servlet3.0的学习（二）

来源：互联网发布：淘宝极速退款卖家拒签编辑：程序博客网时间：2024/06/10 20:41

Servlet 3.0 异步传输的使用

AjaxCometServlet.java

Java代码  
import java.io.IOException;  
import java.io.PrintWriter;  
import java.util.Queue;  
import java.util.concurrent.ConcurrentLinkedQueue;  
import java.util.concurrent.BlockingQueue;  
import java.util.concurrent.LinkedBlockingQueue;  
  
import javax.servlet.AsyncContext;  
import javax.servlet.AsyncEvent;  
import javax.servlet.AsyncListener;  
import javax.servlet.ServletConfig;  
import javax.servlet.ServletException;  
import javax.servlet.annotation.WebServlet;  
import javax.servlet.http.HttpServlet;  
import javax.servlet.http.HttpServletRequest;  
import javax.servlet.http.HttpServletResponse;  
  
@WebServlet(urlPatterns = {"/chat"}, asyncSupported = true)  
public class AjaxCometServlet extends HttpServlet {  
  
    private static final Queue<AsyncContext> queue = new ConcurrentLinkedQueue<AsyncContext>();  
  
    private static final BlockingQueue<String> messageQueue = new LinkedBlockingQueue<String>();  
  
    private static final String BEGIN_SCRIPT_TAG = "<script type='text/javascript'>\n";  
  
    private static final String END_SCRIPT_TAG = "</script>\n";  
  
    private static final long serialVersionUID = -2919167206889576860L;  
  
    private Thread notifierThread = null;  
  
    @Override  
    public void init(ServletConfig config) throws ServletException {  
        Runnable notifierRunnable = new Runnable() {  
            public void run() {  
                boolean done = false;  
                while (!done) {  
                    String cMessage = null;  
                    try {  
                        cMessage = messageQueue.take();  
                        for (AsyncContext ac : queue) {  
                            try {  
                                PrintWriter acWriter = ac.getResponse().getWriter();  
                                acWriter.println(cMessage);  
                                acWriter.flush();  
                            } catch(IOException ex) {  
                                System.out.println(ex);  
                                queue.remove(ac);  
                            }  
                        }  
                    } catch(InterruptedException iex) {  
                        done = true;  
                        System.out.println(iex);  
                    }  
                }  
            }  
        };  
        notifierThread = new Thread(notifierRunnable);  
        notifierThread.start();  
    }  
  
    @Override  
    protected void doGet(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException {  
        res.setContentType("text/html");  
        res.setHeader("Cache-Control", "private");  
        res.setHeader("Pragma", "no-cache");  
        PrintWriter writer = res.getWriter();  
        // for IE  
        writer.println("<!-- Comet is a programming technique that enables web servers to send data to the client without having any need for the client to request it. -->\n");  
        writer.flush();  
  
        final AsyncContext ac = req.startAsync();  
        ac.setTimeout(10  * 60 * 1000);  
        ac.addListener(new AsyncListener() {  
            public void onComplete(AsyncEvent event) throws IOException {  
                queue.remove(ac);  
            }  
  
            public void onTimeout(AsyncEvent event) throws IOException {  
                queue.remove(ac);  
            }  
  
            public void onError(AsyncEvent event) throws IOException {  
                queue.remove(ac);  
            }  
  
            public void onStartAsync(AsyncEvent event) throws IOException {  
            }  
        });  
        queue.add(ac);  
    }  
  
    @Override  
    @SuppressWarnings("unchecked")  
    protected void doPost(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException {  
        res.setContentType("text/plain");  
        res.setHeader("Cache-Control", "private");  
        res.setHeader("Pragma", "no-cache");  
  
        req.setCharacterEncoding("UTF-8");  
        String action = req.getParameter("action");  
        String name = req.getParameter("name");  
  
        if ("login".equals(action)) {  
            String cMessage = BEGIN_SCRIPT_TAG + toJsonp("System Message", name + " has joined.") + END_SCRIPT_TAG;  
            notify(cMessage);  
  
            res.getWriter().println("success");  
        } else if ("post".equals(action)) {  
            String message = req.getParameter("message");  
            String cMessage = BEGIN_SCRIPT_TAG + toJsonp(name, message) + END_SCRIPT_TAG;  
            notify(cMessage);  
  
            res.getWriter().println("success");  
        } else {  
            res.sendError(422, "Unprocessable Entity");  
        }  
    }  
  
    @Override  
    public void destroy() {  
        queue.clear();  
        notifierThread.interrupt();  
    }  
  
    private void notify(String cMessage) throws IOException {  
        try {  
            messageQueue.put(cMessage);  
        } catch(Exception ex) {  
            IOException t = new IOException();  
            t.initCause(ex);  
            throw t;  
        }  
    }  
  
    private String escape(String orig) {  
        StringBuffer buffer = new StringBuffer(orig.length());  
  
