How to get a EntityManager in a POJO?

Question

I am currently refactoring old legacy code and replace or remove all EJB 2.0 references with EJB 3.0 / 3.1. I have come across a utility class which provides the current Date (java.util.Date) or Timestamp (java.sql.Timestamp) of our Oracle Database (11g / 12c). The access to the database is implemented via a java.sql.Connection which is obtained through a lookup on a javax.naming.InitialContext.

I want to resolve this over JPA or Hibernate and use the new Java Date/Time API. So I rewrote the utility class, but I am unable to get a valid javax.persistence.EntityManager instance.

The utility class is packaged together with other existing stateless session and entity beans in an server.jar which is contained inside an ear. The persistence unit "seller-em" already exists and is used by session and entity beans. When I try to call the function getEm() I get a java.lang.NullPointerException when emf.createEntitymanager is executed.

I also tried to let Wildfly (8.2.1 Final) inject the entity manager with:

@PersistenceContext(unitName = "seller-em")
private EntityManager em;

But then em is null.

I have already spent a day with looking for hints on google and here. Any ideas where I went wrong or can anyone give me a hint into the right direction?

Best regards,
CB

Environment:
Java 8 (1.8.0_77)
Eclipse Mars R2 (4.5.2)
Maven 3.3.3
(JBoss) Wildfly 8.2.1 Final

Attachment:

package org.example.server.seller.tools;

import java.sql.Timestamp;
import java.time.Instant;
import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.LocalTime;
import java.time.ZoneId;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;
import javax.persistence.Query;

public class DateUtility {
    private static final String ORACLE_ISO_8601_FORMAT_STRING = "YYYY-MM-DD\"T\"HH:MI:SS.FF6TZH:TZM";
    // 12/31/2999 00:00:00.000000 +01:00 (ECT / European Central Time / TZ:Europe/Berlin)
    // Using Z time, because +01:00, ECT, ECT, UTC+1, etc. results in a java.time.format.DateTimeParseException.
    private static final Instant MAXIMUM_DATE_TIME = Instant.parse("2999-12-30T23:00:00.000000Z");
    private static final Object TREE_LOCK = new Object();

    private static EntityManager getEm() {
        EntityManagerFactory emf = Persistence.createEntityManagerFactory("seller-em");
        return emf.createEntityManager();
    }

    public static Instant getDatabaseSystemTimestamp() {
        // EntityManager is not thread-safe, we need to synchronie it.
        synchronized (TREE_LOCK) {
            Query query = getEm().createNativeQuery("SELECT TO_CHAR( SYSTIMESTAMP, :formatString) FROM DUAL");
            query.setParameter("formatString", ORACLE_ISO_8601_FORMAT_STRING);
            String iso8601String = (String) query.getSingleResult();
            return Instant.parse(iso8601String);
        }
    }

    public static Instant getMaximumDateTime() {
        return MAXIMUM_DATE_TIME;
    }

    public static LocalDateTime getCurrentDateTime() {
        return LocalDateTime.ofInstant(getDatabaseSystemTimestamp(), ZoneId.of("Europe/Berlin"));
    }

    public static LocalDate getCurrentDate() {
        return getCurrentDateTime().toLocalDate();
    }

    public static LocalTime getCurrentTime() {
        return getCurrentDateTime().toLocalTime();
    }

    /*
     * Just for backwards compatibility. Opted for java.sql.Timestamp since it is an extension of java.util.Date and
     * therefore can also be used a Date.
     */
    @Deprecated
    public static Timestamp getCurrentDateTimeAsTimestamp() {
        return Timestamp.from(getDatabaseSystemTimestamp());
    }
}

And the stacktrace:

