PersistenceContext EntityManager injection NullPointerException
Solution 1
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)
Solution 2
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.
Comments
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rich almost 2 years
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:
<?xml version="1.0" encoding="UTF-8"?> <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"> <persistence-unit name="test"> <provider>org.hibernate.ejb.HibernatePersistence</provider> <jta-data-source>java:/TestDS</jta-data-source> <properties> <property name="hibernate.dialect" value="org.hibernate.dialect.PostgreSQLDialect"/> <property name="hibernate.hbm2ddl.auto" value="update" /> <property name="hibernate.show_sql" value="true" /> </properties> </persistence-unit> </persistence>
web.xml:
<!DOCTYPE web-app PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN" "http://java.sun.com/dtd/web-app_2_3.dtd" > <web-app> <display-name>Test Web Application</display-name> <context-param> <param-name>resteasy.scan</param-name> <param-value>true</param-value> </context-param> <listener> <listener-class>org.jboss.resteasy.plugins.server.servlet.ResteasyBootstrap</listener-class> </listener> <servlet> <servlet-name>Resteasy</servlet-name> <servlet-class>org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher</servlet-class> </servlet> <servlet-mapping> <servlet-name>Resteasy</servlet-name> <url-pattern>/service/*</url-pattern> </servlet-mapping> <resource-ref> <res-ref-name>TestDS</res-ref-name> <res-type>javax.sql.DataSource</res-type> <res-auth>Container</res-auth> <res-sharing-scope>Shareable</res-sharing-scope> </resource-ref> </web-app>
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.
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rich over 13 yearsGuess there's problems with posting XML in code sections?!
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adrianboimvaser over 13 yearsYou would have to escape < and > ->< and >
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BalusC over 13 yearsI've never tried it in practice, so don't pin me on it, but is it really possible to run JPA on a webapp which is been declared to run as Servlet 2.3 (J2EE 1.3) instead of Servlet 2.5 (Java EE 5, when JPA was introduced for first time)?
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rich over 13 yearsWorth a try and wanted doing anyway, but updating to a 2.5 declaration didn't change the behaviour.
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rich over 13 yearsThanks, similar problem though in that I get an NPE on this line:<pre><code> EntityManager entityManager = entityManagerFactory.createEntityManager(); </code></pre>
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Kode Charlie almost 11 yearsThanks, this worked for me! I'm using CXF 2.7.5, Hibernate 4.x, Spring 3.x, and JPA 2.x.
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user1503117 almost 10 yearsPlease lemme know why I am not able to inject an entity manager in Stateless beans @PersistenceContext(unitName = "Tester2PU") private EntityManager em; in tomcat 7.0.27 is null. thanks senthil
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Evan Hu over 9 years@user1503117 hi, tomcat is not a EJB container. Please try TomEE or GlassFish or JBoss AS.
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Mike Argyriou almost 9 years@Andre: "An entity manager can only be injected in classes running inside a transaction". I don't think this is absolutely correct. You can inject an EXTENDED entity manager and use it in an non-transactional method and then call a transactional method and join the transaction (automatically or by calling EntityManager@joinTransaction()).
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Jin Kwon almost 8 yearsIs this still true?