ClassUtils.java

/*
 * Copyright (c) 2012 Diamond Light Source Ltd.
 *
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 */
package uk.ac.diamond.scisoft.analysis.utils;

import java.io.File;
import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.net.JarURLConnection;
import java.net.URL;
import java.net.URLConnection;
import java.net.URLDecoder;
import java.util.ArrayList;
import java.util.Enumeration;
import java.util.jar.JarEntry;
import java.util.jar.JarFile;

public class ClassUtils {

	 /**
     * Attempts to list all the classes in the specified package as determined
     * by the context class loader
     * 
     * @param pckgname
     *            the package name to search
     * @return a list of classes that exist within that package
     * @throws ClassNotFoundException
     *             if something went wrong
     */
    public static ArrayList<Class<?>> getClassesForPackage( final ClassLoader cld, String pckgname)  throws ClassNotFoundException {
        final ArrayList<Class<?>> classes = new ArrayList<Class<?>>();

        try {
 
            if (cld == null)
                throw new ClassNotFoundException("Can't get class loader.");

            final Enumeration<URL> resources = cld.getResources(pckgname
                    .replace('.', '/'));
            URLConnection connection;

            for (URL url = null; resources.hasMoreElements()
                    && ((url = resources.nextElement()) != null);) {
                try {
                    connection = url.openConnection();

                    if (connection instanceof JarURLConnection) {
                        checkJarFile((JarURLConnection) connection, pckgname,
                                classes);
                    } else {
                        try {
                            checkDirectory(
                                    new File(URLDecoder.decode(url.getPath(),
                                            "UTF-8")), pckgname, classes);
                        } catch (final UnsupportedEncodingException ex) {
                            throw new ClassNotFoundException(
                                    pckgname
                                            + " does not appear to be a valid package (Unsupported encoding)",
                                    ex);
                        }
                    }
                } catch (final IOException ioex) {
                    throw new ClassNotFoundException(
                            "IOException was thrown when trying to get all resources for "
                                    + pckgname, ioex);
                }
            }
        } catch (final NullPointerException ex) {
            throw new ClassNotFoundException(
                    pckgname
                            + " does not appear to be a valid package (Null pointer exception)",
                    ex);
        } catch (final IOException ioex) {
            throw new ClassNotFoundException(
                    "IOException was thrown when trying to get all resources for "
                            + pckgname, ioex);
        }

        return classes;
    }
   
    /**
     * Private helper method
     * 
     * @param directory
     *            The directory to start with
     * @param pckgname
     *            The package name to search for. Will be needed for getting the
     *            Class object.
     * @param classes
     *            if a file isn't loaded but still is in the directory
     * @throws ClassNotFoundException
     */
    private static void checkDirectory(File directory, String pckgname,
            ArrayList<Class<?>> classes) throws ClassNotFoundException {
        File tmpDirectory;

        if (directory.exists() && directory.isDirectory()) {
            final String[] files = directory.list();

            for (final String file : files) {
                if (file.endsWith(".class")) {
                    try {
                        classes.add(Class.forName(pckgname + '.'
                                + file.substring(0, file.length() - 6)));
                    } catch (final NoClassDefFoundError e) {
                        // do nothing. this class hasn't been found by the
                        // loader, and we don't care.
                    }
                } else if ((tmpDirectory = new File(directory, file))
                        .isDirectory()) {
                    checkDirectory(tmpDirectory, pckgname + "." + file, classes);
                }
            }
        }
    }

    /**
     * Private helper method.
     * 
     * @param connection
     *            the connection to the jar
     * @param pckgname
     *            the package name to search for
     * @param classes
     *            the current ArrayList of all classes. This method will simply
     *            add new classes.
     * @throws ClassNotFoundException
     *             if a file isn't loaded but still is in the jar file
     * @throws IOException
     *             if it can't correctly read from the jar file.
     */
    private static void checkJarFile(JarURLConnection connection,
            String pckgname, ArrayList<Class<?>> classes)
            throws ClassNotFoundException, IOException {
        final JarFile jarFile = connection.getJarFile();
        final Enumeration<JarEntry> entries = jarFile.entries();
        String name;

        for (JarEntry jarEntry = null; entries.hasMoreElements()
                && ((jarEntry = entries.nextElement()) != null);) {
            name = jarEntry.getName();

            if (name.contains(".class")) {
                name = name.substring(0, name.length() - 6).replace('/', '.');

                if (name.contains(pckgname)) {
                    classes.add(Class.forName(name));
                }
            }
        }
    }


}