uimaj-2.2.0-incubating/uimaj-core/src/main/java/org/apache/uima/internal/util/UIMAClassLoader.java

/*
 * 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.uima.internal.util;

import java.io.File;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.ArrayList;
import java.util.StringTokenizer;

/**
 * UIMAClassLoader is used as extension ClassLoader for UIMA to load additional components like
 * annotators and resources. The classpath of the classloader is specified as string.
 * 
 * The strategy for this ClassLoader tries to load the class itself before the classloading is
 * delegated to the application class loader.
 * 
 */
public class UIMAClassLoader extends URLClassLoader {
  /**
   * Transforms the string classpath to and URL array based classpath.
   * 
   * The classpath string must be separated with the filesystem path separator.
   * 
   * @param classpath
   *          a classpath string
   * @return URL[] array of wellformed URL's
   * @throws MalformedURLException
   *           if a malformed URL has occurred in the classpath string.
   */
  public static URL[] transformClasspath(String classpath) throws MalformedURLException {
    // initialize StringTokenizer to separate the classpath
    StringTokenizer tok = new StringTokenizer(classpath, File.pathSeparator);
    // pathList of the classpath entries
    ArrayList pathList = new ArrayList();

    // extract all classpath entries and add them to the pathList
    while (tok.hasMoreTokens()) {
      pathList.add(tok.nextToken());
    }
    final int max = pathList.size();
    URL[] urlArray = new URL[max];

    // transform all classpath entries to an URL and add them to an URL array
    for (int i = 0; i < max; i++) {
      urlArray[i] = (new File((String) pathList.get(i))).toURI().toURL();
      // calling toURI() first handles spaces in classpath
    }

    return urlArray;
  }

  /**
   * Creates a new UIMAClassLoader based on a classpath string
   * 
   * @param classpath
   *          a classpath string
   * 
   * @throws MalformedURLException
   *           if a malformed URL has occurred in the classpath string.
   */
  public UIMAClassLoader(String classpath) throws MalformedURLException {
    super(transformClasspath(classpath));
  }

  /**
   * Creates a new UIMAClassLoader based on a classpath URL's
   * 
   * @param classpath
   *          an array of wellformed classpath URL's
   */
  public UIMAClassLoader(URL[] classpath) {
    super(classpath);
  }

  /**
   * Creates a new UIMAClassLoader based on a classpath URL's. Also a parent ClassLoader can be
   * specified.
   * 
   * @param classpath
   *          an array of wellformed classpath URL's
   * @param parent
   *          specify the parent of the classloader
   */
  public UIMAClassLoader(URL[] classpath, ClassLoader parent) {
    super(classpath, parent);
  }

  /**
   * Creates a new UIMAClassLoader based on a classpath string. Also a parent ClassLoader can be
   * specified.
   * 
   * @param classpath
   *          a classpath string
   * @param parent
   *          specify the parent of the classloader
   * 
   * @throws MalformedURLException
   *           if a malformed URL has occurred in the classpath string.
   */
  public UIMAClassLoader(String classpath, ClassLoader parent) throws MalformedURLException {
    super(transformClasspath(classpath), parent);
  }

  /**
   * Do not use this factory method - throws unsupportedOperationException
   */
  public static URLClassLoader newInstance(final URL[] urls) {
    throw new UnsupportedOperationException();
  }

  /**
   * Do not use this factory method - throws unsupportedOperationException
   */
  public static URLClassLoader newInstance(final URL[] urls, final ClassLoader parent) {
    throw new UnsupportedOperationException();
  }

  /*
   * Try to load the class itself before delegate the class loading to its parent
   */
  protected synchronized Class loadClass(String name, boolean resolve)
          throws ClassNotFoundException {
    // First, check if the class has already been loaded
    Class c = findLoadedClass(name);
    if (c == null) {
      try {
        // try to load class
        c = findClass(name);
      } catch (ClassNotFoundException e) {
        // delegate class loading for clas
        c = super.loadClass(name, false);
      }
    }
    if (resolve) {
      resolveClass(c);
    }
    return c;
  }

}