/* * ModuleLoader - A generic, policy-driven class loader. * Copyright (c) 2004, Richard S. Hall * All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * *   * Redistributions of source code must retain the above copyright *     notice, this list of conditions and the following disclaimer. *   * Redistributions in binary form must reproduce the above copyright *     notice, this list of conditions and the following disclaimer in *     the documentation and/or other materials provided with the *     distribution. *   * Neither the name of the ungoverned.org nor the names of its *     contributors may be used to endorse or promote products derived *     from this software without specific prior written permission. * * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. * * Contact: Richard S. Hall (heavy@ungoverned.org) * Contributor(s): ***/package org.ungoverned.moduleloader.search.selection;import java.util.Iterator;import java.util.Map;import java.util.HashMap;import org.ungoverned.moduleloader.Module;import org.ungoverned.moduleloader.ModuleEvent;import org.ungoverned.moduleloader.ModuleListener;import org.ungoverned.moduleloader.search.ImportSearchPolicy;import org.ungoverned.moduleloader.search.SelectionPolicy;import org.ungoverned.moduleloader.search.CompatibilityPolicy;/** * This class implements a reasonably simple selection policy for the * <tt>ImportSearchPolicy</tt>. When given a choice, this selection * policy will always select the newest version of the available * candidates to satisfy the import identifier. In the case where * a candidate has already been selected for a given import identifier, * then the previously selected module will be returned, if possible. * If it is not possible to return the previously selected module, then * a <tt>null</tt> is returned. This policy assumes that classes are * shared globally.**/public class SimpleSelectionPolicy implements SelectionPolicy, ModuleListener{    private Map m_resolvedPackageMap = new HashMap();    private Map m_resolvedModuleMap = new HashMap();    /**     * Selects a single module to resolve the specified import identifier     * from the array of compatible candidate modules. If the import     * identifier has not been resolved before, then this selection policy     * chooses the module that exports the newest version of the     * import identifer. If the import identifier has been resolved already,     * then the same module that was chosen before is chosen again.     * This ensures that all modules use the same version of all     * exported classes.     * @param module the module that is importing the target.     * @param identifier the identifier of the import target.     * @param version the version number of the import target.     * @param candidates array of compatible candidate modules from which to choose.     * @return the selected module or <tt>null</tt> if no module     *         can be selected.    **/    public synchronized Module select(Module module, Object identifier,        Object version, Module[] candidates, CompatibilityPolicy compatPolicy)    {        // See if package is already resolved.        Module selModule = (Module) m_resolvedPackageMap.get(identifier);        // If no module was previously selected to export the package,        // then try to choose one now.        if (selModule == null)        {            Object selVersion = null;            // Examine all exported instances of the identifier and            // choose the one with the newest version number. If            // there is more than one source for the newest version,            // then just select the first one found.            for (int i = 0; i < candidates.length; i++)            {                Object tmpVersion =                    ImportSearchPolicy.getExportVersion(candidates[i], identifier);                // If this is the first comparison, then                // just record it.                if (selVersion == null)                {                    selModule = candidates[i];                    selVersion = tmpVersion;                }                // If the current export package version is greater                // than the selected export package version, then                // record it instead.                else if (compatPolicy.compare(identifier, tmpVersion, identifier, selVersion) >= 0)                {                    selModule = candidates[i];                    selVersion = tmpVersion;                }            }            m_resolvedPackageMap.put(identifier, selModule);            m_resolvedModuleMap.put(selModule, selModule);        }        // See if the previously selected export module satisfies        // the current request, otherwise return null.        else        {            Object selVersion =                ImportSearchPolicy.getExportVersion(selModule, identifier);            Module tmpModule = selModule;            selModule = null;            if (compatPolicy.isCompatible(identifier, selVersion, identifier, version))            {                selModule = tmpModule;            }        }        return selModule;    }    public void moduleAdded(ModuleEvent event)    {    }    public void moduleReset(ModuleEvent event)    {        moduleRemoved(event);    }    public synchronized void moduleRemoved(ModuleEvent event)    {        // If the module that was removed was chosen for        // exporting identifier, then flush it from our        // data structures; we assume here that the application        // will flush references to the removed module's classes.        if (m_resolvedModuleMap.get(event.getModule()) != null)        {            // Remove from module map.            m_resolvedModuleMap.remove(event.getModule());            // Remove each exported package from package map.            Iterator iter = m_resolvedPackageMap.entrySet().iterator();            while (iter.hasNext())            {                Map.Entry entry = (Map.Entry) iter.next();                if (entry.getValue() == event.getModule())                {                    iter.remove();                }            }        }    }}