org.roda.core.util.ClassLoaderUtility.java Source code

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Here is the source code for org.roda.core.util.ClassLoaderUtility.java

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/**
 * 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();
    }

}