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
– Eng.Fouad

2013-04-09 23:07:04 +00:00
Commented Apr 9, 2013 at 23:07 — Eng.Fouad
– Eng.Fouad, Commented Apr 9, 2013 at 23:07
And what, may I ask, is on line 50?

Boris the Spider
– Boris the Spider

2013-04-09 23:07:06 +00:00
Commented Apr 9, 2013 at 23:07 — Boris the Spider
– Boris the Spider, Commented Apr 9, 2013 at 23:07
Start debugging at line 50 of AsyncServlet.java.

Oswald
– Oswald

2013-04-09 23:08:56 +00:00
Commented Apr 9, 2013 at 23:08 — Oswald
– Oswald, Commented Apr 9, 2013 at 23:08
updated with line50 content

user375868
– user375868

2013-04-09 23:17:01 +00:00
Commented Apr 9, 2013 at 23:17 — user375868
– user375868, Commented Apr 9, 2013 at 23:17

Stephen C · Accepted Answer · 2013-04-09 23:18:22Z

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 9, 2013 at 23:18

Stephen C

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1 Comment

user375868 Over a year ago

you are right, I executed System.out.println(request.getAttribute("executor")); and got Null

christopher · Accepted Answer · 2013-04-09 23:18:19Z

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 9, 2013 at 23:18

christopher

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