PersistenceContext 和 EntityManager nullPointerException

【问题标题】：PersistenceContext and EntityManager nullPointerExceptionPersistenceContext 和 EntityManager nullPointerException
【发布时间】：2021-07-22 19:33:03
【问题描述】：

我的应用程序中的 EntityManager 有问题。我使用 @PersistenceContext 注释创建 EntityManager。但是当我尝试通过我的 Dao 获取数据时，我遇到了错误。

这是我的文件：

persistence.xml

<persistence version="2.1"
  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">
  <persistence-unit name="primary" transaction-type="JTA">
    <provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>
    <jta-data-source>jdbc/app</jta-data-source>
    <properties>
      <property name="hibernate.dialect" value="org.hibernate.dialect.PostgreSQL10Dialect"/>
    </properties>
  </persistence-unit>
</persistence>

Resources.java

package com.app;

import javax.enterprise.context.ApplicationScoped;
import javax.enterprise.inject.Produces;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;

@ApplicationScoped
public class Resources {

  @Produces
  @PersistenceContext(name = "primary")
  private EntityManager entityManager;
}

然后我将 EntityManager 注入到我的 BaseDao 类中：

BaseDao.java

package com.app.dao;

import javax.inject.Inject;
import javax.persistence.EntityManager;

public abstract class BaseDao {

  @Inject
  protected EntityManager entityManager;
}

ClubDao.java

package com.app.dao;

import javax.enterprise.context.ApplicationScoped;
import javax.persistence.TypedQuery;

import com.app.entity.Club;

@ApplicationScoped

public class ClubDao extends BaseDao {

  public Club getClubById(long id) {
    String jpql = "FROM Club where id = :id";
    TypedQuery<Club> query = entityManager.createQuery(jpql, Club.class).setParameter("id", id);
    return query.getSingleResult();
  }
}

