java ee - Nullpointerexception in entitymanager -

hy,

i'm having trouble in using entitymanager in java web applicaton.

my code is:

public class helloworldresource extends serverresource { @persistencecontext(unitname = "testrestletpu") entitymanagerfactory emf;  @get   public string represent() {     entitymanager em = emf.createentitymanager();      if(em.isopen())         return "good";     else          return "bad"; }  

and persistence.xml is

<?xml version="1.0" encoding="utf-8"?> <persistence version="2.0" xmlns="http://java.sun.com/xml/ns/persistence"  xmlns:xsi="http://www.w3.org/2001/xmlschema-instance"         xsi:schemalocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns    /persistence/persistence_2_0.xsd">   <persistence-unit name="testrestletpu" transaction-type="jta">     <jta-data-source>test</jta-data-source>     <exclude-unlisted-classes>false</exclude-unlisted-classes>     <properties/>   </persistence-unit> </persistence>  

all entity classes , persistence.xml auto generated, therefore think there shouldn't wrong.

i got everytime error:

java.lang.nullpointerexception     @ firststeps.helloworldresource.represent(helloworldresource.java:23)     @ sun.reflect.nativemethodaccessorimpl.invoke0(native method)     @ sun.reflect.nativemethodaccessorimpl.invoke(nativemethodaccessorimpl.java:39)     @ sun.reflect.delegatingmethodaccessorimpl.invoke(delegatingmethodaccessorimpl.java:25)     @ java.lang.reflect.method.invoke(method.java:597)     @ org.restlet.resource.serverresource.dohandle(serverresource.java:449)     @ org.restlet.resource.serverresource.get(serverresource.java:645)     @ org.restlet.resource.serverresource.dohandle(serverresource.java:527)     @ org.restlet.resource.serverresource.donegotiatedhandle(serverresource.java:587)     @ org.restlet.resource.serverresource.doconditionalhandle(serverresource.java:299)     @ org.restlet.resource.serverresource.handle(serverresource.java:846)     @ org.restlet.resource.finder.handle(finder.java:510)     @ org.restlet.routing.filter.dohandle(filter.java:156)     @ org.restlet.routing.filter.handle(filter.java:203)     @ org.restlet.routing.router.dohandle(router.java:497)     @ org.restlet.routing.router.handle(router.java:737)     @ org.restlet.routing.filter.dohandle(filter.java:156)     @ org.restlet.routing.filter.handle(filter.java:203)     @ org.restlet.routing.filter.dohandle(filter.java:156)     @ org.restlet.routing.filter.handle(filter.java:203)     @ org.restlet.routing.filter.dohandle(filter.java:156)     @ org.restlet.engine.application.statusfilter.dohandle(statusfilter.java:151)     @ org.restlet.routing.filter.handle(filter.java:203)     @ org.restlet.routing.filter.dohandle(filter.java:156)     @ org.restlet.routing.filter.handle(filter.java:203)     @ org.restlet.engine.chainhelper.handle(chainhelper.java:111)     @ org.restlet.engine.application.applicationhelper.handle(applicationhelper.java:72)     @ org.restlet.application.handle(application.java:388)     @ org.restlet.routing.filter.dohandle(filter.java:156)     @ org.restlet.routing.filter.handle(filter.java:203)     @ org.restlet.routing.router.dohandle(router.java:497)     @ org.restlet.routing.router.handle(router.java:737)     @ org.restlet.routing.filter.dohandle(filter.java:156)     @ org.restlet.routing.filter.handle(filter.java:203)     @ org.restlet.routing.router.dohandle(router.java:497)     @ org.restlet.routing.router.handle(router.java:737)     @ org.restlet.routing.filter.dohandle(filter.java:156)     @ org.restlet.engine.application.statusfilter.dohandle(statusfilter.java:151)     @ org.restlet.routing.filter.handle(filter.java:203)     @ org.restlet.routing.filter.dohandle(filter.java:156)     @ org.restlet.routing.filter.handle(filter.java:203)     @ org.restlet.engine.chainhelper.handle(chainhelper.java:111)     @ org.restlet.component.handle(component.java:388)     @ org.restlet.server.handle(server.java:488)     @ org.restlet.engine.http.connector.baseserverhelper.handle(baseserverhelper.java:158)     @ org.restlet.engine.http.connector.baseserverhelper.handleinbound(baseserverhelper.java:167)     @ org.restlet.engine.http.connector.basehelper.handlenextinbound(basehelper.java:418)     @ org.restlet.engine.http.connector.connection.readmessages(connection.java:695)     @ org.restlet.engine.http.connector.controller$2.run(controller.java:95)     @ java.util.concurrent.threadpoolexecutor$worker.runtask(threadpoolexecutor.java:886)     @ java.util.concurrent.threadpoolexecutor$worker.run(threadpoolexecutor.java:908)     @ java.lang.thread.run(thread.java:662) 

can me out.

i think class needs marked @stateless or @statefull use @persistencecontext