chatapplet.java

java网络高级编程的配套源码,java网络高级编程为清华出版社出版.

/*源程序清单5-22*/

import java.applet.Applet;
import java.awt.*;
import java.net.URL;
import java.net.URLConnection;
import java.net.URLEncoder;
import java.net.UnknownHostException;
import java.net.MalformedURLException;
import java.io.*;
import java.util.*;

public class  ChatApplet extends Applet implements Runnable
{
	//用于提醒客户输入用户名或信息
	Label userInfo;
	//用于标识显示聊天内容的区域
	Label messageInfo;
	//用于标识显示正在"聊天室"的用户的区域;
	Label listInfo;
	//用于发送用户输入的用户名或信息;
	Button sendButton;
	//用于接收用户输入的信息;
	TextField userText;
	//用于显示聊天内容;
	TextArea messageText;
	//用于保存正在"聊天室"的用户
	List userList;
	//用户建立与服务器的连接
	URL chatURL;
	URLConnection connect;
	//用于标识用户是否登录
	volatile private boolean loggedin=false;

	String username;
	Thread pollThread=null;

	//返回描述applet的信息
	public String getAppletInfo()
	{
		return "ChatApplet -applet to communicate with ChatServlet, written by ding song";
	}

	public synchronized void init()
	{
		if(pollThread!=null) 
		  return;
		super.init();
		resize(500,300);
		userInfo=new Label("Enter User Name(Max 10 char):");
		messageInfo=new Label("Message Text:");
		userText=new TextField(40);
		sendButton=new Button("Send");
		messageText=new TextArea(10,40);
		messageText.setEditable(false);

		Panel mainPanel=new Panel();
		GridBagLayout gbl=new GridBagLayout();
		GridBagConstraints gbc=new GridBagConstraints();
		gbc.weightx=0;
		gbc.weighty=0;
		gbc.gridx=0;
		gbc.gridy=0;
		gbc.gridwidth=10;
		gbc.gridheight=1;
		gbc.anchor=GridBagConstraints.CENTER;
		gbc.fill=GridBagConstraints.NONE;
		mainPanel.setLayout(gbl);
		gbl.setConstraints(userInfo,gbc);
		mainPanel.add(userInfo);
		gbc.gridy=1;
		gbc.gridwidth=9;
		gbc.fill=GridBagConstraints.HORIZONTAL;
		gbl.setConstraints(userText,gbc);
		mainPanel.add(userText);
		gbc.gridx=9;
		gbc.gridwidth=1;
		gbc.fill=GridBagConstraints.NONE;
		gbl.setConstraints(sendButton,gbc);
		mainPanel.add(sendButton);
		gbc.gridx=0;
		gbc.gridy=2;
		gbc.gridwidth=10;
		gbl.setConstraints(messageInfo,gbc);
		mainPanel.add(messageInfo);
		gbc.gridy=3;
		gbc.weighty=100;
		gbc.gridheight=10;
		gbc.fill=GridBagConstraints.BOTH;
		gbl.setConstraints(messageText,gbc);
		mainPanel.add(messageText);

		Panel userPanel=new Panel();
		userPanel.setLayout(new BorderLayout());
		userPanel.add("North",listInfo);
		userList=new List(10,false);
		userList.addItem("None logged in");
		userPanel.add("Center",userList);

		setLayout(new BorderLayout());
		add("Center",mainPanel);
		add("East",userPanel);

		chatURL=getCodeBase();

		int currPriority=Thread.currentThread().getPriority();
		int newPriority=currPriority==Thread.MIN_PRIORITY?Thread.MIN_PRIORITY:currPriority-1;
		pollThread=new Thread(this,"ChatPoll");
		pollThread.setDaemon(true);

		pollThread.setPriority(newPriority);
		pollThread.start();
		p("Chat:starting polling");
	}

	public synchronized void start()
	{
		if(!isLoggedin()&&username!=null)
		  login();
		if(pollThread!=null&&pollThread.isAlive())
		{
			pollThread.resume();
			p("Chat:resuming poll");
		}
		else
		{
			p("Chat:No poll thread!");
			pollThread=new Thread(this,"ChatPoll");
			pollThread.setDaemon(true);
			pollThread.start();
			p("Chat:starting poll");
		}
	}

