org.springframework.beans.factory.support.CglibSubclassingInstantiationStrategy Maven / Gradle / Ivy
/*
* Copyright 2002-2007 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.beans.factory.support;
import java.lang.reflect.Constructor;
import java.lang.reflect.Method;
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.beans.factory.BeanFactory;
/**
* Default object instantiation strategy for use in BeanFactories.
* Uses CGLIB to generate subclasses dynamically if methods need to be
* overridden by the container, to implement Method Injection.
*
* Using Method Injection features requires CGLIB on the classpath.
* However, the core IoC container will still run without CGLIB being available.
*
* @author Rod Johnson
* @since 1.1
*/
public class CglibSubclassingInstantiationStrategy extends SimpleInstantiationStrategy {
/**
* Index in the CGLIB callback array for passthrough behavior,
* in which case the subclass won't override the original class.
*/
private static final int PASSTHROUGH = 0;
/**
* Index in the CGLIB callback array for a method that should
* be overridden to provide method lookup.
*/
private static final int LOOKUP_OVERRIDE = 1;
/**
* Index in the CGLIB callback array for a method that should
* be overridden using generic Methodreplacer functionality.
*/
private static final int METHOD_REPLACER = 2;
protected Object instantiateWithMethodInjection(
RootBeanDefinition beanDefinition, String beanName, BeanFactory owner) {
// Must generate CGLIB subclass.
return new CglibSubclassCreator(beanDefinition, owner).instantiate(null, null);
}
protected Object instantiateWithMethodInjection(
RootBeanDefinition beanDefinition, String beanName, BeanFactory owner,
Constructor ctor, Object[] args) {
return new CglibSubclassCreator(beanDefinition, owner).instantiate(ctor, args);
}
/**
* An inner class so we don't have a CGLIB dependency in core.
*/
private static class CglibSubclassCreator {
private static final Log logger = LogFactory.getLog(CglibSubclassCreator.class);
private final RootBeanDefinition beanDefinition;
private final BeanFactory owner;
public CglibSubclassCreator(RootBeanDefinition beanDefinition, BeanFactory owner) {
this.beanDefinition = beanDefinition;
this.owner = owner;
}
/**
* Create a new instance of a dynamically generated subclasses implementing the
* required lookups.
* @param ctor constructor to use. If this is null, use the
* no-arg constructor (no parameterization, or Setter Injection)
* @param args arguments to use for the constructor.
* Ignored if the ctor parameter is null.
* @return new instance of the dynamically generated class
*/
public Object instantiate(Constructor ctor, Object[] args) {
Enhancer enhancer = new Enhancer();
enhancer.setSuperclass(this.beanDefinition.getBeanClass());
enhancer.setCallbackFilter(new CallbackFilterImpl());
enhancer.setCallbacks(new Callback[] {
NoOp.INSTANCE,
new LookupOverrideMethodInterceptor(),
new ReplaceOverrideMethodInterceptor()
});
return (ctor == null) ?
enhancer.create() :
enhancer.create(ctor.getParameterTypes(), args);
}
/**
* Class providing hashCode and equals methods required by CGLIB to
* ensure that CGLIB doesn't generate a distinct class per bean.
* Identity is based on class and bean definition.
*/
private class CglibIdentitySupport {
/**
* Exposed for equals method to allow access to enclosing class field
*/
protected RootBeanDefinition getBeanDefinition() {
return beanDefinition;
}
public int hashCode() {
return beanDefinition.hashCode();
}
public boolean equals(Object other) {
return (other.getClass() == getClass()) &&
((CglibIdentitySupport) other).getBeanDefinition() == beanDefinition;
}
}
/**
* CGLIB MethodInterceptor to override methods, replacing them with an
* implementation that returns a bean looked up in the container.
*/
private class LookupOverrideMethodInterceptor extends CglibIdentitySupport implements MethodInterceptor {
public Object intercept(Object obj, Method method, Object[] args, MethodProxy mp) throws Throwable {
// Cast is safe, as CallbackFilter filters are used selectively.
LookupOverride lo = (LookupOverride) beanDefinition.getMethodOverrides().getOverride(method);
return owner.getBean(lo.getBeanName());
}
}
/**
* CGLIB MethodInterceptor to override methods, replacing them with a call
* to a generic MethodReplacer.
*/
private class ReplaceOverrideMethodInterceptor extends CglibIdentitySupport implements MethodInterceptor {
public Object intercept(Object obj, Method method, Object[] args, MethodProxy mp) throws Throwable {
ReplaceOverride ro = (ReplaceOverride) beanDefinition.getMethodOverrides().getOverride(method);
// TODO could cache if a singleton for minor performance optimization
MethodReplacer mr = (MethodReplacer) owner.getBean(ro.getMethodReplacerBeanName());
return mr.reimplement(obj, method, args);
}
}
/**
* CGLIB object to filter method interception behavior.
*/
private class CallbackFilterImpl extends CglibIdentitySupport implements CallbackFilter {
public int accept(Method method) {
MethodOverride methodOverride = beanDefinition.getMethodOverrides().getOverride(method);
if (logger.isTraceEnabled()) {
logger.trace("Override for '" + method.getName() + "' is [" + methodOverride + "]");
}
if (methodOverride == null) {
return PASSTHROUGH;
}
else if (methodOverride instanceof LookupOverride) {
return LOOKUP_OVERRIDE;
}
else if (methodOverride instanceof ReplaceOverride) {
return METHOD_REPLACER;
}
throw new UnsupportedOperationException(
"Unexpected MethodOverride subclass: " + methodOverride.getClass().getName());
}
}
}
}