Caused by: java.lang.NullPointerException in JBoss Wildfly a

Question

我尝试将我的实体管理器从JPAUtil.class简单地注入到我的DAO。 当我创建一个实例时，它可以工作，但是当尝试进行@Inject时，我得到一个空指针异常。也许是一件容易的事情，但我不明白。

坚持不懈.xml

<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_2_0.xsd"
version="2.0">
<persistence-unit name="jpa" transaction-type="JTA">
<provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>
<class>model.Client</class>
<properties>
<property name="hibernate.dialect" value="org.hibernate.dialect.PostgreSQL9Dialect" />
<property name="hibernate.connection.driver_class" value="org.postgresql.Driver" />
<property name="hibernate.connection.url" value="jdbc:postgresql://localhost:5432/prueba1" />
<property name="hibernate.connection.username" value="kevinsantiago" />
<property name="hibernate.connection.password" value="" />
<!--<property name="hibernate.show_sql" value="true"/>
<property name="hibernate.format_sql" value="true"/>
<property name="hibernate.flushMode" value="FLUSH_AUTO" />
<property name="hibernate.hbm2ddl.auto" value="update" />-->
</properties>
</persistence-unit>
</persistence>

类道

package dao;
import model.Client;
import model.JPAutil;
import javax.inject.Inject;
import javax.inject.Named;
import javax.persistence.EntityManager;
import javax.persistence.Query;
import java.util.List;
/**
* Diese Class ist die verbindung
* mit die Data base Erzeugen
*/
public class ClientDAO {
//HIER WORKS WOTHOUT PROBLEM
//EntityManager entity = JPAutil.getEntityManeger();
//HIER DOES NOT WORK
@Inject
@Named("Pruebe")
private EntityManager entity;
public void create(Client client) {
entity.getTransaction().begin();
entity.persist(client);
entity.getTransaction().commit();
}
public void update(Client client) {
entity.getTransaction().begin();
entity.merge(client);
entity.getTransaction().commit();
}
public List<Client> findall() {
Query q = entity.createQuery("SELECT c FROM Client c");
List<Client> listaC = q.getResultList();
return listaC;
}
public Client findbyId(int idc) {
Query q = entity.createQuery("SELECT c FROM Client c WHERE id=" + idc);
Client C  = (Client) q.getSingleResult();
return C;
}
public void remove(int id) {
Client c = new Client();
c = entity.find(Client.class, id);
entity.getTransaction().begin();
entity.remove(c);
entity.getTransaction().commit();
}
}

太平绅士

import javax.enterprise.inject.Produces;
import javax.inject.Named;
import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.Persistence;

/**
* Hier ist erzeugt die entitty manager,
* um in die Dao zu nutzen
*/
public class JPAutil{
private static final String PUName = "jpa";
private static EntityManagerFactory factory;
private static EntityManager em;
@Produces
@Named("Pruebe")
public static EntityManager getEntityManeger() {
if (factory == null) {
factory = Persistence.createEntityManagerFactory(PUName);
em = factory.createEntityManager();
}
return em;
}
public static EntityManagerFactory getEntityManegerFactory() {
if (factory == null) {
factory = Persistence.createEntityManagerFactory(PUName);
}
return factory;
}
public static void shutDown() {
if (factory != null) {
factory.close();
}
}

