Package org.springframework.context.annotation

Annotation Interface EnableLoadTimeWeaving

@Target(TYPE) @Retention(RUNTIME) @Documented @Import(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: see DefaultContextLoadTimeWeaver.

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: