Java 为什么 EJB 为空？

Why EJB is null?

提问by Mr Kohn Doew

I'm working on rest service and learning EJB at the same time. I just run my application with simple chain controller -> service -> DAO and my EJB hotelService is not injected -- it is null.

我正在同时从事休息服务和学习 EJB。我只是使用简单的链控制器 -> 服务 -> DAO 运行我的应用程序，并且我的 EJB hotelService 没有被注入——它是空的。

@Path("/hotels")
public class HotelsController {

@EJB
private HotelService hotelService;


@GET
@Produces(MediaType.APPLICATION_JSON)
public Response getHotelsList(@QueryParam("startDate") String startDate,
                              @QueryParam("endDate") String endDate) {
    List<HotelsEntity> list = hotelService.getAll();
    return ResponseFactory.response(Response.Status.OK, list);
}
}

Service

服务

@Stateless
@EJB(beanInterface = HotelService.class, name = "HotelService")
public class HotelService {

@EJB
private HotelDAO hotelDAO;

public List<HotelsEntity> getAll() {
    return hotelDAO.getAll();
}

public Hotel getHotelById(final String id) {
    return hotelDAO.getHotelById(id);
}
}

DAO

道

@Stateless
public class HotelDAO {

@PersistenceContext(unitName = Constants.PERSISTENCE_UNIT)
private EntityManager em;

public List<HotelsEntity> getAll() {
    // TODO complete me
    CriteriaBuilder builder = em.getCriteriaBuilder();
    CriteriaQuery<HotelsEntity> criteria = builder.createQuery(HotelsEntity.class);
    Root<HotelsEntity> root = criteria.from(HotelsEntity.class);
    criteria.select(root);
    TypedQuery<HotelsEntity> resultQuery = em.createQuery(criteria);
    return resultQuery.getResultList();
}

I thought that issue may be in some eror during instatiation of HotelDAO but even without it mt HotelService is null.

我认为这个问题可能在 HotelDAO 的 instatiation 过程中出现了一些错误，但即使没有它，mt HotelService 也是空的。

Do you a have any opinion where is an issue can be?

你有什么意见可能出在哪里？

I use glassfish 4.0 My pom is:

我使用 glassfish 4.0 我的 pom 是：

  <modelVersion>4.0.0</modelVersion>
<groupId>HospitalityRestServer</groupId>
<artifactId>HospitalityRestServer</artifactId>
<packaging>war</packaging>

<version>1.0-SNAPSHOT</version>
<name>HospitalityRestServer Maven Webapp</name>
<url>http://maven.apache.org</url>

<dependencies>
    <dependency>
        <groupId>org.hibernate</groupId>
        <artifactId>hibernate-entitymanager</artifactId>
        <version>4.3.5.Final</version>
    </dependency>
    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>3.8.1</version>
        <scope>test</scope>
    </dependency>
    <dependency>
        <groupId>javax.ws.rs</groupId>
        <artifactId>javax.ws.rs-api</artifactId>
        <version>2.0</version>
    </dependency>
    <dependency>
        <groupId>org.glassfish.jersey.core</groupId>
        <artifactId>jersey-server</artifactId>
        <version>2.7</version>
    </dependency>
    <dependency>
        <groupId>org.glassfish.jersey.media</groupId>
        <artifactId>jersey-media-json-Hymanson</artifactId>
        <version>2.4</version>
    </dependency>
    <dependency>
        <groupId>org.apache.tomcat</groupId>
        <artifactId>annotations-api</artifactId>
        <version>6.0.29</version>
    </dependency>
    <dependency>
        <groupId>org.glassfish</groupId>
        <artifactId>javax.ejb</artifactId>
        <version>3.1</version>
    </dependency>
</dependencies>

Log:

日志：

[2014-04-28T17:58:05.828+0400] [glassfish 4.0] [WARNING] [] [javax.enterprise.web] 
tid: _ThreadID=22 _ThreadName=http-listener-1(4)] [timeMillis: 1398693485828] [levelValue: 900] [[

