httpchatapplet.java

一个用java实现的bbs论坛系统...........................

/**
 * @author [e-mail]
 * @version v0 110100
 */

import java.applet.*;
import java.awt.*;
import java.io.*;
import java.net.*;
import java.util.*;

public class HttpChatApplet extends Applet implements Runnable {

  private static final boolean DEBUG = false;
  TextArea text;
  Label label;
  TextField input;
  Thread thread;
  String user;

  public void init() {
    // Check if this applet was loaded directly from the filesystem.
    // If so, explain to the user that this applet needs to be loaded
    // from a server in order to communicate with that server's servlets.
    URL codebase = getCodeBase();
    if (!"http".equals(codebase.getProtocol())) {
      System.out.println();
      System.out.println("*** Whoops! ***");
      System.out.println("This applet must be loaded from a web server.");
      System.out.println("Please try again, this time fetching the HTML");
      System.out.println("file containing this servlet as");
      System.out.println("\"http://server:port/file.html\".");
      System.out.println();
      System.exit(1);  // Works only from appletviewer
                       // Browsers throw an exception and muddle on
    }

    // Get this user's name from an applet parameter set by the servlet
    // We could just ask the user, but this demonstrates a
    // form of servlet->applet communication.
    user = getParameter("user");
    if (user == null) user = "anonymous";

    // Set up the user interface...
    // On top, a large TextArea showing what everyone's saying.
    // Underneath, a labeled TextField to accept this user's input.
    text = new TextArea();
    text.setEditable(false);
    label = new Label("Say something: ");
    input = new TextField();
    input.setEditable(true);

    setLayout(new BorderLayout());
    Panel panel = new Panel();
    panel.setLayout(new BorderLayout());

    add("Center", text);
    add("South", panel);

    panel.add("West", label);
    panel.add("Center", input);
  }

  public void start() {
    thread = new Thread(this);
    thread.start();
  }

  String getNextMessage() {
    String nextMessage = null;
    while (nextMessage == null) {
      try {
        URL url = new URL(getCodeBase(), "/servlet/ChatServlet");
        HttpMessage msg = new HttpMessage(url);
        InputStream in = msg.sendGetMessage();

        // The following is modified by woexpert to properly convert
        // bytes to chars.
        // DataInputStream.readLine() is deprecated.
        //DataInputStream data = new DataInputStream(
        //                       new BufferedInputStream(in));
        BufferedReader data = new BufferedReader(new InputStreamReader(in));

        nextMessage = data.readLine();
      }
      catch (SocketException e) {
        // Can't connect to host, report it and wait before trying again
        System.out.println("Can't connect to host: " + e.getMessage());
        try { Thread.sleep(5000); } catch (InterruptedException ignored) { }
      }
      catch (FileNotFoundException e) {
        // Servlet doesn't exist, report it and wait before trying again
        System.out.println("Resource not found: " + e.getMessage());
        try { Thread.sleep(5000); } catch (InterruptedException ignored) { }
      }
      catch (Exception e) {
        // Some other problem, report it and wait before trying again
        System.out.println("General exception: " +
          e.getClass().getName() + ": " + e.getMessage());
        try { Thread.sleep(1000); } catch (InterruptedException ignored) { }
      }
    }
    return nextMessage + "\n";
  }

  public void run() {
    while (true) {
      //text.appendText(getNextMessage()); // deprecated
      text.append(getNextMessage());
    }
  }

  public void stop() {
    thread.stop();
    thread = null;
  }

  void broadcastMessage(String message) {
    message = user + ": " + message;  // Pre-pend the speaker's name
    try {
      URL url = new URL(getCodeBase(), "/servlet/ChatServlet");
      HttpMessage msg = new HttpMessage(url);
      Properties props = new Properties();
      props.put("message", message);
      msg.sendPostMessage(props);
    }
    catch (SocketException e) {
      // Can't connect to host, report it and abandon the broadcast
      System.out.println("Can't connect to host: " + e.getMessage());
    }
    catch (FileNotFoundException e) {
      // Servlet doesn't exist, report it and abandon the broadcast
      System.out.println("Resource not found: " + e.getMessage());
    }
    catch (Exception e) {
      // Some other problem, report it and abandon the broadcast
      System.out.println("General exception: " +
        e.getClass().getName() + ": " + e.getMessage());
    }
  }

