spring ConfigurationClassEnhancer 源码
spring ConfigurationClassEnhancer 代码
文件路径：/spring-context/src/main/java/org/springframework/context/annotation/ConfigurationClassEnhancer.java
/*
* Copyright 2002-2022 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
*
* https://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.Field;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.lang.reflect.Proxy;
import java.util.Arrays;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.aop.scope.ScopedProxyFactoryBean;
import org.springframework.asm.Opcodes;
import org.springframework.asm.Type;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.BeanFactoryAware;
import org.springframework.beans.factory.NoSuchBeanDefinitionException;
import org.springframework.beans.factory.config.BeanDefinition;
import org.springframework.beans.factory.config.BeanFactoryPostProcessor;
import org.springframework.beans.factory.config.ConfigurableBeanFactory;
import org.springframework.beans.factory.support.SimpleInstantiationStrategy;
import org.springframework.cglib.core.ClassGenerator;
import org.springframework.cglib.core.ClassLoaderAwareGeneratorStrategy;
import org.springframework.cglib.core.SpringNamingPolicy;
import org.springframework.cglib.proxy.Callback;
import org.springframework.cglib.proxy.CallbackFilter;
import org.springframework.cglib.proxy.Enhancer;
import org.springframework.cglib.proxy.Factory;
import org.springframework.cglib.proxy.MethodInterceptor;
import org.springframework.cglib.proxy.MethodProxy;
import org.springframework.cglib.proxy.NoOp;
import org.springframework.cglib.transform.ClassEmitterTransformer;
import org.springframework.cglib.transform.TransformingClassGenerator;
import org.springframework.lang.Nullable;
import org.springframework.objenesis.ObjenesisException;
import org.springframework.objenesis.SpringObjenesis;
import org.springframework.util.Assert;
import org.springframework.util.ClassUtils;
import org.springframework.util.ObjectUtils;
import org.springframework.util.ReflectionUtils;
/**
* Enhances {@link Configuration} classes by generating a CGLIB subclass which
* interacts with the Spring container to respect bean scoping semantics for
* {@code @Bean} methods. Each such {@code @Bean} method will be overridden in
* the generated subclass, only delegating to the actual {@code @Bean} method
* implementation if the container actually requests the construction of a new
* instance. Otherwise, a call to such an {@code @Bean} method serves as a
* reference back to the container, obtaining the corresponding bean by name.
*
* @author Chris Beams
* @author Juergen Hoeller
* @since 3.0
* @see #enhance
* @see ConfigurationClassPostProcessor
*/
class ConfigurationClassEnhancer {
// The callbacks to use. Note that these callbacks must be stateless.
private static final Callback[] CALLBACKS = new Callback[] {
new BeanMethodInterceptor(),
new BeanFactoryAwareMethodInterceptor(),
NoOp.INSTANCE
};
private static final ConditionalCallbackFilter CALLBACK_FILTER = new ConditionalCallbackFilter(CALLBACKS);
private static final String BEAN_FACTORY_FIELD = "$$beanFactory";
private static final Log logger = LogFactory.getLog(ConfigurationClassEnhancer.class);
private static final SpringObjenesis objenesis = new SpringObjenesis();
/**
* 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 the enhanced subclass
*/
public Class<?> enhance(Class<?> configClass, @Nullable ClassLoader classLoader) {
if (EnhancedConfiguration.class.isAssignableFrom(configClass)) {
if (logger.isDebugEnabled()) {
logger.debug(String.format("Ignoring request to enhance %s as it has " +
"already been enhanced. This usually indicates that more than one " +
"ConfigurationClassPostProcessor has been registered (e.g. via " +
"<context:annotation-config>). This is harmless, but you may " +
"want check your configuration and remove one CCPP if possible",
configClass.getName()));
}
return configClass;
}
Class<?> enhancedClass = createClass(newEnhancer(configClass, classLoader));
if (logger.isTraceEnabled()) {
logger.trace(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<?> configSuperClass, @Nullable ClassLoader classLoader) {
Enhancer enhancer = new Enhancer();
enhancer.setSuperclass(configSuperClass);
enhancer.setInterfaces(new Class<?>[] {EnhancedConfiguration.class});
enhancer.setUseFactory(false);
enhancer.setNamingPolicy(SpringNamingPolicy.INSTANCE);
enhancer.setStrategy(new BeanFactoryAwareGeneratorStrategy(classLoader));
enhancer.setCallbackFilter(CALLBACK_FILTER);
enhancer.setCallbackTypes(CALLBACK_FILTER.getCallbackTypes());
return enhancer;
}
/**
* Uses enhancer to generate a subclass of superclass,
* ensuring that callbacks are registered for the new subclass.
