NullPointerException when processing asyncServlet

Question

I am following this tutorial -

When I send request like this-

http://localhost:9090/AsyncServlet?id=99&dispatch=true&timeout=false

I am getting following-

Apr 09, 2013 4:01:09 PM com.mycompany.mavenproject1.AsyncServlet doGet
INFO: AsyncServlet: Processing request: 99. on thread: 27:qtp2072997125-27[4/9/13 4:01 PM]
2013-04-09 16:01:09.503:WARN:oejs.ServletHandler:/AsyncServlet
java.lang.NullPointerException
    at com.mycompany.mavenproject1.AsyncServlet.doGet(AsyncServlet.java:50)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:735)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:848)
    at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:669)
    at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:457)
    at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:137)
    at org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:557)
    at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:231)
    at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1075)
    at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:384)
    at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:193)
    at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1009)
    at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:135)
    at org.eclipse.jetty.server.handler.ContextHandlerCollection.handle(ContextHandlerCollection.java:255)
    at org.eclipse.jetty.server.handler.HandlerCollection.handle(HandlerCollection.java:154)
    at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:116)
    at org.eclipse.jetty.server.Server.handle(Server.java:368)
    at org.eclipse.jetty.server.AbstractHttpConnection.handleRequest(AbstractHttpConnection.java:489)
    at org.eclipse.jetty.server.AbstractHttpConnection.headerComplete(AbstractHttpConnection.java:942)
    at org.eclipse.jetty.server.AbstractHttpConnection$RequestHandler.headerComplete(AbstractHttpConnection.java:1004)
    at org.eclipse.jetty.http.HttpParser.parseNext(HttpParser.java:640)
    at org.eclipse.jetty.http.HttpParser.parseAvailable(HttpParser.java:235)
    at org.eclipse.jetty.server.AsyncHttpConnection.handle(AsyncHttpConnection.java:82)
    at org.eclipse.jetty.io.nio.SelectChannelEndPoint.handle(SelectChannelEndPoint.java:628)
    at org.eclipse.jetty.io.nio.SelectChannelEndPoint$1.run(SelectChannelEndPoint.java:52)
    at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:608)
    at org.eclipse.jetty.util.thread.QueuedThreadPool$3.run(QueuedThreadPool.java:543)
    at java.lang.Thread.run(Thread.java:722)

I just don't know even where to start debugging. My web.xml looks like this-

<web-app xmlns="http://java.sun.com/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
         version="3.0"> 

<servlet>
    <servlet-name>AsyncServlet</servlet-name>
    <servlet-class>com.mycompany.mavenproject1.AsyncServlet
    </servlet-class>        
    <async-supported>true</async-supported>

</servlet>
<servlet-mapping>
    <servlet-name>AsyncServlet</servlet-name>
    <url-pattern>/AsyncServlet/*</url-pattern>
</servlet-mapping>

</web-app>

Line50: executor.execute(new AsyncRequestProcessor(asyncCtx, dispatch));

Check the line at `AsyncServlet.java:50`. – Eng.Fouad Apr 09 '13 at 23:07 — Eng.Fouad, Apr 09 '13 at 23:07
And what, may I ask, is on line 50? – Boris the Spider Apr 09 '13 at 23:07 — Boris the Spider, Apr 09 '13 at 23:07
Start debugging at line 50 of AsyncServlet.java. – Oswald Apr 09 '13 at 23:08 — Oswald, Apr 09 '13 at 23:08
updated with line50 content – user375868 Apr 09 '13 at 23:17 — user375868, Apr 09 '13 at 23:17

score 1 · Answer 1 · answered Apr 09 '13 at 23:18

1

The only thing that could force a NullPointerException to be thrown from that line is if the executor object has not been intialised properly.

answered Apr 09 '13 at 23:18

christopher

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score 1 · Accepted Answer · answered Apr 09 '13 at 23:18

1

If line 50 is this:

executor.execute(new AsyncRequestProcessor(asyncCtx, dispatch));

then the most likely immediate cause of the NPE is that executor is null.

If asyncCtx or dispatch where boxed primitive types, then you could get an NPE from unboxing null. However this seems highly unlikely given the names of the variables. They look like names of "regular" class instances to me.

answered Apr 09 '13 at 23:18

Stephen C

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you are right, I executed `System.out.println(request.getAttribute("executor"));` and got Null – user375868 Apr 10 '13 at 00:17

NullPointerException when processing asyncServlet

2 Answers2