  public boolean handleEvent(Event event) {
    switch (event.id) {
      case Event.ACTION_EVENT:
        if (event.target == input) {
          broadcastMessage(input.getText());
          input.setText("");
          return true;
        }
    }
    return false;
  }

  //public void processEvent(AWTEvent awte) {
  //  if (DEBUG) System.out.println("in HttpChatApplet.processEvnet");
  //  super.processEvent(awte);
  //}

}

class HttpMessage {

  URL servlet = null;
  Hashtable headers = null;

  /**
   * Constructs a new HttpMessage that can be used to communicate with the 
   * servlet at the specified URL.
   *
   * @param servlet the server resource (typically a servlet) with which 
   * to communicate
   */
  public HttpMessage(URL servlet) {
    this.servlet = servlet;
  }

  /**
   * Performs a GET request to the servlet, with no query string.
   *
   * @return an InputStream to read the response
   * @exception IOException if an I/O error occurs
   */
  public InputStream sendGetMessage() throws IOException {
    return sendGetMessage(null);
  }

  /**
   * Performs a GET request to the servlet, building
   * a query string from the supplied properties list.
   *
   * @param args the properties list from which to build a query string
   * @return an InputStream to read the response
   * @exception IOException if an I/O error occurs
   */
  public InputStream sendGetMessage(Properties args) throws IOException {
    String argString = "";  // default

    if (args != null) {
      argString = "?" + toEncodedString(args);
    }
    URL url = new URL(servlet.toExternalForm() + argString); 

    // Turn off caching
    URLConnection con = url.openConnection();
    con.setUseCaches(false);

    // Send headers
    sendHeaders(con);

    return con.getInputStream();
  }

  /**
   * Performs a POST request to the servlet, building
   * post data from the supplied properties list.
   *
   * @param args the properties list from which to build the post data
   * @return an InputStream to read the response
   * @exception IOException if an I/O error occurs
   */
  public InputStream sendPostMessage(Properties args) throws IOException {
    String argString = "";  // default
    if (args != null) {
      argString = toEncodedString(args);  // notice no "?"
    }

    URLConnection con = servlet.openConnection();

    // Prepare for both input and output
    con.setDoInput(true);
    con.setDoOutput(true);

    // Turn off caching
    con.setUseCaches(false);

    // Work around a Netscape bug
    con.setRequestProperty("Content-Type",
                           "application/x-www-form-urlencoded");

    // Send headers
    sendHeaders(con);

    // Write the arguments as post data
    DataOutputStream out = new DataOutputStream(con.getOutputStream());
    out.writeBytes(argString);
    out.flush();
    out.close();

    return con.getInputStream();
  }

  // Send the contents of the headers hashtable to the server

  private void sendHeaders(URLConnection con) {
    if (headers != null) {
      Enumeration enum = headers.keys();
      while (enum.hasMoreElements()) {
        String name = (String) enum.nextElement();
        String value = (String) headers.get(name);
        con.setRequestProperty(name, value);
      }
    }
  }

  /**
   * Converts a properties list to a URL-encoded query string
   */

  private String toEncodedString(Properties args) {
    StringBuffer buf = new StringBuffer();
    Enumeration names = args.propertyNames();
    while (names.hasMoreElements()) {
      String name = (String) names.nextElement();
      String value = args.getProperty(name);
      buf.append(URLEncoder.encode(name) + "=" + URLEncoder.encode(value));
      if (names.hasMoreElements()) buf.append("&");
    }
    return buf.toString();
  }

}