org.springframework.instrument.classloading.InstrumentationLoadTimeWeaver Maven / Gradle / Ivy
/*
* Copyright 2002-2019 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.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.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.util.ClassUtils;
/**
* {@link LoadTimeWeaver} relying on VM {@link Instrumentation}.
*
* Start the JVM specifying the Java agent to be used — for example, as
* follows where spring-instrument-{version}.jar is a JAR file
* containing the {@link InstrumentationSavingAgent} class shipped with Spring
* and where {version} is the release version of the Spring
* Framework (e.g., {@code 5.1.5.RELEASE}).
*
*
-javaagent:path/to/spring-instrument-{version}.jar
*
*
In Eclipse, for example, add something similar to the following to the
* JVM arguments for the Eclipse "Run configuration":
*
*
-javaagent:${project_loc}/lib/spring-instrument-{version}.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());
@Nullable
private final ClassLoader classLoader;
@Nullable
private final Instrumentation instrumentation;
private final List 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(@Nullable ClassLoader classLoader) {
this.classLoader = classLoader;
this.instrumentation = getInstrumentation();
}
@Override
public void addTransformer(ClassFileTransformer transformer) {
Assert.notNull(transformer, "Transformer must not be null");
FilteringClassFileTransformer actualTransformer =
new FilteringClassFileTransformer(transformer, this.classLoader);
synchronized (this.transformers) {
Assert.state(this.instrumentation != null,
"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.
*/
@Override
public ClassLoader getInstrumentableClassLoader() {
Assert.state(this.classLoader != null, "No ClassLoader available");
return this.classLoader;
}
/**
* This implementation always returns a {@link SimpleThrowawayClassLoader}.
*/
@Override
public ClassLoader getThrowawayClassLoader() {
return new SimpleThrowawayClassLoader(getInstrumentableClassLoader());
}
/**
* Remove all registered transformers, in inverse order of registration.
*/
public void removeTransformers() {
synchronized (this.transformers) {
if (this.instrumentation != null && !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()
*/
@Nullable
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;
@Nullable
private final ClassLoader targetClassLoader;
public FilteringClassFileTransformer(
ClassFileTransformer targetTransformer, @Nullable ClassLoader targetClassLoader) {
this.targetTransformer = targetTransformer;
this.targetClassLoader = targetClassLoader;
}
@Override
@Nullable
public byte[] transform(ClassLoader loader, String className, Class classBeingRedefined,
ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException {
if (this.targetClassLoader != loader) {
return null;
}
return this.targetTransformer.transform(
loader, className, classBeingRedefined, protectionDomain, classfileBuffer);
}
@Override
public String toString() {
return "FilteringClassFileTransformer for: " + this.targetTransformer.toString();
}
}
}