网络编程

InetAddress

import java.net.InetAddress;
import java.net.UnknownHostException;

public class test01 {
    /**
     * 端口号与IP地址的组合得出一个网络套接字：Socket
     *
     * 1. 本地回路地址：127.0.0.1 对应着：localhost
     * 2. InetAddress的两个实例化方法：getByName(String host)、getLocalHost()
     * 3. InetAddress的两个常用方法：getHostName()、getHostAddress()
     * @param args
     */
    public static void main(String[] args) throws UnknownHostException {

        InetAddress inet1 = InetAddress.getByName("192.168.10.23");
        System.out.println(inet1);

        InetAddress inet2 = InetAddress.getByName("www.baidu.com");
        System.out.println(inet2);

        InetAddress inet3 = InetAddress.getByName("127.0.0.1");
        System.out.println(inet3);

        InetAddress inet4 = InetAddress.getLocalHost();
        System.out.println(inet4);

        //getHostName()
        System.out.println(inet2.getHostName());
        //getHostAddress()
        System.out.println(inet2.getHostAddress());

    }
}

TCP

1.客户端发送内容给服务端，服务端将内容打印到控制台上

import org.junit.Test;

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

public class test02 {    

    //客户端
    @Test
    public void client() throws IOException {
        //1.创建一个Socket对象，指明服务器端的ip和端口号
        InetAddress inet = InetAddress.getByName("127.0.0.1");
        Socket socket = new Socket(inet, 8899);

        //2.获取一个输出流，用于传输数据
        OutputStream os = socket.getOutputStream();
        os.write("你好，我是客户端".getBytes());

        //3.关闭资源
        os.close();
        socket.close();
    }

    //服务器
    @Test
    public void server() throws IOException {
        //1.创建服务器端的ServerSocket，指明自己的端口号
        ServerSocket ss = new ServerSocket(8899);

        //2.调用accept()表示接收来自客户端的socket
        Socket socket = ss.accept();

        //3.获取输入流
        InputStream is = socket.getInputStream();


        //4.读取数据
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        byte[] buffer = new byte[5];
        int len;
        while((len = is.read(buffer)) != -1){
            baos.write(buffer, 0, len);
        }

        System.out.println(baos.toString());

        //5.关闭资源
        baos.close();
        is.close();
        socket.close();
        ss.close();
    }
}

2.客户端发送文件给服务端，服务端将文件保存在本地

import com.sun.security.ntlm.Server;
import org.junit.Test;

import java.io.*;
import java.net.InetAddress;
import java.net.ServerSocket;
import java.net.Socket;
import java.net.UnknownHostException;

public class test03 {   

    //客户端
    @Test
    public void client() throws IOException {
        //1.
        Socket socket = new Socket(InetAddress.getByName("127.0.0.1"), 9090);

        //2.
        OutputStream os = socket.getOutputStream();

        FileInputStream fis = new FileInputStream(new File("hello.jpg"));

        //3.
        byte[] buffer = new byte[1024];
        int len;
        while((len = fis.read(buffer)) != -1){
            os.write(buffer, 0, len);
        }

        //4.
        fis.close();
        os.close();
        socket.close();
    }

    //服务器
    @Test
    public void server() throws IOException {
        //1.
        ServerSocket ss = new ServerSocket();

        //2.
        Socket socket = ss.accept();

        //3.
        InputStream is = socket.getInputStream();

        FileOutputStream fos = new FileOutputStream(new File("feifei.jpg"));

        //4.
        byte[] buffer = new byte[1024];
        int len;
        while((len = is.read(buffer)) != -1){
            fos.write(buffer, 0, len);
        }

        //5.
        fos.close();
        is.close();
        socket.close();
        ss.close();
    }
}

3.从客户端发送文件给服务端，服务端保存到本地。并返回“发送成功”给 客户端。并关闭相应的连接

import org.junit.Test;

import java.io.*;
import java.net.InetAddress;
import java.net.ServerSocket;
import java.net.Socket;

public class test04 {    

    //客户端
    @Test
    public void client() throws IOException {
        //1.
        Socket socket = new Socket(InetAddress.getByName("127.0.0.1"), 9090);

        //2.
        OutputStream os = socket.getOutputStream();

        FileInputStream fis = new FileInputStream(new File("hello.jpg"));

        //3.
        byte[] buffer = new byte[1024];
        int len;
        while((len = fis.read(buffer)) != -1){
            os.write(buffer, 0, len);
        }

        //图片传完了，不再发了
        socket.shutdownOutput();

        //4.接收来自服务器端的数据，并显示到控制台上
        InputStream is = socket.getInputStream();
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        byte[] buffer2 = new byte[20];
        int len2;
        while((len2 = is.read(buffer2)) != -1){
            baos.write(buffer2, 0, len2);
        }
        System.out.println(baos.toString());

        //5.
        fis.close();
        os.close();
        socket.close();
        is.close();
        baos.close();
    }

    //服务器
    @Test
    public void server() throws IOException {
        //1.
        ServerSocket ss = new ServerSocket();

        //2.
        Socket socket = ss.accept();

        //3.
        InputStream is = socket.getInputStream();

        FileOutputStream fos = new FileOutputStream(new File("feifei.jpg"));

        //4.
        byte[] buffer = new byte[1024];
        int len;
        while((len = is.read(buffer)) != -1){
            fos.write(buffer, 0, len);
        }

        //5.服务器端给予客户反馈
        OutputStream os = socket.getOutputStream();
        os.write("我已经收到消息了".getBytes());

        //6.
        fos.close();
        is.close();
        socket.close();
        ss.close();
        os.close();
    }
}

UDP

import org.junit.Test;

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;
import java.net.InetAddress;
import java.net.SocketException;

public class test05 {
    //发送端
    @Test
    public void sender() throws IOException {

        DatagramSocket socket = new DatagramSocket();

        String str = "我是通过UDP发送的消息";
        byte[] data = str.getBytes();
        InetAddress inet = InetAddress.getLocalHost();
        DatagramPacket packet = new DatagramPacket(data, 0, data.length, inet, 9090);

        socket.send(packet);

        socket.close();
    }

    //接受端
    @Test
    public void receiver() throws IOException {

        DatagramSocket socket = new DatagramSocket(9090);

        byte[] buffer = new byte[100];
        DatagramPacket packet = new DatagramPacket(buffer, 0, buffer.length);

        socket.receive(packet);

        System.out.println(new String(packet.getData(), 0, packet.getLength()));

        socket.close();
    }
}

URL

import org.junit.Test;

import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLConnection;

public class test07 {
    @Test
    public void testURL() throws IOException {

        URL url = new URL("http://localhost:8080/examples/hello.jpg");

        HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();

        urlConnection.connect();

        InputStream is = urlConnection.getInputStream();
        FileOutputStream fos = new FileOutputStream("hello2.jpg");

        byte[] buffer = new byte[1024];
        int len;
        while((len = is.read(buffer)) != -1){
            fos.write(buffer, 0, len);
        }

        //关闭资源
        is.close();
        fos.close();
        urlConnection.disconnect();
    }
}

来源：https://www.cnblogs.com/xiaoran991/p/12543899.html