JAVA笔记26-网络编程（不等于网站编程）

一、网络基础（TCP/IP详解）

1、IP协议（Internet Protocol）：网络层，支持网间数据报通信。无连接数据报传送，数据报路由选择和差错控制。

IPv4 32位（4字节），IPv6 128位（16字节）。P

ping ICMP协议

2、TCP协议、UDP协议

（1）TCP（transmission control protocol 打电话）：专门设计用于在不可靠的因特网上提供可靠的、端到端的字节流通信的协议。它是一种面向连接的协议。有三次握手。慢

（2）UDP（user data protocol 寄信）：提供了一种发送封装的原始IP数据报的方法、并且发送时无需建立连接，是一种不可靠的连接。快

二、Socket

两个Java应用程序可以通过一个双向的网络通信连接实现数据交换，这个双向链路的一端称为一个Socket。

Socket通常用来实现client-server连接。

java.net包中定义的两个类Socket和ServerSocket，分别用来实现双向连接（TCP连接）的client和server端。

建立连接时所需的寻址信息为远程计算机的IP地址和端口号（Port number）。端口号2字节，可以区分不同的应用程序。端口号又分TCP端口和UDP端口，每个都是65536个端口。

例如：

收邮件 POP3 110

STMP 25

FTP 21

HTTP 80

1、TCP Socket通信模型

这只是练习，实际上的网络编程都是异步式的。System.in,accept(),readUTF()都是阻塞式的（非重点）

例1

import java.net.*;
import java.io.*;
public class TCPServer{
    public static void main(String args[]) throws Exception{
        ServerSocket ss = new ServerSocket(6666);//端口号6666
        while(true){
            Socket s = ss.accept();
            System.out.println("a client connect!");
            DataInputStream dis = new DataInputStream(s.getInputStream());
            System.out.println(dis.readUTF());
            dis.close();
            s.close();
        }
    }
}

import java.net.*;
import java.io.*;
public class TCPClient{
    public static void main(String args[]) throws Exception{
        Socket s = new Socket("127.0.0.1",6666);
        OutputStream os = s.getOutputStream();
        DataOutputStream dos = new DataOutputStream(os);
        dos.writeUTF("hello server!");
        dos.flush();
        dos.close();
        s.close();
    }
}

例2

import java.io.*;
import java.net.*;
public class TestServer{
    public static void main(String[] args){
        try{
            ServerSocket s = new ServerSocket(8888);//服务器端口号8888
            while(true){
                Socket s1 = s.accept();
                OutputStream os = s1.getOutputStream();
                DataOutputStream dos = new DataOutputStream(os);
                dos.writeUTF("Hello,"+s1.getInetAddress()+"port#"+s1.getPort()+" byebye!");//客户端的IP地址和端口号
                dos.close();
                s1.close();
            }
        }catch(IOException e){
            e.printStackTrace();
        }
    }
}

import java.net.*;
import java.io.*;
public class TestClient{
    public static void main(String[] args){
        try{
            Socket s1 = new Socket("127.0.0.1",8888);//服务器地址和端口号
            InputStream is = s1.getInputStream();
            DataInputStream dis = new DataInputStream(is);
            System.out.println(dis.readUTF());
            dis.close();
            s1.close();
        }catch(ConnectException e){
            e.printStackTrace();
        }catch(IOException e){
            e.printStackTrace();
        }
    }
}

例3

import java.io.*;
import java.net.*;
public class TestServer{
    public static void main(String[] args){
        InputStream in = null;
        OutputStream out = null;
        try{
            ServerSocket ss = new ServerSocket(5888);//设置端口号
            Socket s1 = ss.accept();
            in = s1.getInputStream();
            out = s1.getOutputStream();
            DataOutputStream dos = new DataOutputStream(out);
            DataInputStream dis = new DataInputStream(in);
            String s = null;
            if((s=dis.readUTF())!=null){
                System.out.println(s);
                System.out.println("from: "+s1.getInetAddress());
                System.out.println("Port: "+s1.getPort());
            }
            dos.writeUTF("hi,hello");
            dis.close();
            dos.close();
            s1.close();
        }catch(IOException e){
            e.printStackTrace();
        }
    }
}

import java.net.*;
import java.io.*;
public class TestClient{
    public static void main(String[] args){
        InputStream in = null;
        OutputStream out = null;
        try{
            Socket s1 = new Socket("localhost",5888);//服务器地址和端口号
            in = s1.getInputStream();
            out = s1.getOutputStream();
            DataInputStream dis = new DataInputStream(in);
            DataOutputStream dos = new DataOutputStream(out);
            dos.writeUTF("hey");
            String s = null;
            if((s=dis.readUTF())!=null){
                System.out.println(s);
            }
            dos.close();
            dis.close();
            s1.close();
        }catch(UnknownHostException e){
            e.printStackTrace();
        }catch(IOException e){
            e.printStackTrace();
        }
    }
}

