es中的Plugin机制

node在初始化时，会创建PluginsService对象。

this.pluginsService = new PluginsService(tmpSettings, initialEnvironment.configFile(), initialEnvironment.modulesFile(),initialEnvironment.pluginsFile(), classpathPlugins);

参数包含modules目录，plugins目录。PluginsService构造函数中完成对modules目录、plugins目录下插件的加载。

扫描插件文件下的plugin-descriptor.properties文件，加载生成PluginInfo。plugin-descriptor.properties文件有一些必须的属性,如name, description, version, elasticsearch.version,java.version，还包含非必需属性，如extend.plugins,has.native.controller,type, classname, java.opts,licensed, 不能包含其它属性。
扫描插件文件夹下的jar文件，加载生成url
利用反射机制生成ClassLoader，加载Class, 初始化Plugin

生成PluginInfo

public static PluginInfo readFromProperties(final Path path) throws IOException {final Path descriptor = path.resolve(ES_PLUGIN_PROPERTIES);final Map<String, String> propsMap;{final Properties props = new Properties();try (InputStream stream = Files.newInputStream(descriptor)) {props.load(stream);}propsMap = props.stringPropertyNames().stream().collect(Collectors.toMap(Function.identity(), props::getProperty));}final String name = propsMap.remove("name");if (name == null || name.isEmpty()) {throw new IllegalArgumentException("property [name] is missing in [" + descriptor + "]");}final String description = propsMap.remove("description");if (description == null) {throw new IllegalArgumentException("property [description] is missing for plugin [" + name + "]");}final String version = propsMap.remove("version");if (version == null) {throw new IllegalArgumentException("property [version] is missing for plugin [" + name + "]");}final String esVersionString = propsMap.remove("elasticsearch.version");if (esVersionString == null) {throw new IllegalArgumentException("property [elasticsearch.version] is missing for plugin [" + name + "]");}final Version esVersion = Version.fromString(esVersionString);final String javaVersionString = propsMap.remove("java.version");if (javaVersionString == null) {throw new IllegalArgumentException("property [java.version] is missing for plugin [" + name + "]");}JarHell.checkVersionFormat(javaVersionString);final String extendedString = propsMap.remove("extended.plugins");final List<String> extendedPlugins;if (extendedString == null) {extendedPlugins = Collections.emptyList();} else {extendedPlugins = Arrays.asList(Strings.delimitedListToStringArray(extendedString, ","));}final boolean hasNativeController = parseBooleanValue(name, "has.native.controller", propsMap.remove("has.native.controller"));final PluginType type = getPluginType(name, propsMap.remove("type"));final String classname = getClassname(name, type, propsMap.remove("classname"));final String javaOpts = propsMap.remove("java.opts");if (type != PluginType.BOOTSTRAP && Strings.isNullOrEmpty(javaOpts) == false) {throw new IllegalArgumentException("[java.opts] can only have a value when [type] is set to [bootstrap] for plugin [" + name + "]");}boolean isLicensed = parseBooleanValue(name, "licensed", propsMap.remove("licensed"));if (propsMap.isEmpty() == false) {throw new IllegalArgumentException("Unknown properties for plugin [" + name + "] in plugin descriptor: " + propsMap.keySet());}return new PluginInfo(name, description, version, esVersion, javaVersionString,classname, extendedPlugins, hasNativeController, type, javaOpts, isLicensed);}

生成Bundle

static Set<Bundle> getModuleBundles(Path modulesDirectory) throws IOException {return findBundles(modulesDirectory, "module");}private static Set<Bundle> findBundles(final Path directory, String type) throws IOException {final Set<Bundle> bundles = new HashSet<>();for (final Path plugin : findPluginDirs(directory)) {final Bundle bundle = readPluginBundle(plugin, type);if (bundles.add(bundle) == false) {throw new IllegalStateException("duplicate " + type + ": " + bundle.plugin);}if (type.equals("module") && bundle.plugin.getName().startsWith("test-") && Build.CURRENT.isSnapshot() == false) {throw new IllegalStateException("external test module [" + plugin.getFileName() + "] found in non-snapshot build");}}logger.trace(() -> "findBundles("+ type+ ") returning: "+ bundles.stream().map(b -> b.plugin.getName()).sorted().collect(Collectors.toList()));return bundles;}Bundle(PluginInfo plugin, Path dir) throws IOException {this.plugin = Objects.requireNonNull(plugin);Set<URL> urls = new LinkedHashSet<>();// gather urls for jar filestry (DirectoryStream<Path> jarStream = Files.newDirectoryStream(dir, "*.jar")) {for (Path jar : jarStream) {// normalize with toRealPath to get symlinks out of our hairURL url = jar.toRealPath().toUri().toURL();if (urls.add(url) == false) {throw new IllegalStateException("duplicate codebase: " + url);}}}this.urls = Objects.requireNonNull(urls);}