*/
private Class<?> createClass(Enhancer enhancer) {
Class<?> subclass = enhancer.createClass();
// Registering callbacks statically (as opposed to thread-local)
// is critical for usage in an OSGi environment (SPR-5932)...
Enhancer.registerStaticCallbacks(subclass, CALLBACKS);
return subclass;
}
/**
* Marker interface to be implemented by all @Configuration CGLIB subclasses.
* Facilitates idempotent behavior for {@link ConfigurationClassEnhancer#enhance}
* through checking to see if candidate classes are already assignable to it, e.g.
* have already been enhanced.
* <p>Also extends {@link BeanFactoryAware}, as all enhanced {@code @Configuration}
* classes require access to the {@link BeanFactory} that created them.
* <p>Note that this interface is intended for framework-internal use only, however
* must remain public in order to allow access to subclasses generated from other
* packages (i.e. user code).
*/
public interface EnhancedConfiguration extends BeanFactoryAware {
}
/**
* Conditional {@link Callback}.
* @see ConditionalCallbackFilter
*/
private interface ConditionalCallback extends Callback {
boolean isMatch(Method candidateMethod);
}
/**
* A {@link CallbackFilter} that works by interrogating {@link Callback Callbacks} in the order
* that they are defined via {@link ConditionalCallback}.
*/
private static class ConditionalCallbackFilter implements CallbackFilter {
private final Callback[] callbacks;
private final Class<?>[] callbackTypes;
public ConditionalCallbackFilter(Callback[] callbacks) {
this.callbacks = callbacks;
this.callbackTypes = new Class<?>[callbacks.length];
for (int i = 0; i < callbacks.length; i++) {
this.callbackTypes[i] = callbacks[i].getClass();
}
}
@Override
public int accept(Method method) {
for (int i = 0; i < this.callbacks.length; i++) {
Callback callback = this.callbacks[i];
if (!(callback instanceof ConditionalCallback conditional) || conditional.isMatch(method)) {
return i;
}
}
throw new IllegalStateException("No callback available for method " + method.getName());
}
public Class<?>[] getCallbackTypes() {
return this.callbackTypes;
}
}
/**
* Custom extension of CGLIB's DefaultGeneratorStrategy, introducing a {@link BeanFactory} field.
* Also exposes the application ClassLoader as thread context ClassLoader for the time of
* class generation (in order for ASM to pick it up when doing common superclass resolution).
*/
private static class BeanFactoryAwareGeneratorStrategy extends
ClassLoaderAwareGeneratorStrategy {
public BeanFactoryAwareGeneratorStrategy(@Nullable ClassLoader classLoader) {
super(classLoader);
}
@Override
protected ClassGenerator transform(ClassGenerator cg) throws Exception {
ClassEmitterTransformer transformer = new ClassEmitterTransformer() {
@Override
public void end_class() {
declare_field(Opcodes.ACC_PUBLIC, BEAN_FACTORY_FIELD, Type.getType(BeanFactory.class), null);
super.end_class();
}
};
return new TransformingClassGenerator(cg, transformer);
}
}
/**
* Intercepts the invocation of any {@link BeanFactoryAware#setBeanFactory(BeanFactory)} on
* {@code @Configuration} class instances for the purpose of recording the {@link BeanFactory}.
