Question

我正在尝试通过名为IUserDAO.java的接口注入dao-class。两个类实现了这个接口：UserDAO.java，它使用List来管理用户，UserDAOJPA.java，它使用实体管理器来管理数据库中的用户。

问题是，当我声明接口时，它返回null。当我直接拨打UserDAO时，它可以正常工作。

这是我服务类的代码：

@Named(value = "userService")
@Stateless
public class UserService{

    @Inject
    private IUserDAO userDAO; 
//apperantly null. If I declare UserDAO instead, it works

    public UserService() {
        initUsers();
    }

    public void create(User user) {
        userDAO.create(user);
    }

...

    userDAO.create(u1);
    userDAO.create(u2);
    userDAO.create(u3);
    userDAO.create(u4);

我的界面名为public interface IUserDAO。

UserDAO类如下所示：

@Alternative
@Stateless
public class UserDAO implements Serializable, IUserDAO {

    private List<User> users;

    public UserDAO() {
        users = new ArrayList();
    }

我的UserDAOJPA课程就是这样开始的：

@Stateless
@Alternative
public class UserDAOJPA implements IUserDAO, Serializable{

    @PersistenceContext
    private EntityManager em;

    public UserDAOJPA() {

    }

我让网站通过beans.xml文件决定使用哪个类。

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

       <alternatives>
           <class>dao.UserDAO</class>
       </alternatives>
</beans>

我做错了什么或者我错过了什么？错误消息如下：

SEVERE: Exception while invoking class org.glassfish.ejb.startup.EjbDeployer load method
java.lang.RuntimeException: EJB Container initialization error
    at org.glassfish.ejb.startup.EjbApplication.loadContainers(EjbApplication.java:242)
    at org.glassfish.ejb.startup.EjbDeployer.load(EjbDeployer.java:305)
    at org.glassfish.ejb.startup.EjbDeployer.load(EjbDeployer.java:108)
    at org.glassfish.internal.data.ModuleInfo.load(ModuleInfo.java:186)
    at org.glassfish.internal.data.ApplicationInfo.load(ApplicationInfo.java:264)
    at com.sun.enterprise.v3.server.ApplicationLifecycle.deploy(ApplicationLifecycle.java:460)
    at com.sun.enterprise.v3.server.ApplicationLifecycle.deploy(ApplicationLifecycle.java:240)
    at org.glassfish.deployment.admin.DeployCommand.execute(DeployCommand.java:389)
    at com.sun.enterprise.v3.admin.CommandRunnerImpl$1.execute(CommandRunnerImpl.java:348)
    at com.sun.enterprise.v3.admin.CommandRunnerImpl.doCommand(CommandRunnerImpl.java:363)
    at com.sun.enterprise.v3.admin.CommandRunnerImpl.doCommand(CommandRunnerImpl.java:1085)
    at com.sun.enterprise.v3.admin.CommandRunnerImpl.access$1200(CommandRunnerImpl.java:95)
    at com.sun.enterprise.v3.admin.CommandRunnerImpl$ExecutionContext.execute(CommandRunnerImpl.java:1291)
    at com.sun.enterprise.v3.admin.CommandRunnerImpl$ExecutionContext.execute(CommandRunnerImpl.java:1259)
    at com.sun.enterprise.v3.admin.AdminAdapter.doCommand(AdminAdapter.java:461)
    at com.sun.enterprise.v3.admin.AdminAdapter.service(AdminAdapter.java:212)
    at com.sun.grizzly.tcp.http11.GrizzlyAdapter.service(GrizzlyAdapter.java:179)
    at com.sun.enterprise.v3.server.HK2Dispatcher.dispath(HK2Dispatcher.java:117)
    at com.sun.enterprise.v3.services.impl.ContainerMapper$Hk2DispatcherCallable.call(ContainerMapper.java:354)
    at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:195)
    at com.sun.grizzly.http.ProcessorTask.invokeAdapter(ProcessorTask.java:860)
    at com.sun.grizzly.http.ProcessorTask.doProcess(ProcessorTask.java:757)
    at com.sun.grizzly.http.ProcessorTask.process(ProcessorTask.java:1056)
    at com.sun.grizzly.http.DefaultProtocolFilter.execute(DefaultProtocolFilter.java:229)
    at com.sun.grizzly.DefaultProtocolChain.executeProtocolFilter(DefaultProtocolChain.java:137)
    at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:104)
    at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:90)
    at com.sun.grizzly.http.HttpProtocolChain.execute(HttpProtocolChain.java:79)
    at com.sun.grizzly.ProtocolChainContextTask.doCall(ProtocolChainContextTask.java:54)
    at com.sun.grizzly.SelectionKeyContextTask.call(SelectionKeyContextTask.java:59)
    at com.sun.grizzly.ContextTask.run(ContextTask.java:71)
    at com.sun.grizzly.util.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:532)
    at com.sun.grizzly.util.AbstractThreadPool$Worker.run(AbstractThreadPool.java:513)
    at java.lang.Thread.run(Thread.java:722)
Caused by: java.lang.NullPointerException
    at service.userService.initUsers(userService.java:65)
    at service.userService.<init>(userService.java:21)
at service.__EJB31_Generated__KwetterService__Intf____Bean__.<init>(Unknown Source)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:525)
    at java.lang.Class.newInstance0(Class.java:372)
    at java.lang.Class.newInstance(Class.java:325)
    at com.sun.ejb.containers.BaseContainer.instantiateOptionalEJBLocalBusinessObjectImpl(BaseContainer.java:3887)
    at com.sun.ejb.containers.StatelessSessionContainer.initializeHome(StatelessSessionContainer.java:253)
    at com.sun.ejb.containers.ContainerFactoryImpl.createContainer(ContainerFactoryImpl.java:167)
    at org.glassfish.ejb.startup.EjbApplication.loadContainers(EjbApplication.java:230)
    ... 33 more

Answer 1

显然，上面的代码都是正确的。我清理了Glassfish服务器并小睡了，当我醒来再次启动它时，它几乎起作用了。

声明具有两个备用类的接口会给出null

1 个答案: