关于webservlet 请求异步处理,链接未关闭出现的bug

webservlet  +redis 的消息发布订阅 ,挺好的

当请求到来,向redis server申请一个频道 ,然后等着另一端架设是B 处理完毕获得到处理信息调用redis ,使用redis 往当前申请的频道号 发送消息,在接收者C此时会收到一个事件的方式处理结果.

redis.subscribe(subscriber, channel);    //通过subscribe 的api去订阅，入参是订阅者和频道名    

servlet不跳转页面、注意事项:

webservlet 启动异步线程有个timeout 超时事件 

AsyncContext asyncContext = request.startAsync();
asyncContext.setTimeout(3000);
asyncContext.addListener(new AppAsyncListener(subscriber));  //通过AppAsyncListener 接收超时事件

在超时之后返回事件中可以返回超时的信息给请求端,必须要做关闭链接,异步线程结束 的操作,因为我的项目中订阅了redis消息.在此直关闭链接和关闭异步线程,还是不够的,还需要 中间取消订阅,也就是把事件给解绑了,要不异步线程实际没结束,事件还存在,

java接口异步不等待、当有个redis 消息事件过来,而此时的链接已经关闭,会出现一个bug  : AsyncContext has already completed ,异步报文已经结束的bug ,实际此时,事件还是能接收到的.于是异步线程未全部退出,导致每次请求一次,多一个现在在debug内无法退出.

java.lang.IllegalStateException: The request associated with the AsyncContext has already completed processing.  at org.apache.catalina.core.AsyncContextImpl.check(AsyncContextImpl.java:521)  at org.apache.catalina.core.AsyncContextImpl.getResponse(AsyncContextImpl.java:245)  

所以,需要在AppAsyncListener 注入subscriber 订阅者这个对象,这个对象是接收消息的事件对象,扩展了Subscriber extends JedisPubSub.只有这样才能调用unsubscriber解绑所绑定频道其实感觉就是个接触事件绑定.

请求得到之后,需要关闭频道号,关闭这次异步启用的线程,也就是让当前启动的线程退出, 如果这个异步线程未退出,那bug 简直会让你头晕......

java异步请求。AsyncContext asyncContext = request.startAsync();
asyncContext.setTimeout(3000);
Work work = new Work(asyncContext,"3856111302");
subscriber = new Subscriber(asyncContext);
asyncContext.addListener(new AppAsyncListener(subscriber));   // 异步状态监听 类注入 redis订阅者对象subscriber,这样当异步线程出现timeout时,调用AppAsyncListener类中void onTimeout 时 可以通过subscriber  对象调用

                                                          // unSubscriber(),解除订阅订阅的频道...关闭链接, 关闭异步线程.此次请求的异步线程完美退出. 

new Thread(work).start();

上边是异步线程启动的地方

java异步返回结果、下边是timeout 后再listener 中调用 suscriber类中的解绑方法

 public void unSubscriber() //给timeout 之后 解除事件用
        {PrintWriter out;try {out = response.getWriter();Gson gson = new Gson();String gsonString = gson.toJson("214");out.println(gsonString);out.flush();out.close();unsubscribe("3856111302");asyncContext.complete();} catch (IOException e) {// TODO Auto-generated catch block
                e.printStackTrace();}

@WebListener
public class AppAsyncListener implements AsyncListener {
String devcmdid; 
Subscriber subscriber;
public AppAsyncListener(){}
public AppAsyncListener(Subscriber subscriber){    
// this.devcmdid=devcmdid;
this.subscriber=subscriber;
}@Overridepublic void onTimeout(AsyncEvent asyncEvent) throws IOException {/*  ServletResponse response = asyncEvent.getAsyncContext().getResponse();PrintWriter out = response.getWriter();        out.write("SystemMessageContents.ErrorCode.MESSAGE_REQUEST_TIMEOUT""214");  //超时214out.flush();out.close();asyncEvent.getAsyncContext().complete();System.out.println("AppAsyncListener timeout");*/subscriber.unSubscriber();// unsubscribe("3856111302");}

 

由于异步线程启动之后加载了redis的订阅频道,在这里应该是 加载了redis 的频道事件,事件一旦加载了,这个线程是一直存在的, 它不像别的没有while的线程,运行完了线程就结束了

java的servlet。在此加载了事件后,线程不会出退出

RedisImpl redis = new RedisImpl(); 
redis.subscribe(subscriber, channel); //通过subscribe 的api去订阅，入参是订阅者和频道名

所以当收到消息后 ,必须运行  asyncContext.complete(); 对这个线程进行关闭,否则会等到 asyncContext的timeout 时间结束之后才结束.这就是我那程序里没加这句,导致每次请求完之后都要运行一次AppAsyncListener  implements AsyncListener 里边的timeout事件返回消息

@Override
public void onTimeout(AsyncEvent asyncEvent) throws IOException     // 后因结束异常,程序改为上边的方式

  @Overridepublic void onMessage(String channel, String message) {       //收到消息会调用ServletResponse response = asyncContext.getResponse();PrintWriter out;try {out = response.getWriter();Gson gson = new Gson();String gsonString = gson.toJson("resever");out.println(gsonString);out.flush();out.close();unsubscribe("3856111302");asyncContext.complete();} catch (IOException e) {

 2:一个常识方面的bug

public class Subscriber extends JedisPubSub {private AsyncContext asyncContext;ServletResponse response = asyncContext.getResponse();   public Subscriber(AsyncContext asyncContext){this.asyncContext=asyncContext;response = asyncContext.getResponse();}

ServletResponse response = asyncContext.getResponse();    这段程序 在类下边直接去获取,在类初始化时由于还未载入asyncContext,出现asyncContext为null的bug,所以此处应该如下

public class Subscriber extends JedisPubSub {private AsyncContext asyncContext;ServletResponse response =null;//= asyncContext.getResponse();public Subscriber(AsyncContext asyncContext){this.asyncContext=asyncContext;response = asyncContext.getResponse();}

3:类构造方法无参未写出现初始化的错误 .init() 的bug

public class AppAsyncListener  implements AsyncListener {String devcmdid; Subscriber subscriber;public AppAsyncListener(){}   //后来加上这个问题解决public AppAsyncListener(Subscriber subscriber){// 	this.devcmdid=devcmdid;this.subscriber=subscriber;}

　　

4:线程不停的循环读取redis 的值,当运行 getResource(); 时,而此时redis server未打开,出现JedisConnectionException 抛出异常,这里jedis 做的不够啊,用try catch 还抓取不到这个异常...等有空有时间做处理