antclassloader.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;

import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.Reader;
import java.lang.reflect.Constructor;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.Collections;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.Hashtable;
import java.util.Map;
import java.util.StringTokenizer;
import java.util.Vector;
import java.util.Locale;
import java.util.jar.Attributes;
import java.util.jar.Attributes.Name;
import java.util.jar.JarFile;
import java.util.jar.Manifest;
import java.util.zip.ZipEntry;
import java.util.zip.ZipFile;
import org.apache.tools.ant.types.Path;
import org.apache.tools.ant.util.CollectionUtils;
import org.apache.tools.ant.util.FileUtils;
import org.apache.tools.ant.util.JavaEnvUtils;
import org.apache.tools.ant.util.LoaderUtils;
import org.apache.tools.ant.launch.Locator;

/**
 * Used to load classes within ant with a different classpath from
 * that used to start ant. Note that it is possible to force a class
 * into this loader even when that class is on the system classpath by
 * using the forceLoadClass method. Any subsequent classes loaded by that
 * class will then use this loader rather than the system class loader.
 *
 * <p>
 * Note that this classloader has a feature to allow loading
 * in reverse order and for "isolation".
 * Due to the fact that a number of
 * methods in java.lang.ClassLoader are final (at least
 * in java 1.4 getResources) this means that the
 * class has to fake the given parent.
 * </p>
 *
 */
public class AntClassLoader extends ClassLoader implements SubBuildListener {

    private static final FileUtils FILE_UTILS = FileUtils.getFileUtils();

    /**
     * An enumeration of all resources of a given name found within the
     * classpath of this class loader. This enumeration is used by the
     * ClassLoader.findResources method, which is in
     * turn used by the ClassLoader.getResources method.
     *
     * @see AntClassLoader#findResources(String)
     * @see java.lang.ClassLoader#getResources(String)
     */
    private class ResourceEnumeration implements Enumeration {
        /**
         * The name of the resource being searched for.
         */
        private String resourceName;

        /**
         * The index of the next classpath element to search.
         */
        private int pathElementsIndex;

        /**
         * The URL of the next resource to return in the enumeration. If this
         * field is <code>null</code> then the enumeration has been completed,
         * i.e., there are no more elements to return.
         */
        private URL nextResource;

        /**
         * Constructs a new enumeration of resources of the given name found
         * within this class loader's classpath.
         *
         * @param name the name of the resource to search for.
         */
        ResourceEnumeration(String name) {
            this.resourceName = name;
            this.pathElementsIndex = 0;
            findNextResource();
        }

        /**
         * Indicates whether there are more elements in the enumeration to
         * return.
         *
         * @return <code>true</code> if there are more elements in the
         *         enumeration; <code>false</code> otherwise.
         */
        public boolean hasMoreElements() {
            return (this.nextResource != null);
        }

        /**
         * Returns the next resource in the enumeration.
         *
         * @return the next resource in the enumeration
         */
        public Object nextElement() {
            URL ret = this.nextResource;
            findNextResource();
            return ret;
        }

        /**
         * Locates the next resource of the correct name in the classpath and
         * sets <code>nextResource</code> to the URL of that resource. If no
         * more resources can be found, <code>nextResource</code> is set to
         * <code>null</code>.
         */
        private void findNextResource() {
            URL url = null;
            while ((pathElementsIndex < pathComponents.size())
                   && (url == null)) {
                try {
                    File pathComponent
                        = (File) pathComponents.elementAt(pathElementsIndex);
                    url = getResourceURL(pathComponent, this.resourceName);
                    pathElementsIndex++;
                } catch (BuildException e) {
                    // ignore path elements which are not valid relative to the
                    // project
                }
            }
            this.nextResource = url;
        }
    }

    /**
     * The size of buffers to be used in this classloader.
     */
    private static final int BUFFER_SIZE = 8192;
    /**
     * Number of array elements in a test array of strings
     */
    private static final int NUMBER_OF_STRINGS = 256;

    /**
     * The components of the classpath that the classloader searches
     * for classes.
     */
    private Vector pathComponents  = new Vector();

    /**
     * The project to which this class loader belongs.
     */
    private Project project;

    /**
     * Indicates whether the parent class loader should be
     * consulted before trying to load with this class loader.
     */
    private boolean parentFirst = true;

    /**
     * These are the package roots that are to be loaded by the parent class
     * loader regardless of whether the parent class loader is being searched
     * first or not.
     */
    private Vector systemPackages = new Vector();

    /**
     * These are the package roots that are to be loaded by this class loader
     * regardless of whether the parent class loader is being searched first
     * or not.
     */
    private Vector loaderPackages = new Vector();

    /**
     * Whether or not this classloader will ignore the base
     * classloader if it can't find a class.
     *
     * @see #setIsolated(boolean)
     */
    private boolean ignoreBase = false;

    /**
     * The parent class loader, if one is given or can be determined.
     */
    private ClassLoader parent = null;

    /**
     * A hashtable of zip files opened by the classloader (File to ZipFile).
     */
    private Hashtable zipFiles = new Hashtable();

