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\r\n".getBytes());
                    os.write("Content-Type:text/html\r\n".getBytes());
                    os.write("\r\n".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();
    }
}