NET

网络协议分层

TCP三次握手

IP解决了每个电脑唯一的一个ID的问题

TCP传输比较可靠，需要建立连接，确保数据送达，但是速度较慢

UDP传输不可靠，不需要建立连接，只需要发送，速度快

一、TCP

分为服务器端和客户端，要先建立连接

服务器端new一个ServerSocket，指定好端口

然后accpet客户端

服务器端：

package netSocket;
import java.net.*;
import java.io.*;
public class TCPServer {//服务器端
	public static void main(String[] args) {
		InputStream in = null;
		OutputStream out = null;
		try{
			ServerSocket ss = new ServerSocket(5888);
			Socket socket = ss.accept();//接收到返回的是Scoket类
			in = socket.getInputStream();
			out = socket.getOutputStream();
			DataInputStream dis = new DataInputStream(in);
			DataOutputStream dos = new DataOutputStream(out);
			String s = null;
			if( (s = dis.readUTF() ) != null ) {//读客户端的数据
				System.out.println(s);
				System.out.println("from:"+ socket.getInetAddress() );//获得客户端的IP
				System.out.print("Port:" + socket.getPort() );//获得端口
			}
			dos.writeUTF("hi, hello");
			dis.close();
			dos.close();
			socket.close();			
		}catch(IOException e){
			e.printStackTrace();
		}

}
}

客户端：

new的时候指定好IP地址和端口

package netSocket;
import java.io.*;
import java.net.*;
public class TCPclient {
	public static void main(String[] args) throws Exception{
		InputStream is = null;
		OutputStream os = null;
		try{
			Socket socket = new Socket("localhost", 5888);
			is = socket.getInputStream();
			os = socket.getOutputStream();
			DataInputStream dis = new DataInputStream(is);
			DataOutputStream dos = new DataOutputStream(os);
			dos.writeUTF("hello! Several!");
			String s = null;
			if( (s = dis.readUTF() ) != null);
				System.out.println(s);			
			dos.close();
			dis.close();
			socket.close();
		}catch(IOException e){
			e.printStackTrace();
		}
}
}

用TCP实现单次聊天

客户端

package netSocket;
import java.io.*;
import java.net.*;
public class TalkClient {
	public static void main(String[] args){
		try{
			Socket socket = new Socket("127.0.0.1",8888);
			BufferedReader br = new BufferedReader( new InputStreamReader(socket.getInputStream()) );//从服务器读
			PrintWriter pw = new PrintWriter(socket.getOutputStream());//向服务器输出
			BufferedReader sin = new BufferedReader(new InputStreamReader( System.in) );
			String readline = null;
			readline = sin.readLine();
			while( ! readline.equals("exit") ){
				pw.println(readline);
				pw.flush();
				System.out.println("client: "+ readline);
				System.out.println("Server: "+ br.readLine() );
				readline = sin.readLine();
			}
			br.close();
			pw.close();
			sin.close();
			socket.close();
		}catch(Exception e){
			e.printStackTrace();
		}
	}

}

服务器端

package netSocket;
import java.net.*;
import java.io.*;
public class TalkServer {
	public static void main(String[] args){
		try{
			ServerSocket servel = new ServerSocket(8888);
			Socket socket = servel.accept();
			BufferedReader br = new BufferedReader(new InputStreamReader( socket.getInputStream()) );//读客户端
			PrintWriter pw = new PrintWriter( socket.getOutputStream() );//往客户端写
			BufferedReader sin = new BufferedReader( new InputStreamReader(System.in) );//读键盘
			String line = null;
			
			System.out.println("client"+ br.readLine());//从客户端读一句话
			line = sin.readLine();
			while( !line.equals("exit") ){
				pw.println(line);//把服务器的话写到服务端
				pw.flush();
				System.out.println("Server: "+ line);
				System.out.println("client: "+ br.readLine());
				line = sin.readLine();
			}
			
			br.close();
			pw.close();
			socket.close();
			servel.close();
		}catch(Exception e){
			e.printStackTrace();
		}
	}
}

UDP

UDP不需要建立连接

传输通过包来传输：DatagramPacket

然后DatagramSocket设置端口

经常用字节数组来存储数据

服务器端

package netSocket;
import java.net.*;
import java.io.*;
public class UDPServer {
	public static void main(String[] args) throws Exception{
		byte buf[] = new byte[1024];
		DatagramPacket dp = new DatagramPacket(buf, buf.length);//包
		DatagramSocket ds = new DatagramSocket(5678);//端口
		while(true){
			ds.receive(dp);//接收到字节数组中
			ByteArrayInputStream bais = new ByteArrayInputStream(buf);//从字节数组中读东西
			DataInputStream dis = new DataInputStream(bais);
			System.out.println(dis.readLong());
		}
	}
}

客户端

package netSocket;
import java.io.*;
import java.net.*;
public class UDPClient {
	public static void main(String[] args){
		long n = 10000L;
		ByteArrayOutputStream baos = new ByteArrayOutputStream();//用字节输出流
		DataOutputStream dos = new DataOutputStream(baos);
		try{dos.writeLong(n);//把long写入字节数组
		}catch(IOException e){
			System.out.println("IOEx");
		}
		
		byte[] buf = baos.toByteArray();//转化为字节数组
		DatagramPacket dp = new DatagramPacket(buf, buf.length,//UDP要打包传输
								new InetSocketAddress("127.0.0.1",5678) );//要传输的IP地址和端口地址
		try{DatagramSocket ds = new DatagramSocket(9999);//设置客户端的端口
		ds.send(dp);//发送包
		ds.close();
		}catch(Exception e){
			e.printStackTrace();
		}
	}
}