StandardWrapperValve[javax.ws.rs.core.Application]: Servlet.service() for servlet javax.ws.rs.core.Application threw exception java.lang.NullPointerException at com.example.controller.HotelsController.getHotelsList(HotelsController.java:29) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:606) at org.glassfish.jersey.server.model.internal.ResourceMethodInvocationHandlerFactory$1.invoke(ResourceMethodInvocationHandlerFactory.java:81) at org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.invoke(AbstractJavaResourceMethodDispatcher.java:125) at org.glassfish.jersey.server.model.internal.JavaResourceMethodDispatcherProvider$ResponseOutInvoker.doDispatch(JavaResourceMethodDispatcherProvider.java:152) at org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.dispatch(AbstractJavaResourceMethodDispatcher.java:91) at org.glassfish.jersey.server.model.ResourceMethodInvoker.invoke(ResourceMethodInvoker.java:346) at org.glassfish.jersey.server.model.ResourceMethodInvoker.apply(ResourceMethodInvoker.java:341) at org.glassfish.jersey.server.model.ResourceMethodInvoker.apply(ResourceMethodInvoker.java:101) at org.glassfish.jersey.server.ServerRuntime$1.run(ServerRuntime.java:224) 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:198) at org.glassfish.jersey.server.ApplicationHandler.handle(ApplicationHandler.java:946) at org.glassfish.jersey.servlet.WebComponent.service(WebComponent.java:323) at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:372) at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:335) at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:218) 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:357) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:260) at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:188) at org.glassfish.grizzly.http.server.HttpHandler.runService(HttpHandler.java:191) at org.glassfish.grizzly.http.server.HttpHandler.doHandle(HttpHandler.java:168) at org.glassfish.grizzly.http.server.HttpServerFilter.handleRead(HttpServerFilter.java:189) at org.glassfish.grizzly.filterchain.ExecutorResolver$9.execute(ExecutorResolver.java:119) at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeFilter(DefaultFilterChain.java:288) at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeChainPart(DefaultFilterChain.java:206) at org.glassfish.grizzly.filterchain.DefaultFilterChain.execute(DefaultFilterChain.java:136) at org.glassfish.grizzly.filterchain.DefaultFilterChain.process(DefaultFilterChain.java:114) at org.glassfish.grizzly.ProcessorExecutor.execute(ProcessorExecutor.java:77) at org.glassfish.grizzly.nio.transport.TCPNIOTransport.fireIOEvent(TCPNIOTransport.java:838) at org.glassfish.grizzly.strategies.AbstractIOStrategy.fireIOEvent(AbstractIOStrategy.java:113) at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.run0(WorkerThreadIOStrategy.java:115) at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.access$100(WorkerThreadIOStrategy.java:55) at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy$WorkerThreadRunnable.run(WorkerThreadIOStrategy.java:135) at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:564) at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.run(AbstractThreadPool.java:544) at java.lang.Thread.run(Thread.java:745) ]]

