Dozer Singleton Startup Bean injetced as Null

问题

I have created an instatiator bean for Dozer (http://dozer.sourceforge.net/). But when I Inject this EJB it throws nullpointer exception.

Here is my Singleton Startup Bean for intialising Dozer

package com.unijunction.ordercloud.common.rest;

import javax.annotation.PostConstruct;
import javax.annotation.PreDestroy;
import javax.inject.Singleton;
import javax.ejb.Startup;

import org.dozer.DozerBeanMapper;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
@Startup
@Singleton
public class DozerInstantiator {

private DozerBeanMapper mapper;

private Logger log = LoggerFactory.getLogger(DozerInstantiator.class);

public enum States {
    BEFORESTARTED, STARTED, PAUSED, SHUTTINGDOWN
};

private States state;

//TODO: DozerIsntantiator is retunring null

@PostConstruct
public void initialize() throws Throwable {
    log.info("---------------Dozer  Starting Up-----------------");
    try{
        state = States.BEFORESTARTED;
        this.mapper = new DozerBeanMapper();

     } catch (Throwable e) {
            log.error("Cause: " + e.getCause());
            log.error("Message: " + e.getMessage());
            log.error("Class: " + e.getClass());
            log.error("StackTrace: " + e.getStackTrace());
            throw e;
        }

    state = States.STARTED;
    log.info("---------------Dozer  Started-----------------");
}


@PreDestroy
public void terminate() {
    state = States.SHUTTINGDOWN;
    // Perform termination
    log.info("---------------Dozer  Shuttingdown-----------------");
}

public States getState() {
    return this.state;
}

public void setState(States state) {
    this.state = state;
}

public DozerBeanMapper getMapper() {
    return this.mapper;
}
 }

The class it is being injected into is a generic class and looks like this:

public class DtoConverter<T1, T>  {

protected final Class<T> entityClass;

@EJB
DozerInstantiator dozerInstantiator;

//instance for dozer to convert beans
protected DozerBeanMapper mapper;

private Logger log = LoggerFactory.getLogger(DozerInstantiator.class);

public DtoConverter(){
    this.entityClass = null;
}

/**
 * Setup the class
 *
 */
public DtoConverter(Class<T> entityClass) {
    this.entityClass = entityClass;
    //TODO: only allow one instance of this to exist
    //https://ordercloud.atlassian.net/browse/API-80
    try{
        mapper = dozerInstantiator.getMapper(); //<--- This throws null pointer
    }catch(Exception e){
        mapper = new DozerBeanMapper();
    }
}

It throws a null pointer exception. I have tried using it as a Stateless and Statefull bean but the result remains the same.

Any help would be appreciated. This is JAVA EE running on JBOSS AEP 6.

回答1:

It turns out that the CDI spec does not allow a singleton to be injected into a generic type class. So I wrote a lazy initialization of a static final dozer instance.

I added the following two methods to the DozerInstantiator:

public static DozerBeanMapper getInstance(){
    return MapperHolder.instance;
}

private static class MapperHolder{
    static final DozerBeanMapper instance = new DozerBeanMapper(mappingList);
}

It is then called in the generic type class :

DozerInstantiator dozerInstantiator = new DozerInstantiator();

    try{
        mapper = dozerInstantiator.getInstance();
    }catch(Exception e){
        log.error("Failed to initialise singleton Dozer bean");
    }

回答2:

A singleton is included within Dozer API / this method should match your needs

Mapper getMapper() {
        return DozerBeanMapperSingletonWrapper.getInstance();
    }

If you want to turn it to CDI, see @Produce annotation specs.

来源：https://stackoverflow.com/questions/17596251/dozer-singleton-startup-bean-injetced-as-null

标签

java-ee

singleton

startup

dozer

jboss-eap-6