	//当Applet在浏览器中不可见时，就挂起线程pollthread,并退出"聊天室"
	public synchronized void stop()
	{
		if (pollThread.isAlive())
		{
			pollThread.suspend();
			p("Chat:suspending poll");
		}
		else
		{
			p("Chat:Dead poll thread in stop()!");
		}
		logout();
	}

	//当用户退出浏览器时，删除线程pollthread，退出聊天室
	public synchronized void destroy()
	{
		if (pollThread != null && pollThread.isAlive())
		{
			pollThread.stop();
			pollThread = null;
			p("Chat:stopping poll!");
		}
		logout();
	}

	//每隔3秒从服务器中取别的用户输入的信息和加入聊天室的用户
	public void run()
	{
		p("Chat: starting the poll run");
		while (!Thread.interrupted())
		{
			//若用户已经登陆，则不时的取回别的用户输入的信息
			//和机如的的用户名
			if (isLoggedin())
			{
				pollList();
				poll();
				p("Chat:poll!");
			}
			//若没有用户登陆，则取回正在聊天室中的用户
			else
			{
				pollList();
				p("Chat: not loggeding for poll!");
			}
			try
			{
				//睡眠3秒钟
				Thread.sleep(1000*3);
			}
			catch (InterruptedException e)
			{				
			}
		}
		p("Chat: exiting run()!");
	}

	//登陆到服务器
	private void login()
	{
		if (username ==null) return;
		String queryString = "chatservlet?mode=login&user="
		+URLEncoder.encode(username); 
		p("Attemping login as " + username);
		//与服务器通信
		try
		{
			connect = (new URL(chatURL,queryString)).openConnection();
			connect.setDefaultUseCaches(false);
			connect.setUseCaches(false);
			connect.setDoInput(true);
			connect.setDoOutput(false);
			connect.connect();
			p("Mading connection to " + connect);
			DataInputStream in = new DataInputStream(connect.getInputStream());
			String response = in.readLine();
			if (response.startsWith("+"))
			{
				//标识用户已经登陆
				setLoggedin(true);
				showStatus("Logged into chat as user " + username);
				p("Logged in as " + username);
				//提示用户输入信息
				userInfo.setText("Type message:");
				repaint();
			}
			else
			{
				showStatus("Error logging in " + response);
				p("Could not log in as " + username);
				System.err.println("Error logging in " + response);
			}
		}
		catch (MalformedURLException e2)
		{
			System.err.println("MalformedURLException logging in!");
			e2.printStackTrace(System.err);
			showStatus("Error logging in!");
		}
		catch (IOException e1)
		{
			System.err.println("IOException logging in!");
			e1.printStackTrace(System.err);
			showStatus("Error logging in!");
		}
	}

	//退出聊天室
	private void logout()
	{
		if (!isLoggedin() || username ==null)
		{
			return;
		}
		String queryString = "chatservlet?mode=logout&username=" + 
		URLEncoder.encode(username);
		//与服务器通信
		try
		{
			connect = (new URL(chatURL,queryString)).openConnection();
			connect.setUseCaches(false);
			connect.setDoInput(true);
			connect.setDoOutput(false);
			connect.connect();
			DataInputStream in = new DataInputStream(connect.getInputStream());
			String response = in.readLine();
			if (response.startsWith("+"))
			{
				//标识用户已经退出聊天室
				setLoggedin(false);
				showStatus("User " + username + "Logged out of Chat!");
			}
			else
			{
				showStatus("Error logging out" + response);
				System.err.println("Error logging out" + response);
			}
		}
		catch (MalformedURLException e2)
		{
			System.err.println("MalformedURLException logging out!");
			e2.printStackTrace(System.err);
			showStatus("Error logging out!");
		}
		catch (IOException e1)
		{
			System.err.println("IOException logging out!");
			e1.printStackTrace(System.err);
			showStatus("Error logging out!");
		}
	}

	//发送用户输入的信息
	private void send()
	{
		String message = userText.getText();