练习4：（by myself）

import java.io.*;
import java.net.*;
public class TestServer{
    public static void main(String[] args){
        InputStream in = null;
        OutputStream out = null;
        String si = null;
        String so = "";
        try{
            ServerSocket ss = new ServerSocket(5888);//设置端口号
            while(true){
                Socket s1 = ss.accept();
                in = s1.getInputStream();//接收数据
                out = s1.getOutputStream();//发送数据
                DataInputStream dis = new DataInputStream(in);
                DataOutputStream dos = new DataOutputStream(out);
                //从键盘读入
                InputStreamReader isr2 = new InputStreamReader(System.in);
                BufferedReader br2 = new BufferedReader(isr2);
                while(!so.equals("exit")){
                    if((so=br2.readLine())!=null&&!so.equals("exit")){
                        System.out.println("Server:"+so);
                        dos.writeUTF(so);
                    }
                    if((si=dis.readUTF())!=null){
                        System.out.println("Client:"+si);
                    }
                }
                dis.close();
                br2.close();
                dos.close();
                s1.close();
            }
        }catch(IOException e){
            e.printStackTrace();
        }
    }
}

import java.net.*;
import java.io.*;
public class TestClient{
    public static void main(String[] args){
        InputStream in = null;
        OutputStream out = null;
        String si = null;
        String so= "";
        try{
            Socket s1 = new Socket("127.0.0.1",5888);//服务器地址和端口号
            in = s1.getInputStream();//接收
            out = s1.getOutputStream();//发送
            DataInputStream dis = new DataInputStream(in);
            DataOutputStream dos = new DataOutputStream(out);
            //从键盘读入
            InputStreamReader isr2 = new InputStreamReader(System.in);
            BufferedReader br2 = new BufferedReader(isr2);
            while(!so.equals("exit")){
                if((si=dis.readUTF())!=null){
                    System.out.println("Server:"+si);
                }
                if((so=br2.readLine())!=null&&!so.equals("exit")){
                    System.out.println("Client:"+so);
                    dos.writeUTF(so);
                }
            }
            dis.close();
            br2.close();
            dos.close();
            s1.close();
        }catch(UnknownHostException e){
            e.printStackTrace();
        }catch(IOException e){
            e.printStackTrace();
        }
    }
}

2、UDP Socket通信模型

没有server,client的概念，不区分两者的socket。receive()方法也是阻塞式的。

例1

import java.net.*;
public class TestUDPServer{
    public static void main(String args[]) throws Exception{
        byte buf[] = new byte[1024];
        DatagramPacket dp = new DatagramPacket(buf, buf.length);
        DatagramSocket ds = new DatagramSocket(5678);
        while(true){
            ds.receive(dp);
            System.out.println(new String(buf, 0, dp.getLength()));
        }
    }
}

import java.net.*;
public class TestUDPClient{
    public static void main(String args[]) throws Exception{
        byte[] buf = (new String("Hello")).getBytes();
        DatagramPacket dp = new DatagramPacket(buf, buf.length, new InetSocketAddress("127.0.0.1", 5678));
        DatagramSocket ds = new DatagramSocket(9999);
        ds.send(dp);
        ds.close();
    }
}

例2

import java.net.*;
import java.io.*;
public class TestUDPServer{
    public static void main(String args[]) throws Exception{
        byte buf[] = new byte[1024];
        ByteArrayInputStream bais = new ByteArrayInputStream(buf);//从字节数组读数据
        DataInputStream dis = new DataInputStream(bais);
        DatagramPacket dp = new DatagramPacket(buf, buf.length);
        DatagramSocket ds = new DatagramSocket(5678);
        while(true){
            ds.receive(dp);
            long l = dis.readLong();
            System.out.println(l);
        }
    }
}

import java.net.*;
import java.io.*;
public class TestUDPClient{
    public static void main(String args[]) throws Exception{
        long n = 10000L;
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        DataOutputStream dos = new DataOutputStream(baos);
        dos.writeLong(n);
        byte[] buf = baos.toByteArray();
        System.out.println(buf.length);
        DatagramPacket dp = new DatagramPacket(buf,buf.length,new InetSocketAddress("127.0.0.1",5678));
        DatagramSocket ds = new DatagramSocket(9999);
        ds.send(dp);
        ds.close();
    }
}