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网络编程

URL对象

URL类
1. URL(Uniform Resource Locator)
  
  一致资源定位器的简称，表示Internet上某一资源的地址
2. URL的组成
  
  protocol:resourceNamae
  
  协议名指明获取资源所使用的的传输协议，如http、ftp等，资源名则是资源的完整地址，包括主机名、端口号或文件内部的一个引用。
3. 获取URL对象属性
```
Public String getProtocol()

Public String getHost()

public String getPort()

public String getFile()
```

URLConnection对象

一个URLConnection对象代表一个URL资源与Java程序的通讯连接，可以通过它对这个URL资源读或写。
与URL的区别
1. URL是单向的，URLConnection是双向的
2. 可以查看服务器的响应消息的首部
3. 可以设置客户端请求消息的首部

使用示例

关键步骤：构造一个URL对象，调用URL对象的openConnection()方法获取对应该URL的URLConnection对象。

public class URLConnector {
    public static void main(String[] args) {
        try {
            URL cs = new URL("http://www.sina.com/");
            URLConnection tc = cs.openConnection();
            BufferedReader in = new BufferedReader(new InputStreamReader(tc.getInputStream()));
            String inputLine;
            while((inputLine = in.readLine()) != null) {
                System.out.println(inputLine);
            }
            in.close();
        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Get与Post请求

示例

public static String sendGet(String url, String param) {
    String result = "";
    BufferedReader in = null;
    try {
        String urlNameString = url + "?" +param;
        URL realUrl = new URL(urlNameString);
        URLConnection connection = realUrl.openConnection();
        connection.setRequestProperty("accept", "*/*");
        connection.setRequestProperty("connection", "Keep-Alive");
        connection.connect();
        in = new BufferedReader(new InputStreamReader(connection.getInputStream()));
        String line;
        while((line=in.readLine()) != null) {
            result += line;
        }
    } catch (MalformedURLException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    } finally {
        try {
            if (in != null) {
                in.close();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
        return result;
    }
}

public static String sendPost(String url, String param) {
    PrintWriter out = null;
    BufferedReader in = null;
    String result = "";
    try {
        URL realUrl = new URL(url);
        URLConnection connection = realUrl.openConnection();
        connection.setRequestProperty("accept", "*/*");
        connection.setRequestProperty("connection", "Keep-Alive");
        connection.setDoOutput(true);
        out = new PrintWriter(connection.getOutputStream());
        out.print(param);
        out.flush();
        in = new BufferedReader(new InputStreamReader(connection.getInputStream()));
        String line;
        while((line=in.readLine()) != null) {
            result += line;
        }
    } catch (MalformedURLException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    } finally {
        try {
            if (in != null) {
                in.close();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
        return result;
    }
}

HttpURLConnection类

在URLConnection的基础上提供一系列针对http请求的内容
1. HTTP状态码（例如HTTP_OK:200)
2. setRequestMethod（设置请求方法GETPOST等)
3. getResponseCode（获取HTTP的响应）

Socket通信原理

TCP传输协议（Transport Control Protocol）

面向连接的能够提供可靠的流式数据传输的协议

URL，URLConnection，Sokcet，ServerSocket等类都使用TCP协议进行网络通讯。
socket通讯

网络上的两个程序通过一个双向的通讯连接实现数据的交换，这个双向链路的一端称为一个socket。

Socket通信实现

创建socket

使用Socket类构造
客户端socket的建立
服务端socket的建立
打开输入输出流

关闭socket

注意先关闭流再关闭socket

@TalkClient.java

import java.net.*;
import java.io.*;

public class TalkClient {
    public static void main(String[] args) {
        System.out.println("Client Start...");
        try {
            Socket socket = new Socket("127.0.0.1", 8888);
            BufferedReader sin = new BufferedReader(new InputStreamReader(System.in));
            PrintWriter os = new PrintWriter(socket.getOutputStream());
            BufferedReader is = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            String readline;
            readline = sin.readLine();
            while (!readline.equals("bye")) {
                os.println(readline);
                os.flush();
                System.out.println("Client:" + readline);
                System.out.println("Server:" + is.readLine());
                readline = sin.readLine();
            }
            os.close();
            is.close();
            socket.close();
        } catch (UnknownHostException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

