@Injection is not working for CDI bean

问题

I have a CDI bean where I'm using @ConversationScoped. When I try to do an @Inject for the Conversation object, I get a NPE.

  @ConversationScoped
@Named("customerbean")
public class CustomerBean implements Serializable {

    @Inject
    private Conversation conversation;    

    private static final EntityManagerFactory emf = Persistence.createEntityManagerFactory("ba");
    private EntityManager em;
    private Customer customer;
    boolean disabled;    

    public CustomerBean() {
        beginConversation();
        customer = new Customer();
        em = emf.createEntityManager();
        disabled = false;
    }

    private void beginConversation() {
        if (this.conversation.isTransient()) {
            this.conversation.begin();
            return;
        }
        throw new IllegalStateException();
    }

I have the beans.xml file (although empty) in the WEB-INF directory. The exception looks like this:

INFO: Exception when handling error trying to reset the response.
com.google.common.collect.ComputationException: java.lang.RuntimeException: java
.lang.NullPointerException
        at com.google.common.collect.ComputingConcurrentHashMap$ComputingMapAdap
ter.get(ComputingConcurrentHashMap.java:397)
        at org.jboss.weld.bean.proxy.ClientProxyProvider.getClientProxy(ClientPr
oxyProvider.java:102)
        at org.jboss.weld.el.AbstractWeldELResolver.lookup(AbstractWeldELResolve
r.java:115)
        at org.jboss.weld.el.AbstractWeldELResolver.getValue(AbstractWeldELResol
ver.java:96)
        at org.jboss.weld.environment.servlet.util.ForwardingELResolver.getValue
(ForwardingELResolver.java:49)
        at javax.el.CompositeELResolver.getValue(CompositeELResolver.java:67)
        at com.sun.faces.el.DemuxCompositeELResolver._getValue(DemuxCompositeELR
esolver.java:176)

回答1:

You must not create a CDI bean using new, nor use a constructor for any sort of initialization logic.

The reason behind this is that CDI beans (like EJBs, Spring beans, JSF beans) have an independent lifecycle and are managed by the relevant container. You cannot rely on the "traditional" understanding of when (and how often) new will be called. Use producers to create new beans, and use @PostConstruct for any logic to be performed after creation.

This should give you a good start with CDI. Feel free to post further questions :)

回答2:

As Jan says, you're adding logic into the constructor. Injection doesn't happen until after the constructor is called.

来源：https://stackoverflow.com/questions/12368888/injection-is-not-working-for-cdi-bean

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java

jsf

cdi