java.lang.NullPointerException
    at org.hibernate.engine.transaction.internal.jta.JtaStatusHelper.getStatus(JtaStatusHelper.java:76)
    at org.hibernate.engine.transaction.internal.jta.JtaStatusHelper.isActive(JtaStatusHelper.java:118)
    at org.hibernate.engine.transaction.internal.jta.CMTTransaction.join(CMTTransaction.java:149)
    at org.hibernate.jpa.spi.AbstractEntityManagerImpl.joinTransaction(AbstractEntityManagerImpl.java:1602)
    at org.hibernate.jpa.spi.AbstractEntityManagerImpl.postInit(AbstractEntityManagerImpl.java:210)
    at org.hibernate.jpa.internal.EntityManagerImpl.<init>(EntityManagerImpl.java:91)
    at org.hibernate.jpa.internal.EntityManagerFactoryImpl.internalCreateEntityManager(EntityManagerFactoryImpl.java:345)
    at org.hibernate.jpa.internal.EntityManagerFactoryImpl.createEntityManager(EntityManagerFactoryImpl.java:313)
    at org.example.server.seller.tools.DateUtility.getEm(DateUtility.java:26)
    at org.example.server.seller.tools.DateUtility.getDatabaseSystemTimestamp(DateUtility.java:32)
    at org.example.server.seller.tools.DateUtilityTest.testDateUtility(DateUtilityTest.java:94)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:47)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:44)
    at org.jboss.arquillian.junit.Arquillian$6$1.invoke(Arquillian.java:270)
    at org.jboss.arquillian.container.test.impl.execution.LocalTestExecuter.execute(LocalTestExecuter.java:60)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at org.jboss.arquillian.core.impl.ObserverImpl.invoke(ObserverImpl.java:94)
    at org.jboss.arquillian.core.impl.EventContextImpl.invokeObservers(EventContextImpl.java:99)
    at org.jboss.arquillian.core.impl.EventContextImpl.proceed(EventContextImpl.java:81)
    at org.jboss.arquillian.core.impl.ManagerImpl.fire(ManagerImpl.java:135)
    at org.jboss.arquillian.core.impl.ManagerImpl.fire(ManagerImpl.java:115)
    at org.jboss.arquillian.core.impl.EventImpl.fire(EventImpl.java:67)
    at org.jboss.arquillian.container.test.impl.execution.ContainerTestExecuter.execute(ContainerTestExecuter.java:38)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at org.jboss.arquillian.core.impl.ObserverImpl.invoke(ObserverImpl.java:94)
    at org.jboss.arquillian.core.impl.EventContextImpl.invokeObservers(EventContextImpl.java:99)
    at org.jboss.arquillian.core.impl.EventContextImpl.proceed(EventContextImpl.java:81)
    at org.jboss.arquillian.test.impl.TestContextHandler.createTestContext(TestContextHandler.java:102)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at org.jboss.arquillian.core.impl.ObserverImpl.invoke(ObserverImpl.java:94)
    at org.jboss.arquillian.core.impl.EventContextImpl.proceed(EventContextImpl.java:88)
    at org.jboss.arquillian.test.impl.TestContextHandler.createClassContext(TestContextHandler.java:84)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at org.jboss.arquillian.core.impl.ObserverImpl.invoke(ObserverImpl.java:94)
    at org.jboss.arquillian.core.impl.EventContextImpl.proceed(EventContextImpl.java:88)
    at org.jboss.arquillian.test.impl.TestContextHandler.createSuiteContext(TestContextHandler.java:65)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at org.jboss.arquillian.core.impl.ObserverImpl.invoke(ObserverImpl.java:94)
    at org.jboss.arquillian.core.impl.EventContextImpl.proceed(EventContextImpl.java:88)
    at org.jboss.arquillian.core.impl.ManagerImpl.fire(ManagerImpl.java:135)
    at org.jboss.arquillian.test.impl.EventTestRunnerAdaptor.test(EventTestRunnerAdaptor.java:111)
    at org.jboss.arquillian.junit.Arquillian$6.evaluate(Arquillian.java:263)
    at org.jboss.arquillian.junit.Arquillian$4.evaluate(Arquillian.java:226)
    at org.jboss.arquillian.junit.Arquillian.multiExecute(Arquillian.java:314)
    at org.jboss.arquillian.junit.Arquillian.access$100(Arquillian.java:46)
    at org.jboss.arquillian.junit.Arquillian$5.evaluate(Arquillian.java:240)
    at org.junit.runners.ParentRunner.runLeaf(ParentRunner.java:271)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:70)
    at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:50)
    at org.junit.runners.ParentRunner$3.run(ParentRunner.java:238)
    at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:63)
    at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:236)
    at org.junit.runners.ParentRunner.access$000(ParentRunner.java:53)
    at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:229)
    at org.jboss.arquillian.junit.Arquillian$2.evaluate(Arquillian.java:185)
    at org.jboss.arquillian.junit.Arquillian.multiExecute(Arquillian.java:314)
    at org.jboss.arquillian.junit.Arquillian.access$100(Arquillian.java:46)
    at org.jboss.arquillian.junit.Arquillian$3.evaluate(Arquillian.java:199)
    at org.junit.runners.ParentRunner.run(ParentRunner.java:309)
    at org.jboss.arquillian.junit.Arquillian.run(Arquillian.java:147)
    at org.junit.runner.JUnitCore.run(JUnitCore.java:160)
    at org.junit.runner.JUnitCore.run(JUnitCore.java:138)
    at org.jboss.arquillian.junit.container.JUnitTestRunner.execute(JUnitTestRunner.java:65)
    at org.jboss.arquillian.protocol.servlet.runner.ServletTestRunner.executeTest(ServletTestRunner.java:160)
    at org.jboss.arquillian.protocol.servlet.runner.ServletTestRunner.execute(ServletTestRunner.java:126)
    at org.jboss.arquillian.protocol.servlet.runner.ServletTestRunner.doGet(ServletTestRunner.java:90)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:687)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:790)
    at io.undertow.servlet.handlers.ServletHandler.handleRequest(ServletHandler.java:86)
    at io.undertow.servlet.handlers.security.ServletSecurityRoleHandler.handleRequest(ServletSecurityRoleHandler.java:62)
    at io.undertow.servlet.handlers.ServletDispatchingHandler.handleRequest(ServletDispatchingHandler.java:36)
    at org.wildfly.extension.undertow.security.SecurityContextAssociationHandler.handleRequest(SecurityContextAssociationHandler.java:78)
    at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
    at io.undertow.servlet.handlers.security.SSLInformationAssociationHandler.handleRequest(SSLInformationAssociationHandler.java:131)
    at io.undertow.servlet.handlers.security.ServletAuthenticationCallHandler.handleRequest(ServletAuthenticationCallHandler.java:57)
    at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
    at io.undertow.security.handlers.AbstractConfidentialityHandler.handleRequest(AbstractConfidentialityHandler.java:46)
    at io.undertow.servlet.handlers.security.ServletConfidentialityConstraintHandler.handleRequest(ServletConfidentialityConstraintHandler.java:64)
    at io.undertow.security.handlers.AuthenticationMechanismsHandler.handleRequest(AuthenticationMechanismsHandler.java:58)
    at io.undertow.servlet.handlers.security.CachedAuthenticatedSessionHandler.handleRequest(CachedAuthenticatedSessionHandler.java:70)
    at io.undertow.security.handlers.SecurityInitialHandler.handleRequest(SecurityInitialHandler.java:76)
    at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
    at org.wildfly.extension.undertow.security.jacc.JACCContextIdHandler.handleRequest(JACCContextIdHandler.java:61)
    at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
    at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
    at io.undertow.servlet.handlers.ServletInitialHandler.handleFirstRequest(ServletInitialHandler.java:261)
    at io.undertow.servlet.handlers.ServletInitialHandler.dispatchRequest(ServletInitialHandler.java:248)
    at io.undertow.servlet.handlers.ServletInitialHandler.access$000(ServletInitialHandler.java:77)
    at io.undertow.servlet.handlers.ServletInitialHandler$1.handleRequest(ServletInitialHandler.java:167)
    at io.undertow.server.Connectors.executeRootHandler(Connectors.java:199)
    at io.undertow.server.HttpServerExchange$1.run(HttpServerExchange.java:761)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at java.lang.Thread.run(Thread.java:745)

