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/*
* Copyright (C) 2010 The Android Open Source Project
*
* 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 tests.util;
import java.io.File;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
/**
* Builds a configured class loader. The constructed class loader can load a
* private copy of a class in addition to the copy in the application class
* loader. It can also refuse to load a class altogether, even if that class
* exists on the classpath.
*/
public final class ClassLoaderBuilder {
private ClassLoader parent = ClassLoaderBuilder.class.getClassLoader();
private final Set<String> prefixesToNotInherit = new HashSet<String>();
private final Set<String> prefixesToLoad = new HashSet<String>();
public ClassLoaderBuilder parent(ClassLoader parent) {
this.parent = parent;
return this;
}
/**
* @param classNamePrefix the prefix of classes that can be loaded by both
* the constructed class loader and the application class loader.
*/
public ClassLoaderBuilder withPrivateCopy(String classNamePrefix) {
prefixesToLoad.add(classNamePrefix);
return this;
}
/**
* @param classNamePrefix the prefix of classes that will not be loaded by
* this class loader. Attempts to load such classes will fail at runtime
* with a NoClassDefFoundError.
*/
public ClassLoaderBuilder without(String classNamePrefix) {
prefixesToNotInherit.add(classNamePrefix);
return this;
}
public ClassLoader build() {
// make a defensive copy in case this builder is reused!
final Set<String> prefixesToNotInherit = new HashSet<String>(this.prefixesToNotInherit);
final Set<String> prefixesToLoad = new HashSet<String>(this.prefixesToLoad);
/*
* To load two copies of a given class in the VM, we end up creating two
* new class loaders: a bridge class loader and a leaf class loader.
*
* The bridge class loader is a child of the application class loader.
* It never loads any classes. All it does is decide when to delegate to
* the application class loader (which has a copy of everything) and
* when to fail.
*
* The leaf class loader is a child of the bridge class loader. It
* uses the same classpath as the application class loader. It loads
* anything that its parent failed on.
*/
ClassLoader bridge = new ClassLoader(parent) {
@Override protected Class<?> loadClass(String className, boolean resolve)
throws ClassNotFoundException {
for (String prefix : prefixesToLoad) {
if (className.startsWith(prefix)) {
/* ClassNotFoundException causes the child loader to load the class. */
throw new ClassNotFoundException();
}
}
for (String prefix : prefixesToNotInherit) {
if (className.startsWith(prefix)) {
/* NoClassDefFoundError prevents the class from being loaded at all. */
throw new NoClassDefFoundError();
}
}
return super.loadClass(className, resolve);
}
};
try {
// first try to create a PathClassLoader for a dalvik VM...
String classPath = getApplicationClassPath();
return (ClassLoader) Class.forName("dalvik.system.PathClassLoader")
.getConstructor(String.class, ClassLoader.class)
.newInstance(classPath, bridge);
} catch (Exception ignored) {
}
// fall back to a URLClassLoader on a JVM
List<URL> classpath = new ArrayList<URL>();
classpath.addAll(classpathToUrls("java.class.path"));
classpath.addAll(classpathToUrls("sun.boot.class.path"));
return new URLClassLoader(classpath.toArray(new URL[classpath.size()]), bridge);
}
/**
* Returns a path containing the application's classes. When running in the
* Android framework this will be the APK file; otherwise it's the runtime's
* reported class path.
*/
private String getApplicationClassPath() {
String manifestFile = "AndroidManifest.xml";
String suffix = "!/" + manifestFile;
ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
URL manifest = classLoader.getResource(manifestFile);
if (manifest != null) {
String manifestString = manifest.toString();
if (manifestString.endsWith(suffix)) {
return manifestString.substring(0, manifestString.length() - suffix.length());
}
}
return System.getProperty("java.class.path");
}
private List<URL> classpathToUrls(String propertyName) {
try {
String classpath = System.getProperty(propertyName);
List<URL> result = new ArrayList<URL>();
for (String pathElement : classpath.split(File.pathSeparator)) {
result.add(new File(pathElement).toURI().toURL());
}
return result;
} catch (MalformedURLException e) {
throw new RuntimeException(e);
}
}
}
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