Spring Framework

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
 EnableLoadTimeWeaving.AspectJWeaving aspectjWeaving
          Whether AspectJ weaving should be enabled.
 

aspectjWeaving

public abstract EnableLoadTimeWeaving.AspectJWeaving aspectjWeaving
Whether AspectJ weaving should be enabled.

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

Spring Framework