使用@Configurable进行Spring自动装配

Question

I'm playing with the idea of using Spring @Configurable and @Autowire to inject DAOs into domain objects so that they do not need direct knowledge of the persistence layer.

I'm trying to follow http://static.springsource.org/spring/docs/3.0.x/spring-framework-reference/html/aop.html#aop-atconfigurable , but my code seems to have no effect.

Basically, I have:

@Configurable
public class Artist {

    @Autowired
    private ArtistDAO artistDao;

    public void setArtistDao(ArtistDAO artistDao) {
        this.artistDao = artistDao;
    }

    public void save() {
        artistDao.save(this);
    }

}

And:

public interface ArtistDAO {

    public void save(Artist artist);

}

and

@Component
public class ArtistDAOImpl implements ArtistDAO {

    @Override
    public void save(Artist artist) {
        System.out.println("saving");
    }

}

In application-context.xml, I have:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN" "http://www.springsource.org/dtd/spring-beans-2.0.dtd">
<beans>

    <bean class="org.springframework.aop.aspectj.annotation.AnnotationAwareAspectJAutoProxyCreator" />
    <bean class="org.springframework.beans.factory.aspectj.AnnotationBeanConfigurerAspect" factory-method="aspectOf"/>

</beans>

Class path scanning and initialisation is performed by the spring module for Play! framework, although other autowired beans work, so I'm pretty sure this is not the root cause. I'm using Spring 3.0.5.

In other code (inside a method in bean that's injected into my controller using Spring, in fact), I'm doing this:

Artist artist = new Artist();
artist.save();

This gives me a NullPointerException trying to access the artistDao in Artist.save().

Any idea what I'm doing wrong?

Martin

Answer 1

You need to enable load-time weaving (or other kinds of weaving) in order to use @Configurable . Make sure you enabled it correctly, as described in 7.8.4 Load-time weaving with AspectJ in the Spring Framework .

Answer 2

I was having this problem with Tomcat 7 using LTW trying to autowire beans into my domain classes.

There was some updates to the doc for 3.2.x at http://static.springsource.org/spring/docs/3.2.x/spring-framework-reference/html/aop.html#aop-configurable-container that revealed that one can use @EnableSpringConfigured instead of the xml configuration .

So I have the following annotation on my Domain object:

@Configurable(preConstruction=true,dependencyCheck=true,autowire=Autowire.BY_TYPE)
@EnableSpringConfigured

@EnableSpringConfigured is a substitue for

<context:spring-configured />

and don't forget to add this to your context xml file:

<context:load-time-weaver weaver-class="org.springframework.instrument.classloading.ReflectiveLoadTimeWeaver" aspectj-weaving="on"/>

Of course I needed to setup Tomcat for load time weaving first.

Also, I ran into a bug in 3.2.0 (null pointer) so I needed to upgrade to Spring 3.2.1 ( https://jira.springsource.org/browse/SPR-10108 )

All is well now!

Answer 3

First, enable Spring debug logging. I use Log4j to do it. I've created a logger like so (with Log4j xml configuration so I can use RollingFileAppender):

<log4j:configuration>
  <appender name="roll" class="org.apache.log4j.rolling.RollingFileAppender">
     blah blah configuration blah blah
  </appender>
  <logger name="org.springframework">
    <level value="debug" />
    <appender-ref ref="roll" />
  </logger>
</log4j:configuration>

This will allow you to see what Spring is doing and when.

Second, you have ArtistDAO autowired but I don't see where you have a bean named ArtistDAO. Your DAO component bean will be named "artistDaoImpl" by default. Try changing @Component to @Component("artistDao") and applying @Autowired to the setter instead:

private ArtistDAO artistDao;

@Autowired
public void setArtistDao(ArtistDAO artistDao) 
{
  this.artistDao = artistDao;
}

Answer 4

You should just look how Spring Roo does it since it does exactly what you want to do.

There are lots of things that can cause the NPE your having but most of the time it has to do with not compiling properly with AspectJ compiler and not having the Spring Aspects jar in your AspectJ lib path (this is different than your classpath).

