LogbackPlugin.java

package org.hotswap.agent.plugin.logback;

import org.hotswap.agent.annotation.FileEvent;
import org.hotswap.agent.annotation.Init;
import org.hotswap.agent.annotation.OnClassLoadEvent;
import org.hotswap.agent.annotation.Plugin;
import org.hotswap.agent.javassist.*;
import org.hotswap.agent.logging.AgentLogger;
import org.hotswap.agent.util.IOUtils;
import org.hotswap.agent.util.PluginManagerInvoker;
import org.hotswap.agent.watch.WatchFileEvent;
import org.hotswap.agent.watch.WatchEventListener;
import org.hotswap.agent.watch.Watcher;

import java.net.URI;
import java.net.URL;
import java.util.HashSet;
import java.util.Set;

/**
 * Logback configuration file reload.
 *
 * @author Jiri Bubnik
 */
@Plugin(name = "Logback", description = "Logback configuration reload.",
        testedVersions = {"1.0.6"}
)
public class LogbackPlugin {
    private static AgentLogger LOGGER = AgentLogger.getLogger(LogbackPlugin.class);

    @Init
    Watcher watcher;

    @Init
    ClassLoader appClassLoader;

    // ensure uri registered only once
    Set<URI> registeredURIs = new HashSet<URI>();

    /**
     * Callback method from ch.qos.logback.core.joran.GenericConfigurator.
     *
     * @param configurator the configurator object
     * @param url          configuration file url
     */
    public void initLogback(final Object configurator, final URL url) {
        try {
            final URI uri = url.toURI();

            // skip double registration on reload
            if (registeredURIs.contains(uri))
                return;

            LOGGER.debug("Watching '{}' URL for Logback configuration changes.", url);
            registeredURIs.add(uri);
            watcher.addEventListener(appClassLoader, uri, new WatchEventListener() {
                @Override
                public void onEvent(WatchFileEvent event) {
                    if (event.getEventType() != FileEvent.DELETE)
                        reload(configurator, url);
                }
            });
        } catch (Exception e) {
            LOGGER.error("Exception initializing logback configurator {} on url {}.", e, configurator, url);
        }
    }

    /**
     * Do the reload using logback configurator.
     *
     * @param configurator ch.qos.logback.core.joran.GenericConfigurator instance
     * @param url          URL with configuration file
     */
    protected void reload(Object configurator, URL url) {

        try {
            IOUtils.toByteArray(url.toURI());
        } catch (Exception e) {
            LOGGER.warning("Unable to open logback configuration file {}, is it deleted?", url);
            return;
        }

        try {
            //noinspection SynchronizationOnLocalVariableOrMethodParameter
            synchronized (configurator) {
                ClassLoader classLoader = configurator.getClass().getClassLoader();

                Class<?> configuratorClass = classLoader.loadClass("ch.qos.logback.core.joran.GenericConfigurator");
                Class<?> contextAwareBaseClass = classLoader.loadClass("ch.qos.logback.core.spi.ContextAwareBase");
                Class<?> contextClass = classLoader.loadClass("ch.qos.logback.classic.LoggerContext");

                // reset current context
                Object context = contextAwareBaseClass.getDeclaredMethod("getContext").invoke(configurator);
                contextClass.getDeclaredMethod("reset").invoke(context);

                // configure the URL
                configuratorClass.getDeclaredMethod("doConfigure", URL.class).invoke(configurator, url);

                LOGGER.reload("Logback configuration reloaded from url '{}'.", url);
            }
        } catch (Exception e) {
            LOGGER.error("Unable to reload {} with logback configurator {}", e, url, configurator);
        }
    }

    /**
     * Transform configurator class to register logback config URL.
     */
    @OnClassLoadEvent(classNameRegexp = "ch.qos.logback.core.joran.GenericConfigurator")
    public static void registerConfigurator(ClassPool classPool, CtClass ctClass) throws NotFoundException, CannotCompileException {
        CtMethod m = ctClass.getDeclaredMethod("doConfigure", new CtClass[]{classPool.get("java.net.URL")});

        m.insertAfter(PluginManagerInvoker.buildInitializePlugin(LogbackPlugin.class));
        m.insertAfter(PluginManagerInvoker.buildCallPluginMethod(LogbackPlugin.class, "initLogback",
                "this", "java.lang.Object",
                "url", "java.net.URL"));
    }

}