persistence.xml:

<?xml version="1.0" encoding="UTF-8"?>
<persistence xmlns="http://xmlns.jcp.org/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
             xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence http://xmlns.jcp.org/xml/ns/persistence/persistence_2_1.xsd"
             version="2.1">

    <persistence-unit name="seller-em">
        <provider>org.hibernate.ejb.HibernatePersistence</provider>
        <jta-data-source>java:/DBUNIT</jta-data-source>
        <properties>
            <property name="hibernate.show_sql" value="true" />
            <property name="hibernate.dialect" value="org.hibernate.dialect.Oracle10gDialect" />
        </properties>
    </persistence-unit>

</persistence>

If you get some NPE then would have expected it to be the FIRST thing to be posted along with the stack trace and a statement of what object is null! — Neil Stockton, Apr 13 '16 at 17:13
Hello Neil Stockton, thank you for your reply. To add a stacktrace would be common sense, i just forgot to add it. Sorry. I have edited my original post and appended the stacktrace. — Crazy Bytes, Apr 14 '16 at 07:10
since it is having a problem with transactions (JTA) then post your persistence.xml and check what datasource you are providing — Neil Stockton, Apr 14 '16 at 07:26
I appended the persistence.xml. But it shouldn't be a problem, because existing beans are already using this persistence unit and the configured datasource for it. I doubled checked the standalone.xml of my Wildfly server. Everything looks like it is meant to be. — Crazy Bytes, Apr 14 '16 at 08:16

score 0 · Accepted Answer · edited Jun 20 '20 at 09:12

I found a solution by myself. After posting the stacktrace I looked up the NPE on the class JtaStatusHelper and landed a hit here on stackoverflow. in this thread I found the decisive hint.

I added the following line to my persistence.xml and it worked:

<property name="hibernate.transaction.jta.platform" value="org.hibernate.service.jta.platform.internal.JBossAppServerJtaPlatform" />

Thanks for your help.
Best rehards,
CB

How to get a EntityManager in a POJO?

1 Answers1