檢索引擎Elasticsearch支持插件模式，有些時候你可能需要安裝一些插件，甚至自己開發插件，這里就提供一個開始ES插件開發示例，ES版本為2.2.0。

自定義插件類繼承org.elasticsearch.plugins.Plugin

HelloWorldPlugin：

package org.elasticsearch.plugin.helloworld;import java.util.Collection; import java.util.Collections; import org.elasticsearch.common.inject.Module; import org.elasticsearch.plugins.Plugin; public class HelloWorldPlugin extends Plugin { @Override public String name() { return "hello-world"; } @Override public String description() { return "hello-world"; } @Override public Collection<Module> nodeModules() { //加入自定義處理模塊 return Collections.<Module> singletonList(new HelloWorldModule()); } }
HelloWorldModule：

package org.elasticsearch.plugin.helloworld;import org.elasticsearch.common.inject.AbstractModule; import org.elasticsearch.rest.action.helloworld.HelloWorldAction; public class HelloWorldModule extends AbstractModule { @Override protected void configure() { bind(HelloWorldAction.class).asEagerSingleton(); } }
HelloWorldAction： package org.elasticsearch.rest.action.helloworld;import static org.elasticsearch.rest.RestRequest.Method.GET; import java.io.IOException; import org.elasticsearch.action.ActionListener; import org.elasticsearch.action.get.GetRequest; import org.elasticsearch.action.get.GetResponse; import org.elasticsearch.client.Client; import org.elasticsearch.common.inject.Inject; import org.elasticsearch.common.io.stream.BytesStreamOutput; import org.elasticsearch.common.settings.Settings; import org.elasticsearch.common.xcontent.XContentBuilder; import org.elasticsearch.common.xcontent.XContentBuilderString; import org.elasticsearch.common.xcontent.XContentFactory; import org.elasticsearch.common.xcontent.XContentType; import org.elasticsearch.index.get.GetField; import org.elasticsearch.rest.BaseRestHandler; import org.elasticsearch.rest.BytesRestResponse; import org.elasticsearch.rest.RestChannel; import org.elasticsearch.rest.RestController; import org.elasticsearch.rest.RestRequest; import org.elasticsearch.rest.RestStatus; public class HelloWorldAction extends BaseRestHandler { public static String INDEX = "example"; public static String TYPE = "person"; @Inject public HelloWorldAction(Settings settings, Client client, RestController controller) { super(settings, controller, client); // Define REST endpoints controller.registerHandler(GET, "/_hello/", this); controller.registerHandler(GET, "/_hello/{name}", this); } public static XContentBuilder restContentBuilder(RestRequest request) throws IOException { XContentType contentType = XContentType .fromRestContentType(request.header("Content-Type")); if (contentType == null) { // try and guess it from the body, if exists if (request.hasContent()) { contentType = XContentFactory.xContentType(request.content()); } } if (contentType == null) { // default to JSON contentType = XContentType.JSON; } BytesStreamOutput out = new BytesStreamOutput(); XContentBuilder builder = new XContentBuilder( XContentFactory.xContent(contentType), out); if (request.paramAsBoolean("pretty", false)) { builder.prettyPrint(); } String casing = request.param("case"); if (casing != null && "camelCase".equals(casing)) { builder.fieldCaseConversion( XContentBuilder.FieldCaseConversion.CAMELCASE); } else { builder.fieldCaseConversion( XContentBuilder.FieldCaseConversion.NONE); } return builder; } @Override protected void handleRequest(final RestRequest request, final RestChannel channel, Client client) throws Exception { logger.info("HelloWorldAction.handleRequest called"); final String name = request.hasParam("name") ? request.param("name") : "world"; logger.info("name={}", name); final GetRequest getRequest = new GetRequest(INDEX, TYPE, name); getRequest.operationThreaded(true); String[] fields = {"msg"}; getRequest.fields(fields); client.get(getRequest, new ActionListener<GetResponse>() { @Override public void onResponse(GetResponse response) { try { XContentBuilder builder = restContentBuilder(request); GetField field = response.getField("msg"); String greeting = (field != null) ? (String) field.getValues().get(0) : "Sorry, do I know you?"; builder.startObject() .field(new XContentBuilderString("hello"), name) .field(new XContentBuilderString("greeting"), greeting) .endObject(); if (!response.isExists()) { channel.sendResponse(new BytesRestResponse( RestStatus.NOT_FOUND, builder)); } else { channel.sendResponse( new BytesRestResponse(RestStatus.OK, builder)); } } catch (Exception e) { onFailure(e); } } @Override public void onFailure(Throwable e) { try { channel.sendResponse( new BytesRestResponse(channel, RestStatus.OK, e)); } catch (IOException e1) { logger.error("Failed to send failure response", e1); } } }); } }
打包后j將jar包上傳至${ES_HOME}/plugins/HelloWorld目錄下（新建HelloWorld）
HelloWorld目錄下新建文件plugin-descriptor.properties，文件內容如下
description=hello for ElasticSearch
version=1.0
name=HelloWorldPlugin
jvm=true
classname=org.elasticsearch.plugin.helloworld.HelloWorldPlugin
java.version=1.7（當時我這里寫的是1.7但實際裝的是jdk1.8.0_91倒也能正常運行）
elasticsearch.version=2.2.0

