MultiClassLoader.java

/*
Copyright 2011-2016 Google Inc. All Rights Reserved.

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 com.google.security.zynamics.zylib.plugins;

import java.util.Hashtable;

/**
 * A simple test class loader capable of loading from multiple sources, such as local files or a
 * URL.
 * 
 * This class is derived from an article by Chuck McManis
 * http://www.javaworld.com/javaworld/jw-10-1996/indepth.src.html with large modifications.
 * 
 * Note that this has been updated to use the non-deprecated version of defineClass() -- JDM.
 * 
 * @author Jack Harich - 8/18/97
 * @author John D. Mitchell - 99.03.04
 */
@Deprecated
public abstract class MultiClassLoader extends ClassLoader {

  // ---------- Fields --------------------------------------
  private final Hashtable<String, Class<?>> classes = new Hashtable<String, Class<?>>();
  private char classNameReplacementChar;

  protected boolean monitorOn = false;
  protected boolean sourceMonitorOn = true;

  // ---------- Initialization ------------------------------
  public MultiClassLoader() {
  }

  // --- Std
  protected static void print(final String text) {
    System.out.println(text);
  }

  protected String formatClassName(final String className) {
    if (classNameReplacementChar == '\u0000') {
      // '/' is used to map the package to the path
      return className.replace('.', '/') + ".class";
    } else {
      // Replace '.' with custom char, such as '_'
      return className.replace('.', classNameReplacementChar) + ".class";
    }
  }

  // ---------- Protected Methods ---------------------------
  protected abstract byte[] loadClassBytes(String className);

  protected void monitor(final String text) {
    if (monitorOn) {
      print(text);
    }
  }

  // ---------- Superclass Overrides ------------------------
  /**
   * This is a simple version for external clients since they will always want the class resolved
   * before it is returned to them.
   */
  @Override
  public Class<?> loadClass(final String className) throws ClassNotFoundException {
    return loadClass(className, true);
  }

  // ---------- Abstract Implementation ---------------------
  @Override
  public synchronized Class<?> loadClass(final String className, final boolean resolveIt)
      throws ClassNotFoundException {

    Class<?> result;
    byte[] classBytes;
    monitor(">> MultiClassLoader.loadClass(" + className + ", " + resolveIt + ")");

    // ----- Check our local cache of classes
    result = classes.get(className);
    if (result != null) {
      monitor(">> returning cached result.");
      return result;
    }

    // ----- Check with the primordial class loader
    try {
      result = super.findSystemClass(className);
      monitor(">> returning system class (in CLASSPATH).");
      return result;
    } catch (final ClassNotFoundException e) {
      monitor(">> Not a system class.");
    }

    // ----- Try to load it from preferred source
    // Note loadClassBytes() is an abstract method
    classBytes = loadClassBytes(className);
    if (classBytes == null) {
      throw new ClassNotFoundException();
    }

    // ----- Define it (parse the class file)
    result = defineClass(className, classBytes, 0, classBytes.length);
    if (result == null) {
      throw new ClassFormatError();
    }

    // ----- Resolve if necessary
    if (resolveIt) {
      resolveClass(result);
    }

    // Done
    classes.put(className, result);
    monitor(">> Returning newly loaded class.");
    return result;
  }

  // ---------- Public Methods ------------------------------
  /**
   * This optional call allows a class name such as "COM.test.Hello" to be changed to
   * "COM_test_Hello", which is useful for storing classes from different packages in the same
   * retrival directory. In the above example the char would be '_'.
   */
  public void setClassNameReplacementChar(final char replacement) {
    classNameReplacementChar = replacement;
  }

} // End class