src/main/java/org/apache/log4j/helpers/Loader.java

/*
 * Copyright 1999,2004 The Apache Software Foundation.
 *
 * 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 org.apache.log4j.helpers;

import java.net.URL;



/**
   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
  private static boolean java1 = true;
  private static 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);
    }
  }

  /**
   *  Get 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.
   */
  public static URL getResource(String resource, Class clazz) {
      return getResource(resource);
  }

  /**
     This method will search for <code>resource</code> in different
     places. The search order is as follows:

     <ol>

     <p><li>Search for <code>resource</code> using the thread context
     class loader under Java2. This step is performed only if the <code>
     skipTCL</code> parameter is false.</li>

     <p><li>If the previous step failed, search for <code>resource</code> using
     the class loader that loaded this class (<code>Loader</code>).</li>

     <p><li>Try one last time with
     <code>ClassLoader.getSystemResource(resource)</code>, that is is
     using the system class loader in JDK 1.2 and virtual machine's
     built-in class loader in JDK 1.1.

     </ol>
  */
  public static URL getResource(String resource) {
    ClassLoader classLoader = null;
    URL url = null;

    try {
      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 <code>null<code>.
    *
    *  */
  private static ClassLoader getTCL() {
    return Thread.currentThread().getContextClassLoader();
  }

  /**
   * If running under JDK 1.2 load the specified class using the
   *  <code>Thread</code> <code>contextClassLoader</code> if that
   *  fails try Class.forname. Under JDK 1.1 only Class.forName is
   *  used.
   *
   */
  public static 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);
      }
    }
  }
}