org.springframework.instrument.classloading.tomcat.TomcatInstrumentableClassLoader Maven / Gradle / Ivy
/*
* Copyright 2002-2006 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.tomcat;
import java.lang.instrument.ClassFileTransformer;
import java.lang.reflect.Field;
import java.lang.reflect.Modifier;
import org.apache.catalina.loader.ResourceEntry;
import org.apache.catalina.loader.WebappClassLoader;
import org.springframework.instrument.classloading.WeavingTransformer;
/**
* Extension of Tomcat's default class loader which adds instrumentation
* to loaded classes without the need of using a VM-wide agent.
*
* To be registered using a Loader tag in Tomcat's Context
* definition in the server.xml file, with the Spring-provided
* "spring-tomcat-weaver.jar" file deployed into Tomcat's "server/lib" directory.
* The required configuration tag looks as follows:
*
*
* <Loader loaderClass="org.springframework.instrument.classloading.tomcat.TomcatInstrumentableClassLoader"/>
*
* Typically used in combination with a
* {@link org.springframework.instrument.classloading.ReflectiveLoadTimeWeaver}
* defined in the Spring application context. The addTransformer and
* getThrowawayClassLoader methods mirror the corresponding methods
* in the LoadTimeWeaver interface, as expected by ReflectiveLoadTimeWeaver.
*
*
See the PetClinic sample application for a full example of this
* ClassLoader in action.
*
*
NOTE: Requires Apache Tomcat version 5.0 or higher.
*
* @author Costin Leau
* @since 2.0
* @see #addTransformer
* @see #getThrowawayClassLoader
* @see org.springframework.instrument.classloading.ReflectiveLoadTimeWeaver
*/
public class TomcatInstrumentableClassLoader extends WebappClassLoader {
/** Use an internal WeavingTransformer */
private final WeavingTransformer weavingTransformer;
public TomcatInstrumentableClassLoader() {
super();
this.weavingTransformer = new WeavingTransformer();
}
public TomcatInstrumentableClassLoader(ClassLoader classLoader) {
super(classLoader);
this.weavingTransformer = new WeavingTransformer(classLoader);
}
/**
* Delegate for LoadTimeWeaver's addTransformer method.
* Typically called through ReflectiveLoadTimeWeaver.
* @see org.springframework.instrument.classloading.LoadTimeWeaver#addTransformer
* @see org.springframework.instrument.classloading.ReflectiveLoadTimeWeaver
*/
public void addTransformer(ClassFileTransformer transformer) {
this.weavingTransformer.addTransformer(transformer);
}
/**
* Delegate for LoadTimeWeaver's getThrowawayClassLoader method.
* Typically called through ReflectiveLoadTimeWeaver.
* @see org.springframework.instrument.classloading.LoadTimeWeaver#getThrowawayClassLoader
* @see org.springframework.instrument.classloading.ReflectiveLoadTimeWeaver
*/
public ClassLoader getThrowawayClassLoader() {
WebappClassLoader tempLoader = new WebappClassLoader();
// Use reflection to copy all the fields since most of them are private
// on pre-5.5 Tomcat.
shallowCopyFieldState(this, tempLoader);
return tempLoader;
}
@Override
protected ResourceEntry findResourceInternal(String name, String path) {
ResourceEntry entry = super.findResourceInternal(name, path);
// Postpone String parsing as much as possible (it is slow).
if (entry != null && entry.binaryContent != null && path.endsWith(".class")) {
byte[] transformed = this.weavingTransformer.transformIfNecessary(name, entry.binaryContent);
entry.binaryContent = transformed;
}
return entry;
}
@Override
public String toString() {
StringBuilder sb = new StringBuilder(getClass().getName());
sb.append("\r\n");
sb.append(super.toString());
return sb.toString();
}
// The code below is orginially taken from ReflectionUtils and optimized for
// local usage. There is no dependency on ReflectionUtils to keep this class
// self-contained (since it gets deployed into Tomcat's server class loader).
/**
* Given the source object and the destination, which must be the same class
* or a subclass, copy all fields, including inherited fields. Designed to
* work on objects with public no-arg constructors.
* @throws IllegalArgumentException if arguments are incompatible or either
* is null
*/
private static void shallowCopyFieldState(final Object src, final Object dest) throws IllegalArgumentException {
if (src == null) {
throw new IllegalArgumentException("Source for field copy cannot be null");
}
if (dest == null) {
throw new IllegalArgumentException("Destination for field copy cannot be null");
}
Class targetClass = findCommonAncestor(src.getClass(), dest.getClass());
// Keep backing up the inheritance hierarchy.
do {
// Copy each field declared on this class unless it's static or
// file.
Field[] fields = targetClass.getDeclaredFields();
for (int i = 0; i < fields.length; i++) {
Field field = fields[i];
// Skip static and final fields (the old FieldFilter)
// do not copy resourceEntries - it's a cache that holds class entries.
if (!(Modifier.isStatic(field.getModifiers()) || Modifier.isFinal(field.getModifiers()) ||
field.getName().equals("resourceEntries"))) {
try {
// copy the field (the old FieldCallback)
field.setAccessible(true);
Object srcValue = field.get(src);
field.set(dest, srcValue);
}
catch (IllegalAccessException ex) {
throw new IllegalStateException(
"Shouldn't be illegal to access field '" + fields[i].getName() + "': " + ex);
}
}
}
targetClass = targetClass.getSuperclass();
}
while (targetClass != null && targetClass != Object.class);
}
private static Class findCommonAncestor(Class one, Class two) throws IllegalArgumentException {
Class ancestor = one;
while (ancestor != Object.class || ancestor != null) {
if (ancestor.isAssignableFrom(two)) {
return ancestor;
}
ancestor = ancestor.getSuperclass();
}
// try the other class hierarchy
ancestor = two;
while (ancestor != Object.class || ancestor != null) {
if (ancestor.isAssignableFrom(one)) {
return ancestor;
}
ancestor = ancestor.getSuperclass();
}
return null;
}
}