如何解决PersistenceContext 和 EntityManager nullPointerException
我的应用程序中的 EntityManager 有问题。我用 @PersistenceContext 注释创建了 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 控制台上收到错误：
[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，我应该改变什么或忘记添加什么。
解决方法
您必须在 PersistenceContext-Annotation 中使用“unitName”而不是“name”。
并且您不需要 Resources 类，只需在您需要的任何地方注入 EntityManager。
@Entity
data class ArmyEntity(
@PrimaryKey(autoGenerate = true)
val armyId: Long,val userOwnerId: Long,val descriptionRes: Int = R.string.abc,// this is true for multi-languages
val iconUri: String = "",)
fun getDescription(context: Context,armyEntity : ArmyEntity,textView: TextView){
textView.text = context.getString(armyEntity.descriptionRes)
}
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