Spring自动装配bean导致空指针

Question

I have a logger class that makes use of a service. Each time a new logger is created, I expect to have access to the singleton scoped logging service.

I autowire the logging service into the logger however, a null pointer exception is returned. I have tried a few solutions:

1. manually defining the bean in the application context,
2. Trying to get the logger to be spring managed but that just resulted in more issues.

I am trying to get this to work in my junit tests, and I do specify the context file to make use of a different application context. However even if kept identical it does not resolve the issue.

Please find code below:

The following is an excerpt from the application context.

<context:component-scan base-package="com.platform"/>
<bean id="asyncLoggingService" class="com.platform.services.AsyncLoggingServiceImplementation" scope="prototype"/>

The following is the Logger class.

package com.platform.utils;


import com.platform.services.AsyncLoggingService;
import org.joda.time.DateTime;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;

public class OurLogger
{

  private static Logger logger;

  @Autowired
  private AsyncLoggingervice asyncLoggingService;

  public OurLogger(Class Clazz)
  {
    logger = LoggerFactory.getLogger(Clazz);
  }


  public void trace(TraceableObject object, String message)
  { 
    //Do nothing yet
  }

}

I then make use of the Logger in another service in order to log whats going on. (The reason I am writing another logger is to make use of an RabbitMQ server) In the service I instantiate a new instance of the Logger and then use it accordingly.

@Service
public class AsyncAccountServiceImplementation implements AsyncAccountService
{
  private static final String GATEWAY_IP_BLOCK = "1";

  private static OurLogger logger = new      OurLogger(AsyncAccountServiceImplementation.class);

...
}

The null pointer occurs in the OurLogger when I try to call any method on the asyncLoggingService .

I then am trying to test the AsyncAccountService using JUnit. I make sure I add the different application context but it still seems to result in the null pointer exception.

If you need further information please let me know. I have seen ways to fix this but they don't seem to work so perhaps I have made a mistake somewhere or I am not understanding this all quite correctly.

Answer 1

When you create an object by new, autowire\\inject don't work...

See this link and this link for some workaround.

Anyway if you would inject a logger i suggest you this my answer to another topic.

Answer 2

Just want to add my 2 cents.

I once encountered the same issue when I was not quite used to the life in the IoC world . The @Autowired field of one of my beans is null at runtime.

The root cause is, instead of using the auto-created bean maintained by the Spring IoC container (whose @Autowired field is indeed properly injected), I am newing my own instance of that bean and using it. Of course this one's @Autowired field is null because Spring has no chance to inject it.

Answer 3

If you are using AspectJ you can use @Configurable :

@Configurable
public class OurLogger {
  ..
}

See: Using AspectJ to dependency inject domain objects with Spring

Answer 4

Within your application context you have to do reference your Logger :

<context:component-scan base-package="com.platform"/>
<bean id="asyncLoggingService" class="com.platform.services.AsyncLoggingServiceImplementation" scope="prototype"/>
<bean id="ourLogger" class="com.platform.utils.OurLogger"/>

Then you've to inject it into your service :

@Service
public class AsyncAccountServiceImplementation implements AsyncAccountService
{

 private static final String GATEWAY_IP_BLOCK = "1";

 @Autowired
 private OurLogger logger;

}

Answer 5

Use spring framework Unit test instead of JUnit test to inject your spring bean.

May be that will help you.