@Autowired return null after adding Spring AOP

Question

I have spring boot project, that is working very fine. But when i add the spring AOP it causes nullpointer when i used the @Autowired variable.

Here is my code for the AOP .

    @Autowired
    private Service service;
    
    private final org.apache.commons.logging.Log log = LogFactory.getLog(this.getClass());
    
    @Around("execution(* com.kpi.ninja..*.*(..))")
    public Object logTimeMethod(ProceedingJoinPoint joinPoint) throws Throwable {
            StopWatch stopWatch = new StopWatch();
            stopWatch.start();
            System.out.println("Entering in Method :  " + joinPoint.getSignature().getName());
            System.out.println("Class Name :  " + joinPoint.getSignature().getDeclaringTypeName());
            System.out.println("Target class : " + joinPoint.getTarget().getClass().getName());
            Object retVal = joinPoint.proceed();

            stopWatch.stop();
            
            
            StringBuffer logMessage = new StringBuffer();
            logMessage.append(joinPoint.getTarget().getClass().getName());
            logMessage.append(".");
            logMessage.append(joinPoint.getSignature().getName());
            logMessage.append("(");
            // append args
            Object[] args = joinPoint.getArgs();
            for (int i = 0; i < args.length; i++) {
                logMessage.append(args[i]).append(",");
            }
            if (args.length > 0) {
                logMessage.deleteCharAt(logMessage.length() - 1);
            }

            logMessage.append(")");
            logMessage.append(" execution time: ");
            logMessage.append(stopWatch.getTotalTimeMillis());
            logMessage.append(" ms");
            log.info(logMessage.toString());
            
            return retVal;
    }

Answer 1

You're advising all of your methods: @Around("execution(* com.kpi.ninja..*.*(..))")

So I guess Spring AOP excludes your MyAspect class to avoid infinite recursion.

Try to narrow down the @Around poincut to a single method first to see if it works.

After that use Point cut annotation to exclude your logTimeMethod from being advised.

Answer 2

Please Make sure that the class in which you are using the @Autowired is annotated with @Component/@Service/@Bean.The code you have posted does not include the initial class definition nor the spring XML so am not sure you have added the annotation in it or not.

@Component or @Controller or @Bean or @Service/@Repository 
Class ACB{

@Autowired
private Service service;

.....

}

Autowiring happens by placing an instance of one bean into the desired field in an instance of another bean. Both classes should be beans, i.e. they should be defined to live in the application context.

Answer 3

This happens when you @Autowired a private variable. Because AOP is not able to delegate a private variable, the variable becomes null in the AOP delegate class. To avoid this, you can create and use a getter for the private, autowired variable in your class instead of using the private variable directly.

See this example:

@Autowired
private SomeClass someClass;

Instead of using someClass.doSomething(), you should create a getter and use getSomeClass().doSomething().

Answer 4

You are having nullpointer because spring cannot initialize the Service class, you need to add the service in spring context xml, so declare a new bean:

<bean id="service" class="[package].Service"></bean>

If you don't have the context, you should create one and add the annotation in class declaration to set the path location of context.xml:

   @ContextConfiguration(locations = { "classpath:/context.xml" })
   public class YourClass{
       @Autowired
       Service service

      ...methods
   }

Answer 5

[https://stackoverflow.com/questions/828747/why-does-springs-configurable-sometimes-work-and-sometimes-not/63498314#63498314]:here is the answer

I found the reason. Because custom beans regist without order. If your bean be used before the Spring bean "org.springframework.context.config.internalBeanConfigurerAspect" was loaded,then @Configurable autowire will not work. And my solution is like below:

@Configuration
@EnableTransactionManagement(mode = AdviceMode.ASPECTJ)
@EnableLoadTimeWeaving(aspectjWeaving = AspectJWeaving.ENABLED)
@EnableSpringConfigured
@ComponentScan(basePackages = "zhibo")
public class AppConfig extends WebMvcConfigurationSupport {

    @Bean
    public DemoProcessor demoProcessor() {
        return new DemoProcessor();
    }
}


public class DemoProcessor implements BeanPostProcessor,BeanDefinitionRegistryPostProcessor {

@Override
public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
    return BeanPostProcessor.super.postProcessAfterInitialization(bean, beanName);
}
@Override
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
    String[] beanDefinitionNames = beanFactory.getBeanDefinitionNames();
    Stream.of(beanDefinitionNames).forEach(System.err::println);
}
@Override
public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {
    String[] beanDefinitionNames = registry.getBeanDefinitionNames();
    Map<String, BeanDefinition> zhiboBeans = new LinkedHashMap<>();
    //1. remove your beans. let spring's beans go ahead
    Stream.of(beanDefinitionNames).forEach(beanName->{
        BeanDefinition bd = registry.getBeanDefinition(beanName);
        if(bd.getBeanClassName()!=null && bd.getBeanClassName().startsWith("zhibo.")) {
            registry.removeBeanDefinition(beanName);
            zhiboBeans.put(beanName, bd);
        }
    });
    //2. regist your beans again
    zhiboBeans.forEach((k,v)->registry.registerBeanDefinition(k, v));
    }
}