java-网络编程

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网络编程本质还是在处理IO流上。

InetAddress类

这个类主要用来表示IP地址，有两个子类：Inet4Address和Inet6Address

import java.net.InetAddress;

public class InetAddressDemo {
    public static void main(String[] args) throws Exception{
        InetAddress locAdd = InetAddress.getLocalHost();
        InetAddress remAdd = InetAddress.getByName("luxuantao.github.io");
        System.out.println("本机IP地址"+locAdd.getHostAddress());
        System.out.println("我的博客的IP地址"+remAdd.getHostAddress());
        System.out.println("本机是否可达"+locAdd.isReachable(5000));
    }
}

URL类

import java.net.URL;

//URL类的基本方法
public class ParseURL {
    public static void main(String[] args) throws Exception{
        URL Aurl = new URL("http://java.sun.com:80/docs/books/"); //基地址
        URL tuto = new URL(Aurl,"tutorial.intro.html#DOWNLOADING"); //相对地址
        System.out.println("协议信息"+tuto.getProtocol());
        System.out.println("地址"+tuto.getHost());
        System.out.println("文件名"+tuto.getFile());
        System.out.println("端口"+tuto.getPort());
        System.out.println("引用信息"+tuto.getRef());
        System.out.println("查询信息"+tuto.getQuery());
        System.out.println("路径"+tuto.getPath());
        System.out.println("用户信息"+tuto.getUserInfo());
        System.out.println("权限信息"+tuto.getAuthority());
    }
}

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.URL;

//从URL读取网络资源
public class URLReader {
    public static void main(String[] args) throws Exception {
        URL tire = new URL("https://luxuantao.github.io/");
        BufferedReader in = new BufferedReader(new InputStreamReader(tire.openStream()));
        String inputLine;
        while((inputLine = in.readLine()) != null) {
            System.out.println(inputLine);
        }
        in.close();
    }
}

URLConnection类

URL是单向的，而URLConnection是双向的，可以通过它对URL资源读或写。

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.URL;
import java.net.URLConnection;

//与指定URL建立动态链接,可向服务器发送请求
public class URLConnectionDemo {
    public static void main(String[] args) throws Exception{
        URL url = new URL("http://www.mldnjava.cn");
        URLConnection urlCon = url.openConnection(); //建立连接
        System.out.println("内容大小"+urlCon.getContentLength());
        System.out.println("内容类型"+urlCon.getContentType());
        BufferedReader in = new BufferedReader(new 		InputStreamReader((urlCon.getInputStream())));
        String inputline;
        while ((inputline = in.readLine()) != null) {
            System.out.println(inputline);
        }
        in.close();
    }
}

服务端与客户端简单交互

单向传输（服务端给客户端）

示例：服务端传输helloworld给客户端。

客户端代码：

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.Socket;
import java.net.UnknownHostException;

public class HelloClient {
    public static void main(String[] args) throws UnknownHostException, IOException{
        Socket client = new Socket("localhost",8888);
        BufferedReader br = new BufferedReader(new InputStreamReader(client.getInputStream()));
        String context = br.readLine();
        System.out.println("当前服务端输出的语句是："+context);
        br.close();
        client.close();
    }
}

服务端代码：

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

public class HelloServer {
    public static void main(String[] args) throws IOException{
        ServerSocket server = new ServerSocket(8888);
        System.out.println("服务器运行，等待客户端连接");
        Socket client = server.accept();
        OutputStream out = client.getOutputStream();
        PrintWriter pw =new PrintWriter(out);
        pw.println("hello world!");
        pw.close();
        client.close();
        server.close();
    }
}

一对一TCP传输（单个服务端和单个客户端）

示例：客户端发送半径给服务端，服务端算出圆的面积后把结果返回给客户端。

客户端代码：

import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.net.Socket;
import java.rmi.UnknownHostException;
import java.util.Scanner;

public class RadiusClient {
    public static void main(String[] args) throws UnknownHostException, IOException{
        Socket client = new Socket("localhost",8888);
        Scanner sc = new Scanner(System.in);
        DataInputStream fromServer = new DataInputStream(client.getInputStream());
        DataOutputStream toServer = new DataOutputStream(client.getOutputStream());
        while (true) {
            System.out.println("请输入半径：");
            double radius = sc.nextDouble();
            toServer.writeDouble(radius);
            toServer.flush();
            double area = fromServer.readDouble();
            System.out.println("客户端：输入的半径是："+radius);
            System.out.println("客户端：收到的圆的面积是："+area);
        }
    }
}

服务端代码：

import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.Date;

public class RadiusServer {
    public static void main(String[] args) throws IOException{
        ServerSocket server = new ServerSocket(8888);
        System.out.println("服务器启动成功，时间是"+new Date());
        Socket client = server.accept();
        DataInputStream inputFromClient = new DataInputStream(client.getInputStream());
        DataOutputStream outputToClient = new DataOutputStream(client.getOutputStream());
        while(true) {
            double radius = inputFromClient.readDouble();
            double area = radius*radius*Math.PI;
            System.out.println("服务端：接受到客户端半径为："+radius);
            System.out.println("服务端：计算面积为："+area);
            outputToClient.writeDouble(area);
        }
    }
}

一对多TCP传输（单个服务端和多个客户端）

当多个客户端同时对服务器发送请求时，上面的方法就不行了（在IDE上的表现就是多次启动了客户端程序，这时只有第一个客户端程序能够成功连接上服务端）。

不过，可以通过多线程解决这个问题。

客户端代码：

import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.net.Socket;
import java.rmi.UnknownHostException;
import java.util.Scanner;

public class RadiusClient {
    public static void main(String[] args) throws UnknownHostException, IOException{
        Socket client = new Socket("localhost",8888);
        Scanner sc = new Scanner(System.in);
        DataInputStream fromServer = new DataInputStream(client.getInputStream());
        DataOutputStream toServer = new DataOutputStream(client.getOutputStream());
        while (true) {
            System.out.println("请输入半径：");
            double radius = sc.nextDouble();
            toServer.writeDouble(radius);
            toServer.flush();
            double area = fromServer.readDouble();
            System.out.println("客户端：输入的半径是："+radius);
            System.out.println("客户端：收到的圆的面积是："+area);
        }
    }
}

服务端代码：

import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.Date;

public class RadiusServer {
    public static void main(String[] args) throws IOException {
        ServerSocket server = new ServerSocket(8888);
        System.out.println("服务器启动成功，时间是"+new Date());
        while(true) {
            Socket client = server.accept();
            Thread thread = new Thread(new AreaRunnable(client)); //多创建一个线程回应请求
            thread.start();
        }
    }
}

AreaRunnable类（处理每个线程）：

import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.net.Socket;

public class AreaRunnable implements Runnable {
    private Socket client;
    public AreaRunnable(Socket client) {
        this.client = client;
    }

    @Override
    public void run() {
        try {
            DataInputStream inputFromClient = new DataInputStream(client.getInputStream());
            DataOutputStream outputToClient = new DataOutputStream(client.getOutputStream());
            while (true) {
                double radius = inputFromClient.readDouble();
                double area = radius * radius * Math.PI;
                System.out.println("服务端：接受到客户端半径为：" + radius);
                System.out.println("服务端：计算面积为：" + area);
                outputToClient.writeDouble(area);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

以上这些内容基本上都属于TCP（要先进行服务端与客户端的连接），而实际上现在用的更多的是UDP（非连接，直接发送数据包），今后有空再研究了。