* @see EnhancedConfiguration
*/
private static class BeanFactoryAwareMethodInterceptor implements MethodInterceptor, ConditionalCallback {
@Override
@Nullable
public Object intercept(Object obj, Method method, Object[] args, MethodProxy proxy) throws Throwable {
Field field = ReflectionUtils.findField(obj.getClass(), BEAN_FACTORY_FIELD);
Assert.state(field != null, "Unable to find generated BeanFactory field");
field.set(obj, args[0]);
// Does the actual (non-CGLIB) superclass implement BeanFactoryAware?
// If so, call its setBeanFactory() method. If not, just exit.
if (BeanFactoryAware.class.isAssignableFrom(ClassUtils.getUserClass(obj.getClass().getSuperclass()))) {
return proxy.invokeSuper(obj, args);
}
return null;
}
@Override
public boolean isMatch(Method candidateMethod) {
return isSetBeanFactory(candidateMethod);
}
public static boolean isSetBeanFactory(Method candidateMethod) {
return (candidateMethod.getName().equals("setBeanFactory") &&
candidateMethod.getParameterCount() == 1 &&
BeanFactory.class == candidateMethod.getParameterTypes()[0] &&
BeanFactoryAware.class.isAssignableFrom(candidateMethod.getDeclaringClass()));
}
}
/**
* 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, ConditionalCallback {
/**
* Enhance a {@link Bean @Bean} method to check the supplied BeanFactory for the
* existence of this bean object.
* @throws Throwable as a catch-all for any exception that may be thrown when invoking the
* super implementation of the proxied method i.e., the actual {@code @Bean} method
*/
@Override
@Nullable
public Object intercept(Object enhancedConfigInstance, Method beanMethod, Object[] beanMethodArgs,
MethodProxy cglibMethodProxy) throws Throwable {
ConfigurableBeanFactory beanFactory = getBeanFactory(enhancedConfigInstance);
String beanName = BeanAnnotationHelper.determineBeanNameFor(beanMethod);
// Determine whether this bean is a scoped-proxy
if (BeanAnnotationHelper.isScopedProxy(beanMethod)) {
String scopedBeanName = ScopedProxyCreator.getTargetBeanName(beanName);
if (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(beanFactory, BeanFactory.FACTORY_BEAN_PREFIX + beanName) &&
factoryContainsBean(beanFactory, beanName)) {
Object factoryBean = beanFactory.getBean(BeanFactory.FACTORY_BEAN_PREFIX + beanName);
if (factoryBean instanceof ScopedProxyFactoryBean) {
// 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, beanMethod.getReturnType(), beanFactory, beanName);
}
}
if (isCurrentlyInvokedFactoryMethod(beanMethod)) {
// The factory is calling the bean method in order to instantiate and register the bean
// (i.e. via a getBean() call) -> invoke the super implementation of the method to actually
// create the bean instance.
if (logger.isInfoEnabled() &&
BeanFactoryPostProcessor.class.isAssignableFrom(beanMethod.getReturnType())) {
logger.info(String.format("@Bean method %s.%s is non-static and returns an object " +
"assignable to Spring's BeanFactoryPostProcessor interface. This will " +
"result in a failure to process annotations such as @Autowired, " +
"@Resource and @PostConstruct within the method's declaring " +
"@Configuration class. Add the 'static' modifier to this method to avoid " +
"these container lifecycle issues; see @Bean javadoc for complete details.",
beanMethod.getDeclaringClass().getSimpleName(), beanMethod.getName()));
}
return cglibMethodProxy.invokeSuper(enhancedConfigInstance, beanMethodArgs);
}
return resolveBeanReference(beanMethod, beanMethodArgs, beanFactory, beanName);
}
private Object resolveBeanReference(Method beanMethod, Object[] beanMethodArgs,
ConfigurableBeanFactory beanFactory, String beanName) {
// The user (i.e. not the factory) is requesting this bean through a call to
// the bean method, direct or indirect. The bean may have already been marked
// as 'in creation' in certain autowiring scenarios; if so, temporarily set
// the in-creation status to false in order to avoid an exception.