加载Bundle

private List<Tuple<PluginInfo,Plugin>> loadBundles(Set<Bundle> bundles) {List<Tuple<PluginInfo, Plugin>> plugins = new ArrayList<>();Map<String, Plugin> loaded = new HashMap<>();Map<String, Set<URL>> transitiveUrls = new HashMap<>();List<Bundle> sortedBundles = sortBundles(bundles);for (Bundle bundle : sortedBundles) {if (bundle.plugin.getType() != PluginType.BOOTSTRAP) {checkBundleJarHell(JarHell.parseClassPath(), bundle, transitiveUrls);final Plugin plugin = loadBundle(bundle, loaded);plugins.add(new Tuple<>(bundle.plugin, plugin));}}loadExtensions(plugins);return Collections.unmodifiableList(plugins);}private Plugin loadBundle(Bundle bundle, Map<String, Plugin> loaded) {String name = bundle.plugin.getName();verifyCompatibility(bundle.plugin);// collect loaders of extended pluginsList<ClassLoader> extendedLoaders = new ArrayList<>();for (String extendedPluginName : bundle.plugin.getExtendedPlugins()) {Plugin extendedPlugin = loaded.get(extendedPluginName);assert extendedPlugin != null;if (ExtensiblePlugin.class.isInstance(extendedPlugin) == false) {throw new IllegalStateException("Plugin [" + name + "] cannot extend non-extensible plugin [" + extendedPluginName + "]");}extendedLoaders.add(extendedPlugin.getClass().getClassLoader());}// create a child to load the plugin in this bundleClassLoader parentLoader = PluginLoaderIndirection.createLoader(getClass().getClassLoader(), extendedLoaders);ClassLoader loader = URLClassLoader.newInstance(bundle.urls.toArray(new URL[0]), parentLoader);// reload SPI with any new services from the pluginreloadLuceneSPI(loader);ClassLoader cl = Thread.currentThread().getContextClassLoader();try {// Set context class loader to plugin's class loader so that plugins// that have dependencies with their own SPI endpoints have a chance to load// and initialize them appropriately.AccessController.doPrivileged((PrivilegedAction<Void>) () -> {Thread.currentThread().setContextClassLoader(loader);return null;});Class<? extends Plugin> pluginClass = loadPluginClass(bundle.plugin.getClassname(), loader);if (loader != pluginClass.getClassLoader()) {throw new IllegalStateException("Plugin [" + name + "] must reference a class loader local Plugin class ["+ bundle.plugin.getClassname()+ "] (class loader [" + pluginClass.getClassLoader() + "])");}Plugin plugin = loadPlugin(pluginClass, settings, configPath);loaded.put(name, plugin);return plugin;} finally {AccessController.doPrivileged((PrivilegedAction<Void>) () -> {Thread.currentThread().setContextClassLoader(cl);return null;});}}private Plugin loadPlugin(Class<? extends Plugin> pluginClass, Settings settings, Path configPath) {final Constructor<?>[] constructors = pluginClass.getConstructors();if (constructors.length == 0) {throw new IllegalStateException("no public constructor for [" + pluginClass.getName() + "]");}if (constructors.length > 1) {throw new IllegalStateException("no unique public constructor for [" + pluginClass.getName() + "]");}final Constructor<?> constructor = constructors[0];if (constructor.getParameterCount() > 2) {throw new IllegalStateException(signatureMessage(pluginClass));}final Class<?>[] parameterTypes = constructor.getParameterTypes();try {if (constructor.getParameterCount() == 2 && parameterTypes[0] == Settings.class && parameterTypes[1] == Path.class) {return (Plugin)constructor.newInstance(settings, configPath);} else if (constructor.getParameterCount() == 1 && parameterTypes[0] == Settings.class) {return (Plugin)constructor.newInstance(settings);} else if (constructor.getParameterCount() == 0) {return (Plugin)constructor.newInstance();} else {throw new IllegalStateException(signatureMessage(pluginClass));}} catch (final ReflectiveOperationException e) {throw new IllegalStateException("failed to load plugin class [" + pluginClass.getName() + "]", e);}}

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