}

现在只想复制错误

Context Path:/JSFJPA_HelloWorld_war_exploded
Servlet Path:/index.xhtml
Path Info:null
Query String:null
Stack Trace:
javax.servlet.ServletException
at [e-mail]//javax.faces.webapp.FacesServlet.executeLifecyle(FacesServlet.java:725)
at [e-mail]//javax.faces.webapp.FacesServlet.service(FacesServlet.java:451)
at [e-mail]//io.undertow.servlet.handlers.ServletHandler.handleRequest(ServletHandler.java:74)
at [e-mail]//io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:129)
at io.opentracing.contrib.opentracing-jaxrs2//io.opentracing.contrib.jaxrs2.server.SpanFinishingFilter.doFilter(SpanFinishingFilter.java:52)
at [e-mail]//io.undertow.servlet.core.ManagedFilter.doFilter(ManagedFilter.java:61)
at [e-mail]//io.undertow.servlet.handlers.FilterHandler$FilterChainImpl.doFilter(FilterHandler.java:131)
at [e-mail]//io.undertow.servlet.handlers.FilterHandler.handleRequest(FilterHandler.java:84)
at [e-mail]//io.undertow.servlet.handlers.security.ServletSecurityRoleHandler.handleRequest(ServletSecurityRoleHandler.java:62)
at [e-mail]//io.undertow.servlet.handlers.ServletChain$1.handleRequest(ServletChain.java:68)
at [e-mail]//io.undertow.servlet.handlers.ServletDispatchingHandler.handleRequest(ServletDispatchingHandler.java:36)
at [e-mail]//org.wildfly.extension.undertow.security.SecurityContextAssociationHandler.handleRequest(SecurityContextAssociationHandler.java:78)
at [e-mail]//io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
at [e-mail]//io.undertow.servlet.handlers.RedirectDirHandler.handleRequest(RedirectDirHandler.java:68)
at [e-mail]//io.undertow.servlet.handlers.security.SSLInformationAssociationHandler.handleRequest(SSLInformationAssociationHandler.java:132)
at [e-mail]//io.undertow.servlet.handlers.security.ServletAuthenticationCallHandler.handleRequest(ServletAuthenticationCallHandler.java:57)
at [e-mail]//io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
at [e-mail]//io.undertow.security.handlers.AbstractConfidentialityHandler.handleRequest(AbstractConfidentialityHandler.java:46)
at [e-mail]//io.undertow.servlet.handlers.security.ServletConfidentialityConstraintHandler.handleRequest(ServletConfidentialityConstraintHandler.java:64)
at [e-mail]//io.undertow.security.handlers.AuthenticationMechanismsHandler.handleRequest(AuthenticationMechanismsHandler.java:60)
at [e-mail]//io.undertow.servlet.handlers.security.CachedAuthenticatedSessionHandler.handleRequest(CachedAuthenticatedSessionHandler.java:77)
at [e-mail]//io.undertow.security.handlers.NotificationReceiverHandler.handleRequest(NotificationReceiverHandler.java:50)
at [e-mail]//io.undertow.security.handlers.AbstractSecurityContextAssociationHandler.handleRequest(AbstractSecurityContextAssociationHandler.java:43)
at [e-mail]//io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
at [e-mail]//org.wildfly.extension.undertow.security.jacc.JACCContextIdHandler.handleRequest(JACCContextIdHandler.java:61)
at [e-mail]//io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
at [e-mail]//org.wildfly.extension.undertow.deployment.GlobalRequestControllerHandler.handleRequest(GlobalRequestControllerHandler.java:68)
at [e-mail]//io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43)
at [e-mail]//io.undertow.servlet.handlers.ServletInitialHandler.handleFirstRequest(ServletInitialHandler.java:269)
at [e-mail]//io.undertow.servlet.handlers.ServletInitialHandler.access$100(ServletInitialHandler.java:78)
at [e-mail]//io.undertow.servlet.handlers.ServletInitialHandler$2.call(ServletInitialHandler.java:133)
at [e-mail]//io.undertow.servlet.handlers.ServletInitialHandler$2.call(ServletInitialHandler.java:130)
at [e-mail]//io.undertow.servlet.core.ServletRequestContextThreadSetupAction$1.call(ServletRequestContextThreadSetupAction.java:48)
at [e-mail]//io.undertow.servlet.core.ContextClassLoaderSetupAction$1.call(ContextClassLoaderSetupAction.java:43)
at [e-mail]//org.wildfly.extension.undertow.security.SecurityContextThreadSetupAction.lambda$create$0(SecurityContextThreadSetupAction.java:105)
at [e-mail]//org.wildfly.extension.undertow.deployment.UndertowDeploymentInfoService$UndertowThreadSetupAction.lambda$create$0(UndertowDeploymentInfoService.java:1504)
at [e-mail]//org.wildfly.extension.undertow.deployment.UndertowDeploymentInfoService$UndertowThreadSetupAction.lambda$create$0(UndertowDeploymentInfoService.java:1504)
at [e-mail]//org.wildfly.extension.undertow.deployment.UndertowDeploymentInfoService$UndertowThreadSetupAction.lambda$create$0(UndertowDeploymentInfoService.java:1504)
at [e-mail]//org.wildfly.extension.undertow.deployment.UndertowDeploymentInfoService$UndertowThreadSetupAction.lambda$create$0(UndertowDeploymentInfoService.java:1504)
at [e-mail]//org.wildfly.extension.undertow.deployment.UndertowDeploymentInfoService$UndertowThreadSetupAction.lambda$create$0(UndertowDeploymentInfoService.java:1504)
at [e-mail]//io.undertow.servlet.handlers.ServletInitialHandler.dispatchRequest(ServletInitialHandler.java:249)
at [e-mail]//io.undertow.servlet.handlers.ServletInitialHandler.access$000(ServletInitialHandler.java:78)
at [e-mail]//io.undertow.servlet.handlers.ServletInitialHandler$1.handleRequest(ServletInitialHandler.java:99)
at [e-mail]//io.undertow.server.Connectors.executeRootHandler(Connectors.java:376)
at [e-mail]//io.undertow.server.HttpServerExchange$1.run(HttpServerExchange.java:830)
at [e-mail]//org.jboss.threads.ContextClassLoaderSavingRunnable.run(ContextClassLoaderSavingRunnable.java:35)
at [e-mail]//org.jboss.threads.EnhancedQueueExecutor.safeRun(EnhancedQueueExecutor.java:1982)
at [e-mail]//org.jboss.threads.EnhancedQueueExecutor$ThreadBody.doRunTask(EnhancedQueueExecutor.java:1486)
at [e-mail]//org.jboss.threads.EnhancedQueueExecutor$ThreadBody.run(EnhancedQueueExecutor.java:1377)
at java.base/java.lang.Thread.run(Thread.java:834)
Caused by: java.lang.NullPointerException
at deployment.JSFJPA_HelloWorld_war_exploded.war//dao.ClientDAO.findall(ClientDAO.java:43)
at deployment.JSFJPA_HelloWorld_war_exploded.war//controller.ClientBean.AllClients(ClientBean.java:41)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:566)
at [e-mail]//javax.el.ELUtil.invokeMethod(ELUtil.java:245)
at [e-mail]//javax.el.BeanELResolver.invoke(BeanELResolver.java:338)
at [e-mail]//javax.el.CompositeELResolver.invoke(CompositeELResolver.java:198)
at org.glassfish.jakarta.el@3.0.2//com.sun.el.parser.AstValue.getValue(AstValue.java:111)
at org.glassfish.jakarta.el@3.0.2//com.sun.el.parser.AstValue.getValue(AstValue.java:179)
at org.glassfish.jakarta.el@3.0.2//com.sun.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:202)
at [e-mail]//org.jboss.weld.module.web.el.WeldValueExpression.getValue(WeldValueExpression.java:50)
at [e-mail]//org.jboss.weld.module.web.el.WeldValueExpression.getValue(WeldValueExpression.java:50)
at [e-mail]04//com.sun.faces.facelets.el.TagValueExpression.getValue(TagValueExpression.java:73)
at [e-mail]//javax.faces.component.ComponentStateHelper.eval(ComponentStateHelper.java:170)
at [e-mail]//javax.faces.component.ComponentStateHelper.eval(ComponentStateHelper.java:157)
at [e-mail]//javax.faces.component.UIData.getValue(UIData.java:736)
at [e-mail]//javax.faces.component.UIData.getDataModel(UIData.java:1849)
at [e-mail]//javax.faces.component.UIData.setRowIndexWithoutRowStatePreserved(UIData.java:479)
at [e-mail]//javax.faces.component.UIData.setRowIndex(UIData.java:468)
at [e-mail]04//com.sun.faces.renderkit.html_basic.TableRenderer.encodeBegin(TableRenderer.java:57)
at [e-mail]//javax.faces.component.UIComponentBase.encodeBegin(UIComponentBase.java:540)
at [e-mail]//javax.faces.component.UIData.encodeBegin(UIData.java:1153)
at [e-mail]//javax.faces.component.UIComponent.encodeAll(UIComponent.java:1644)
at [e-mail]//javax.faces.component.UIComponent.encodeAll(UIComponent.java:1650)
at [e-mail]//javax.faces.component.UIComponent.encodeAll(UIComponent.java:1650)
at [e-mail]04//com.sun.faces.application.view.FaceletViewHandlingStrategy.renderView(FaceletViewHandlingStrategy.java:468)
at [e-mail]04//com.sun.faces.application.view.MultiViewHandler.renderView(MultiViewHandler.java:170)
at [e-mail]//javax.faces.application.ViewHandlerWrapper.renderView(ViewHandlerWrapper.java:132)
at [e-mail]//javax.faces.application.ViewHandlerWrapper.renderView(ViewHandlerWrapper.java:132)
at [e-mail]04//com.sun.faces.lifecycle.RenderResponsePhase.execute(RenderResponsePhase.java:102)
at [e-mail]04//com.sun.faces.lifecycle.Phase.doPhase(Phase.java:76)
at [e-mail]04//com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:199)
at [e-mail]//javax.faces.webapp.FacesServlet.executeLifecyle(FacesServlet.java:708)
... 49 more