boolean alreadyInCreation = beanFactory.isCurrentlyInCreation(beanName);
try {
if (alreadyInCreation) {
beanFactory.setCurrentlyInCreation(beanName, false);
}
boolean useArgs = !ObjectUtils.isEmpty(beanMethodArgs);
if (useArgs && beanFactory.isSingleton(beanName)) {
// Stubbed null arguments just for reference purposes,
// expecting them to be autowired for regular singleton references?
// A safe assumption since @Bean singleton arguments cannot be optional...
for (Object arg : beanMethodArgs) {
if (arg == null) {
useArgs = false;
break;
}
}
}
Object beanInstance = (useArgs ? beanFactory.getBean(beanName, beanMethodArgs) :
beanFactory.getBean(beanName));
if (!ClassUtils.isAssignableValue(beanMethod.getReturnType(), beanInstance)) {
// Detect package-protected NullBean instance through equals(null) check
if (beanInstance.equals(null)) {
if (logger.isDebugEnabled()) {
logger.debug(String.format("@Bean method %s.%s called as bean reference " +
"for type [%s] returned null bean; resolving to null value.",
beanMethod.getDeclaringClass().getSimpleName(), beanMethod.getName(),
beanMethod.getReturnType().getName()));
}
beanInstance = null;
}
else {
String msg = String.format("@Bean method %s.%s called as bean reference " +
"for type [%s] but overridden by non-compatible bean instance of type [%s].",
beanMethod.getDeclaringClass().getSimpleName(), beanMethod.getName(),
beanMethod.getReturnType().getName(), beanInstance.getClass().getName());
try {
BeanDefinition beanDefinition = beanFactory.getMergedBeanDefinition(beanName);
msg += " Overriding bean of same name declared in: " + beanDefinition.getResourceDescription();
}
catch (NoSuchBeanDefinitionException ex) {
// Ignore - simply no detailed message then.
}
throw new IllegalStateException(msg);
}
}
Method currentlyInvoked = SimpleInstantiationStrategy.getCurrentlyInvokedFactoryMethod();
if (currentlyInvoked != null) {
String outerBeanName = BeanAnnotationHelper.determineBeanNameFor(currentlyInvoked);
beanFactory.registerDependentBean(beanName, outerBeanName);
}
return beanInstance;
}
finally {
if (alreadyInCreation) {
beanFactory.setCurrentlyInCreation(beanName, true);
}
}
}
@Override
public boolean isMatch(Method candidateMethod) {
return (candidateMethod.getDeclaringClass() != Object.class &&
!BeanFactoryAwareMethodInterceptor.isSetBeanFactory(candidateMethod) &&
BeanAnnotationHelper.isBeanAnnotated(candidateMethod));
}
private ConfigurableBeanFactory getBeanFactory(Object enhancedConfigInstance) {
Field field = ReflectionUtils.findField(enhancedConfigInstance.getClass(), BEAN_FACTORY_FIELD);
Assert.state(field != null, "Unable to find generated bean factory field");
Object beanFactory = ReflectionUtils.getField(field, enhancedConfigInstance);
Assert.state(beanFactory != null, "BeanFactory has not been injected into @Configuration class");
Assert.state(beanFactory instanceof ConfigurableBeanFactory,
"Injected BeanFactory is not a ConfigurableBeanFactory");
return (ConfigurableBeanFactory) beanFactory;
}
/**
* 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(ConfigurableBeanFactory beanFactory, String beanName) {
return (beanFactory.containsBean(beanName) && !beanFactory.isCurrentlyInCreation(beanName));
}
/**
* Check whether the given method corresponds to the container's currently invoked
* factory method. Compares method name and parameter types only in order to work
* around a potential problem with covariant return types (currently only known
* to happen on Groovy classes).
