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Spring Framework example source code file (CglibSubclassingInstantiationStrategy.java)

This example Spring Framework source code file (CglibSubclassingInstantiationStrategy.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Spring Framework tags/keywords

beanfactory, beanfactory, cglibidentitysupport, cglibidentitysupport, cglibsubclasscreator, lookup_override, lookupoverride, methodreplacer, object, object, passthrough, reflection, replaceoverride, rootbeandefinition, rootbeandefinition

The Spring Framework CglibSubclassingInstantiationStrategy.java source code

/*
 * 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.
 *
 * <p>Using Method Injection features requires CGLIB on the classpath.
 * However, the core IoC container will still run without CGLIB being available.
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @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 <code>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 <code>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 boolean equals(Object other) {
				return (other.getClass().equals(getClass()) &&
						((CglibIdentitySupport) other).getBeanDefinition().equals(beanDefinition));
			}

			public int hashCode() {
				return beanDefinition.hashCode();
			}
		}


		/**
		 * 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());
			}
		}
	}

}

Other Spring Framework examples (source code examples)

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