StandardWrapperValve[javax.ws.rs.core.Application]：servlet javax.ws.rs.core.Application 的 Servlet.service() 在 com.example.controller.HotelsController.getHotelsList(HotelsController.java) 抛出异常 java.lang.NullPointerException :29) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang. org.glassfish.jersey.server.model.internal.ResourceMethodInvocationHandlerFactory$1.invoke(ResourceMethodInvocationHandlerFactory.java:81) 处的reflect.Method.invoke(Method.java:606) org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher .invoke(AbstractJavaResourceMethodDispatcher.java:125) 在 org.glassfish。jersey.server.model.internal.JavaResourceMethodDispatcherProvider$ResponseOutInvoker.doDispatch(JavaResourceMethodDispatcherProvider.java:152) 在 org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.dispatch(AbstractJavaResourceMethodDispatcher.java:91) 在 org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.dispatch(AbstractJavaResourceMethodDispatcher.java:91) 在 org.glassfish. server.model.ResourceMethodInvoker.invoke(ResourceMethodInvoker.java:346) at org.glassfish.jersey.server.model.ResourceMethodInvoker.apply(ResourceMethodInvoker.java:341) at org.glassfish.jersey.server.model.ResourceMethodInvoker.apply( ResourceMethodInvoker.java:101) at org.glassfish.jersey.server.ServerRuntime$1.run(ServerRuntime.java:224) at org.glassfish.jersey.internal.Errors$1.call(Errors.java:271) at org.glassfish .jersey.internal.Errors$1.call(Errors.java:267) 在 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:198) at org.glassfish.jersey.server.ApplicationHandler.handle(ApplicationHandler) .java:946) 在 org.glassfish.jersey.servlet.WebComponent.service(WebComponent.java:323) 在 org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:372) 在 org.glassfish.jersey。 servlet.ServletContainer.service(ServletContainer.java:335) 在 org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:218) 在 org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1682) 在 org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:318) 在 org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:160) 在 org.apache.StandardPicore. .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:357) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter. java:260) 在 com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:188) 在 org.glassfish.grizzly.http.server.HttpHandler.runService(HttpHandler.java:191) 在 org.glassfish.grizzly.http.server.HttpHandler.doHandle(HttpHandler.java:168) 在 org.glassfish.grizzly.http.server.HttpServerFilter.handleRead(HttpServerFilter.java:189) 在 org.glassfish.grizzly .filterchain.ExecutorResolver$9.execute(ExecutorResolver.java:119) at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeFilter(DefaultFilterChain.java:288) at org.glassfish.grizzly.filterchain.DefaultFilterChain.executeChainPart(DefaultFilterChain.java: 206) 在 org.glassfish.grizzly.filterchain.DefaultFilterChain.execute(DefaultFilterChain.java:136) 在 org.glassfish.grizzly.filterchain.DefaultFilterChain.process(DefaultFilterChain.java:114) 在 org.glassfish.grizzly.ProcessorExecutor.execute (ProcessorExecutor.java:77) 在 org.glassfish.grizzly.nio.transport.TCPNIOTransport.fireIOEvent(TCPNIOTransport.java:838) 在 org.glassfish.grizzly.strategies.AbstractIOStrategy.fireIOEvent(AbstractIOStrategy.java:113) 在 org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.run0(WorkerThreadIOStrategy.java:115) 在 org.glassfish.grizzly.strategies.WorkerThreadIOStrategy .access$100(WorkerThreadIOStrategy.java:55) 在 org.glassfish.grizzly.strategies.WorkerThreadIOStrategy$WorkerThreadRunnable.run(WorkerThreadIOStrategy.java:135) 在 org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java: 564) 在 org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.run(AbstractThreadPool.java:544) 在 java.lang.Thread.run(Thread.java:745) ]]run0(WorkerThreadIOStrategy.java:115) at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.access$100(WorkerThreadIOStrategy.java:55) at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy$WorkerThreadRunnable.run(WorkerThreadIOStrategy.java:135) at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:564) 在 org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.run(AbstractThreadPool.java:544) 在 java.lang.Thread.run(线程.java:745)]]run0(WorkerThreadIOStrategy.java:115) at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy.access$100(WorkerThreadIOStrategy.java:55) at org.glassfish.grizzly.strategies.WorkerThreadIOStrategy$WorkerThreadRunnable.run(WorkerThreadIOStrategy.java:135) at org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:564) 在 org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.run(AbstractThreadPool.java:544) 在 java.lang.Thread.run(线程.java:745)]]java:564) 在 org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.run(AbstractThreadPool.java:544) 在 java.lang.Thread.run(Thread.java:745) ]]java:564) 在 org.glassfish.grizzly.threadpool.AbstractThreadPool$Worker.run(AbstractThreadPool.java:544) 在 java.lang.Thread.run(Thread.java:745) ]]

采纳答案by jgitter

You need to either implement a @Local annotated interface that expresses the local view of that EJB bean, or you need to add the @LocalBean annotation to the HotelService class itself to explicitly state that it is a local no-interface view of that EJB.

您需要实现一个@Local 注释接口来表达该EJB bean 的本地视图，或者您需要将@LocalBean 注释添加到HotelService 类本身以明确声明它是该EJB 的本地无接口视图。

@Stateless
@EJB(beanInterface = HotelService.class, name = "HotelService")
@LocalBean
public class HotelService {
    // ...
}

If you want the service to be available outside of the container for RMI or EJB client execution, you'll need to create a @Local and @Remote view of that service and implement both.

如果您希望该服务在 RMI 或 EJB 客户端执行的容器之外可用，则需要创建该服务的 @Local 和 @Remote 视图并实现两者。