CODEWITHSUNDEEP
ejbjava-ee-6dao
ChrisGeo
ChrisGeo

Reputation: 3907

EJB 3.1 Generic DAO

I am trying to implement a Generic DAO to use in my project. The code I have implemented thus far is the following:

Base DAO

public abstract class BaseDAO<T> {

    private Class<T> entityClass;

    public BaseDAO(Class<T> entityClass) {
        this.entityClass = entityClass;
    }

    protected abstract EntityManager getEntityManager();

    public T persist(T entity) {
        getEntityManager().persist(entity);
        return entity;
    }

    public T edit(T entity) {
        getEntityManager().merge(entity);
        return entity;
    }

    public T remove(T entity) {
        getEntityManager().remove(entity);
        return entity;
    }

    public List<T> findAll() {

    Query q = getEntityManager().createQuery("SELECT e FROM " + entityClass.getName()
                + " e");
        List<T> list = (List<T>) q.getResultList();
        return list;
    }

    public T find(Long id) {
        T e = getEntityManager().find(entityClass, id);
        return e;
    }

}

Extended DAO

@Stateless
public class CustomerDAO extends BaseDAO<Customer> {

    @PersistenceContext(unitName="customerPersistenceUnit")
    private EntityManager em;

    public CustomerDAO(Class<Customer> entityClass) {
            super(entityClass);
    }

    @Override
    protected EntityManager getEntityManager() {
        return em;
    }

}

The Controller Class

@ManagedBean
@RequestScoped
public class CustomerController {

    @EJB
    private CustomerDAO customerDAO;

    private Customer customer;
    private List<Customer> list;

    @PostConstruct
    public void init() {
        customer = new Customer();
        list = customerDAO.findAll();
    }

    public void saveCustomer(ActionEvent event) {

        customer = customerDAO.persist(this.customer);
        list = customerDAO.findAll();
    }

    public Customer getCustomer() {
        return customer;
    }

    public void setCustomer(Customer customer) {
        this.customer = customer;
    }

    public List<Customer> getList() {
        return list;
    }

    public void setList(List<Customer> list) {
        this.list = list;
    }

}

Everything seems to work perfectly when I use a Non-Generic DAO, however when I try out the Generic DAO I get the following exception:

SEVERE: EJB5070: Exception creating stateless session bean : [CustomerDAO]
WARNING: EJB5184:A system exception occurred during an invocation on EJB CustomerDAO, method: public java.util.List example.BaseDAO.findAll()
WARNING: javax.ejb.EJBException: javax.ejb.EJBException: javax.ejb.CreateException: Could not create stateless EJB
    at com.sun.ejb.containers.StatelessSessionContainer._getContext(StatelessSessionContainer.java:454)
    at com.sun.ejb.containers.BaseContainer.getContext(BaseContainer.java:2547)
    at com.sun.ejb.containers.BaseContainer.preInvoke(BaseContainer.java:1899)
    at com.sun.ejb.containers.EJBLocalObjectInvocationHandler.invoke(EJBLocalObjectInvocationHandler.java:212)
    at com.sun.ejb.containers.EJBLocalObjectInvocationHandlerDelegate.invoke(EJBLocalObjectInvocationHandlerDelegate.java:89)
    at $Proxy216.findAll(Unknown Source)
    at example.__EJB31_Generated__CustomerDAO__Intf____Bean__.findAll(Unknown Source)
    at example.CustomerController.init(CustomerController.java:27)
    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:601)
    at org.glassfish.faces.integration.GlassFishInjectionProvider$2.run(GlassFishInjectionProvider.java:382)
    at java.security.AccessController.doPrivileged(Native Method)
    at org.glassfish.faces.integration.GlassFishInjectionProvider.invokeLifecycleMethod(GlassFishInjectionProvider.java:376)
    at org.glassfish.faces.integration.GlassFishInjectionProvider.invokePostConstruct(GlassFishInjectionProvider.java:306)
    at org.glassfish.faces.integration.GlassFishInjectionProvider.invokePostConstruct(GlassFishInjectionProvider.java:229)
    at com.sun.faces.mgbean.BeanBuilder.invokePostConstruct(BeanBuilder.java:223)
    at com.sun.faces.mgbean.BeanBuilder.build(BeanBuilder.java:105)
    at com.sun.faces.mgbean.BeanManager.createAndPush(BeanManager.java:409)
    at com.sun.faces.mgbean.BeanManager.create(BeanManager.java:269)
    at com.sun.faces.el.ManagedBeanELResolver.resolveBean(ManagedBeanELResolver.java:244)
    at com.sun.faces.el.ManagedBeanELResolver.getValue(ManagedBeanELResolver.java:116)
    at com.sun.faces.el.DemuxCompositeELResolver._getValue(DemuxCompositeELResolver.java:176)
    at com.sun.faces.el.DemuxCompositeELResolver.getValue(DemuxCompositeELResolver.java:203)
    at com.sun.el.parser.AstIdentifier.getValue(AstIdentifier.java:103)
    at com.sun.el.parser.AstValue.getValue(AstValue.java:179)
    at com.sun.el.ValueExpressionImpl.getValue(ValueExpressionImpl.java:224)
    at com.sun.faces.facelets.el.TagValueExpression.getValue(TagValueExpression.java:109)
    at javax.faces.component.ComponentStateHelper.eval(ComponentStateHelper.java:194)
    at javax.faces.component.ComponentStateHelper.eval(ComponentStateHelper.java:182)
    at javax.faces.component.UISelectItems.getValue(UISelectItems.java:129)
    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:601)
    at com.sun.faces.facelets.util.DevTools.writeAttributes(DevTools.java:375)
    at com.sun.faces.facelets.util.DevTools.writeStart(DevTools.java:424)
    at com.sun.faces.facelets.util.DevTools.writeComponent(DevTools.java:245)
    at com.sun.faces.facelets.util.DevTools.writeComponent(DevTools.java:264)
    at com.sun.faces.facelets.util.DevTools.writeComponent(DevTools.java:264)
    at com.sun.faces.facelets.util.DevTools.writeComponent(DevTools.java:264)
    at com.sun.faces.facelets.util.DevTools.writeComponent(DevTools.java:264)
    at com.sun.faces.facelets.util.DevTools.writeComponent(DevTools.java:264)
    at com.sun.faces.facelets.util.DevTools.debugHtml(DevTools.java:128)
    at com.sun.faces.renderkit.RenderKitUtils.renderHtmlErrorPage(RenderKitUtils.java:1162)
    at com.sun.faces.context.ExceptionHandlerImpl.throwIt(ExceptionHandlerImpl.java:276)
    at com.sun.faces.context.ExceptionHandlerImpl.handle(ExceptionHandlerImpl.java:142)
    at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:119)
    at com.sun.faces.lifecycle.LifecycleImpl.render(LifecycleImpl.java:139)
    at javax.faces.webapp.FacesServlet.service(FacesServlet.java:594)
    at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1550)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:281)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
    at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:655)
    at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:595)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:161)
    at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:331)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:231)
    at com.sun.enterprise.v3.services.impl.ContainerMapper$AdapterCallable.call(ContainerMapper.java:317)
    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: javax.ejb.EJBException: javax.ejb.CreateException: Could not create stateless EJB
    at com.sun.ejb.containers.StatelessSessionContainer$SessionContextFactory.create(StatelessSessionContainer.java:726)
    at com.sun.ejb.containers.util.pool.NonBlockingPool.getObject(NonBlockingPool.java:247)
    at com.sun.ejb.containers.StatelessSessionContainer._getContext(StatelessSessionContainer.java:449)
    ... 74 more
Caused by: javax.ejb.CreateException: Could not create stateless EJB
    at com.sun.ejb.containers.StatelessSessionContainer.createStatelessEJB(StatelessSessionContainer.java:534)
    at com.sun.ejb.containers.StatelessSessionContainer.access$000(StatelessSessionContainer.java:95)
    at com.sun.ejb.containers.StatelessSessionContainer$SessionContextFactory.create(StatelessSessionContainer.java:724)
    ... 76 more
Caused by: java.lang.InstantiationException: example.CustomerDAO
    at java.lang.Class.newInstance0(Class.java:357)
    at java.lang.Class.newInstance(Class.java:325)
    at com.sun.ejb.containers.BaseContainer._constructEJBInstance(BaseContainer.java:1663)
    at com.sun.ejb.containers.BaseContainer.createEjbInstanceAndContext(BaseContainer.java:1646)
    at com.sun.ejb.containers.StatelessSessionContainer.createStatelessEJB(StatelessSessionContainer.java:475)
    ... 78 more

Upvotes: 4

Views: 6911

Answers (2)

perissf
perissf

Reputation: 16273

You need to provide a proper constructor of the super class when the child class is created with the no-arguments constructor (that is invoked behind the scenes during injection):

public CustomerDAO() {
    super(Customer.class);
}

Upvotes: 5

Rodmar Conde
Rodmar Conde

Reputation: 956

As your exception says your EJB couldn't be injected: 

@EJB
private CustomerDAO customerDAO;

This means that your CustomerDAO object has not been created. Where are you trying to create it for the first time?

Pasting the complete source of the stacktrace can give more clues.

Regards,

Upvotes: 2

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