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/*
 * Copyright 2002-2013 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.context.annotation;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

import org.springframework.context.weaving.DefaultContextLoadTimeWeaver;
import org.springframework.instrument.classloading.LoadTimeWeaver;

/**
 * Activates a Spring {@link LoadTimeWeaver} for this application context, available as
 * a bean with the name "loadTimeWeaver", similar to the {@code }
 * element in Spring XML.
 * To be used
 * on @{@link org.springframework.context.annotation.Configuration 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: *
 * {@code
 * 
 *     
 *     
 * 
 * }
* *

The {@code LoadTimeWeaverAware} interface

* Any bean that implements the {@link * org.springframework.context.weaving.LoadTimeWeaverAware LoadTimeWeaverAware} interface * will then receive the {@code LoadTimeWeaver} reference automatically; for example, * Spring's JPA bootstrap support. * *

Customizing the {@code LoadTimeWeaver}

* The default weaver is determined automatically: see {@link DefaultContextLoadTimeWeaver}. * *

To customize the weaver used, the {@code @Configuration} class annotated with * {@code @EnableLoadTimeWeaving} may also implement the {@link LoadTimeWeavingConfigurer} * interface and return a custom {@code LoadTimeWeaver} instance through the * {@code #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: *

 * {@code
 * 
 *     
 * 
 * }
* *

The code example differs from the XML example in that it actually instantiates the * {@code MyLoadTimeWeaver} type, meaning that it can also configure the instance, e.g. * calling the {@code #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 {@link #aspectjWeaving()} * attribute, which will cause the {@linkplain * org.aspectj.weaver.loadtime.ClassPreProcessorAgentAdapter AspectJ class transformer} to * be registered through {@link LoadTimeWeaver#addTransformer}. 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: *

 * {@code
 * 
 *     
 * 
 * }
* *

The two examples are equivalent with one significant exception: in the XML case, * the functionality of {@code } is implicitly enabled when * {@code aspectj-weaving} is "on". This does not occur when using * {@code @EnableLoadTimeWeaving(aspectjWeaving=ENABLED)}. Instead you must explicitly add * {@code @EnableSpringConfigured} (included in the {@code spring-aspects} module) * * @author Chris Beams * @since 3.1 * @see LoadTimeWeaver * @see DefaultContextLoadTimeWeaver * @see org.aspectj.weaver.loadtime.ClassPreProcessorAgentAdapter */ @Target(ElementType.TYPE) @Retention(RetentionPolicy.RUNTIME) @Documented @Import(LoadTimeWeavingConfiguration.class) public @interface EnableLoadTimeWeaving { /** * Whether AspectJ weaving should be enabled. */ AspectJWeaving aspectjWeaving() default AspectJWeaving.AUTODETECT; public enum AspectJWeaving { /** * Switches on Spring-based AspectJ load-time weaving. */ ENABLED, /** * Switches off Spring-based AspectJ load-time weaving (even if a * "META-INF/aop.xml" resource is present on the classpath). */ DISABLED, /** * Switches on AspectJ load-time weaving if a "META-INF/aop.xml" resource * is present in the classpath. If there is no such resource, then AspectJ * load-time weaving will be switched off. */ AUTODETECT; } }





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