PersistenceContext EntityManager injection NullPointerException

Question

I have a war containing the following   META-INF MANIFEST MF WEB-INF classes META-INF persistence xml WEB-INF classes com test service TestServlet class WEB-INF classes com test service TestEntity class WEB-INF classes jndi properties WEB-INF classes postgresql-ds xml WEB-INF jboss-web xml WEB-INF web xml index jsp  persistence xml    lt  xml version  1 0  encoding  UTF-8   gt   lt persistence 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 1 0 xsd  version  1 0  gt       lt persistence-unit name  test  gt           lt provider gt org hibernate ejb HibernatePersistence lt  provider gt           lt jta-data-source gt java  TestDS lt  jta-data-source gt            lt properties gt               lt property name  hibernate dialect  value  org hibernate dialect PostgreSQLDialect   gt               lt property name  hibernate hbm2ddl auto  value  update    gt               lt property name  hibernate show sql  value  true    gt           lt  properties gt       lt  persistence-unit gt   lt  persistence gt    web xml    lt  DOCTYPE web-app PUBLIC   -  Sun Microsystems  Inc   DTD Web Application 2 3  EN    http   java sun com dtd web-app 2 3 dtd   gt    lt web-app gt     lt display-name gt Test Web Application lt  display-name gt        lt context-param gt           lt param-name gt resteasy scan lt  param-name gt           lt param-value gt true lt  param-value gt       lt  context-param gt       lt listener gt           lt listener-class gt org jboss resteasy plugins server servlet ResteasyBootstrap lt  listener-class gt       lt  listener gt       lt servlet gt           lt servlet-name gt Resteasy lt  servlet-name gt           lt servlet-class gt org jboss resteasy plugins server servlet HttpServletDispatcher lt  servlet-class gt       lt  servlet gt       lt servlet-mapping gt           lt servlet-name gt Resteasy lt  servlet-name gt           lt url-pattern gt  service   lt  url-pattern gt       lt  servlet-mapping gt        lt resource-ref gt           lt res-ref-name gt TestDS lt  res-ref-name gt           lt res-type gt javax sql DataSource lt  res-type gt           lt res-auth gt Container lt  res-auth gt           lt res-sharing-scope gt Shareable lt  res-sharing-scope gt       lt  resource-ref gt   lt  web-app gt    My TestServlet class is as follows   package com test service   import java util    import javax persistence    import javax ws rs      Path   service   public class TestService         PersistenceContext unitName    test       private EntityManager em        GET      Path   get        Produces  application json       public List get             return em createQuery  from TestEntity   getResultList             When the get   method is invoked I get a NullPointerException  the EntityManager hasn t been injected  Any suggestions on what I might be missing or how I can diagnose it  There s very little in the server log   I m sure I had this working without the jboss-web xml or the datasource entry in web xml  I ve deployed the ds xml to the deploy directory separately too and that s definitely picked up - I can see it in the JMX console   Tried using JBoss 4 2 3 and a 6 0 build with the same result

User · Answer

If the component is an EJB  then  there shouldn t be a problem injecting an EM   But    In JBoss 5  the JAX-RS integration isn t great   If you have an EJB  you cannot use scanning and you must manually list in the context-param resteasy jndi resource   If you still have scanning on  Resteasy will scan for the resource class and register it as a vanilla JAX-RS service and handle the lifecycle   This is probably the problem

User · Answer

An entity manager can only be injected in classes running inside a transaction  In other words  it can only be injected in a EJB  Other classe must use an EntityManagerFactory to create and destroy an EntityManager   Since your TestService is not an EJB  the annotation  PersistenceContext is simply ignored  Not only that  in JavaEE 5  it s not possible to inject an EntityManager nor an EntityManagerFactory in a JAX-RS Service  You have to go with a JavaEE 6 server  JBoss 6  Glassfish 3  etc    Here s an example of injecting an EntityManagerFactory   package com test service   import java util    import javax persistence    import javax ws rs      Path   service   public class TestService         PersistenceUnit unitName    test       private EntityManagerFactory entityManagerFactory        GET      Path   get        Produces  application json       public List get             EntityManager entityManager   entityManagerFactory createEntityManager            try               return entityManager createQuery  from TestEntity   getResultList              finally               entityManager close                        The easiest way to go here is to declare your service as a EJB 3 1  assuming you re using a JavaEE 6 server   Related question  Inject an EJB into JAX-RS  RESTful service

User · Answer

If you have any NamedQueries in your entity classes  then check the stack trace for compilation errors   A malformed query which cannot be compiled can cause failure to load the persistence context

[java] PersistenceContext EntityManager injection NullPointerException

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