Spring Framework example source code file (InstrumentationLoadTimeWeaver.java)

This example Spring Framework source code file (InstrumentationLoadTimeWeaver.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

agent_class_present, classfiletransformer, classloader, classloader, filteringclassfiletransformer, filteringclassfiletransformer, illegalstateexception, instrumentation, instrumentation, instrumentationloadtimeweaver, instrumentationloadtimeweaver, java, security, see, string, util

The Spring Framework InstrumentationLoadTimeWeaver.java source code

/*
 * Copyright 2002-2008 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.instrument.classloading;

import java.lang.instrument.ClassFileTransformer;
import java.lang.instrument.IllegalClassFormatException;
import java.lang.instrument.Instrumentation;
import java.security.ProtectionDomain;
import java.util.ArrayList;
import java.util.List;

import org.springframework.instrument.InstrumentationSavingAgent;
import org.springframework.util.Assert;
import org.springframework.util.ClassUtils;

/**
 * {@link LoadTimeWeaver} relying on VM {@link Instrumentation}.
 *
 * <p>Start the JVM specifying the Java agent to be used, like as follows:
 *
 * <p>-javaagent:path/to/spring-agent.jar
 *
 * <p>where spring-agent.jar is a JAR file containing the
 * {@link InstrumentationSavingAgent} class.
 *
 * <p>In Eclipse, for example, set the "Run configuration"'s JVM args
 * to be of the form:
 *
 * <p>-javaagent:${project_loc}/lib/spring-agent.jar
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @since 2.0
 * @see InstrumentationSavingAgent
 */
public class InstrumentationLoadTimeWeaver implements LoadTimeWeaver {

	private static final boolean AGENT_CLASS_PRESENT = ClassUtils.isPresent(
			"org.springframework.instrument.InstrumentationSavingAgent",
			InstrumentationLoadTimeWeaver.class.getClassLoader());


	private final ClassLoader classLoader;

	private final Instrumentation instrumentation;

	private final List<ClassFileTransformer> transformers = new ArrayList(4);


	/**
	 * Create a new InstrumentationLoadTimeWeaver for the default ClassLoader.
	 */
	public InstrumentationLoadTimeWeaver() {
		this(ClassUtils.getDefaultClassLoader());
	}

	/**
	 * Create a new InstrumentationLoadTimeWeaver for the given ClassLoader.
	 * @param classLoader the ClassLoader that registered transformers are supposed to apply to
	 */
	public InstrumentationLoadTimeWeaver(ClassLoader classLoader) {
		Assert.notNull(classLoader, "ClassLoader must not be null");
		this.classLoader = classLoader;
		this.instrumentation = getInstrumentation();
	}


	public void addTransformer(ClassFileTransformer transformer) {
		Assert.notNull(transformer, "Transformer must not be null");
		FilteringClassFileTransformer actualTransformer =
				new FilteringClassFileTransformer(transformer, this.classLoader);
		synchronized (this.transformers) {
			if (this.instrumentation == null) {
				throw new IllegalStateException(
						"Must start with Java agent to use InstrumentationLoadTimeWeaver. See Spring documentation.");
			}
			this.instrumentation.addTransformer(actualTransformer);
			this.transformers.add(actualTransformer);
		}
	}

	/**
	 * We have the ability to weave the current class loader when starting the
	 * JVM in this way, so the instrumentable class loader will always be the
	 * current loader.
	 */
	public ClassLoader getInstrumentableClassLoader() {
		return this.classLoader;
	}

	/**
	 * This implementation always returns a {@link SimpleThrowawayClassLoader}.
	 */
	public ClassLoader getThrowawayClassLoader() {
		return new SimpleThrowawayClassLoader(getInstrumentableClassLoader());
	}

	/**
	 * Remove all registered transformers, in inverse order of registration.
	 */
	public void removeTransformers() {
		synchronized (this.transformers) {
			if (!this.transformers.isEmpty()) {
				for (int i = this.transformers.size() - 1; i >= 0; i--) {
					this.instrumentation.removeTransformer(this.transformers.get(i));
				}
				this.transformers.clear();
			}
		}
	}


	/**
	 * Check whether an Instrumentation instance is available for the current VM.
	 * @see #getInstrumentation()
	 */
	public static boolean isInstrumentationAvailable() {
		return (getInstrumentation() != null);
	}

	/**
	 * Obtain the Instrumentation instance for the current VM, if available.
	 * @return the Instrumentation instance, or <code>null if none found
	 * @see #isInstrumentationAvailable()
	 */
	private static Instrumentation getInstrumentation() {
		if (AGENT_CLASS_PRESENT) {
			return InstrumentationAccessor.getInstrumentation();
		}
		else {
			return null;
		}
	}


	/**
	 * Inner class to avoid InstrumentationSavingAgent dependency.
	 */
	private static class InstrumentationAccessor {

		public static Instrumentation getInstrumentation() {
			return InstrumentationSavingAgent.getInstrumentation();
		}
	}


	/**
	 * Decorator that only applies the given target transformer to a specific ClassLoader.
	 */
	private static class FilteringClassFileTransformer implements ClassFileTransformer {

		private final ClassFileTransformer targetTransformer;

		private final ClassLoader targetClassLoader;

		public FilteringClassFileTransformer(ClassFileTransformer targetTransformer, ClassLoader targetClassLoader) {
			this.targetTransformer = targetTransformer;
			this.targetClassLoader = targetClassLoader;
		}

		public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined,
				ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException {

			if (!this.targetClassLoader.equals(loader)) {
				return null;
			}
			return this.targetTransformer.transform(
					loader, className, classBeingRedefined, protectionDomain, classfileBuffer);
		}

		public String toString() {
			return "FilteringClassFileTransformer for: " + this.targetTransformer.toString();
		}
	}

}