org.springframework.context.annotation

Annotation Type EnableLoadTimeWeaving

@Target(value=TYPE)
@Retention(value=RUNTIME)
@Documented
@Import(value=LoadTimeWeavingConfiguration.class)
public @interface EnableLoadTimeWeaving

Activates a Spring LoadTimeWeaver for this application context, available as a bean with the name "loadTimeWeaver", similar to the <context:load-time-weaver> element in Spring XML. To be used on @Configuration classes; the simplest possible example of which follows:

 @Configuration
 @EnableLoadTimeWeaving
 public class AppConfig {
     // application-specific @Bean definitions ...
 }

The example above is equivalent to the following Spring XML configuration:

 <beans>
     <context:load-time-weaver/>
     <!-- application-specific <bean> definitions -->
 </beans>
 

The LoadTimeWeaverAware interface

Any bean that implements the LoadTimeWeaverAware interface will then receive the LoadTimeWeaver reference automatically; for example, Spring's JPA bootstrap support.

Customizing the LoadTimeWeaver

The default weaver is determined automatically. As of Spring 3.1: detecting Sun's GlassFish, Oracle's OC4J, Spring's VM agent and any ClassLoader supported by Spring's ReflectiveLoadTimeWeaver (for example, the TomcatInstrumentableClassLoader).

To customize the weaver used, the @Configuration class annotated with @EnableLoadTimeWeaving may also implement the LoadTimeWeavingConfigurer interface and return a custom LoadTimeWeaver instance through the #getLoadTimeWeaver method:

 @Configuration
 @EnableLoadTimeWeaving
 public class AppConfig implements LoadTimeWeavingConfigurer {
     @Override
     public LoadTimeWeaver getLoadTimeWeaver() {
         MyLoadTimeWeaver ltw = new MyLoadTimeWeaver();
         ltw.addClassTransformer(myClassFileTransformer);
         // ...
         return ltw;
     }
 }

The example above can be compared to the following Spring XML configuration:

 <beans>
     <context:load-time-weaver weaverClass="com.acme.MyLoadTimeWeaver"/>
 </beans>
 

The code example differs from the XML example in that it actually instantiates the MyLoadTimeWeaver type, meaning that it can also configure the instance, e.g. calling the #addClassTransformer method. This demonstrates how the code-based configuration approach is more flexible through direct programmatic access.

Enabling AspectJ-based weaving

AspectJ load-time weaving may be enabled with the aspectjWeaving() attribute, which will cause the AspectJ class transformer to be registered through LoadTimeWeaver.addTransformer(java.lang.instrument.ClassFileTransformer). AspectJ weaving will be activated by default if a "META-INF/aop.xml" resource is present on the classpath. Example:

 @Configuration
 @EnableLoadTimeWeaving(aspectjWeaving=ENABLED)
 public class AppConfig {
 }

The example above can be compared to the following Spring XML configuration:

 <beans>
     <context:load-time-weaver aspectj-weaving="on"/>
 </beans>
 

The two examples are equivalent with one significant exception: in the XML case, the functionality of <context:spring-configured> is implicitly enabled when aspectj-weaving is "on". This does not occur when using @EnableLoadTimeWeaving(aspectjWeaving=ENABLED). Instead you must explicitly add @EnableSpringConfigured (included in the spring-aspects module)

Since:

3.1

Author:

Chris Beams

See Also:

LoadTimeWeaver, DefaultContextLoadTimeWeaver, ClassPreProcessorAgentAdapter

Optional Element Summary

Optional Elements

Modifier and Type	Optional Element and Description
EnableLoadTimeWeaving.AspectJWeaving	aspectjWeaving Whether AspectJ weaving should be enabled.

Element Detail

aspectjWeaving

public abstract EnableLoadTimeWeaving.AspectJWeaving aspectjWeaving

Whether AspectJ weaving should be enabled.

Default:

org.springframework.context.annotation.EnableLoadTimeWeaving.AspectJWeaving.AUTODETECT