当我对这些数据使用端点时，我在 Glassfish 控制台上遇到错误：

[2021-07-22T21:31:13.951+0200] [Payara 4.1] [WARNING] [] [javax.enterprise.web] [tid: _ThreadID=39 _ThreadName=http-thread-pool::http-listener-1(5)] [timeMillis: 1626982273951] [levelValue: 900] [[
  StandardWrapperValve[com.app.AppConfig]: Servlet.service() for servlet com.app.AppConfig threw exception
java.lang.NullPointerException
    at org.jboss.weld.bean.builtin.ee.EEResourceProducerField.create(EEResourceProducerField.java:144)
    at org.jboss.weld.context.unbound.DependentContextImpl.get(DependentContextImpl.java:70)
    at org.jboss.weld.bean.ContextualInstanceStrategy$DefaultContextualInstanceStrategy.get(ContextualInstanceStrategy.java:100)
    at org.jboss.weld.bean.ContextualInstance.get(ContextualInstance.java:50)
    at org.jboss.weld.manager.BeanManagerImpl.getReference(BeanManagerImpl.java:758)
    at org.jboss.weld.manager.BeanManagerImpl.getInjectableReference(BeanManagerImpl.java:858)
    at org.jboss.weld.injection.FieldInjectionPoint.inject(FieldInjectionPoint.java:92)
    at org.jboss.weld.util.Beans.injectBoundFields(Beans.java:358)
    at org.jboss.weld.util.Beans.injectFieldsAndInitializers(Beans.java:369)
    at org.jboss.weld.injection.producer.ResourceInjector$1.proceed(ResourceInjector.java:70)
    at org.glassfish.weld.services.InjectionServicesImpl.aroundInject(InjectionServicesImpl.java:173)
    at org.jboss.weld.injection.InjectionContextImpl.run(InjectionContextImpl.java:46)
    at org.jboss.weld.injection.producer.ResourceInjector.inject(ResourceInjector.java:72)
    at org.jboss.weld.injection.producer.BasicInjectionTarget.inject(BasicInjectionTarget.java:117)
    at org.jboss.weld.bean.ManagedBean.create(ManagedBean.java:159)
    at org.jboss.weld.context.AbstractContext.get(AbstractContext.java:96)
    at org.jboss.weld.bean.ContextualInstanceStrategy$DefaultContextualInstanceStrategy.get(ContextualInstanceStrategy.java:100)
    at org.jboss.weld.bean.ContextualInstanceStrategy$ApplicationScopedContextualInstanceStrategy.get(ContextualInstanceStrategy.java:140)
    at org.jboss.weld.bean.ContextualInstance.get(ContextualInstance.java:50)
    at org.jboss.weld.bean.proxy.ContextBeanInstance.getInstance(ContextBeanInstance.java:99)
    at org.jboss.weld.bean.proxy.ProxyMethodHandler.getInstance(ProxyMethodHandler.java:125)
    at com.app.dao.ClubDao$Proxy$_$$_WeldClientProxy.getClubById(Unknown Source)
    at com.app.service.ClubService.getClub(ClubService.java:24)
    at com.app.service.ClubService$Proxy$_$$_WeldClientProxy.getClub(Unknown Source)
    at com.app.assembler.ClubAssembler.getClub(ClubAssembler.java:16)
    at com.app.assembler.ClubAssembler$Proxy$_$$_WeldClientProxy.getClub(Unknown Source)
    at com.app.controller.ClubApiController.getClub(ClubApiController.java:22)
    at com.app.controller.ClubApiController$Proxy$_$$_WeldClientProxy.getClub(Unknown Source)
    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:498)
    at org.glassfish.jersey.server.model.internal.ResourceMethodInvocationHandlerFactory$1.invoke(ResourceMethodInvocationHandlerFactory.java:81)
    at org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher$1.run(AbstractJavaResourceMethodDispatcher.java:144)
    at org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.invoke(AbstractJavaResourceMethodDispatcher.java:161)
    at org.glassfish.jersey.server.model.internal.JavaResourceMethodDispatcherProvider$ResponseOutInvoker.doDispatch(JavaResourceMethodDispatcherProvider.java:160)
    at org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.dispatch(AbstractJavaResourceMethodDispatcher.java:99)
    at org.glassfish.jersey.server.model.ResourceMethodInvoker.invoke(ResourceMethodInvoker.java:389)
    at org.glassfish.jersey.server.model.ResourceMethodInvoker.apply(ResourceMethodInvoker.java:347)
    at org.glassfish.jersey.server.model.ResourceMethodInvoker.apply(ResourceMethodInvoker.java:102)
    at org.glassfish.jersey.server.ServerRuntime$2.run(ServerRuntime.java:326)
    at org.glassfish.jersey.internal.Errors$1.call(Errors.java:271)
    at org.glassfish.jersey.internal.Errors$1.call(Errors.java:267)
    at org.glassfish.jersey.internal.Errors.process(Errors.java:315)
    at org.glassfish.jersey.internal.Errors.process(Errors.java:297)
    at org.glassfish.jersey.internal.Errors.process(Errors.java:267)
    at org.glassfish.jersey.process.internal.RequestScope.runInScope(RequestScope.java:317)
    at org.glassfish.jersey.server.ServerRuntime.process(ServerRuntime.java:305)
    at org.glassfish.jersey.server.ApplicationHandler.handle(ApplicationHandler.java:1154)
    at org.glassfish.jersey.servlet.WebComponent.serviceImpl(WebComponent.java:473)
    at org.glassfish.jersey.servlet.WebComponent.service(WebComponent.java:427)
    at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:388)
    at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:341)
    at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:228)
    at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1606)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:258)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:160)
    at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:654)
    at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:593)
    at com.sun.enterprise.web.WebPipeline.invoke(WebPipeline.java:99)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:155)
    at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:371)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:238)
    at com.sun.enterprise.v3.services.impl.ContainerMapper$HttpHandlerCallable.call(ContainerMapper.java:466)
    at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:169)
    at org.glassfish.grizzly.http.server.HttpHandler.runService(HttpHandler.java:206)
    at org.glassfish.grizzly.http.server.HttpHandler.doHandle(HttpHandler.java:180)
    at org.glassfish.grizzly.http.server.HttpServerFilter.handleRead(HttpServerFilter.java:235)
    at org.glassfish.grizzly.filterchain.ExecutorResolver$9.execute(ExecutorResolver.java:119)
    at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeFilter(DefaultFilterChain.java:284)
    at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeChainPart(DefaultFilterChain.java:201)
    at org.glassfish.grizzly.filterchain.DefaultFilterChain.execute(DefaultFilterChain.java:133)
    at org.glassfish.grizzly.filterchain.DefaultFilterChain.process(DefaultFilterChain.java:112)
    at org.glassfish.grizzly.ProcessorExecutor.execute(ProcessorExecutor.java:77)
    at org.glassfish.grizzly.nio.transport.TCPNIOTransport.fireIOEvent(TCPNIOTransport.java:539)
    at org.glassfish.grizzly.strategies.AbstractIOStrategy.fireIOEvent(AbstractIOStrategy.java:112)
    at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.run0(WorkerThreadIOStrategy.java:117)
    at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.access$100(WorkerThreadIOStrategy.java:56)
    at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy$WorkerThreadRunnable.run(WorkerThreadIOStrategy.java:137)
    at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:593)
    at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.run(AbstractThreadPool.java:573)
    at java.lang.Thread.run(Thread.java:748)
]]

我在这里和其他页面上阅读了一些主题，但没有任何帮助。请给我一些建议，我应该改变什么或者我忘记添加什么。

【问题讨论】：

    标签： java hibernate jta


    【解决方案1】：

    您必须在 PersistenceContext-Annotation 中使用“unitName”而不是“name”。
    而且您不需要 Resources 类，只需在您需要的任何地方注入 EntityManager。

    @PersistenceContext(unitName = "primary")
private EntityManager entityManager;

    【讨论】：

    • 这没有帮助。我用您在此处发布的建议更改了我的BaseDao 课程并删除了Resources 课程。现在我收到另一个错误 - 调试器进入ClubDao 中的getClubById 方法，但entityManager 为空。我还尝试将 entityManager 和 @PersistenceContext 放在 ClubDao 中 - 没有 BaseDao 并且结果相同。
    • 那我只能试着猜测了。我在您的persistence-xml 中认出了hibernate-provider。 Glassfish 通常使用 eclipse-link。你的 Pom 中有 hibernate-entitymangaer 的依赖吗？也许您可以从 persistence.xml 中删除提供程序和与休眠相关的属性。只是为了检查是否注入了Entitymanger。
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