org.apache.log4j.helpers.Loader Maven / Gradle / Ivy
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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.apache.log4j.helpers;
import java.net.URL;
/**
* Loads resources (or images) from various sources.
*/
public class Loader {
static final String TSTR = "Caught Exception while in Loader.getResource. This may be innocuous.";
static private boolean ignoreTCL;
static {
final String ignoreTCLProp = OptionConverter.getSystemProperty("log4j.ignoreTCL", null);
if (ignoreTCLProp != null) {
ignoreTCL = OptionConverter.toBoolean(ignoreTCLProp, true);
}
}
/**
* This method will search for resource in different places. The search order is as follows:
*
*
*
- Search for
resource using the thread context class loader under Java2. If that fails, search for
* resource using the class loader that loaded this class (Loader).
*
*
*
- Try one last time with
ClassLoader.getSystemResource(resource).
*
*
*/
static public URL getResource(final String resource) {
ClassLoader classLoader = null;
URL url = null;
try {
if (!ignoreTCL) {
classLoader = getTCL();
if (classLoader != null) {
LogLog.debug("Trying to find [" + resource + "] using context classloader " + classLoader + ".");
url = classLoader.getResource(resource);
if (url != null) {
return url;
}
}
}
// We could not find resource. Ler us now try with the
// ClassLoader that loaded this class.
classLoader = Loader.class.getClassLoader();
if (classLoader != null) {
LogLog.debug("Trying to find [" + resource + "] using " + classLoader + " class loader.");
url = classLoader.getResource(resource);
if (url != null) {
return url;
}
}
} catch (final Throwable t) {
// can't be InterruptedException or InterruptedIOException
// since not declared, must be error or RuntimeError.
LogLog.warn(TSTR, t);
}
// Last ditch attempt: get the resource from the class path. It
// may be the case that clazz was loaded by the Extentsion class
// loader which the parent of the system class loader. Hence the
// code below.
LogLog.debug("Trying to find [" + resource + "] using ClassLoader.getSystemResource().");
return ClassLoader.getSystemResource(resource);
}
/**
* Gets a resource by delegating to getResource(String).
*
* @param resource resource name
* @param clazz class, ignored.
* @return URL to resource or null.
* @deprecated as of 1.2.
*/
@Deprecated
public static URL getResource(final String resource, final Class clazz) {
return getResource(resource);
}
/**
* Shorthand for {@code Thread.currentThread().getContextClassLoader()}.
*/
private static ClassLoader getTCL() {
return Thread.currentThread().getContextClassLoader();
}
/**
* Always returns false since Java 1.x support is long gone.
*
* @return Always false.
*/
public static boolean isJava1() {
return false;
}
/**
* Loads the specified class using the Thread contextClassLoader, if that fails try
* Class.forname.
*
* @param clazz The class to load.
* @return The Class.
* @throws ClassNotFoundException Never thrown, declared for compatibility.
*/
static public Class loadClass(final String clazz) throws ClassNotFoundException {
// Just call Class.forName(clazz) if we are instructed to ignore the TCL.
if (ignoreTCL) {
return Class.forName(clazz);
}
try {
return getTCL().loadClass(clazz);
} catch (final Throwable t) {
// ignore
}
return Class.forName(clazz);
}
}