Mega Code Archive
Loading resources and classes in a fault tolerant manner
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/*
* Copyright (c) 2002-2003 by OpenSymphony
* All rights reserved.
*/
import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
import java.util.Collections;
/**
* This class is extremely useful for loading resources and classes in a fault tolerant manner
* that works across different applications servers.
* <p/>
* It has come out of many months of frustrating use of multiple application servers at Atlassian,
* please don't change things unless you're sure they're not going to break in one server or another!
*
* @author plightbo
* @author tmjee
* @version $Date: 2007-11-30 18:45:26 +0800 (Fri, 30 Nov 2007) $ $Id: ClassLoaderUtils.java 2977 2007-11-30 10:45:26Z tm_jee $
*/
public class ClassLoaderUtils {
/**
* Load a given resource.
* <p/>
* This method will try to load the resource using the following methods (in order):
* <ul>
* <li>From {@link Thread#getContextClassLoader() Thread.currentThread().getContextClassLoader()}
* <li>From {@link Class#getClassLoader() ClassLoaderUtil.class.getClassLoader()}
* <li>From the {@link Class#getClassLoader() callingClass.getClassLoader() }
* </ul>
*
* @param resourceName The name of the resource to load
* @param callingClass The Class object of the calling object
*/
public static URL getResource(String resourceName, Class callingClass) {
URL url = null;
url = Thread.currentThread().getContextClassLoader().getResource(resourceName);
if (url == null) {
url = ClassLoaderUtils.class.getClassLoader().getResource(resourceName);
}
if (url == null) {
url = callingClass.getClassLoader().getResource(resourceName);
}
return url;
}
/**
* This is a convenience method to load a resource as a stream.
* <p/>
* The algorithm used to find the resource is given in getResource()
*
* @param resourceName The name of the resource to load
* @param callingClass The Class object of the calling object
*/
public static InputStream getResourceAsStream(String resourceName, Class callingClass) {
URL url = getResource(resourceName, callingClass);
try {
return (url != null) ? url.openStream() : null;
} catch (IOException e) {
return null;
}
}
/**
* Load a class with a given name.
* <p/>
* It will try to load the class in the following order:
* <ul>
* <li>From {@link Thread#getContextClassLoader() Thread.currentThread().getContextClassLoader()}
* <li>Using the basic {@link Class#forName(java.lang.String) }
* <li>From {@link Class#getClassLoader() ClassLoaderUtil.class.getClassLoader()}
* <li>From the {@link Class#getClassLoader() callingClass.getClassLoader() }
* </ul>
*
* @param className The name of the class to load
* @param callingClass The Class object of the calling object
* @throws ClassNotFoundException If the class cannot be found anywhere.
*/
public static Class loadClass(String className, Class callingClass) throws ClassNotFoundException {
try {
return Thread.currentThread().getContextClassLoader().loadClass(className);
} catch (ClassNotFoundException e) {
try {
return Class.forName(className);
} catch (ClassNotFoundException ex) {
try {
return ClassLoaderUtils.class.getClassLoader().loadClass(className);
} catch (ClassNotFoundException exc) {
return callingClass.getClassLoader().loadClass(className);
}
}
}
}
/**
* Prints the current classloader hierarchy - useful for debugging.
*/
public static void printClassLoader() {
System.out.println("ClassLoaderUtils.printClassLoader");
printClassLoader(Thread.currentThread().getContextClassLoader());
}
/**
* Prints the classloader hierarchy from a given classloader - useful for debugging.
*/
public static void printClassLoader(ClassLoader cl) {
System.out.println("ClassLoaderUtils.printClassLoader(cl = " + cl + ")");
if (cl != null) {
printClassLoader(cl.getParent());
}
}
}
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