elasticSearch源码分析之插件机制

89ou

前面已经部署了elasticSearch源码，并了解了ES组件（Modules）的组织方式，可以大致的认为ES是由一个一个的组件构成的，本文讨论ES的插件机制，插件机制只是它的一个组件，具体在(PluginsModule)。
   Modules里面有一个方法处理预处理组件：

/**
* 处理预处理组件
* @param modules
*/
public static void processModules(Iterable<Module> modules) {
for (Module module : modules) {
if (module instanceof PreProcessModule) {
for (Module module1 : modules) {
((PreProcessModule) module).processModule(module1);
}
}
}
}


插件调用的层次为：Modules->PluginsModule->PluginsService->XXPlugin；都是调用void processModule(Module module)方法。
区别在于
1：PluginsModule实现的是PreProcessModule接口。
2：PluginsService是自己本来的方法。
3：XXPlugin实现的是Plugin接口。
虽然他们都有processModule方法，但不是实现的同一个类。
接下来我们可以看一下插件服务具体实现的类PluginsService，具体做了什么？
查看代码：

/**
* Constructs a new PluginService
* @param settings The settings of the system
* @param environment The environment of the system
*/
public PluginsService(Settings settings, Environment environment) {
super(settings);
this.environment = environment;
this.checkLucene = componentSettings.getAsBoolean("check_lucene", true);
this.esPluginPropertiesFile = componentSettings.get(ES_PLUGIN_PROPERTIES_FILE_KEY, ES_PLUGIN_PROPERTIES);
this.loadClasspathPlugins = componentSettings.getAsBoolean(LOAD_PLUGIN_FROM_CLASSPATH, true);
ImmutableList.Builder<Tuple<PluginInfo, Plugin>> tupleBuilder = ImmutableList.builder();
// first we load all the default plugins from the settings
String[] defaultPluginsClasses = settings.getAsArray("plugin.types");
for (String pluginClass : defaultPluginsClasses) {
Plugin plugin = loadPlugin(pluginClass, settings);
PluginInfo pluginInfo = new PluginInfo(plugin.name(), plugin.description(), hasSite(plugin.name()), true, PluginInfo.VERSION_NOT_AVAILABLE);
if (logger.isTraceEnabled()) {
logger.trace("plugin loaded from settings [{}]", pluginInfo);
}
tupleBuilder.add(new Tuple<>(pluginInfo, plugin));
}
// now, find all the ones that are in the classpath
loadPluginsIntoClassLoader();
if (loadClasspathPlugins) {
tupleBuilder.addAll(loadPluginsFromClasspath(settings));
}
this.plugins = tupleBuilder.build();
// We need to build a List of jvm and site plugins for checking mandatory plugins
Map<String, Plugin> jvmPlugins = Maps.newHashMap();
List<String> sitePlugins = Lists.newArrayList();
for (Tuple<PluginInfo, Plugin> tuple : this.plugins) {
jvmPlugins.put(tuple.v2().name(), tuple.v2());
if (tuple.v1().isSite()) {
sitePlugins.add(tuple.v1().getName());
}
}
// we load site plugins
ImmutableList<Tuple<PluginInfo, Plugin>> tuples = loadSitePlugins();
for (Tuple<PluginInfo, Plugin> tuple : tuples) {
sitePlugins.add(tuple.v1().getName());
}
// Checking expected plugins
String[] mandatoryPlugins = settings.getAsArray("plugin.mandatory", null);
if (mandatoryPlugins != null) {
Set<String> missingPlugins = Sets.newHashSet();
for (String mandatoryPlugin : mandatoryPlugins) {
if (!jvmPlugins.containsKey(mandatoryPlugin) && !sitePlugins.contains(mandatoryPlugin) && !missingPlugins.contains(mandatoryPlugin)) {
missingPlugins.add(mandatoryPlugin);
}
}
if (!missingPlugins.isEmpty()) {
throw new ElasticsearchException("Missing mandatory plugins [" + Strings.collectionToDelimitedString(missingPlugins, ", ") + "]");
}
}
logger.info("loaded {}, sites {}", jvmPlugins.keySet(), sitePlugins);
MapBuilder<Plugin, List<OnModuleReference>> onModuleReferences = MapBuilder.newMapBuilder();
for (Plugin plugin : jvmPlugins.values()) {
List<OnModuleReference> list = Lists.newArrayList();
for (Method method : plugin.getClass().getDeclaredMethods()) {
if (!method.getName().equals("onModule")) {
continue;
}
if (method.getParameterTypes().length == 0 || method.getParameterTypes().length > 1) {
logger.warn("Plugin: {} implementing onModule with no parameters or more than one parameter", plugin.name());
continue;
}
Class moduleClass = method.getParameterTypes()[0];
if (!Module.class.isAssignableFrom(moduleClass)) {
logger.warn("Plugin: {} implementing onModule by the type is not of Module type {}", plugin.name(), moduleClass);
continue;
}
method.setAccessible(true);
list.add(new OnModuleReference(moduleClass, method));
}
if (!list.isEmpty()) {
onModuleReferences.put(plugin, list);
}
}
this.onModuleReferences = onModuleReferences.immutableMap();
this.refreshInterval = componentSettings.getAsTime("info_refresh_interval", TimeValue.timeValueSeconds(10));
}

可以看出其功能是注册ES根目录/[plugins]文件夹下的所有插件。