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/* This file is part of the project "Hilbert II" - http://www.qedeq.org
*
* Copyright 2000-2013, Michael Meyling .
*
* "Hilbert II" is free software; you can redistribute
* it and/or modify it under the terms of the GNU General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*/
package org.qedeq.base.io;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.net.URL;
import org.qedeq.base.trace.Trace;
/**
* Utility methods for accessing classes and resources using an appropriate class loader.
* Adapted from org.apache.myfaces.trinidad.util.ClassLoaderUtils.
*
* @author Michael Meyling
*/
public final class ResourceLoaderUtility {
/** This class. */
private static final Class CLASS = ResourceLoaderUtility.class;
/**
* Constructor, should never be called.
*/
private ResourceLoaderUtility() {
// don't call me
}
/**
* Loads the class with the specified name. For Java 2 callers, the current thread's context
* class loader is preferred, falling back on the system class loader of the caller when the
* current thread's context is not set, or the caller is pre Java 2.
*
* @param name Name of class to load.
* @return The resulting Class object
* @exception ClassNotFoundException Class was not found.
*/
public static Class loadClass(final String name) throws ClassNotFoundException {
return loadClass(name, null);
}
/**
* Locates the resource with the specified name. For Java 2 callers, the current thread's
* context class loader is preferred, falling back on the system class loader of the caller when
* the current thread's context is not set, or the caller is pre Java 2.
*
* @param name Resource name.
* @return Resulting URL object. Maybe null.
*/
public static URL getResourceUrl(final String name) {
return getResourceUrl(name, ResourceLoaderUtility.class.getClassLoader());
}
/**
* Locates the stream resource with the specified name. For Java 2 callers, the current thread's
* context class loader is preferred, falling back on the system class loader of the caller when
* the current thread's context is not set, or the caller is pre Java 2.
*
* @param name the name of the resource
* @return the resulting InputStream object
*/
public static InputStream getResourceAsStream(final String name) {
return getResourceAsStream(name, null);
}
/**
* Loads the class with the specified name. For Java 2 callers, the current thread's context
* class loader is preferred, falling back on the class loader of the caller when the current
* thread's context is not set, or the caller is pre Java 2. If the callerClassLoader is null,
* then fall back on the system class loader.
*
* @param name the name of the class
* @param callerClassLoader the calling class loader context
* @return the resulting Class object
* @exception ClassNotFoundException if the class was not found
*/
public static Class loadClass(final String name, final ClassLoader callerClassLoader)
throws ClassNotFoundException {
Class clazz = null;
try {
final ClassLoader loader = getContextClassLoader();
if (loader != null) {
clazz = loader.loadClass(name);
}
} catch (ClassNotFoundException e) {
// treat as though loader not set
}
if (clazz == null) {
if (callerClassLoader != null) {
clazz = callerClassLoader.loadClass(name);
} else {
clazz = Class.forName(name);
}
}
return clazz;
}
/**
* Locates the resource with the specified name. For Java 2 callers, the current thread's
* context class loader is preferred, falling back on the class loader of the caller when the
* current thread's context is not set, or the caller is pre Java 2. If the callerClassLoader is
* null, then fall back on the system class loader.
*
* @param name the name of the resource
* @param callerClassLoader the calling class loader context
* @return the resulting URL object
*/
public static URL getResourceUrl(final String name, final ClassLoader callerClassLoader) {
checkResourceName(name);
URL url = null;
final ClassLoader loader = getContextClassLoader();
if (loader != null) {
url = loader.getResource(name);
}
if (url == null) {
// no success, now we try the given class loader
if (callerClassLoader != null) {
url = callerClassLoader.getResource(name);
} else {
// last try: get resource via classpath
url = ClassLoader.getSystemResource(name);
}
}
return url;
}
/**
* Locates the resource stream with the specified name. For Java 2 callers, the current thread's
* context class loader is preferred, falling back on the class loader of the caller when the
* current thread's context is not set, or the caller is pre Java 2. If the callerClassLoader is
* null, then fall back on the system class loader.
*
* @param name the name of the resource
* @param callerClassLoader the calling class loader context
* @return the resulting InputStream object
*/
public static InputStream getResourceAsStream(final String name,
final ClassLoader callerClassLoader) {
checkResourceName(name);
InputStream stream = null;
final ClassLoader loader = getContextClassLoader();
if (loader != null) {
stream = loader.getResourceAsStream(name);
}
if (stream == null) {
if (callerClassLoader != null) {
stream = callerClassLoader.getResourceAsStream(name);
} else {
stream = ClassLoader.getSystemResourceAsStream(name);
}
}
return stream;
}
/**
* Dynamically accesses the current context class loader. Returns null if there is
* no per-thread context class loader. Also if the JRE is below 1.2 or something else went wrong
* the method returns null.
*
* @return ClassLoader.
*/
public static ClassLoader getContextClassLoader() {
try {
final Method method = Thread.class.getMethod("getContextClassLoader", null);
return (ClassLoader) method.invoke(Thread.currentThread(), null);
} catch (RuntimeException e) {
return null;
} catch (IllegalAccessException e) {
return null;
} catch (InvocationTargetException e) {
return null;
} catch (NoSuchMethodException e) {
return null;
}
}
private static void checkResourceName(final String name) {
if ((name != null) && name.startsWith("/")) {
Trace.info(CLASS, "ClassLoaderUtility", "checkResourceName",
"resource name not portable: " + name);
}
}
/**
* Get resource file. The resource is located within the file system if it exists already.
* If not it is loaded as resource and then saved as a file.
*
* @param startDirectory Start looking from this directory.
* @param resourceDirectoryName Within this directory
* (relative to startDirectory).
* @param resourceName Look for this resource file.
* @return Resource file.
*/
public static File getResourceFile(final File startDirectory,
final String resourceDirectoryName, final String resourceName) {
final File resourceDir = new File(startDirectory, resourceDirectoryName);
final File resource = new File(resourceDir, resourceName);
if (!resource.exists()) {
final URL url = getResourceUrl(resourceDirectoryName + "/" + resourceName);
if (url == null) {
Trace.info(ResourceLoaderUtility.class, "getResourceUrlAndMakeLocalCopy",
"URL not found for: " + resourceDirectoryName + "/" + resourceName);
return null;
}
try {
if (!resourceDir.exists()) {
if (!resourceDir.mkdirs()) {
Trace.info(ResourceLoaderUtility.class, "getResourceUrlAndMakeLocalCopy",
"creation failed: " + resourceDir);
}
}
IoUtility.saveFile(url, resource);
} catch (IOException e) {
Trace.fatal(ResourceLoaderUtility.class, "getResourceUrlAndMakeLocalCopy",
"resource can not be saved", e);
}
}
return resource;
}
}