重啟es，插件便安裝成功了。

注意：在編寫plugin-descriptor.properties文件的時候每行的后面一定不要有空格，我一開始就是直接粘貼過去的，結果每行末尾都有兩個空格，重啟es會報下面這個錯，耗費了很長時間，這里吐槽一下CSDN，當你在它的文本編輯器中將這個josn復制過去再展示的時候你會發現每行后面自動就會有兩個空格，真是坑死我了！

[hadoop@h153 ~]$ ./elasticsearch-2.2.0/bin/elasticsearch [2017-10-12 01:19:08,902][INFO ][node ] [node-1] version[2.2.0], pid[8548], build[8ff36d1/2016-01-27T13:32:39Z] [2017-10-12 01:19:08,903][INFO ][node ] [node-1] initializing ... Exception in thread "main" ElasticsearchException[Could not find plugin class [org.elasticsearch.plugin.helloworld.HelloWorldPlugin]]; nested: ClassNotFoundException[org.elasticsearch.plugin.helloworld.HelloWorldPlugin]; Likely root cause: java.lang.ClassNotFoundException: org.elasticsearch.plugin.helloworld.HelloWorldPluginat java.net.URLClassLoader.findClass(URLClassLoader.java:381)at java.lang.ClassLoader.loadClass(ClassLoader.java:424)at java.net.FactoryURLClassLoader.loadClass(URLClassLoader.java:814)at java.lang.ClassLoader.loadClass(ClassLoader.java:357)at org.elasticsearch.plugins.PluginsService.loadPluginClass(PluginsService.java:463)at org.elasticsearch.plugins.PluginsService.loadBundles(PluginsService.java:431)at org.elasticsearch.plugins.PluginsService.<init>(PluginsService.java:129)at org.elasticsearch.node.Node.<init>(Node.java:146)at org.elasticsearch.node.Node.<init>(Node.java:128)at org.elasticsearch.node.NodeBuilder.build(NodeBuilder.java:145)at org.elasticsearch.bootstrap.Bootstrap.setup(Bootstrap.java:178)at org.elasticsearch.bootstrap.Bootstrap.init(Bootstrap.java:285)at org.elasticsearch.bootstrap.Elasticsearch.main(Elasticsearch.java:35) Refer to the log for complete error details.
下面進行插件的驗證：

先創建相應的索引： [hadoop@h153 ~]$ curl -XPOST http://192.168.205.153:9200/example {"acknowledged":true}[hadoop@h153 ~]$ curl -XGET http://192.168.205.153:9200/_hello {"hello":"world","greeting":"Sorry, do I know you?"}[hadoop@h153 ~]$ curl -XGET http://192.168.205.153:9200/_hello/xmine {"hello":"xmine","greeting":"Sorry, do I know you?"}[hadoop@h153 ~]$ curl -XPUT http://192.168.205.153:9200/example/person/xmine?pretty -d '{"msg":"elasticsearch"}' {"_index" : "example","_type" : "person","_id" : "xmine","_version" : 1,"_shards" : {"total" : 2,"successful" : 1,"failed" : 0},"created" : true } [hadoop@h153 ~]$ curl -XGET http://192.168.205.153:9200/_hello/xmine {"hello":"xmine","greeting":"elasticsearch"}
補充：為插件添加頁面
如果你想為你的插件添加訪問頁面，則可以在ES_HOME/plugins/HelloWorld目錄下創建一個名為"_site"的目錄，該目錄名稱必須為_site，然后將相應的html頁面放置進_site目錄即可，如果放置了一個名為index.html文件，則可以通過localhost:9200/_plugin/HelloWorld/index.html進行訪問。
由于Elasticsearch提供了js客戶端API，所以使用html靜態頁面與js就可以完成相應的功能了。

參考：
http://blog.csdn.net/xtayfjpk/article/details/47005219
http://blog.csdn.net/l253272670/article/details/54141169
https://stackoverflow.com/questions/33538903/elasticsearch-2-0-plugin-installation-info

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