Retrieves the resource as an input stream via the context class loader of the current thread, and if not found, via the class loaders of the optionally specified classes in the order of their specification, and if not found, from the class loader of ClassLoaderHelper as the last resort. - Java Reflection

Description

Retrieves the resource as an input stream via the context class loader of the current thread, and if not found, via the class loaders of the optionally specified classes in the order of their specification, and if not found, from the class loader of ClassLoaderHelper as the last resort.

Demo Code

/*//from w  ww  .j a v a  2  s.  c om
 * Copyright 2011-2013 Amazon Technologies, Inc.
 *
 * 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://aws.amazon.com/apache2.0
 *
 * This file 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.
 */
import java.io.IOException;
import java.io.InputStream;
import java.net.URL;

public class Main{
    public static void main(String[] argv) throws Exception{
        String resource = "java2s.com";
        Class classes = String.class;
        System.out.println(getResourceAsStream(resource,classes));
    }
    /**
     * Retrieves the resource as an input stream via
     * the context class loader of the current thread, and if not found, via the
     * class loaders of the optionally specified classes in the order of their
     * specification, and if not found, from the class loader of
     * {@link ClassLoaderHelper} as the last resort.
     * 
     * @param resource
     *            resource to be loaded
     * @param classes
     *            class loader providers
     * @return the resource loaded as an input stream or null if not found.
     */
    public static InputStream getResourceAsStream(String resource,
            Class<?>... classes) {
        return getResourceAsStream(resource, false, classes);
    }
    /**
     * If classesFirst is false, retrieves the resource as an input stream via
     * the context class loader of the current thread, and if not found, via the
     * class loaders of the optionally specified classes in the order of their
     * specification, and if not found, from the class loader of
     * {@link ClassLoaderHelper} as the last resort.
     * <p>
     * If classesFirst is true, retrieves the resource as an input stream via
     * the optionally specified classes in the order of their specification, and
     * if not found, via the context class loader of the current thread, and if
     * not found, from the class loader of {@link ClassLoaderHelper} as the last
     * resort.
     * 
     * @param resource
     *            resource to be loaded
     * @param classesFirst
     *            true if the class loaders of the optionally specified classes
     *            take precedence over the context class loader of the current
     *            thread; false if the opposite is true.
     * @param classes
     *            class loader providers
     * @return the resource loaded as an input stream or null if not found.
     */
    public static InputStream getResourceAsStream(String resource,
            boolean classesFirst, Class<?>... classes) {
        URL url = getResource(resource, classesFirst, classes);
        try {
            return url != null ? url.openStream() : null;
        } catch (IOException e) {
            return null;
        }
    }
    /**
     * Retrieves the resource via the context class loader of the current
     * thread, and if not found, via the class loaders of the optionally
     * specified classes in the order of their specification, and if not
     * found, from the class loader of {@link ClassLoaderHelper} as the last
     * resort.
     * 
     * @param resource
     *            resource to be loaded
     * @param classes class loader providers
     * @return the resource loaded as an URL or null if not found.
     */
    public static URL getResource(String resource, Class<?>... classes) {
        return getResource(resource, false, classes);
    }
    /**
     * If classesFirst is false, retrieves the resource via the context class
     * loader of the current thread, and if not found, via the class loaders of
     * the optionally specified classes in the order of their specification, and
     * if not found, from the class loader of {@link ClassLoaderHelper} as the
     * last resort.
     * <p>
     * If classesFirst is true, retrieves the resource via the optionally
     * specified classes in the order of their specification, and if not found,
     * via the context class loader of the current thread, and if not found,
     * from the class loader of {@link ClassLoaderHelper} as the last resort.
     * 
     * @param resource
     *            resource to be loaded
     * @param classesFirst
     *            true if the class loaders of the optionally specified classes
     *            take precedence over the context class loader of the current
     *            thread; false if the opposite is true.
     * @param classes
     *            class loader providers
     * @return the resource loaded as an URL or null if not found.
     */
    public static URL getResource(String resource, boolean classesFirst,
            Class<?>... classes) {
        URL url;
        if (classesFirst) {
            url = getResourceViaClasses(resource, classes);
            if (url == null) {
                url = getResourceViaContext(resource);
            }
        } else {
            url = getResourceViaContext(resource);
            if (url == null) {
                url = getResourceViaClasses(resource, classes);
            }
        }
        return url == null ? ClassLoaderHelper.class.getResource(resource)
                : url;
    }
    private static URL getResourceViaClasses(String resource,
            Class<?>[] classes) {
        if (classes != null) {
            for (Class<?> c : classes) {
                URL url = c.getResource(resource);
                if (url != null)
                    return url;
            }
        }
        return null;
    }
    private static URL getResourceViaContext(String resource) {
        ClassLoader loader = Thread.currentThread().getContextClassLoader();
        return loader == null ? null : loader.getResource(resource);
    }
}

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