    /** Static map of jar file/time to manifest class-path entries */
    private static Map/*<String,String>*/ pathMap = Collections.synchronizedMap(new HashMap());

    /**
     * The context loader saved when setting the thread's current
     * context loader.
     */
    private ClassLoader savedContextLoader = null;
    /**
     * Whether or not the context loader is currently saved.
     */
    private boolean isContextLoaderSaved = false;

    /**
     * Create an Ant ClassLoader for a given project, with
     * a parent classloader and an initial classpath.
     * @since Ant 1.7.
     * @param parent the parent for this classloader.
     * @param project The project to which this classloader is to
     *                belong.
     * @param classpath The classpath to use to load classes.
     */
    public AntClassLoader(
        ClassLoader parent, Project project, Path classpath) {
        setParent(parent);
        setClassPath(classpath);
        setProject(project);
    }

    /**
     * Create an Ant Class Loader
     */
    public AntClassLoader() {
        setParent(null);
    }

    /**
     * Creates a classloader for the given project using the classpath given.
     *
     * @param project The project to which this classloader is to belong.
     *                Must not be <code>null</code>.
     * @param classpath The classpath to use to load the classes.  This
     *                is combined with the system classpath in a manner
     *                determined by the value of ${build.sysclasspath}.
     *                May be <code>null</code>, in which case no path
     *                elements are set up to start with.
     */
    public AntClassLoader(Project project, Path classpath) {
        setParent(null);
        setProject(project);
        setClassPath(classpath);
    }

    /**
     * Creates a classloader for the given project using the classpath given.
     *
     * @param parent The parent classloader to which unsatisfied loading
     *               attempts are delegated. May be <code>null</code>,
     *               in which case the classloader which loaded this
     *               class is used as the parent.
     * @param project The project to which this classloader is to belong.
     *                Must not be <code>null</code>.
     * @param classpath the classpath to use to load the classes.
     *                  May be <code>null</code>, in which case no path
     *                  elements are set up to start with.
     * @param parentFirst If <code>true</code>, indicates that the parent
     *                    classloader should be consulted  before trying to
     *                    load the a class through this loader.
     */
    public AntClassLoader(ClassLoader parent, Project project, Path classpath,
                          boolean parentFirst) {
        this(project, classpath);
        if (parent != null) {
            setParent(parent);
        }
        setParentFirst(parentFirst);
        addJavaLibraries();
    }


    /**
     * Creates a classloader for the given project using the classpath given.
     *
     * @param project The project to which this classloader is to belong.
     *                Must not be <code>null</code>.
     * @param classpath The classpath to use to load the classes. May be
     *                  <code>null</code>, in which case no path
     *                  elements are set up to start with.
     * @param parentFirst If <code>true</code>, indicates that the parent
     *                    classloader should be consulted before trying to
     *                    load the a class through this loader.
     */
    public AntClassLoader(Project project, Path classpath,
                          boolean parentFirst) {
        this(null, project, classpath, parentFirst);
    }

    /**
     * Creates an empty class loader. The classloader should be configured
     * with path elements to specify where the loader is to look for
     * classes.
     *
     * @param parent The parent classloader to which unsatisfied loading
     *               attempts are delegated. May be <code>null</code>,
     *               in which case the classloader which loaded this
     *               class is used as the parent.
     * @param parentFirst If <code>true</code>, indicates that the parent
     *                    classloader should be consulted before trying to
     *                    load the a class through this loader.
     */
    public AntClassLoader(ClassLoader parent, boolean parentFirst) {
        setParent(parent);
        project = null;
        this.parentFirst = parentFirst;
    }

    /**
     * Set the project associated with this class loader
     *
     * @param project the project instance
     */
    public void setProject(Project project) {
        this.project = project;
        if (project != null) {
            project.addBuildListener(this);
        }
    }

    /**
     * Set the classpath to search for classes to load. This should not be
     * changed once the classloader starts to server classes
     *
     * @param classpath the search classpath consisting of directories and
     *        jar/zip files.
     */
    public void setClassPath(Path classpath) {
        pathComponents.removeAllElements();
        if (classpath != null) {
            Path actualClasspath = classpath.concatSystemClasspath("ignore");
            String[] pathElements = actualClasspath.list();
            for (int i = 0; i < pathElements.length; ++i) {
                try {
                    addPathElement(pathElements[i]);
                } catch (BuildException e) {
                    // ignore path elements which are invalid
                    // relative to the project
                }
            }
        }
    }

    /**
     * Set the parent for this class loader. This is the class loader to which
     * this class loader will delegate to load classes
     *
     * @param parent the parent class loader.
     */
    public void setParent(ClassLoader parent) {
        if (parent == null) {
            this.parent = AntClassLoader.class.getClassLoader();
        } else {
            this.parent = parent;
        }
    }

    /**
     * Control whether class lookup is delegated to the parent loader first
     * or after this loader. Use with extreme caution. Setting this to
     * false violates the class loader hierarchy and can lead to Linkage errors
     *
     * @param parentFirst if true, delegate initial class search to the parent
     *                    classloader.
     */
    public void setParentFirst(boolean parentFirst) {
        this.parentFirst = parentFirst;
    }