/*
* Copyright 2002-2010 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.reflect.Method;
import java.util.ArrayList;
import java.util.List;
import net.sf.cglib.proxy.Callback;
import net.sf.cglib.proxy.CallbackFilter;
import net.sf.cglib.proxy.Enhancer;
import net.sf.cglib.proxy.MethodInterceptor;
import net.sf.cglib.proxy.MethodProxy;
import net.sf.cglib.proxy.NoOp;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.aop.scope.ScopedProxyFactoryBean;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.FactoryBean;
import org.springframework.beans.factory.config.ConfigurableBeanFactory;
import org.springframework.core.annotation.AnnotationUtils;
import org.springframework.util.Assert;
/**
* Enhances {@link Configuration} classes by generating a CGLIB subclass capable of
* interacting with the Spring container to respect bean semantics.
*
* @author Chris Beams
* @author Juergen Hoeller
* @since 3.0
* @see #enhance
* @see ConfigurationClassPostProcessor
*/
class ConfigurationClassEnhancer {
private static final Log logger = LogFactory.getLog(ConfigurationClassEnhancer.class);
private final List<Callback> callbackInstances = new ArrayList<Callback>();
private final List<Class<? extends Callback>> callbackTypes = new ArrayList<Class<? extends Callback>>();
private final CallbackFilter callbackFilter;
/**
* Creates a new {@link ConfigurationClassEnhancer} instance.
*/
public ConfigurationClassEnhancer(ConfigurableBeanFactory beanFactory) {
Assert.notNull(beanFactory, "BeanFactory must not be null");
this.callbackInstances.add(new BeanMethodInterceptor(beanFactory));
this.callbackInstances.add(NoOp.INSTANCE);
for (Callback callback : this.callbackInstances) {
this.callbackTypes.add(callback.getClass());
}
// Set up the callback filter to return the index of the BeanMethodInterceptor when
// handling a @Bean-annotated method; otherwise, return index of the NoOp callback.
callbackFilter = new CallbackFilter() {
public int accept(Method candidateMethod) {
return (AnnotationUtils.findAnnotation(candidateMethod, Bean.class) != null ? 0 : 1);
}
};
}
/**
* Loads the specified class and generates a CGLIB subclass of it equipped with
* container-aware callbacks capable of respecting scoping and other bean semantics.
* @return fully-qualified name of the enhanced subclass
*/
public Class<?> enhance(Class<?> configClass) {
Class<?> enhancedClass = createClass(newEnhancer(configClass));
if (logger.isDebugEnabled()) {
logger.debug(String.format("Successfully enhanced %s; enhanced class name is: %s",
configClass.getName(), enhancedClass.getName()));
}
return enhancedClass;
}
/**
* Creates a new CGLIB {@link Enhancer} instance.
*/
private Enhancer newEnhancer(Class<?> superclass) {
Enhancer enhancer = new Enhancer();
// Because callbackFilter and callbackTypes are dynamically populated
// there's no opportunity for caching. This does not appear to be causing
// any performance problem.
enhancer.setUseCache(false);
enhancer.setSuperclass(superclass);
enhancer.setUseFactory(false);
enhancer.setCallbackFilter(this.callbackFilter);
enhancer.setCallbackTypes(this.callbackTypes.toArray(new Class[this.callbackTypes.size()]));
return enhancer;
}
/**
* Uses enhancer to generate a subclass of superclass, ensuring that
* {@link #callbackInstances} are registered for the new subclass.
*/
private Class<?> createClass(Enhancer enhancer) {
Class<?> subclass = enhancer.createClass();
// registering callbacks statically (as opposed to threadlocal) is critical for usage in an OSGi env (SPR-5932)
Enhancer.registerStaticCallbacks(subclass, this.callbackInstances.toArray(new Callback[this.callbackInstances.size()]));
return subclass;
}
/**
* Intercepts calls to {@link FactoryBean#getObject()}, delegating to calling
* {@link BeanFactory#getBean(String)} in order to respect caching / scoping.
* @see BeanMethodInterceptor#intercept(Object, Method, Object[], MethodProxy)
* @see BeanMethodInterceptor#enhanceFactoryBean(Class, String)
*/
private static class GetObjectMethodInterceptor implements MethodInterceptor {
private final ConfigurableBeanFactory beanFactory;
private final String beanName;
public GetObjectMethodInterceptor(ConfigurableBeanFactory beanFactory, String beanName) {
this.beanFactory = beanFactory;
this.beanName = beanName;
}
public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable {
return beanFactory.getBean(beanName);
}
}
/**
* Intercepts the invocation of any {@link Bean}-annotated methods in order to ensure proper
* handling of bean semantics such as scoping and AOP proxying.
