Java 网络编程

Java 中网络编程接口在java.net 包中

在使用C/C++进行网络编程时，针对TCP Server端需要这些操作

1. 创建SOCKET
2. 绑定
3. 监听
4. 接受连接
5. 收取数据包
6. 发送数据包

TCP Client端需要这些操作

1. 创建SOCKET
2. 连接Server端
3. 发送数据包
4. 读取响应包

Java中针对Server 端和Client端分别提供了两个类 ServerSocket 和 Socket

ServerScoket 使用步骤如下:

1. 创建ServerSocket 对象并传入一个端口号到构造函数中。在构造的时候会自动创建Socket对象并执行绑定端口、监听端口的操作
2. 调用对象的 accept 方法等待连接
3. 调用对象的 getInputStream 和 getOutputStream 获取输入输出流，并通过输入输出流来进行收发数据
4. 在不用时调用 close 方法关闭套接字

Socket 类使用步骤如下:

1. 创建 Socket 对象
2. 调用 connet 方法连接到指定服务器端口(或者在构造时传入服务器和端口进行连接)
3. 调用对象的 getInputStream 和 getOutputStream 获取输入输出流，并通过输入输出流来进行收发数据
4. 在不用时调用 close 方法关闭套接字

一个普通的TCP通信的实例如下:

import java.net.ServerSocket;
import java.net.Socket;
import java.io.IOException;
import java.io.OutputStream;
import java.io.InputStream;

public class TCPServer{
	public static void main(String[] args) throws IOException{
		ServerSocket server = new ServerSocket(6666);
		Socket socket = server.accept() ;
		
		InputStream is = socket.getInputStream();
		OutputStream os = socket.getOutputStream();
		
		byte[] bytes = new byte[1024];
		int len = is.read(bytes);
		os.write(("echo:" + new String(bytes, 0, len)).getBytes());
		
		server.close();
		socket.close();
	}
}

import java.net.Socket;
import java.io.IOException;
import java.io.OutputStream;
import java.io.InputStream;

public class TCPClient{
	public static void main(String[] args)throws IOException{
		Socket socket = new Socket("127.0.0.1", 6666);
		
		InputStream is = socket.getInputStream();
		OutputStream os = socket.getOutputStream();
		
		os.write("hello world!".getBytes());
		byte[] bytes = new byte[1024];
		int len = is.read(bytes);
		
		System.out.println(new String(bytes, 0, len));
		
		socket.close();
	}
}

下面是一个使用TCP协议进行文件传输的例子:

import java.net.Socket;
import java.io.IOException;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.net.ServerSocket;

public class FileUploadServer{
	public static void main(String[] args) throws IOException{
		ServerSocket server = new ServerSocket(6666);
		FileOutputStream fos = new FileOutputStream("1.avi");
		Socket socket = server.accept();
		InputStream is = socket.getInputStream();
		byte[] buff = new byte[1024];
		int len = 0;
		while((len = is.read(buff)) != -1){
			fos.write(buff, 0, len);
		}
		
		System.out.println("upload success!");
		fos.close();
		server.close();
		socket.close();
	}
}

import java.net.Socket;
import java.io.IOException;
import java.io.FileInputStream;
import java.io.OutputStream;

public class FileUploadClient{
	public static void main(String[] args) throws IOException{
		Socket socket = new Socket("127.0.0.1", 6666);
		
		FileInputStream fis = new FileInputStream("1.avi");
		OutputStream os = socket.getOutputStream();
		int len = 0;
		byte[] buff = new byte[1024];
		while((len = fis.read(buff)) != -1){
			os.write(buff, 0, len);
		}
		
		fis.close();
		socket.close();
	}
}

最后提供一个简易的http server 的例子

import java.net.Socket;
import java.net.ServerSocket;
import java.io.InputStreamReader;
import java.io.InputStream;
import java.io.FileInputStream;
import java.io.OutputStream;
import java.io.BufferedReader;
import java.io.IOException;

public class HttpServer{
	public static void main(String[] args)throws IOException{
		ServerSocket server = new ServerSocket(8080);
		while(true){
			Socket socket = server.accept();
			new Thread(()->{
				try{
					BufferedReader bf = new BufferedReader(new InputStreamReader(socket.getInputStream()));
					OutputStream os = socket.getOutputStream();
					String head = bf.readLine();
					String path = head.split(" ")[1].substring(1);
					System.out.println(path);
					FileInputStream fis = new FileInputStream(path);
					int len = 0;
					byte[] buff = new byte[1024];
					os.write("HTTP/1.1 200 OK
".getBytes());
					os.write("Content-Type:text/html
".getBytes());
					os.write("
".getBytes());
					while((len = fis.read(buff)) != -1){
						os.write(buff, 0, len);
					}
					
					bf.close();
					fis.close();
					socket.close();
				}catch(IOException e){
					e.printStackTrace();
				}
			}).start();
		}
		
		//server.close();
	}
}

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