new PrintWriter(socketOut,true);
>     	}
>     	
>     	private BufferedReader getReader(Socket socket) throws IOException{
>     		InputStream socketIn=socket.getInputStream();
>     		return new BufferedReader(new InputStreamReader(socketIn));
>     	}
>     	
>     	public void service(){
>     		while(true){
>     			Socket socket=null;
>     			try {
>     				socket=serverSocket.accept();
>     				System.out.println("New connection accepted"+socket.getInetAddress()+":"+socket.getPort());
>     				
>     				BufferedReader br=getReader(socket);
>     				PrintWriter pw=getWriter(socket);
>     				
>     				String msg=null;
>     				while((msg=br.readLine())!=null){
>     					System.out.println(msg);
>     					pw.println(echo(msg));
>     					if(msg.equals("bye")){
>     						break;
>     					}
>     				}
>     			} catch (IOException e) {
>     				e.printStackTrace();
>     			}finally{
>     				try {
>     					if(socket!=null){
>     						socket.close();
>     					}
>     				} catch (IOException e) {
>     					e.printStackTrace();
>     				}
>     			}
>     		}
>     	}
>     }

在EchoClient类中，最主要的方法为talk()方法。该方法不断读取用户从控制台输入的字符串，然后把它发送给EchoServer，在把EchoServer返回的字符串打印到控制台。如果用户输入的字符串为“bye”，就会结束与EchoServer的通信，调用socket.close()方法断开连接。

运行范例是，需要打开两个Dos界面，先在一个DOS界面中运行“java EchoServer”命令，再在另一个DOS界面中运行“java EchoClient”命令。如下图运行两个程序的DOS界面。在EchoClient控制台，用户输入字符串"hello",程序就会输出：“echo：hello”。

![20180427153645700][]![20180427153658739][]

运行EchoServer和EchoClient程序

![20180427154042461][]

![20180427154056687][]

[20180427131001932]: /images/20210720/675741a815b941828b74690c70629f9a.png
[20180427131832350]: https://img-blog.csdn.net/20180427131832350
[2018042713501267]: https://img-blog.csdn.net/2018042713501267
[20180427152610145]: https://img-blog.csdn.net/20180427152610145
[20180427153645700]: https://img-blog.csdn.net/20180427153645700
[20180427153658739]: https://img-blog.csdn.net/20180427153658739
[20180427154042461]: https://img-blog.csdn.net/20180427154042461
[20180427154056687]: https://img-blog.csdn.net/20180427154056687