Elasticsearch：从零开始创建一个 REST handler 插件

Posted 2022-09-08 Elastic 中国社区官方博客

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在 Kibana 的 console 中，我们可以使用一些命令对 Elasticsearch 进行交互。那么我们是否可以扩展我们需要的一些命令呢？比如：

在上面，我们打入 GET _cat/example，它将显示右边的输出。这个是我们扩展的一个命令。

Elasticsearch 带有一组可以执行各种任务的功能。但是，如果你想实现自己的任何功能，则需要在 Elasticsearch 的主代码库中实现。为了保护你免受所有这些额外步骤的影响，Elasticsearch 提供了在 Elasticsearch 代码中添加插件的选项，该插件能够实现你的功能。

在今天的展示中，我将使用最新的 Elastic Stack 8.4.0 来进行展示。

安装

如果你还没有安装好自己的 Elastic Stack，请参考如下的文章来安装 Elasticsearch 及 Kibana：

创建插件模板

在我之前的文章

我已经展示了如何为 ingest pipeline 创建 processors。在上面的第二篇文章中，我使用了一个叫做 elasticsearch-plugin-archtype 的插件。我们可以使用如下的命令来创建一个最为基本的插件模板：

mvn archetype:generate \\
    -DarchetypeGroupId=org.codelibs \\
    -DarchetypeArtifactId=elasticsearch-plugin-archetype \\
    -DarchetypeVersion=6.6.0 \\
    -DgroupId=com.liuxg \\
    -DartifactId=elasticsearch-plugin \\
    -Dversion=1.0-SNAPSHOT \\
    -DpluginName=rest_handler

上面已经帮我们创建了一个最为基本的插件模板。它在当前的目录下创建了一个叫做 elasticsearch-plugin 的目录。我们首先进入到该目录中：

$ pwd
/Users/liuxg/java/plugins/elasticsearch-plugin
$ tree -L 8
.
├── pom.xml
└── src
    └── main
        ├── assemblies
        │   └── plugin.xml
        ├── java
        │   └── com
        │       └── liuxg
        │           ├── rest
        │           │   └── Restrest_handlerAction.java
        │           └── rest_handlerPlugin.java
        └── plugin-metadata
            └── plugin-descriptor.properties

上面是它的文件结构。因为我们想为 Elastic Stack 8.4.0 构建插件，所以，我们必须在 pom.xml 中修改相应的版本信息：

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
	<name>elasticsearch-plugin</name>
	<modelVersion>4.0.0</modelVersion>
	<groupId>com.liuxg</groupId>
	<artifactId>elasticsearch-plugin</artifactId>
	<version>1.0-SNAPSHOT</version>
	<packaging>jar</packaging>
	<description>elasticsearch rest_handler plugin</description>
	<inceptionYear>2019</inceptionYear>
	<licenses>
		<license>
			<name>The Apache Software License, Version 2.0</name>
			<url>http://www.apache.org/licenses/LICENSE-2.0.txt</url>
			<distribution>repo</distribution>
		</license>
	</licenses>
	<properties>
		<elasticsearch.version>8.4.0</elasticsearch.version>
		<elasticsearch.plugin.classname>com.liuxg.rest_handlerPlugin</elasticsearch.plugin.classname>
		<log4j.version>2.11.1</log4j.version>
		<maven.compiler.source>1.8</maven.compiler.source>
		<maven.compiler.target>1.8</maven.compiler.target>
	</properties>
	<build>
		<plugins>
			<plugin>
				<artifactId>maven-compiler-plugin</artifactId>
				<version>3.8.0</version>
				<configuration>
					<source>$maven.compiler.source</source>
					<target>$maven.compiler.target</target>
					<encoding>UTF-8</encoding>
				</configuration>
			</plugin>
			<plugin>
				<artifactId>maven-surefire-plugin</artifactId>
				<version>2.22.1</version>
				<configuration>
					<includes>
						<include>**/*Tests.java</include>
					</includes>
				</configuration>
			</plugin>
			<plugin>
				<artifactId>maven-source-plugin</artifactId>
				<version>3.0.1</version>
				<executions>
					<execution>
						<id>attach-sources</id>
						<goals>
							<goal>jar</goal>
						</goals>
					</execution>
				</executions>
			</plugin>
			<plugin>
				<artifactId>maven-assembly-plugin</artifactId>
				<version>3.1.0</version>
				<configuration>
					<appendAssemblyId>false</appendAssemblyId>
					<outputDirectory>$project.build.directory/releases/</outputDirectory>
					<descriptors>
						<descriptor>$basedir/src/main/assemblies/plugin.xml</descriptor>
					</descriptors>
				</configuration>
				<executions>
					<execution>
						<phase>package</phase>
						<goals>
							<goal>single</goal>
						</goals>
					</execution>
				</executions>
			</plugin>
		</plugins>
	</build>
	<dependencies>
		<dependency>
			<groupId>org.elasticsearch</groupId>
			<artifactId>elasticsearch</artifactId>
			<version>$elasticsearch.version</version>
			<scope>provided</scope>
		</dependency>
		<dependency>
			<groupId>org.apache.logging.log4j</groupId>
			<artifactId>log4j-api</artifactId>
			<version>$log4j.version</version>
			<scope>provided</scope>
		</dependency>
	</dependencies>
</project>

