ClassLoaderUtility.java

/**
 * The contents of this file are subject to the license and copyright
 * detailed in the LICENSE file at the root of the source
 * tree and available online at
 *
 * https://github.com/keeps/roda
 */
package org.roda.core.util;

import java.io.File;
import java.io.IOException;
import java.lang.reflect.Method;
import java.net.URL;
import java.net.URLClassLoader;

import org.apache.commons.lang3.StringUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * @author Rui Castro
 */
public class ClassLoaderUtility {

  // Log object
  private static final Logger LOGGER = LoggerFactory.getLogger(ClassLoaderUtility.class);

  // Parameters
  private static final Class[] PARAMETERS = new Class[] {URL.class};
  private static final ClassLoader CLASS_LOADER = ClassLoaderUtility.class.getClassLoader();

  private ClassLoaderUtility() {
    // do nothing
  }

  /**
   * Add file to CLASSPATH
   * 
   * @param s
   *          File name
   * @throws IOException
   *           IOException
   */
  public static void addFile(String s) throws IOException {
    File f = new File(s);
    addFile(f);
  }

  /**
   * Add file to CLASSPATH
   * 
   * @param f
   *          File object
   * @throws IOException
   *           IOException
   */
  public static void addFile(File f) throws IOException {
    addURL(f.toURL());
  }

  /**
   * Add URL to CLASSPATH
   * 
   * @param url
   *          {@link URL}
   * @throws IOException
   *           IOException
   */
  public static void addURL(URL url) throws IOException {

    URLClassLoader sysLoader = (URLClassLoader) ClassLoader.getSystemClassLoader();
    URL urls[] = sysLoader.getURLs();
    for (int i = 0; i < urls.length; i++) {

      if (StringUtils.equalsIgnoreCase(urls[i].toString(), url.toString())) {
        LOGGER.debug("URL {} is already in the CLASSPATH", url);
        return;
      }
    }

    try {
      Method method = URLClassLoader.class.getDeclaredMethod("addURL", PARAMETERS);
      method.setAccessible(true);
      method.invoke(sysLoader, new Object[] {url});
    } catch (Throwable t) {
      throw new IOException("Error, could not add URL to system classloader", t);
    }
  }

  /**
   * Creates an instance of an object of the given class name.
   * 
   * @param className
   *          the name of the class to create an instance.
   * @return the instance created.
   * 
   * @throws ClassNotFoundException
   * @throws IllegalAccessException
   * @throws InstantiationException
   */
  public static Object createObject(String className)
    throws ClassNotFoundException, InstantiationException, IllegalAccessException {

    if (StringUtils.isBlank(className)) {
      throw new IllegalArgumentException("className cannot be null");
    }

    LOGGER.trace("Loading class {} with ClassLoader {}", className, CLASS_LOADER.getClass().getSimpleName());

    return CLASS_LOADER.loadClass(className).newInstance();
  }

  /**
   * Adds the given {@link URL}s to the classpath and creates an instance of the
   * given class.
   * 
   * @param urls
   *          a list of {@link URL}s to be added to the classpath.
   * @param className
   *          the name of the class for which to create an instance.
   * @return the instance created.
   * 
   * @throws ClassNotFoundException
   * @throws IllegalAccessException
   * @throws InstantiationException
   */
  public static Object createObject(URL[] urls, String className)
    throws ClassNotFoundException, InstantiationException, IllegalAccessException {

    if (StringUtils.isBlank(className)) {
      throw new IllegalArgumentException("className cannot be null");
    }

    URLClassLoader clazzLoader = new URLClassLoader(urls, CLASS_LOADER);

    LOGGER.trace("Loading class {} with ClassLoader {}", className, CLASS_LOADER.getClass().getSimpleName());

    return clazzLoader.loadClass(className).newInstance();
  }

  /**
   * Adds the given file path to the classpath and creates an instance of the
   * given class name.
   * 
   * @param filePath
   *          the path of the file to add to the classpath.
   * @param className
   *          the name of the class for which to create an instance.
   * @return the instance created.
   * 
   * @throws IOException
   * @throws ClassNotFoundException
   * @throws IllegalAccessException
   * @throws InstantiationException
   */
  public static Object createObject(String filePath, String className)
    throws ClassNotFoundException, InstantiationException, IllegalAccessException, IOException {

    if (StringUtils.isBlank(className)) {
      throw new IllegalArgumentException("className cannot be null");
    }

    ClassLoaderUtility.addFile(filePath);
    String path = "jar:file://" + filePath + "!/";
    URL url = new File(path).toURL();

    URLClassLoader clazzLoader = new URLClassLoader(new URL[] {url}, CLASS_LOADER);

    LOGGER.trace("Loading class {} with ClassLoader {}", className, CLASS_LOADER.getClass().getSimpleName());
    return clazzLoader.loadClass(className).newInstance();
  }

}