        for (int i = 0; i < orig.length(); i++) {  
            char c = orig.charAt(i);  
            switch (c) {  
            case '\b':  
                buffer.append("\\b");  
                break;  
            case '\f':  
                buffer.append("\\f");  
                break;  
            case '\n':  
                buffer.append("<br />");  
                break;  
            case '\r':  
                // ignore  
                break;  
            case '\t':  
                buffer.append("\\t");  
                break;  
            case '\'':  
                buffer.append("\\'");  
                break;  
            case '\"':  
                buffer.append("\\\"");  
                break;  
            case '\\':  
                buffer.append("\\\\");  
                break;  
            case '<':  
                buffer.append("&lt;");  
                break;  
            case '>':  
                buffer.append("&gt;");  
                break;  
            case '&':  
                buffer.append("&amp;");  
                break;  
            default:  
                buffer.append(c);  
            }  
        }  
  
        return buffer.toString();  
    }  
  
    private String toJsonp(String name, String message) {  
        return "window.parent.update({ name: \"" + escape(name) + "\", message: \"" + escape(message) + "\" });\n";  
    }  
}  

ajax.js

Java代码  
var count=0;  
$(document).ready(function () {  
     
    var url='/ajax/chat';  
    $('#login-name').focus();  
  
    $('#comet-frame')[0].src=url + '?' + count;  
    count ++;  
     
    $("#login-button").click(function () {  
            var name = $('#login-name').val();  
            if(! name.length > 0) {  
                $('#system-message').css("color","red");  
                $('#login-name').focus();  
                return;  
            }  
            $('#system-message').css("color","#2d2b3d") ;  
            $('#system-message').html(name + ':');  
  
            $('#login-button').disabled = true;  
            $('#login-form').css("display","none");  
            $('#message-form').css("display","");  
  
            var query =  
            'action=login' +  
            '&name=' + encodeURI($('#login-name').val());  
            $.ajax({  
                type:"post",  
                url:url,  
                data:query,  
                success:function (data,status) {  
                    $('#message').focus();  
                },  
                error:function () {  
                    alert("error occured!!!");  
                }  
            });  
    });  
      
  
    $("#post-button").click(function () {  
        var message = $('#message').val();  
        if(!message > 0) {  
            return;  
        }  
        $('#message').disabled = true;  
        $('#post-button').disabled = true;  
  
        var query =  
        'action=post' +  
        '&name=' + encodeURI($('#login-name').val()) +  
        '&message=' + encodeURI(message);  
        $.ajax({  
            type:"post",  
            url:url,  
            data:query,  
            success:function (data,status) {  
                $('#message').disabled = false;  
                $('#post-button').disabled = false;  
                $('#message').focus();  
                $('#message').val("");  
            },  
            error:function () {  
                alert("error occured!!!");  
            }  
        });  
    }  
    )  
});  
  
function update(data){  
    var p = document.createElement('p');  
    p.innerHTML = data.name + ':<br/>' + data.message;  
  
    $('#display')[0].appendChild(p);  
}  

index.html

Java代码  
<?xml version="1.0" encoding="UTF-8" ?>  
<!DOCTYPE html  
PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"  
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">  
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">  
    <head>  
        <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />  
        <title>Glassfish Chat</title>  
        <link rel="stylesheet" href="css/default.css" type="text/css" />  
        <script type="text/javascript" src="js/jquery-1.4.min.js"></script>  
        <script type="text/javascript" src="js/ajax.js"></script>  
    </head>  
    <body>  
        <div id="container">  
            <div id="container-inner">  
                <div id="header">  
                    <h1>Glassfish Chat</h1>  
                </div>  
                <div id="main">  
                    <div id="display">  
                    </div>  
                    <div id="form">  
                        <div id="system-message">Please input your name:</div>  
                        <div id="login-form">  
                            <input id="login-name" type="text" />  
                            <br />  
                            <input id="login-button" type="button" value="Login" />  
                        </div>  
                        <div id="message-form" style="display: none;">  
                            <div>  
                                <textarea id="message" name="message" rows="2" cols="40"></textarea>  
                                <br />  
                                <input id="post-button" type="button" value="Post Message" />  
                            </div>  
                        </div>  
                    </div>  
                </div>  
            </div>  
        </div>  
        <iframe id="comet-frame" style="display: none;"></iframe>  
    </body>  
</html>  

servlet形成异步处理的过程

在init()方法里，开启一条线程从消息队列中读取消息，并且在AsyncContext（异步上下文）中处理这些消息

Java代码  
PrintWriter acWriter = ac.getResponse().getWriter();  
acWriter.println(cMessage);  
acWriter.flush();  

前面的代码写入一个信息，每个异步请求对应AsyncContext。

在doGet方法里，设置超时时间为10分钟，开始异步并且增加AsyncContext到队列中

Java代码  
final AsyncContext ac = req.startAsync();  
ac.setTimeout(10 * 60 * 1000);  
queue.add(ac);  

对AsyncContext注册AsyncListener 监听器，在这种情况下，只有从队列中清理AsyncContext

Java代码  
ac.addListener(new AsyncListener() {  
    public void onComplete(AsyncEvent event) throws IOException {  
        queue.remove(ac);  
    }  
  
    public void onTimeout(AsyncEvent event) throws IOException {  
        queue.remove(ac);  
    }  
  
    public void onError(AsyncEvent event) throws IOException {  
        queue.remove(ac);  
    }  
  
    public void onStartAsync(AsyncEvent event) throws IOException {  
    }  
});  

在doPost方法里，将消息加入到消息队列里，消息在init方法里开启线程执行

问题：不明白在ajax.js中为什么要加上$('#comet-frame')[0].src=url + '?' + count;这么一句，不加上的话，页面显示不了！

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