ClassCastException When Passing an Entity POJO from Stateles

[yxw84]

Here is the scenario. I have a Servlet which calls a simple stateless session bean. The session bean has just a single find method which retrieves an entity bean from the database. Here is the code:

Servlet:
// lookup the session bean
InitialContext ctx = new InitialContext();
SessionTest st = (SessionTest) ctx.lookup(SessionTest.class.getName());

// find an instance of MyObject with id of 1
MyObject mo = st.getMyObject(1);

Stateless Session:
public MyObject getMyObject(int id) {
MyObject result = (MyObject) em.createQuery("FROM MyObject m where m.id = :id")
.setParameter ("id", id)
.getSingleResult();

System.err.println("Query was successful, at least.");
System.err.println("ID = " + result.getId());
return result;
}

Assume that the entity bean works, I've tested it without the session facade. Here is the output:

11:29:15,127 INFO [STDOUT] Query was successful, at least.
11:29:15,127 INFO [STDOUT] ID = 1
11:29:15,135 ERROR [[EJB3Servlet]] Servlet.service() for servlet EJB3Servlet threw exception
java.lang.ClassCastException: MyCompany.MyObject
at $Proxy142.getMyObject(Unknown Source)
at MyCompany.EJB3Servlet.doGet(EJB3Servlet.java:66)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:697)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:810)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:252)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
at org.jboss.web.tomcat.filters.ReplyHeaderFilter.doFilter(ReplyHeaderFilter.java:81)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:202)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:213)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:178)
at org.jboss.web.tomcat.security.CustomPrincipalValve.invoke(CustomPrincipalValve.java:39)
at org.jboss.web.tomcat.security.SecurityAssociationValve.invoke(SecurityAssociationValve.java:153)
at org.jboss.web.tomcat.security.JaccContextValve.invoke(JaccContextValve.java:59)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:126)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:105)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:107)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:148)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:856)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.processConnection(Http11Protocol.java:744)
at org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java:527)
at org.apache.tomcat.util.net.MasterSlaveWorkerThread.run(MasterSlaveWorkerThread.java:112)
at java.lang.Thread.run(Thread.java:595)

What is puzzling is that the instance of MyObject with id of 1 is retrieved from the database, and a method is invoked on it to get its ID, but when it is returned, there is a ClassCastException. MyObject implements Serializable. Also, if we convert the return result to a String, it works just fine.

Does anyone have any insight into what might be causing the problem?

Thanks.

[bill.burke]

The Web (Servlet) classloader looks in itself for classes before looking to its parent for classes. The Web classloader is also isolated from other components (EJB code can see classes in the web loader).

So, do you have copies of classes anywhere? Is MyObject.class within the WAR and your ejb.jar or .par?

[yxw84]

Thank you for the prompt response.

Yes, the same MyObject.class is within both my .war file, which contains the Servlet, and in my .ejb3 file, which contains both the session and entity bean. Should I remove it from one of them?

[bill.burke]

remove it from the war

[yxw84]

Wow, I would never have figured this out by myself. It works perfectly now, thank you!

[bill.burke]

No Problem. In the future you should search in forums/wiki before posting questions. You may get your answer more quickly as somtimes the EJB3 team doesn't have time to respond to every post.