@TalkServer.java

public class TalkServer {
    public static void main (String[] args) {
        System.out.println("Server start...");
        try {
            ServerSocket server = new ServerSocket(8888);
            Socket socket = server.accept();
            String readline;
            BufferedReader is = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            PrintWriter os = new PrintWriter(socket.getOutputStream());
            BufferedReader sin = new BufferedReader(new InputStreamReader(System.in));
            System.out.println("Client: "+is.readLine());
            readline = sin.readLine();
            while (!readline.equals("bye")) {
                os.println(readline);
                os.flush();
                System.out.println("Server:" + readline);
                System.out.println("Client:" + is.readLine());
                readline = sin.readLine();
            }
            os.close();
            is.close();
            socket.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

注意os.print()与os.println()的区别，不要被回车符坑了!!!

Socket多客户端通信

@MultiTalkClient.java

public class MultiTalkClient {
    int num;
    public static void main(String[] args) {
        System.out.println("Client Start...");
        try {
            Socket socket = new Socket("127.0.0.1", 8888);

            BufferedReader sin = new BufferedReader(new InputStreamReader(System.in));
            PrintWriter os = new PrintWriter(socket.getOutputStream());
            BufferedReader is = new BufferedReader(new InputStreamReader(socket.getInputStream()));

            String readline;
            readline = sin.readLine();
            while (!readline.equals("bye")) {
                os.println(readline);
                os.flush();
                System.out.println("Client:" + readline);
                System.out.println("Server:" + is.readLine());
                readline = sin.readLine();
            }
            os.close();
            is.close();
            socket.close();
        } catch (UnknownHostException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

@ServerThread.java

public class ServerThread extends Thread {
    Socket socket = null;
    int clientNum;

    public ServerThread(Socket socket, int num) {
        this.socket = socket;
        this.clientNum = num + 1;
    }

    @Override
    public void run() {
        try {
            String line;

            BufferedReader sin = new BufferedReader(new InputStreamReader(System.in));
            PrintWriter os = new PrintWriter(socket.getOutputStream());
            BufferedReader is = new BufferedReader(new InputStreamReader(socket.getInputStream()));

            System.out.println("Client"+clientNum+":"+is.readLine());
            line = sin.readLine();
            while (!line.equals("bye")) {
                os.println(line);
                os.flush();
                System.out.println("Server:" + line);
                System.out.println("Client"+clientNum+":"+is.readLine());
                line = sin.readLine();
            }
            os.close();
            is.close();
            socket.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

@MultiTalkServer.java

public class MultiTalkServer {
    static int clientNum = 0;
    public static void main (String[] args) {
        System.out.println("Server start...");
        try {
            ServerSocket serverSocket = null;
            Boolean listening = true;
            try {
                serverSocket = new ServerSocket(8888);
            } catch (IOException e) {
                System.out.println("Could not listen on port:8888");
                System.exit(-1);
            }
            while (listening) {
                new ServerThread(serverSocket.accept(), clientNum).start();
                clientNum++;
            }
            serverSocket.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

数据报通信

UDP（User Datagram Protocol)

非面向连接的提供不可靠的数据包式的数据传输协议。

DatagramPacket，DatagramSocket，MulticastSocket等类使用UDP协议进行网络通讯。
TCP（Transport Control Protocol）

面向连接的能够提供可靠的流式数据传输的协议。

URL，URLConnection，Socket，ServerSocket等类都使用TCP协议进行网络通讯。
区别
1. TCP有建立时间
2. UDP传输有大小限制：64k以内
3. TCP的应用：Telnet，ftp
4. UDP的应用：ping
使用数据报通信

