調用EJB方法時出現NullPointerException

我對JavaEE非常陌生。我在本網站和其他網站上查詢了很多關於使用EJB注入的NullPinterException的問題，但還沒有成功。我無法找到解決問題的方案。調用EJB方法時出現NullPointerException

我在Eclipse中使用JPA，JAX-RS和Glassfish Web Extensions構建了DynamicWebProject。這裏是我的項目的sctructure（web.xml文件是在GlassFish-web.xml文件下）：

Project Structure

我嘗試調用它部署到本地主機GlassFish服務器，並嘗試裝getEmployees web服務從我的數據庫（也在本地主機）獲取有關所有員工的信息。以下是我的GetEmployees類的代碼。

package bean; 

import javax.faces.bean.ApplicationScoped; 
import javax.faces.bean.ManagedBean; 
import javax.inject.Inject; 
import javax.ws.rs.GET; 
import javax.ws.rs.Path; 
import javax.ws.rs.Produces; 
import javax.ws.rs.core.Response; 

import com.google.gson.Gson; 

import ejb.EmployeeEJB; 

@ApplicationScoped 
@ManagedBean 
@Path("/getemployees") 
public class GetEmployees { 

    @Inject 
    EmployeeEJB employeeEJB; 

    @GET 
    @Produces("application/json; charset=utf-8") 
    public Response getAllEmployees() throws Exception { 
     Gson gson = new Gson(); 
     String jsonString = null; 
     try { 
      jsonString = gson.toJson(employeeEJB.getAll()); 
     } catch (Exception e) { 
      e.printStackTrace(); 
     } 
     return Response.status(200).entity(jsonString).build(); 
    } 
}

我創建的託管和會話bean。我從我的GetEmployees RESTful webservice類中創建了Managed bean。這是對的嗎？

EmployeeEJB是會話bean：

package ejb; 

import java.util.List; 

import javax.ejb.LocalBean; 
import javax.ejb.Stateless; 
import javax.persistence.EntityManager; 
import javax.persistence.PersistenceContext; 
import javax.persistence.Query; 

import entity.Employee; 

@LocalBean 
@Stateless 
public class EmployeeEJB { 

    @PersistenceContext 
    EntityManager em; 

    public void saveEmployee(Employee employee) { 
     em.merge(employee); 
    } 

    public void deleteEmployee(Employee employee) { 
     em.remove(employee); 
    } 

    public List<Employee> getAll() { 
     Query query = em.createQuery("SELECT emp FROM Employee emp", Employee.class); 
     List<Employee> emp = (List<Employee>) query.getResultList(); 
     return emp; 
    } 

}

這是我的persistence.xml文件。在Glassfish管理控制檯中創建JDBC連接池和JDBC資源。連接到數據庫是好的。

<?xml version="1.0" encoding="UTF-8"?> 
<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="FirstDynamicWebProject"> 
    <provider>org.eclipse.persistence.jpa.PersistenceProvider</provider> 
    <jta-data-source>jdbc/second_attempt_hibernate</jta-data-source> 
    <class>entity.Docstatus</class> 
    <class>entity.Doctype</class> 
    <class>entity.Document</class> 
    <class>entity.Employee</class> 
    <class>entity.Mailorder</class> 
    <class>entity.Mailorderstatus</class> 
    </persistence-unit> 
</persistence>

當我嘗試調用裝getEmployees類的employeeEJB.getAll（）方法NullPointerException異常發生：

2017-04-10T00:59:07.063+0500|Severe: java.lang.NullPointerException 
    at bean.GetEmployees.getAllEmployees(GetEmployees.java:28) 
    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 com.sun.jersey.spi.container.JavaMethodInvokerFactory$1.invoke(JavaMethodInvokerFactory.java:60) 
    at com.sun.jersey.server.impl.model.method.dispatch.AbstractResourceMethodDispatchProvider$TypeOutInvoker._dispatch(AbstractResourceMethodDispatchProvider.java:185) 
    at com.sun.jersey.server.impl.model.method.dispatch.ResourceJavaMethodDispatcher.dispatch(ResourceJavaMethodDispatcher.java:75) 
    at com.sun.jersey.server.impl.uri.rules.HttpMethodRule.accept(HttpMethodRule.java:302) 
    at com.sun.jersey.server.impl.uri.rules.ResourceClassRule.accept(ResourceClassRule.java:108) 
    at com.sun.jersey.server.impl.uri.rules.RightHandPathRule.accept(RightHandPathRule.java:147) 
    at com.sun.jersey.server.impl.uri.rules.RootResourceClassesRule.accept(RootResourceClassesRule.java:84) 
    at com.sun.jersey.server.impl.application.WebApplicationImpl._handleRequest(WebApplicationImpl.java:1542) 
    at com.sun.jersey.server.impl.application.WebApplicationImpl._handleRequest(WebApplicationImpl.java:1473) 
    at com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1419) 
    at com.sun.jersey.server.impl.application.WebApplicationImpl.handleRequest(WebApplicationImpl.java:1409) 
    at com.sun.jersey.spi.container.servlet.WebComponent.service(WebComponent.java:409) 
    at com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:558) 
    at com.sun.jersey.spi.container.servlet.ServletContainer.service(ServletContainer.java:733) 
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:790) 
    at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1682) 
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:318) 
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:160) 
    at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:734) 
    at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:673) 
    at com.sun.enterprise.web.WebPipeline.invoke(WebPipeline.java:99) 
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:174) 
    at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:416) 
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:283) 
    at com.sun.enterprise.v3.services.impl.ContainerMapper$HttpHandlerCallable.call(ContainerMapper.java:459) 
    at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:167) 
    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:283) 
    at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeChainPart(DefaultFilterChain.java:200) 
    at org.glassfish.grizzly.filterchain.DefaultFilterChain.execute(DefaultFilterChain.java:132) 
    at org.glassfish.grizzly.filterchain.DefaultFilterChain.process(DefaultFilterChain.java:111) 
    at org.glassfish.grizzly.ProcessorExecutor.execute(ProcessorExecutor.java:77) 
    at org.glassfish.grizzly.nio.transport.TCPNIOTransport.fireIOEvent(TCPNIOTransport.java:536) 
    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$Worker.doWork(AbstractThreadPool.java:591) 
    at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.run(AbstractThreadPool.java:571) 
    at java.lang.Thread.run(Thread.java:745)

我覺得EmployeeEJB的注入是不正確的，但有沒有想法如何贏得它。

來源

2017-04-09 Rinat

我想問題是你使用了錯誤的包@ApplicationScoped。我認爲你不需要那裏的@ManagedBean。

您正在使用：

import javax.faces.bean.ApplicationScoped;

嘗試以下操作：

import javax.enterprise.context.ApplicationScoped;

參見：

Why are there different bean management annotations

來源

2017-04-09 20:27:33 unwichtich

謝謝你的幫助，男人！我不認爲這會很容易！再次感謝！ – Rinat

歡迎您:) – unwichtich

我剛剛嘗試將項目的war文件部署到另一個Glassfish服務器，該服務器安裝在遠程主機上，並在server.log中獲得相同的異常。我能做什麼？我嘗試清理項目，再次構建，再次清理構建和部署，但沒有任何幫助。你有什麼想法嗎？ – Rinat

調用EJB方法時出現NullPointerException

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