jenkins/core/src/main/java/hudson/PluginManager.java

package hudson;

import hudson.model.Hudson;
import hudson.util.Service;
import java.util.logging.Level;

import javax.servlet.ServletContext;
import java.io.File;
import java.io.FilenameFilter;
import java.io.IOException;
import java.net.URL;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import java.util.logging.Logger;

/**
 * Manages {@link PluginWrapper}s.
 *
 * @author Kohsuke Kawaguchi
 */
public final class PluginManager {
    /**
     * All discovered plugins.
     */
    private final List<PluginWrapper> plugins = new ArrayList<PluginWrapper>();

    /**
     * All active plugins.
     */
    private final List<PluginWrapper> activePlugins = new ArrayList<PluginWrapper>();

    /**
     * Plug-in root directory.
     */
    public final File rootDir;

    public final ServletContext context;

    /**
     * {@link ClassLoader} that can load all the publicly visible classes from plugins
     * (and including the classloader that loads Hudson itself.)
     *
     */
    // implementation is minmal --- just enough to run XStream
    // and load plugin-contributed classes.
    public final ClassLoader uberClassLoader = new UberClassLoader();

    public PluginManager(ServletContext context) {
        this.context = context;
        rootDir = new File(Hudson.getInstance().getRootDir(),"plugins");
        if(!rootDir.exists())
            rootDir.mkdirs();

        File[] archives = rootDir.listFiles(new FilenameFilter() {
            public boolean accept(File dir, String name) {
                return name.endsWith(".hpi")        // plugin jar file
                    || name.endsWith(".hpl");       // linked plugin. for debugging.
            }
        });

        if(archives==null) {
            LOGGER.severe("Hudson is unable to create "+rootDir+"\nPerhaps its security privilege is insufficient");
            return;
        }
        for( File arc : archives ) {
            try {
                PluginWrapper p = new PluginWrapper(this, arc);
                plugins.add(p);
                if(p.isActive())
                    activePlugins.add(p);
            } catch (IOException e) {
                LOGGER.log(Level.SEVERE, "Failed to load a plug-in " + arc, e);
            }
        }
    }

    public List<PluginWrapper> getPlugins() {
        return plugins;
    }

    public PluginWrapper getPlugin(String shortName) {
        for (PluginWrapper p : plugins) {
            if(p.getShortName().equals(shortName))
                return p;
        }
        return null;
    }

    /**
     * Discover all the service provider implementations of the given class,
     * via <tt>META-INF/services</tt>.
     */
    public <T> Collection<Class<? extends T>> discover( Class<T> spi ) {
        Set<Class<? extends T>> result = new HashSet<Class<? extends T>>();

        for (PluginWrapper p : activePlugins) {
            Service.load(spi, p.classLoader, result);
        }

        return result;
    }

    /**
     * Orderly terminates all the plugins.
     */
    public void stop() {
        for (PluginWrapper p : activePlugins) {
            p.stop();
        }
    }

    private final class UberClassLoader extends ClassLoader {
        public UberClassLoader() {
            super(PluginManager.class.getClassLoader());
        }

        @Override
        protected Class<?> findClass(String name) throws ClassNotFoundException {
            for (PluginWrapper p : activePlugins) {
                try {
                    return p.classLoader.loadClass(name);
                } catch (ClassNotFoundException e) {
                    //not found. try next
                }
            }
            // not found in any of the classloader. delegate.
            throw new ClassNotFoundException(name);
        }

        @Override
        protected URL findResource(String name) {
            for (PluginWrapper p : activePlugins) {
                URL url = p.classLoader.getResource(name);
                if(url!=null)
                    return url;
            }
            return null;
        }
    }

    private static final Logger LOGGER = Logger.getLogger(PluginManager.class.getName());

}