*/
private boolean isCurrentlyInvokedFactoryMethod(Method method) {
Method currentlyInvoked = SimpleInstantiationStrategy.getCurrentlyInvokedFactoryMethod();
return (currentlyInvoked != null && method.getName().equals(currentlyInvoked.getName()) &&
Arrays.equals(method.getParameterTypes(), currentlyInvoked.getParameterTypes()));
}
/**
* 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(Object factoryBean, Class<?> exposedType,
ConfigurableBeanFactory beanFactory, String beanName) {
try {
Class<?> clazz = factoryBean.getClass();
boolean finalClass = Modifier.isFinal(clazz.getModifiers());
boolean finalMethod = Modifier.isFinal(clazz.getMethod("getObject").getModifiers());
if (finalClass || finalMethod) {
if (exposedType.isInterface()) {
if (logger.isTraceEnabled()) {
logger.trace("Creating interface proxy for FactoryBean '" + beanName + "' of type [" +
clazz.getName() + "] for use within another @Bean method because its " +
(finalClass ? "implementation class" : "getObject() method") +
" is final: Otherwise a getObject() call would not be routed to the factory.");
}
return createInterfaceProxyForFactoryBean(factoryBean, exposedType, beanFactory, beanName);
}
else {
if (logger.isDebugEnabled()) {
logger.debug("Unable to proxy FactoryBean '" + beanName + "' of type [" +
clazz.getName() + "] for use within another @Bean method because its " +
(finalClass ? "implementation class" : "getObject() method") +
" is final: A getObject() call will NOT be routed to the factory. " +
"Consider declaring the return type as a FactoryBean interface.");
}
return factoryBean;
}
}
}
catch (NoSuchMethodException ex) {
// No getObject() method -> shouldn't happen, but as long as nobody is trying to call it...
}
return createCglibProxyForFactoryBean(factoryBean, beanFactory, beanName);
}
private Object createInterfaceProxyForFactoryBean(Object factoryBean, Class<?> interfaceType,
ConfigurableBeanFactory beanFactory, String beanName) {
return Proxy.newProxyInstance(
factoryBean.getClass().getClassLoader(), new Class<?>[] {interfaceType},
(proxy, method, args) -> {
if (method.getName().equals("getObject") && args == null) {
return beanFactory.getBean(beanName);
}
return ReflectionUtils.invokeMethod(method, factoryBean, args);
});
}
private Object createCglibProxyForFactoryBean(Object factoryBean,
ConfigurableBeanFactory beanFactory, String beanName) {
Enhancer enhancer = new Enhancer();
enhancer.setSuperclass(factoryBean.getClass());
enhancer.setNamingPolicy(SpringNamingPolicy.INSTANCE);
enhancer.setCallbackType(MethodInterceptor.class);
// Ideally create enhanced FactoryBean proxy without constructor side effects,
// analogous to AOP proxy creation in ObjenesisCglibAopProxy...
Class<?> fbClass = enhancer.createClass();
Object fbProxy = null;
if (objenesis.isWorthTrying()) {
try {
fbProxy = objenesis.newInstance(fbClass, enhancer.getUseCache());
}
catch (ObjenesisException ex) {
logger.debug("Unable to instantiate enhanced FactoryBean using Objenesis, " +
"falling back to regular construction", ex);
}
}
if (fbProxy == null) {
try {
fbProxy = ReflectionUtils.accessibleConstructor(fbClass).newInstance();
}
catch (Throwable ex) {
throw new IllegalStateException("Unable to instantiate enhanced FactoryBean using Objenesis, " +
"and regular FactoryBean instantiation via default constructor fails as well", ex);
}
}
((Factory) fbProxy).setCallback(0, (MethodInterceptor) (obj, method, args, proxy) -> {
if (method.getName().equals("getObject") && args.length == 0) {
return beanFactory.getBean(beanName);
}
return proxy.invoke(factoryBean, args);
});
return fbProxy;
}
}
}
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