First just try to get it to work with Maven and the AspectJ compiler plugin. Thats why I recommend Spring Roo as it will generate a POM file with the correct setup.

I have found @Configurable does not really work with LTW (despite one of the answers saying so). You need compile time weaving for @Configurable to work because the advice is happening at object construction time (constructor advice cannot be done with Springs LTW).

Answer 5

I had the same problem and never managed to get the code working with @Configurable and @Autowired. I finally decided to write an aspect myself which would handle the @Configurable and @Autowired annotations. Here is the code:

import java.lang.annotation.Annotation;
import java.lang.reflect.Field;

import org.apache.log4j.Logger;
import org.aspectj.lang.JoinPoint;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;
import org.aspectj.lang.annotation.Pointcut;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;

@SuppressWarnings( "rawtypes" )
@Aspect
public class AutoInjectDependecyAspect implements ApplicationContextAware {
    private static final Logger LOGGER = Logger.getLogger( AutoInjectDependecyAspect.class );

    private ApplicationContext  applicationContext = null;

    @Pointcut( "execution(  (@org.springframework.beans.factory.annotation.Configurable *).new())" )
    public void constructor() {
    }

    @Before( "constructor()" )
    public void injectAutoWiredFields( JoinPoint aPoint ) {
        Class theClass = aPoint.getTarget().getClass();
        try{
            Field[] theFields = theClass.getDeclaredFields();
            for ( Field thefield : theFields ) {
                for ( Annotation theAnnotation : thefield.getAnnotations() ) {
                    if ( theAnnotation instanceof Autowired ) {
                        // found a field annotated with 'AutoWired'
                        if ( !thefield.isAccessible() ) {
                            thefield.setAccessible( true );
                        }

                        Object theBean = applicationContext.getBean( thefield.getType() );
                        if ( theBean != null ) {
                            thefield.set( aPoint.getTarget(), theBean );
                        }
                    }
                }
            }
        } catch ( Exception e ) {
            LOGGER.error( "An error occured while trying to inject bean on mapper '" + aPoint.getTarget().getClass() + "'", e );
        }

    }

    @Override
    public void setApplicationContext( ApplicationContext aApplicationContext ) throws BeansException {
        applicationContext = aApplicationContext;
    }

}

Next in your spring context define the aspect so that the springcontext will be injected into the aspect

<bean class="[package_name].AutoInjectDependecyAspect" factory-method="aspectOf"/>

Answer 6

I had a similar issue that I resolved today. The important thing is that you need to enable load-time weaving and make sure the appropriate aspectj classes are loaded. In your pom.xml you need to add the aspectjweaver artifact :

...
<dependency>
    <groupId>org.aspectj</groupId>
    <artifactId>aspectjweaver</artifactId>
    <version>1.6.12</version>
</dependency>
....

You can change the version if you need to. Then, I would go the xsd route in you application-context.xml instead of the DTD route:

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
       http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
       http://www.springframework.org/schema/context
       http://www.springframework.org/schema/context/spring-context-3.0.xsd">

    <!--Scans the classpath for annotated components @Component, @Repository, @Service, and @Controller -->
    <context:component-scan base-package="your.base.package"/>
    <!--Activates @Required, @Autowired, @PostConstruct, @PreDestroy and @Resource -->
    <context:annotation-config/>
    <!--This switches on the load-time weaving for @Configurable annotated classes -->
    <context:load-time-weaver/>

</beans>

Answer 7

也许使用DAO的@Repository注释就可以了。

Answer 8

try : @Configurable(autowire=Autowire.BY_TYPE). Autowired defaults to off :<

Answer 9

Also, please verify that your version of AspectJ is current. I wasted a few hours trying to make this work, and the cause was an old version of Aspectjweaver.jar. I updated to 1.7.2 and everything worked like a charm.

Answer 10

There is a bug with @Configurable and LTW. If you use your class as a parameter in any method the auto wiring stops working. https://jira.spring.io/plugins/servlet/mobile#issue/SPR-8502