org.pentaho.hadoop.shim.HadoopConfigurationClassLoader.java Source code

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Here is the source code for org.pentaho.hadoop.shim.HadoopConfigurationClassLoader.java

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/*******************************************************************************
 *
 * Pentaho Big Data
 *
 * Copyright (C) 2002-2017 by Hitachi Vantara : http://www.pentaho.com
 *
 *******************************************************************************
 *
 * 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://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.pentaho.hadoop.shim;

import java.io.File;
import java.io.IOException;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.Arrays;
import java.util.Enumeration;
import java.util.HashSet;
import java.util.Set;

/**
 * Loads classes for a Hadoop configuration by looking for resources in the configuration directory first before
 * checking its parent class loader.
 */
public class HadoopConfigurationClassLoader extends URLClassLoader {

    private Set<String> loadClassesFromParent;

    /**
     * Create a class loader capable of loading classes for a Hadoop configuration.
     *
     * @param urls           Paths to directories or jars to load resources from
     * @param parent         Parent class loader to delegate loading of resources to if we cannot find them within the
     *                       list of URLs
     * @param ignoredClasses Classes or package names to explicitly delegate loading to the parent class loader
     */
    public HadoopConfigurationClassLoader(URL[] urls, ClassLoader parent, String... ignoredClasses) {
        super(urls, parent);
        if (parent == null) {
            throw new NullPointerException("parent ClassLoader is required");
        }

        loadClassesFromParent = new HashSet<String>();
        if (ignoredClasses != null) {
            loadClassesFromParent.addAll(Arrays.asList(ignoredClasses));
        }
        loadClassesFromParent.add("org.apache.commons.log");
        loadClassesFromParent.add("org.apache.log4j");
    }

    /**
     * Determine if a class should be ignored by this class loader and loading of it should be delegated to its parent.
     *
     * @param name Name of class
     * @return {@code true} if the class should be ignored by this class loader
     */
    protected boolean ignoreClass(String name) {
        if (name == null || loadClassesFromParent.contains(name)) {
            return true;
        }
        for (String prefix : loadClassesFromParent) {
            if (name.startsWith(prefix)) {
                return true;
            }
        }
        return false;
    }

    @Override
    protected synchronized Class<?> loadClass(String name, boolean resolve) throws ClassNotFoundException {
        if (ignoreClass(name)) {
            Class<?> c = Class.forName(name, false, getParent());
            if (resolve) {
                resolveClass(c);
            }
            return c;
        }
        // Check for a previously loaded class
        Class<?> c = findLoadedClass(name);
        if (c == null) {
            // Try to load it from ourself first
            try {
                c = findClass(name);
            } catch (ClassNotFoundException ex) {
                // If we can't find the class check the parent class loader
                c = Class.forName(name, false, getParent());
            }
        }
        // Resolve the class as needed
        if (resolve) {
            resolveClass(c);
        }
        return c;
    }

    @Override
    public URL getResource(String name) {
        URL url = null;
        if (url == null) {
            url = findResource(name);
        }
        if (url == null) {
            url = super.getResource(name);
        }
        return url;
    }

    @Override
    public Enumeration<URL> getResources(String name) throws IOException {
        final Enumeration<URL> myResources = findResources(name);
        final Enumeration<URL> parentResources = getParent().getResources(name);

        return new Enumeration<URL>() {
            @Override
            public boolean hasMoreElements() {
                return myResources.hasMoreElements() || parentResources.hasMoreElements();
            }

            @Override
            public URL nextElement() {
                if (myResources.hasMoreElements()) {
                    return myResources.nextElement();
                }
                return parentResources.nextElement();
            }
        };
    }

    /**
     * Generates a "java.class.path" compatible String representing the class path available through this class loader.
     *
     * @return A "java.class.path" compatible String
     */
    public String generateClassPathString() {
        StringBuilder sb = new StringBuilder();

        for (URL url : getURLs()) {
            if (sb.length() != 0) {
                sb.append(File.pathSeparator);
            }
            sb.append(url.getFile());
        }

        return sb.toString();
    }
}