DatagramSocket()

DatagramPacket()

收数据报

DatagramPacket packet = new DatagramPacket(buf,256);
socket.recive(packet);

发数据报

DatagramPacket packet = new DatagramPacket(buf,buf.length,address,port);
socket.send(packet);

示例

@QuoteClient.java

public class QuoteClient {
    public static void main(String[] args) throws IOException {
        if (args.length != 1) {
            System.out.println("Usage:java QuoteClient <hostname>");
            return;
        }

        DatagramSocket socket = new DatagramSocket();

        //send request
        byte[] buf = new byte[256];
        InetAddress address = InetAddress.getByName(args[0]);
        DatagramPacket packet = new DatagramPacket(buf,buf.length,address,8888);
        socket.send(packet);

        //get response
        packet = new DatagramPacket(buf,buf.length);
        socket.receive(packet);

        //display response
        String received = new String(packet.getData());
        System.out.println("Quote of the Moment:"+received);

        socket.close();
    }
}

@QuoteServerThread.java

public class QuoteServerThread extends Thread {
    protected DatagramSocket socket = null;
    protected BufferedReader in = null;
    protected boolean moreQuotes = true;

    public QuoteServerThread() throws SocketException {
        this("QuoteServerThread");
    }

    public QuoteServerThread(String name) throws SocketException {
        super(name);
        socket = new DatagramSocket(8888);
        try {
            in = new BufferedReader(new FileReader("one-liners.txt"));
        } catch (FileNotFoundException e) {
            System.err.println("Could not open quote file. Serving time instead.");
        }
    }

    @Override
    public void run() {
        while(moreQuotes) {
            try {
                byte[] buf = new byte[256];
                DatagramPacket packet = new DatagramPacket(buf,buf.length);
                socket.receive(packet);
                String dString = null;
                if (in == null)
                    dString = new Date().toString();
                else
                    dString = getNextQuote();
                buf = dString.getBytes();

                //send response
                InetAddress address = packet.getAddress();
                int port = packet.getPort();
                packet = new DatagramPacket(buf,buf.length,address,port);
                socket.send(packet);
            } catch (IOException e) {
                e.printStackTrace();
                moreQuotes = false;
            }
        }
        socket.close();
    }

    protected String getNextQuote() {
        String res = null;
        try {
            if ((res = in.readLine()) == null) {
                in.close();
                moreQuotes = false;
                res = "No more quotes.";
            }
        } catch (IOException e) {
            res = "IOException occured in server";
        }

        return res;
    }
}

@QuoteServer.java

public class QuoteServer {
    public static void main(String[] args) throws IOException {
        new QuoteServerThread().start();
    }
}

使用数据报进行广播通信

DatagramSocket只允许数据报发往一个目的地址

MulticastSocket将数据报以广播方式发送到该端口的所有客户

MulticastSocket用在客户端，监听服务器广播来的数据

示例

@MulticastClient.java

public class MulticastClient {
    public static void main(String[] args) throws IOException {
        MulticastSocket socket = new MulticastSocket(4396);
        InetAddress address = InetAddress.getByName("230.0.0.1");
        socket.joinGroup(address);
        DatagramPacket packet;

        //get a few quotes
        for(int i=0;i<5;i++) {
            byte[] buf = new byte[256];
            packet = new DatagramPacket(buf,buf.length);
            socket.receive(packet);
            String received = new String(packet.getData());
            System.out.println("Quote of the Moment:"+received);
        }
        socket.leaveGroup(address);
        socket.close();
    }
}

@MulticastServerThread.java

public class MulticastServerThread extends QuoteServerThread{
    private long FIVE_SECOND = 5000;
    public MulticastServerThread() throws IOException {
        super("MulticastServerThread");
    }

