WatchResourcesPlugin.java

package org.hotswap.agent.plugin.watchResources;

import org.hotswap.agent.config.PluginManager;
import org.hotswap.agent.annotation.Init;
import org.hotswap.agent.annotation.Plugin;
import org.hotswap.agent.config.PluginConfiguration;
import org.hotswap.agent.logging.AgentLogger;
import org.hotswap.agent.util.classloader.WatchResourcesClassLoader;
import org.hotswap.agent.util.classloader.URLClassLoaderHelper;
import org.hotswap.agent.watch.Watcher;

import java.net.*;

/**
 * Support for watchResources configuration property.
 *
 * This plugin creates special WatchResourcesClassLoader witch returns only modified resources on watchResources
 * path. It then modifies application classloader to look for resources first in WatchResourcesClassLoader and
 * only if the resource is not found, standard execution proceeds.
 *
 * Works for any java.net.URLClassLoader which delegates to URLClassPath property to findResource() (typical
 * scenario).
 */
@Plugin(name = "WatchResources", description = "Support for watchResources configuration property.",
        testedVersions = {"JDK 1.7.0_45"}, expectedVersions = {"JDK 1.6+"})
public class WatchResourcesPlugin {
    private static AgentLogger LOGGER = AgentLogger.getLogger(WatchResourcesPlugin.class);

    @Init
    Watcher watcher;

    @Init
    ClassLoader appClassLoader;


    // Classloader to return only modified resources on watchResources path.
    WatchResourcesClassLoader watchResourcesClassLoader = new WatchResourcesClassLoader(false);

    /**
     * For each classloader check for watchResources configuration instance with hotswapper.
     */
    @Init
    public static void init(PluginManager pluginManager, PluginConfiguration pluginConfiguration, ClassLoader appClassLoader) {
        LOGGER.debug("Init plugin at classLoader {}", appClassLoader);

        // synthetic classloader, skip
        if (appClassLoader instanceof WatchResourcesClassLoader.UrlOnlyClassLoader)
            return;

        // init only if the classloader contains directly the property file (not in parent classloader)
        if (!pluginConfiguration.containsPropertyFile()) {
            LOGGER.debug("ClassLoader {} does not contain hotswap-agent.properties file, WatchResources skipped.", appClassLoader);
            return;
        }

        // and watch resources are set
        URL[] watchResources = pluginConfiguration.getWatchResources();
        if (watchResources.length == 0) {
            LOGGER.debug("ClassLoader {} has hotswap-agent.properties watchResources empty.", appClassLoader);
            return;
        }

        if (!(appClassLoader instanceof URLClassLoader)) {
            LOGGER.warning("Unable to modify application classloader. Classloader '{}' is of type '{}'," +
                    "but only URLClassLoader is supported.\n" +
                    "*** watchResources configuration property will not be handled on JVM level ***",
                    appClassLoader, appClassLoader.getClass());
            return;
        }


        // create new plugin instance
        WatchResourcesPlugin plugin = (WatchResourcesPlugin) pluginManager.getPluginRegistry()
                .initializePlugin(WatchResourcesPlugin.class.getName(), appClassLoader);

        // and init it with watchResources path
        plugin.init(watchResources);
    }

    /**
     * Init the plugin instance for resources.
     *
     * @param watchResources resources to watch
     */
    private void init(URL[] watchResources) {
        // configure the classloader to return only changed resources on watchResources path
        watchResourcesClassLoader.initWatchResources(watchResources, watcher);

        // modify the application classloader to look for resources first in watchResourcesClassLoader
        URLClassLoaderHelper.setWatchResourceLoader((URLClassLoader)appClassLoader, watchResourcesClassLoader);
    }
}