exhaustivesearchpolicy.java

OSGI 的 源码实现,采用JAVA书写

/*
 * 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 ([e-mail])
 * Contributor(s):
 *
**/
package org.ungoverned.moduleloader.search;

import java.net.URL;

import org.ungoverned.moduleloader.Module;
import org.ungoverned.moduleloader.ModuleManager;
import org.ungoverned.moduleloader.SearchPolicy;

/**
 * <p>
 * This class implements a <tt>ModuleLoader</tt> search policy that
 * exhaustively and linearly searches all modules when trying to load
 * a particular class or resource. As a result of this algorithm, every class loader
 * for every module is essentially identical, meaning that each will
 * load a given class or resource from the same class loader. This search policy
 * provides behavior similar to the standard <tt>CLASSPATH</tt> environment
 * variable approach. The main difference is that modules can be added
 * to the module manager at run time; thus, the class path is dynamically
 * extended. This search policy is not fully dynamic, since it does not
 * support the removal of modules at run time; if a module is removed from
 * the module manager at run time, there is no attempt to clean up its
 * loaded classes.
 * </p>
 * @see org.ungoverned.moduleloader.SearchPolicy
 * @see org.ungoverned.moduleloader.Module
 * @see org.ungoverned.moduleloader.ModuleClassLoader
 * @see org.ungoverned.moduleloader.ModuleManager
**/
public class ExhaustiveSearchPolicy implements SearchPolicy
{
    private ModuleManager m_mgr = null;

    /**
     * This method is part of the <tt>SearchPolicy</tt> interface.
     * This method is called by the <tt>ModuleManager</tt> once to
     * give the search policy instance a reference to its associated
     * module manager. This method should be implemented such that
     * it cannot be called twice; calling this method a second time
     * should produce an illegal state exception.
     * @param mgr the module manager associated with this search policy.
     * @throws java.lang.IllegalStateException if the method is called
     *         more than once.
    **/
    public void setModuleManager(ModuleManager mgr)
        throws IllegalStateException
    {
        if (m_mgr == null)
        {
            m_mgr = mgr;
        }
        else
        {
            throw new IllegalStateException("Module manager is already initialized");
        }
    }

    /**
     * This method finds the specified class for the specified module. It
     * finds the class by linearly asking each module in the module manager
     * for the specific class. As soon as the class is found, it is returned.
     * @param module the target module that is loading the class.
     * @param name the name of the class being loaded.
     * @return the class if found, <tt>null</tt> otherwise.
    **/
    public Class findClass(Module module, String name)
    {
        Module[] modules = m_mgr.getModules();
        for (int i = 0; i < modules.length; i++)
        {
            try {
                Class clazz = modules[i].getClassLoader().searchForClass(name);
                if (clazz != null)
                {
                    return clazz;
                }
            } catch (Throwable th) {
            }
        }

        return null;
    }

    /**
     * This method finds the specified resource for the specified module. It
     * finds the resource by linearly asking each module in the module manager
     * for specific resource. As soon as the resource is found, a <tt>URL</tt>
     * to it is returned.
     * @param module the target module that is loading the resource.
     * @param name the name of the resource being loaded.
     * @return a <tt>URL</tt> to the resource if found, <tt>null</tt> otherwise.
    **/
    public URL findResource(Module module, String name)
    {
        Module[] modules = m_mgr.getModules();
        for (int i = 0; i < modules.length; i++)
        {
            try {
                URL url = modules[i].getClassLoader().searchForResource(name);
                if (url != null)
                {
                    return url;
                }
            } catch (Throwable th) {
            }
        }

        return null;
    }
}