cvs commit: jakarta-commons/jelly/src/java/org/apache/commons/jelly/util ClassLoaderUtils.java

[di...@apache.org]

dion        2004/09/09 08:05:39

  Added:       jelly/src/java/org/apache/commons/jelly/util
                        ClassLoaderUtils.java
  Log:
  Add class to centralize class loader retrieval and loading classes for JELLY-134
  
  Revision  Changes    Path
  1.1                  jakarta-commons/jelly/src/java/org/apache/commons/jelly/util/ClassLoaderUtils.java
  
  Index: ClassLoaderUtils.java
  ===================================================================
  /*
   * Copyright 2002,2004 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.commons.jelly.util;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  
  /**
   * A class to centralize the class loader management code.
   */
  public class ClassLoaderUtils {
  
      /** log for debug etc output */
      private static final Log log = LogFactory.getLog(ClassLoaderUtils.class);
      
      /**
       * Return the class loader to be used for instantiating application objects
       * when required.  This is determined based upon the following rules:
       * <ul>
       * <li>The specified class loader, if any</li>
       * <li>The thread context class loader, if it exists and <code>useContextClassLoader</code> is true</li>
       * <li>The class loader used to load the calling class.
       * <li>The System class loader.
       * </ul>
       */
      public static ClassLoader getClassLoader(ClassLoader specifiedLoader, boolean useContextClassLoader, Class callingClass) {
          if (specifiedLoader != null) {
              return specifiedLoader;
          }
          if (useContextClassLoader) {
              ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
              if (classLoader != null) {
                  return classLoader;
              }
          }
          return getClassLoader(callingClass);
      }
  
      /**
       * Return the class loader to be used for instantiating application objects
       * when a context class loader is not specified.  This is determined based upon the following rules:
       * <ul>
       * <li>The specified class loader, if any</li>
       * <li>The class loader used to load the calling class.
       * <li>The System class loader.
       * </ul>
       */
      public static ClassLoader getClassLoader(ClassLoader specifiedLoader, Class callingClass) {
          if (specifiedLoader != null) {
              return specifiedLoader;
          }
          return getClassLoader(callingClass);
      }
  
      /**
       * Get the loader for the given class. 
       * @param clazz the class to retrieve the loader for
       * @return the class loader that loaded the provided class
       */
      public static ClassLoader getClassLoader(Class clazz) {
          ClassLoader callersLoader = clazz.getClassLoader();
          if (callersLoader == null) {
              callersLoader = ClassLoader.getSystemClassLoader();
          }
          return callersLoader;
      }
  
      /**
       * Loads the given class using the current Thread's context class loader first
       * otherwise use the class loader which loaded this class.
       */
      public static Class loadClass(String className, Class callingClass) throws ClassNotFoundException {
          ClassLoader loader = Thread.currentThread().getContextClassLoader();
          if (loader == null) {
              return getClassLoader(callingClass).loadClass(className);
          } else {
              return loader.loadClass(className);
          }
      }
  
      /**
       * Loads the given class using:
       * <ol>
       * <li>the specified classloader,</li>
       * <li>the current Thread's context class loader first, if asked</li>
       * <li>otherwise use the class loader which loaded this class.</li>
       * </ol>
       */
      public static Class loadClass(String className, ClassLoader specifiedLoader, boolean useContextLoader, Class callingClass) throws ClassNotFoundException {
          Class clazz = null;
          if (specifiedLoader != null) {
              try {
                  clazz = specifiedLoader.loadClass(className);
              } catch (ClassNotFoundException e) {
                  log.debug("couldn't find class in specified loader", e);
              }
          }
          if (clazz == null && useContextLoader) {
              ClassLoader contextLoader = Thread.currentThread().getContextClassLoader();
              if (contextLoader != null) {
                  try {
                      clazz = contextLoader.loadClass(className);
                  } catch (ClassNotFoundException e) {
                      log.debug("couldn't find class in specified loader", e);
                  }
              }
          }
          if (clazz == null) {
              ClassLoader loader = getClassLoader(callingClass);
              clazz = loader.loadClass(className);
          }
          return clazz;
      }
  }
  
  
  

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