如果您有建议或意见，阅读它将是一种乐趣，因为欢迎每个反馈。我刚刚开始学习这项技术。

Answer 1

首先，如果你想使用CDI，你可以避免静态工厂：

@PersistenceContext(unitName = "jpa")
private EntityManager em;
@Produces
public EntityManager getEntityManager(){
return em;
}

将 bean.xml 文件放在 WEB-INF 目录中：

<?xml version="1.0" encoding="UTF-8"?>
<beans xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/beans_1_0.xsd" 
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" >
</beans>

这是文档：

部署 Java EE 应用程序时，CDI 会在 Bean 归档文件中查找 bean。Bean 归档是包含 CDI 运行时可以管理和注入的 bean 的任何模块。有两种类型的 Bean 存档：显式 Bean 存档和隐式 Bean 存档。

显式 Bean 归档是包含 bean.xml 部署描述符的归档文件，该描述符可以是空文件、不包含版本号或包含版本 1.1(Bean 发现模式属性设置为 all(。

隐式 Bean 归档是一个归档文件，它包含一些用作用域类型批注的 bean，不包含 bean.xml 部署描述符，或者包含 bean-discovery-mode 属性设置为注释的 bean.xml 部署描述符。

在隐式归档中，CDI 只能管理和注入使用作用域类型注释的 bean。

现在您可以使用

@Inject
private EntityManager em;

编辑

对于 Web 应用程序，bean .xml部署描述符(如果存在(必须位于 WEB-INF 目录中。对于 EJB 模块或 JAR 文件，bean .xml部署描述符(如果存在(必须位于 META-INF 目录中。