Ant example source code file (Classloader.java)

This example Ant source code file (Classloader.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Ant tags/keywords

adding, antclassloader, antclassloader, classloader, classloader, file, io, object, path, path, setting, string, string, system_loader_ref, task

The Classloader.java source code

/*
 *  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.taskdefs;

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

import java.io.File;

/**
 * EXPERIMENTAL
 * Create or modifies ClassLoader. The required pathRef parameter
 * will be used to add classpath elements.
 *
 * The classpath is a regular path. Currently only file components are
 * supported (future extensions may allow URLs).
 *
 * You can modify the core loader by not specifying any name or using
 * "ant.coreLoader". (the core loader is used to load system ant
 * tasks and for taskdefs that don't specify an explicit path).
 *
 * Taskdef and typedef can use the loader you create if the name follows
 * the "ant.loader.NAME" pattern. NAME will be used as a pathref when
 * calling taskdef.
 *
 * This tasks will not modify the core loader if "build.sysclasspath=only"
 *
 * The typical use is:
 * <pre>
 *  <path id="ant.deps" >
 *     <fileset dir="myDir" >
 *        <include name="junit.jar, bsf.jar, js.jar, etc"/>
 *     </fileset>
 *  </path>
 *
 *  <classloader pathRef="ant.deps" />
 *
 * </pre>
 *
 */
public class Classloader extends Task {
    /** @see MagicNames#SYSTEM_LOADER_REF */
    public static final String SYSTEM_LOADER_REF = MagicNames.SYSTEM_LOADER_REF;

    private String name = null;
    private Path classpath;
    private boolean reset = false;
    private boolean parentFirst = true;
    private String parentName = null;

    /**
     * Default constructor
     */
    public Classloader() {
    }

    /** Name of the loader. If none, the default loader will be modified
     *
     * @param name the name of this loader
     */
    public void setName(String name) {
        this.name = name;
    }

    /**
     * Reset the classloader, if it already exists. A new loader will
     * be created and all the references to the old one will be removed.
     * (it is not possible to remove paths from a loader). The new
     * path will be used.
     *
     * @param b true if the loader is to be reset.
     */
    public void setReset(boolean b) {
        this.reset = b;
    }

    /**
     * Set reverse attribute.
     * @param b if true reverse the normal classloader lookup.
     */
    public void setReverse(boolean b) {
        this.parentFirst = !b;
    }

    /**
     * Set reverse attribute.
     * @param b if true reverse the normal classloader lookup.
     */
    public void setParentFirst(boolean b) {
        this.parentFirst = b;
    }

    /**
     * Set the name of the parent.
     * @param name the parent name.
     */
    public void setParentName(String name) {
        this.parentName = name;
    }


    /** Specify which path will be used. If the loader already exists
     *  and is an AntClassLoader (or any other loader we can extend),
     *  the path will be added to the loader.
     * @param pathRef a reference to a path.
     * @throws BuildException if there is a problem.
     */
    public void setClasspathRef(Reference pathRef) throws BuildException {
        classpath = (Path) pathRef.getReferencedObject(getProject());
    }

    /**
     * Set the classpath to be used when searching for component being defined
     *
     * @param classpath an Ant Path object containing the classpath.
     */
    public void setClasspath(Path classpath) {
        if (this.classpath == null) {
            this.classpath = classpath;
        } else {
            this.classpath.append(classpath);
        }
    }

    /**
     * Create a classpath.
     * @return a path for configuration.
     */
    public Path createClasspath() {
        if (this.classpath == null) {
            this.classpath = new Path(null);
        }
        return this.classpath.createPath();
    }


    /**
     * do the classloader manipulation.
     */
    public void execute() {
        try {
            // Gump friendly - don't mess with the core loader if only classpath
            if ("only".equals(getProject().getProperty("build.sysclasspath"))
                && (name == null || SYSTEM_LOADER_REF.equals(name))) {
                log("Changing the system loader is disabled "
                    + "by build.sysclasspath=only", Project.MSG_WARN);
                return;
            }

            String loaderName = (name == null) ? SYSTEM_LOADER_REF : name;

            Object obj = getProject().getReference(loaderName);
            if (reset) {
                // Are any other references held ? Can we 'close' the loader
                // so it removes the locks on jars ?
                obj = null; // a new one will be created.
            }

            // XXX maybe use reflection to addPathElement (other patterns ?)
            if (obj != null && !(obj instanceof AntClassLoader)) {
                log("Referenced object is not an AntClassLoader",
                        Project.MSG_ERR);
                return;
            }

            AntClassLoader acl = (AntClassLoader) obj;

            if (acl == null) {
                // Construct a new class loader
                Object parent = null;
                if (parentName != null) {
                    parent = getProject().getReference(parentName);
                    if (!(parent instanceof ClassLoader)) {
                        parent = null;
                    }
                }
                // TODO: allow user to request the system or no parent
                if (parent == null) {
                    parent = this.getClass().getClassLoader();
                }

                if (name == null) {
                    // The core loader must be reverse
                    //reverse=true;
                }
                getProject().log("Setting parent loader " + name + " "
                    + parent + " " + parentFirst, Project.MSG_DEBUG);

                // The param is "parentFirst"
                acl = new AntClassLoader((ClassLoader) parent,
                         getProject(), classpath, parentFirst);

                getProject().addReference(loaderName, acl);

                if (name == null) {
                    // This allows the core loader to load optional tasks
                    // without delegating
                    acl.addLoaderPackageRoot("org.apache.tools.ant.taskdefs.optional");
                    getProject().setCoreLoader(acl);
                }
            }
            if (classpath != null) {
                String[] list = classpath.list();
                for (int i = 0; i < list.length; i++) {
                    File f = new File(list[i]);
                    if (f.exists()) {
                        acl.addPathElement(f.getAbsolutePath());
                        log("Adding to class loader " +  acl + " " + f.getAbsolutePath(),
                                Project.MSG_DEBUG);
                    }
                }
            }

            // XXX add exceptions

        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }
}