* @see Bean
* @see ConfigurationClassEnhancer
*/
private static class BeanMethodInterceptor implements MethodInterceptor {
private final ConfigurableBeanFactory beanFactory;
public BeanMethodInterceptor(ConfigurableBeanFactory beanFactory) {
this.beanFactory = beanFactory;
}
/**
* Enhance a {@link Bean @Bean} method to check the supplied BeanFactory for the
* existence of this bean object.
*/
public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable {
// by default the bean name is the name of the @Bean-annotated method
String beanName = method.getName();
// check to see if the user has explicitly set the bean name
Bean bean = AnnotationUtils.findAnnotation(method, Bean.class);
if (bean != null && bean.name().length > 0) {
beanName = bean.name()[0];
}
// determine whether this bean is a scoped-proxy
Scope scope = AnnotationUtils.findAnnotation(method, Scope.class);
if (scope != null && scope.proxyMode() != ScopedProxyMode.NO) {
String scopedBeanName = ScopedProxyCreator.getTargetBeanName(beanName);
if (this.beanFactory.isCurrentlyInCreation(scopedBeanName)) {
beanName = scopedBeanName;
}
}
// to handle the case of an inter-bean method reference, we must explicitly check the
// container for already cached instances
// first, check to see if the requested bean is a FactoryBean. If so, create a subclass
// proxy that intercepts calls to getObject() and returns any cached bean instance.
// this ensures that the semantics of calling a FactoryBean from within @Bean methods
// is the same as that of referring to a FactoryBean within XML. See SPR-6602.
if (factoryContainsBean('&'+beanName) && factoryContainsBean(beanName)) {
Object factoryBean = this.beanFactory.getBean('&'+beanName);
if (factoryBean instanceof ScopedProxyFactoryBean) {
// pass through - scoped proxy factory beans are a special case and should not
// be further proxied
} else {
// it is a candidate FactoryBean - go ahead with enhancement
return enhanceFactoryBean(factoryBean.getClass(), beanName);
}
}
// the bean is not a FactoryBean - check to see if it has been cached
if (factoryContainsBean(beanName)) {
// we have an already existing cached instance of this bean -> retrieve it
return this.beanFactory.getBean(beanName);
}
// no cached instance of the bean exists - actually create and return the bean
return proxy.invokeSuper(obj, args);
}
/**
* Check the beanFactory to see whether the bean named <var>beanName</var> already
* exists. Accounts for the fact that the requested bean may be "in creation", i.e.:
* we're in the middle of servicing the initial request for this bean. From an enhanced
* factory method's perspective, this means that the bean does not actually yet exist,
* and that it is now our job to create it for the first time by executing the logic
* in the corresponding factory method.
* <p>Said another way, this check repurposes
* {@link ConfigurableBeanFactory#isCurrentlyInCreation(String)} to determine whether
* the container is calling this method or the user is calling this method.
* @param beanName name of bean to check for
* @return whether <var>beanName</var> already exists in the factory
*/
private boolean factoryContainsBean(String beanName) {
return (this.beanFactory.containsBean(beanName) && !this.beanFactory.isCurrentlyInCreation(beanName));
}
/**
* Create a subclass proxy that intercepts calls to getObject(), delegating to the current BeanFactory
* instead of creating a new instance. These proxies are created only when calling a FactoryBean from
* within a Bean method, allowing for proper scoping semantics even when working against the FactoryBean
* instance directly. If a FactoryBean instance is fetched through the container via &-dereferencing,
* it will not be proxied. This too is aligned with the way XML configuration works.
*/
private Object enhanceFactoryBean(Class<?> fbClass, String beanName) throws InstantiationException, IllegalAccessException {
Enhancer enhancer = new Enhancer();
enhancer.setUseCache(false);
enhancer.setSuperclass(fbClass);
enhancer.setUseFactory(false);
enhancer.setCallbackFilter(new CallbackFilter() {
public int accept(Method method) {
return method.getName().equals("getObject") ? 0 : 1;
}
});
List<Callback> callbackInstances = new ArrayList<Callback>();
callbackInstances.add(new GetObjectMethodInterceptor(this.beanFactory, beanName));
callbackInstances.add(NoOp.INSTANCE);
List<Class<? extends Callback>> callbackTypes = new ArrayList<Class<? extends Callback>>();
for (Callback callback : callbackInstances) {
callbackTypes.add(callback.getClass());
}
enhancer.setCallbackTypes(callbackTypes.toArray(new Class[callbackTypes.size()]));
Class<?> fbSubclass = enhancer.createClass();
Enhancer.registerCallbacks(fbSubclass, callbackInstances.toArray(new Callback[callbackInstances.size()]));
return fbSubclass.newInstance();
}
}
}