		//用户输入空字符串不发送
		if (message.equals(""))
		{
			return;
		}
		//清除用户在Applet中输入的内容
		userText.setText("");
		showStatus("Sending message!");

		String queryString = "chatservlet?mode=send&user="+
		URLEncoder.encode(username);
		queryString = queryString + "&message="+URLEncoder.encode(message);
		try
		{
			connect = (new URL(chatURL,queryString)).openConnection();
			connect.setUseCaches(false);
			connect.setDoInput(true);
			connect.setDoOutput(false);
			connect.connect();
			DataInputStream in = new DataInputStream(connect.getInputStream());
			String response = in.readLine();
			if (response.startsWith("+"))
			{
				showStatus("Message sent!");
			}
			else
			{
				showStatus("Error sending message " + response);
				System.err.println("Error sending message " + response);
			}
		}
		catch (MalformedURLException e2)
		{
			System.err.println("MalformedURLException logging in!");
			e2.printStackTrace(System.err);
			showStatus("Error logging in!");
		}
		catch (IOException e1)
		{
			System.err.println("IOException logging in!");
			e1.printStackTrace(System.err);
			showStatus("Error logging in!");
		}
	}

	//返回所有用户输入的信息
	private void poll()
	{
		String queryString = "chatservlet?mode=poll&user=" +
		URLEncoder.encode(username);
		try
		{
			DataInputStream in = new DataInputStream(
			new URL(chatURL,queryString).openStream());
			String nextLine = in.readLine();
			if (!nextLine.startsWith("+"))
			{
				showStatus("Error getting messages from server!");
				System.err.println("Error getting messages from server!");
				return;
			}
			nextLine = in.readLine();
			while (nextLine != null && !nextLine.equals("."))
			{
				System.err.println(nextLine);
				messageText.appendText(nextLine + "\r\n");
				repaint();
				nextLine = in.readLine();
			}
		}
		catch (IOException e)
		{
			System.err.println("IOException poll!");
			e.printStackTrace(System.err);
			showStatus("Error Checking Message!");
		}
	}

	//返回正在聊天室中的用户
	private void pollList()
	{
		String queryString = "chatservlet?mode=list";
		Vector users = new Vector();

		try
		{
			URL listURL = new URL(chatURL,queryString);
			URLConnection listConn = listURL.openConnection();
			listConn.setDefaultUseCaches(false);
			listConn.setUseCaches(false);
			listConn.connect();
			DataInputStream in = new DataInputStream(
			listConn.getInputStream());
			String nextLine = in.readLine();
			if (!nextLine.startsWith("+"))
			{
				showStatus("Error getting userlist from server!");
				p("Error  getting userlist from server");
				return;
			}

			nextLine = in.readLine();
			while (nextLine != null && !nextLine.equals("."))
			{
				p("Read user: " + nextLine);
				users.addElement(nextLine);
				nextLine = in.readLine();
			}

			//清除旧的用户表，加入新的
			if (!users.isEmpty())
			{
				userList.clear();
				int size = users.size();
				for (int I=0;I<size ;I++ )
				{
					userList.addItem((String)users.elementAt(I));
				}
			}
			else
			{
				userList.clear();
				userList.addItem("None logged in!");
			}
			repaint();
		}
		catch (IOException e)
		{
			System.err.println("IOException poll!");
			e.printStackTrace(System.err);
			showStatus("Error Checking Message!");
		}
	}
	
	//判断用户是否已经登陆到聊天室
	public boolean isLoggedin()
	{
		return loggedin;
	}

	//设置用户是否登陆的状态
	protected void setLoggedin(boolean newval)
	{
		loggedin = newval;
	}

	//处理用户的动作
	public boolean action(Event evt, Object arg)
	{
		//用户按下按钮和输入信息后按下回车
		if (evt.target == sendButton || evt.target == userText)
		{
			if (isLoggedin())
			{
    			send();
			}
			else
			{
				username = userText.getText();
				if (username.length()>10)
				{
					showStatus("10 or fewer characters,please!");
				}
				else
				{
					userText.setText("");
					login();
				}
			}
			return true;
		}
		return super.action(evt,arg);
	}

	private void p(String debug)
	{
		System.err.println("Chat: " + debug);
	}
 }