Java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GET\POST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:\n"+line+"\n";
                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:\n"+tf.getText()+"\n";
        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：