在上面，我们把 elasticsearch.version 设置为 8.4.0。其它的保持不变。

接下来，我们来修改 rest_handlerPlugin.java 文件：

rest_handlerPlugin.java

package com.liuxg;

import java.util.List;
import java.util.function.Supplier;

import com.liuxg.rest.Restrest_handlerAction;
import org.elasticsearch.cluster.metadata.IndexNameExpressionResolver;
import org.elasticsearch.cluster.node.DiscoveryNodes;
import org.elasticsearch.common.settings.ClusterSettings;
import org.elasticsearch.common.settings.IndexScopedSettings;
import org.elasticsearch.common.settings.Settings;
import org.elasticsearch.common.settings.SettingsFilter;
import org.elasticsearch.plugins.ActionPlugin;
import org.elasticsearch.plugins.Plugin;
import org.elasticsearch.rest.RestController;
import org.elasticsearch.rest.RestHandler;

import static java.util.Collections.singletonList;

public class rest_handlerPlugin extends Plugin implements ActionPlugin 
    @Override
    public List<RestHandler> getRestHandlers(final Settings settings,
                                             final RestController restController,
                                             final ClusterSettings clusterSettings,
                                             final IndexScopedSettings indexScopedSettings,
                                             final SettingsFilter settingsFilter,
                                             final IndexNameExpressionResolver indexNameExpressionResolver,
                                             final Supplier<DiscoveryNodes> nodesInCluster) 
        return singletonList(new Restrest_handlerAction());

这个文件会让 Elasticsearch 知道你的插件。

我们接下来修改 Restrest_handlerAction.java 文件如下：

Restrest_handlerAction.java

package com.liuxg.rest;

import org.elasticsearch.client.internal.node.NodeClient;
import org.elasticsearch.common.Table;
import org.elasticsearch.rest.RestRequest;
import org.elasticsearch.rest.RestResponse;
import org.elasticsearch.rest.action.cat.AbstractCatAction;
import org.elasticsearch.rest.action.cat.RestTable;

import java.util.List;

import static org.elasticsearch.rest.RestRequest.Method.GET;
import static org.elasticsearch.rest.RestRequest.Method.POST;


public class Restrest_handlerAction extends AbstractCatAction 
    @Override
    public List<Route> routes() 
        return List.of(
                new Route(GET, "/_cat/example"),
                new Route(POST, "/_cat/example"));
    

    @Override
    public String getName() 
        return "rest_handler_cat_example";
    

    @Override
    protected RestChannelConsumer doCatRequest(final RestRequest request, final NodeClient client) 
        final String message = request.param("message", "Hello from Cat Example action");

        Table table = getTableWithHeader(request);
        table.startRow();
        table.addCell(message);
        table.endRow();
        return channel -> 
            try 
                channel.sendResponse(RestTable.buildResponse(table, channel));
             catch (final Exception e) 
                channel.sendResponse(new RestResponse(channel, e));
            
        ;
    

    @Override
    protected void documentation(StringBuilder sb) 
        sb.append(documentation());
    

    public static String documentation() 
        return "/_cat/example\\n";
    

    @Override
    protected Table getTableWithHeader(RestRequest request) 
        final Table table = new Table();
        table.startHeaders();
        table.addCell("test", "desc:test");
        table.endHeaders();
        return table;

