classpathutils.java

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/*
 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You 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.apache.tools.ant.util;

import org.apache.tools.ant.AntClassLoader;
import org.apache.tools.ant.BuildException;
import org.apache.tools.ant.Project;
import org.apache.tools.ant.ProjectComponent;
import org.apache.tools.ant.MagicNames;
import org.apache.tools.ant.types.Path;
import org.apache.tools.ant.types.Reference;

// CheckStyle:HideUtilityClassConstructorCheck OFF - bc

/**
 * Offers some helper methods on the Path structure in ant.
 *
 * <p>The basic idea behind this utility class is to use it from inside the
 * different Ant objects (and user defined objects) that need classLoading
 * for their operation.
 * Normally those would have a setClasspathRef() {for the @classpathref}
 * and/or a createClasspath() {for the nested &lt;classpath&gt;}
 * Typically one would have in your Ant Task or DataType</p>
 *
 * <pre><code>
 * ClasspathUtils.Delegate cpDelegate;
 *
 * public void init() {
 *     this.cpDelegate = ClasspathUtils.getDelegate(this);
 *     super.init();
 * }
 *
 * public void setClasspathRef(Reference r) {
 *     this.cpDelegate.setClasspathRef(r);
 * }
 *
 * public Path createClasspath() {
 *     return this.cpDelegate.createClasspath();
 * }
 *
 * public void setClassname(String fqcn) {
 *     this.cpDelegate.setClassname(fqcn);
 * }
 * </code></pre>
 *
 * <p>At execution time, when you actually need the classloading
 * you can just:</p>
 *
 * <pre><code>
 *     Object o = this.cpDelegate.newInstance();
 * </code></pre>
 *
 * @since Ant 1.6
 */
public class ClasspathUtils {

    /**
     * Name of the magic property that controls classloader reuse in Ant 1.4.
     */
    public static final String REUSE_LOADER_REF = MagicNames.REFID_CLASSPATH_REUSE_LOADER;

    /**
     * Convenience overloaded version of {@link
     * #getClassLoaderForPath(Project, Reference, boolean)}.
     *
     * <p>Assumes the logical 'false' for the reverseLoader.</p>
     *
     * @param p the project
     * @param ref the reference
     * @return The class loader
     */
    public static ClassLoader getClassLoaderForPath(
        Project p, Reference ref) {

        return getClassLoaderForPath(p, ref, false);
    }

    /**
     * Convenience overloaded version of {@link #getClassLoaderForPath(Project, Path,
     * String, boolean)}.
     *
     * <p>Delegates to the other one after extracting the referenced
     * Path from the Project. This checks also that the passed
     * Reference is pointing to a Path all right.</p>
     * @param p current Ant project
     * @param ref Reference to Path structure
     * @param reverseLoader if set to true this new loader will take
     * precedence over its parent (which is contra the regular
     * classloader behaviour)
     * @return The class loader
     */
    public static ClassLoader getClassLoaderForPath(
        Project p, Reference ref, boolean reverseLoader) {

        String pathId = ref.getRefId();
        Object path = p.getReference(pathId);
        if (!(path instanceof Path)) {
            throw new BuildException(
                "The specified classpathref "
                    + pathId
                    + " does not reference a Path.");
        }
        String loaderId = MagicNames.REFID_CLASSPATH_LOADER_PREFIX + pathId;
        return getClassLoaderForPath(p, (Path) path, loaderId, reverseLoader);
    }

    /**
     * Convenience overloaded version of {@link
     * #getClassLoaderForPath(Project, Path, String, boolean)}.
     *
     * <p>Assumes the logical 'false' for the reverseLoader.</p>
     *
     * @param p current Ant project
     * @param path the path
     * @param loaderId the loader id string
     * @return The class loader
     */
    public static ClassLoader getClassLoaderForPath(
        Project p, Path path, String loaderId) {

        return getClassLoaderForPath(p, path, loaderId, false);
    }

    /**
     * Convenience overloaded version of {@link
     * #getClassLoaderForPath(Project, Path, String, boolean, boolean)}.
     *
     * <p>Sets value for 'reuseLoader' to true if the magic property
     * has been set.</p>
     *
     * @param p the project
     * @param path the path
     * @param loaderId the loader id string
     * @param reverseLoader if set to true this new loader will take
     * precedence over its parent (which is contra the regular
     * classloader behaviour)
     * @return The class loader
     */
    public static ClassLoader getClassLoaderForPath(
        Project p, Path path, String loaderId, boolean reverseLoader) {
        return getClassLoaderForPath(p, path, loaderId, reverseLoader,
                                     isMagicPropertySet(p));
    }

    /**
     * Gets a classloader that loads classes from the classpath
     * defined in the path argument.
     *
     * <p>Based on the setting of the magic property
     * 'ant.reuse.loader' this will try to reuse the previously
     * created loader with that id, and of course store it there upon
     * creation.</p>
     * @param p             Ant Project where the handled components are living in.
     * @param path          Path object to be used as classpath for this classloader
     * @param loaderId      identification for this Loader,
     * @param reverseLoader if set to true this new loader will take
     *                      precedence over its parent (which is contra the regular
     *                      classloader behaviour)
     * @param reuseLoader   if true reuse the loader if it is found
     * @return              ClassLoader that uses the Path as its classpath.
     */
    public static ClassLoader getClassLoaderForPath(
        Project p, Path path, String loaderId, boolean reverseLoader,
        boolean reuseLoader) {

        ClassLoader cl = null;

        // magic property
        if (loaderId != null && reuseLoader) {
            Object reusedLoader = p.getReference(loaderId);
            if (reusedLoader != null
                && !(reusedLoader instanceof ClassLoader)) {
                throw new BuildException("The specified loader id " + loaderId
                    + " does not reference a class loader");
            }
            cl = (ClassLoader) reusedLoader;
        }
        if (cl == null) {
            cl = getUniqueClassLoaderForPath(p, path, reverseLoader);
            if (loaderId != null && reuseLoader) {
                p.addReference(loaderId, cl);
            }
        }
        return cl;
    }

    /**
     * Gets a fresh, different, previously unused classloader that uses the
     * passed path as its classpath.
     *
     * <p>This method completely ignores the ant.reuse.loader magic
     * property and should be used with caution.</p>
     * @param p             Ant Project where the handled components are living in.
     * @param path          the classpath for this loader
     * @param reverseLoader if set to true this new loader will take
     *                      precedence over its parent (which is contra the regular
     *                      classloader behaviour)
     * @return The fresh, different, previously unused class loader.
     */
    public static ClassLoader getUniqueClassLoaderForPath(
        Project p,
        Path path,
        boolean reverseLoader) {
        AntClassLoader acl = p.createClassLoader(path);
        if (reverseLoader) {
            acl.setParentFirst(false);
            acl.addJavaLibraries();
        }
        return acl;
    }

    /**
     * Creates a fresh object instance of the specified classname.
     *
     * <p> This uses the userDefinedLoader to load the specified class,
     * and then makes an instance using the default no-argument constructor.
     * </p>
     *
     * @param className the full qualified class name to load.
     * @param userDefinedLoader the classloader to use.
     * @return The fresh object instance
     * @throws BuildException when loading or instantiation failed.
     */
    public static Object newInstance(
            String className,
            ClassLoader userDefinedLoader) {
        return newInstance(className, userDefinedLoader, Object.class);
    }

    /**
     * Creates a fresh object instance of the specified classname.
     *
     * <p> This uses the userDefinedLoader to load the specified class,
     * and then makes an instance using the default no-argument constructor.
     * </p>