为什么EJB为null？

debugcn 发表于 Dev

Kohn Doew先生

我正在从事REST服务并同时学习EJB。我只是使用简单的链控制器->服务-> DAO运行我的应用程序，并且未注入我的EJB hotelService-它为null。

@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);
}
}

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

@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();
}

我以为，在HotelDAO实例化期间，该问题可能会出现一些错误，但是即使没有它，mt HotelService也为空。

您对哪里有问题有任何看法吗？

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-jackson</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>

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 javax.ws.rs.core.Application的Servlet.service（）在com.example.controller.HotelsController.getHotelsList（HotelsController.java）处引发了java.lang.NullPointerException异常。：29）位于sun.reflect.NativeMethodAccessorImpl.invoke0（本地方法）位于java.lang处sun.reflect.DelegatingMethodAccessorImpl.invoke（DelegatingMethodAccessorImpl.java:43）处sun.reflect.NativeMethodAccessorImpl.invoke（NativeMethodAccessorImpl.java:57）在org.glassfish.jersey.server.model.internal.ResourceMethodInvocationHandlerFactory $ 1.invoke（ResourceMethodInvocationHandlerFactory.java:81）处的reflect.Method.invoke（Method.java:606）在org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher处org.glassfish.jersey.server.model.internal上的.invoke（AbstractJavaResourceMethodDispatcher.java:125）。org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.dispatch（AbstractJavaResourceMethodDispatcher.java:91）上的JavaResourceMethodDispatcherProvider $ ResponseOutInvoker.doDispatch（JavaResourceMethodDispatcherProvider.java:152） org.org.glassfish.jersey.server.model.ResourceMethodInvoker.apply（ResourceMethodInvoker.java:341）org.org.glassfish.jersey.server.model.ResourceMethodInvoker.apply（ResourceMethodInvoker.java:101）位于org.glassfish.jersey.internal.Errors $ 1的.glassfish.jersey.server.ServerRuntime $ 1.run（ServerRuntime.java:224）位于org.glassfish.jersey.internal.Errors $ 1的call（Errors.java:271）。在org.glassfish.jersey.internal.Errors处调用（Errors.java:267）。org上org.glassfish.jersey.internal.Errors.process（Errors.java:267）的org.glassfish.jersey.process.internal.RequestScope.runInScope（RequestScope.java:317）的process（Errors.java:267）位于org.glassfish.jersey.server.ApplicationHandler.handle（ApplicationHandler.java:946）的.glassfish.jersey.server.ServerRuntime.process（ServerRuntime.java:198）在org.glassfish.jersey.servlet.WebComponent.service（WebComponent） org.glassfish.jersey.servlet.ServletContainer.service（ServletContainer.java:372）上的org.glassfish.jersey.servlet.Servlet.ServletContainer.service（ServletContainer.java:335）上的.java：323）。 org.apache.catalina.core.StandardWrapper.service（StandardWrapper.java:1682）上的servlet.ServletContainer.service（ServletContainer.java:218）org.apache.catalina.core.StandardWrapperValve.invoke（StandardWrapperValve.java:318）在org.apache.catalina。org.apache.catalina.core.StandardPipeline.doInvoke（StandardPipeline.java:734）的core.StandardContextValve.invoke（StandardContextValve.java:160）org.apache.catalina.core.StandardPipeline.invoke（StandardPipeline.java:673）的core.StandardContextValve.invoke（StandardContextValve.java:160）在com.sun.enterprise.web.WebPipeline.invoke（WebPipeline.java:99）在org.apache.catalina.core.StandardHostValve.invoke（StandardHostValve.java:174）在org.apache.catalina.connector.CoyoteAdapter.doService （CoyoteAdapter.java:357）位于org.apache.catalina.connector.CoyoteAdapter.service（CoyoteAdapter.java:260）位于com.sun.enterprise.v3.services.impl.ContainerMapper.service（ContainerMapper.java:188） org.glassfish.grizzly.http.org.glassfish.grizzly.http.server.HttpHandler.runService（HttpHandler.java:191）在org.glassfish.grizzly.http.server.HttpHandler.doHandle（HttpHandler.java:168） server.HttpServerFilter。在org.glassfish.grizzly.filterchain.ExecutorResolver $ 9.execute（ExecutorResolver.java:119）在org.glassfish.grizzly.filterchain.DefaultFilterChain.executeFilter（DefaultFilterChain.java:288）的handleRead（HttpServerFilter.java:189）在org.glassfish.grizzly.filterchain.ExecutorResolver $ 9.execute（ExecutorResolver.java:119）在org。在org.glassfish.grizzly.filterchain.DefaultFilterChain.execute（DefaultFilterChain.java:136）处的glassfish.grizzly.filterchain.DefaultFilterChain.executeChainPart（DefaultFilterChain.java:206）在org.glassfish.grizzly.filterchain.DefaultFilterChain.process（DefaultFilterChain。 org.glassfish.grizzly.ProcessorExecutor.execute（ProcessorExecutor.java:77）的org.glassfish.grizzly.nio.transport.TCPNIOTransport.fireIOEvent（TCPNIOTransport.java:838）的org.glassfish.grizzly.strategies org.glassfish.grizzly.strategies.WorkerThreadIOStrategy上的.AbstractIOStrategy.fireIOEvent（AbstractIOStrategy.java:113）。在org.glassfish.grizzly.strategies.WorkerThreadIOStrategy $ WorkerThreadRunnable.run（WorkerThreadIOStrategy。 org.glassfish.grizzly.threadpool.AbstractThreadPool $ Worker.run（AbstractThreadPool.java:544）上的org.glassfish.grizzly.threadpool.AbstractThreadPool $ Worker.doWork（AbstractThreadPool.java:564）在java.lang.Thread.run（ Thread.java:745）]]java.lang.Thread.run（Thread.java:745）上的threadpool.AbstractThreadPool $ Worker.run（AbstractThreadPool.java:544）]]]java.lang.Thread.run（Thread.java:745）上的threadpool.AbstractThreadPool $ Worker.run（AbstractThreadPool.java:544）]]]

您需要实现一个表示该EJB Bean本地视图的@Local批注接口，或者需要将@LocalBean批注添加到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 {
    // ...
}

如果希望该服务在容器外部可用以执行RMI或EJB客户端，则需要创建该服务的@Local和@Remote视图并同时实现两者。

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编辑于2021-06-7

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