Socket技术
Socket技术也被称为套接字，是操作系统底层提供的一项通信技术，同时支持TCP和UDP。要实现Socket通信，我们必须创建一个数据发送者和一个数据接收者，也就是客户端和服务端，我们需要提前启动服务端，来等待客户端的连接，而客户端只需要随时启动去连接服务端即可！
使用Java启动Socket服务端对象：
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import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;
public class Server {
public static void main(String[] args) {
try(ServerSocket server = new ServerSocket(8080)) {
System.out.println("Waiting for client...");
while (true) {
Socket socket = server.accept();
System.out.println("Client has connected! The ip is: " + socket.getInetAddress().getHostAddress());
}
}catch (IOException e) {
System.out.println("Server error!");
e.printStackTrace();
}
}
}
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创建客户端（实际上就是连接服务端的套接字而已）
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import java.io.IOException;
import java.net.Socket;
public class Client {
public static void main(String[] args) {
try (Socket socket = new Socket("localhost",8080)) {
System.out.println("Connection established!");
} catch (IOException e) {
System.out.println("Connection error!");
e.printStackTrace();
}
}
}
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实际上，建立Socket的过程就是TCP三次握手的过程：
通过在accept()阶段加上循环，就可以实现接受多个客户端的连接。
使用Socket进行数据传输
Socket对象提供了对应的输入输出IO流进行网络数据传输。为了不用一个Byte的读取和发送数据，可以使用OutputStreamWriter和InputStreamReader来实现字符的输入和输出。同时可以使用BufferedReader缓冲字符流从缓冲区中读入数据。
服务端代码如下：
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import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.net.ServerSocket;
import java.net.Socket;
public class Server {
public static void main(String[] args) {
try(ServerSocket server = new ServerSocket(8080)) {
System.out.println("Waiting for client...");
Socket socket = server.accept();
System.out.println("Client has connected! The ip is: " + socket.getInetAddress().getHostAddress());
System.out.println("Waiting for the message...");
BufferedReader reader = new BufferedReader(new InputStreamReader(socket.getInputStream()));
String message = reader.readLine();
System.out.println("Receive message from client: " + message);
OutputStreamWriter writer = new OutputStreamWriter(socket.getOutputStream());
writer.write("Receive message: " + message);
writer.flush();
socket.close();
}catch (IOException e) {
System.out.println("Server error!");
e.printStackTrace();
}
}
}
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客户端代码如下：
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import java.io.*;
import java.net.Socket;
import java.util.Scanner;
public class Client {
public static void main(String[] args) {
try (Socket socket = new Socket("localhost",8080);
Scanner scanner = new Scanner(System.in)) {
System.out.println("Connection established!");
OutputStreamWriter writer = new OutputStreamWriter(socket.getOutputStream());
String text = scanner.nextLine();
writer.write(text + '\n');
writer.flush();
System.out.println("Text has been sent: " + text);
BufferedReader reader = new BufferedReader(new InputStreamReader(socket.getInputStream()));
System.out.println("Receive respond from server: " + reader.readLine());
} catch (IOException e) {
System.out.println("Connection error!");
e.printStackTrace();
}
}
}
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在服务器的设置上，可以手动关闭某个方向的流。
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socket.shutdownOutput(); //关闭输出方向的流
socket.shutdownInput(); //关闭输入方向的流
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同时可以通过调用setSoTimeout()设置超时时间：
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socket.setSoTimeout(3000);
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如果连接的双方发生意外而通知不到对方，导致一方还持有连接，这样就会占用资源，因此我们可以使用setKeepAlive()方法来防止此类情况发生：
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socket.setKeepAlive(true);
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使用Socket传输文件
由于提供了IO网络流，结合文件IO流就可以实现文件的传输。使用FileOutputStream和FileInputStream进行文件的输出和输入。
这里和IO部分的内容差不多，不再进行叙述。
使用浏览器访问Socket服务器
HTTP协议是基于TCP协议的，如果使用HTTP协议访问Socket服务器，服务器就会收到一个HTTP请求：
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import java.io.*;
import java.net.ServerSocket;
import java.net.Socket;
public class Server {
public static void main(String[] args) {
try(ServerSocket server = new ServerSocket(8080)) {
System.out.println("Waiting for client...");
Socket socket = server.accept();
System.out.println("Client has connected! The ip is: " + socket.getInetAddress().getHostAddress());
InputStream stream = socket.getInputStream();
while (true) {
int i = stream.read();
if (i == -1) break;
System.out.print((char) i);
}
}catch (IOException e) {
System.out.println("Server error!");
e.printStackTrace();
}
}
}
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打印出的请求如下：
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Waiting for client...
Client has connected! The ip is: 127.0.0.1
GET / HTTP/1.1
Host: 127.0.0.1:8080
Connection: keep-alive
sec-ch-ua: "Chromium";v="122", "Not(A:Brand";v="24", "Google Chrome";v="122"
sec-ch-ua-mobile: ?0
sec-ch-ua-platform: "Windows"
Upgrade-Insecure-Requests: 1
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/122.0.0.0 Safari/537.36
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/avif,image/webp,image/apng,*/*;q=0.8,application/signed-exchange;v=b3;q=0.7
Sec-Fetch-Site: none
Sec-Fetch-Mode: navigate
Sec-Fetch-User: ?1
Sec-Fetch-Dest: document
Accept-Encoding: gzip, deflate, br, zstd
Accept-Language: zh-CN,zh;q=0.9
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这就是一个标准的HTTP协议请求。但是由于Socket没有返回，所以浏览器不能正常显示页面。
alextang
收录于 Java