    @Override
    public void run() {
        while (moreQuotes) {
            try {
                byte[] buf = new byte[256];
                String dString = null;
                if (in == null)
                    dString = new Date().toString();
                else
                    dString = getNextQuote();
                buf = dString.getBytes();

                //send it
                InetAddress group = InetAddress.getByName("230.0.0.1");
                DatagramPacket packet = new DatagramPacket(buf,buf.length,group,4396);
                socket.send(packet);

                //sleep for a while
                try {
                    sleep((long)(Math.random()*FIVE_SECOND));
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            } catch (IOException e) {
                e.printStackTrace();
                moreQuotes = false;
            }
        }
        socket.close();
    }
}

@MulticastServer.java

public class MulticastServer {
    public static void main(String[] args) throws IOException {
        new MulticastServerThread().start();
    }
}

网络聊天程序

@ChatFrame.java

public class ChatFrame extends JFrame implements ActionListener {
    JTextField tf;
    JTextArea ta;
    JScrollPane sp;
    JButton send;
    JPanel p;

    int port;
    String s = "";
    String myID;
    Date date;
    ServerSocket server;
    Socket mySocket;
    BufferedReader is;
    PrintWriter os;
    String line;

    public ChatFrame(String ID,String remoteID,String IP,int port, boolean isServer) {
        super(ID);
        myID = ID;
        this.port = port;
        ta = new JTextArea();
        ta.setEditable(false);
        sp = new JScrollPane(ta);
        this.setSize(330,400);
        this.setResizable(false);

        try{
            UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
        } catch (Exception e) {
            e.printStackTrace();
        }

        this.getContentPane().add(sp,"Center");
        p = new JPanel();
        this.getContentPane().add(p,"South");
        send = new JButton("发送");
        tf = new JTextField(20);
        tf.requestFocus();
        p.add(tf);
        p.add(send);
        this.setDefaultCloseOperation(EXIT_ON_CLOSE);
        this.setVisible(true);
        send.addActionListener(this);
        tf.addActionListener(this);

        if(isServer) {
            try {
                server = null;
                try {
                    server = new ServerSocket(port);
                }catch (Exception e) {
                    e.printStackTrace();
                }
                mySocket = null;
                try {
                    mySocket = server.accept();
                }catch (Exception e) {
                    e.printStackTrace();
                }
                is = new BufferedReader(new InputStreamReader(mySocket.getInputStream()));
                os = new PrintWriter(mySocket.getOutputStream());
            }catch (Exception e) {
                e.printStackTrace();
            }
        }
        else {
            try {
                mySocket = new Socket(IP,port);
                os = new PrintWriter(mySocket.getOutputStream());
                is = new BufferedReader(new InputStreamReader(mySocket.getInputStream()));
            } catch (Exception e) {
                e.printStackTrace();
            }
        }

        while (true) {
            try {
                line = is.readLine();
                date = new Date();
                SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
                String currentTime = formatter.format(date);
                s+=currentTime+" "+remoteID+"说:
"+line+"
";
                ta.setText(s);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

    @Override
    public void actionPerformed(ActionEvent actionEvent) {
        date = new Date();
        SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        String currentTime = formatter.format(date);
        s+=currentTime+" "+myID+"说:
"+tf.getText()+"
";
        ta.setText(s);
        os.println(tf.getText());
        os.flush();
        tf.setText("");
        tf.requestFocus();
    }
}

@ChatServerFrame.java

public class ChatServerFrame {
    public static void main(String[] args) {
        ChatFrame cserver = new ChatFrame("Cat","Dog","localhost",4396,true);
    }
}

@ChatClientFrame.java

public class ChatClientFrame {
    public static void main(String[] args) {
        ChatFrame cclient = new ChatFrame("Dog","Cat","localhost",4396,false);
    }
}

实际运行如下图所示：

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原文地址：https://www.cnblogs.com/hunter-w/p/13764207.html