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The source code

/*
 * Copyright (C) The Apache Software Foundation. All rights reserved.
 *
 * This software is published under the terms of the Apache Software
 * License version 1.1, a copy of which has been included with this
 * distribution in the LICENSE.txt file.  */

package org.apache.log4j.helpers;

import java.net.URL;
import java.lang.IllegalAccessException;
import java.lang.reflect.Method;
import java.lang.reflect.InvocationTargetException;

//import java.awt.Image;
//import java.awt.Toolkit;

/**
   Load resources (or images) from various sources.
 
  @author Ceki Gülcü
 */

public class Loader  { 

  static final String TSTR = "Caught Exception while in Loader.getResource. This may be innocuous.";

  // We conservatively assume that we are running under Java 1.x
  static private boolean java1 = true;
  
  static private boolean ignoreTCL = false;
  
  static {
    String prop = OptionConverter.getSystemProperty("java.version", null);
    
    if(prop != null) {
      int i = prop.indexOf('.');
      if(i != -1) {	
	if(prop.charAt(i+1) != '1')
	  java1 = false;
      } 
    }
    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 rearch order is as follows:

     

  1. 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). Under JDK 1.1, only the the class loader that loaded this class (Loader) is used.

  2. Try one last time with ClassLoader.getSystemResource(resource), that is is using the system class loader in JDK 1.2 and virtual machine's built-in class loader in JDK 1.1.
*/ static public URL getResource(String resource) { ClassLoader classLoader = null; URL url = null; try { if(!java1) { 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(Throwable t) { 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); } /** Are we running under JDK 1.x? */ public static boolean isJava1() { return java1; } /** * Get the Thread Context Loader which is a JDK 1.2 feature. If we * are running under JDK 1.1 or anything else goes wrong the method * returns null. * * */ private static ClassLoader getTCL() throws IllegalAccessException, InvocationTargetException { // Are we running on a JDK 1.2 or later system? Method method = null; try { method = Thread.class.getMethod("getContextClassLoader", null); } catch (NoSuchMethodException e) { // We are running on JDK 1.1 return null; } return (ClassLoader) method.invoke(Thread.currentThread(), null); } /** * If running under JDK 1.2 load the specified class using the * Thread contextClassLoader if that * fails try Class.forname. Under JDK 1.1 only Class.forName is * used. * */ static public Class loadClass (String clazz) throws ClassNotFoundException { // Just call Class.forName(clazz) if we are running under JDK 1.1 // or if we are instructed to ignore the TCL. if(java1 || ignoreTCL) { return Class.forName(clazz); } else { try { return getTCL().loadClass(clazz); } catch(Throwable e) { // we reached here because tcl was null or because of a // security exception, or because clazz could not be loaded... // In any case we now try one more time return Class.forName(clazz); } } } }
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