该文件将定义插件的路由和处理这些路由的代码。

这样我们就修改完了我们的代码。

编译

我们在项目的根目录下使人如下的命令来进行编译：

mvn clean install

$ mvn clean install
[INFO] Scanning for projects...
[INFO] 
[INFO] -------------------< com.liuxg:elasticsearch-plugin >-------------------
[INFO] Building elasticsearch-plugin 1.0-SNAPSHOT
[INFO] --------------------------------[ jar ]---------------------------------
[INFO] 
[INFO] --- maven-clean-plugin:2.5:clean (default-clean) @ elasticsearch-plugin ---
[INFO] 
[INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ elasticsearch-plugin ---
[WARNING] Using platform encoding (UTF-8 actually) to copy filtered resources, i.e. build is platform dependent!
[INFO] skip non existing resourceDirectory /Users/liuxg/java/plugins/elasticsearch-plugin/src/main/resources
[INFO] 
[INFO] --- maven-compiler-plugin:3.8.0:compile (default-compile) @ elasticsearch-plugin ---
[INFO] Changes detected - recompiling the module!
[INFO] Compiling 2 source files to /Users/liuxg/java/plugins/elasticsearch-plugin/target/classes
[INFO] 
[INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ elasticsearch-plugin ---
[WARNING] Using platform encoding (UTF-8 actually) to copy filtered resources, i.e. build is platform dependent!
[INFO] skip non existing resourceDirectory /Users/liuxg/java/plugins/elasticsearch-plugin/src/test/resources
[INFO] 
[INFO] --- maven-compiler-plugin:3.8.0:testCompile (default-testCompile) @ elasticsearch-plugin ---
[INFO] No sources to compile
[INFO] 
[INFO] --- maven-surefire-plugin:2.22.1:test (default-test) @ elasticsearch-plugin ---
[INFO] No tests to run.
[INFO] 
[INFO] --- maven-jar-plugin:2.4:jar (default-jar) @ elasticsearch-plugin ---
[INFO] Building jar: /Users/liuxg/java/plugins/elasticsearch-plugin/target/elasticsearch-plugin-1.0-SNAPSHOT.jar
[INFO] 
[INFO] >>> maven-source-plugin:3.0.1:jar (attach-sources) > generate-sources @ elasticsearch-plugin >>>
[INFO] 
[INFO] <<< maven-source-plugin:3.0.1:jar (attach-sources) < generate-sources @ elasticsearch-plugin <<<
[INFO] 
[INFO] 
[INFO] --- maven-source-plugin:3.0.1:jar (attach-sources) @ elasticsearch-plugin ---
[INFO] Building jar: /Users/liuxg/java/plugins/elasticsearch-plugin/target/elasticsearch-plugin-1.0-SNAPSHOT-sources.jar
[INFO] 
[INFO] --- maven-assembly-plugin:3.1.0:single (default) @ elasticsearch-plugin ---
[INFO] Reading assembly descriptor: /Users/liuxg/java/plugins/elasticsearch-plugin/src/main/assemblies/plugin.xml
[WARNING] The following patterns were never triggered in this artifact exclusion filter:
o  'org.elasticsearch:elasticsearch'

[INFO] Building zip: /Users/liuxg/java/plugins/elasticsearch-plugin/target/releases/elasticsearch-plugin-1.0-SNAPSHOT.zip
[INFO] 
[INFO] --- maven-install-plugin:2.4:install (default-install) @ elasticsearch-plugin ---
[INFO] Installing /Users/liuxg/java/plugins/elasticsearch-plugin/target/elasticsearch-plugin-1.0-SNAPSHOT.jar to /Users/liuxg/.m2/repository/com/liuxg/elasticsearch-plugin/1.0-SNAPSHOT/elasticsearch-plugin-1.0-SNAPSHOT.jar
[INFO] Installing /Users/liuxg/java/plugins/elasticsearch-plugin/pom.xml to /Users/liuxg/.m2/repository/com/liuxg/elasticsearch-plugin/1.0-SNAPSHOT/elasticsearch-plugin-1.0-SNAPSHOT.pom
[INFO] Installing /Users/liuxg/java/plugins/elasticsearch-plugin/target/elasticsearch-plugin-1.0-SNAPSHOT-sources.jar to /Users/liuxg/.m2/repository/com/liuxg/elasticsearch-plugin/1.0-SNAPSHOT/elasticsearch-plugin-1.0-SNAPSHOT-sources.jar
[INFO] Installing /Users/liuxg/java/plugins/elasticsearch-plugin/target/releases/elasticsearch-plugin-1.0-SNAPSHOT.zip to /Users/liuxg/.m2/repository/com/liuxg/elasticsearch-plugin/1.0-SNAPSHOT/elasticsearch-plugin-1.0-SNAPSHOT.zip
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  5.352 s
[INFO] Finished at: 2022-09-06T10:55:38+08:00
[INFO] ------------------------------------------------------------------------

编译成功后，我们可以在 targe 目录先看到如下的安装文件：

$ pwd
/Users/liuxg/java/plugins/elasticsearch-plugin
$ ls target/releases
elasticsearch-plugin-1.0-SNAPSHOT.zip

上面显示的 elasticsearch-plugin-1.0-SNAPSHOT.zip 就是我们可以安装的插件文件。

安装插件并测试插件

我们接下来换到 Elasticsearch 的安装目录下，并打入如下的命令：

$ pwd
/Users/liuxg/elastic0/elasticsearch-8.4.0
$ bin/elasticsearch-plugin install file:Users/liuxg/java/plugins/elasticsearch-plugin/target/releases/elasticsearch-plugin-1.0-SNAPSHOT.zip
-> Installing file:Users/liuxg/java/plugins/elasticsearch-plugin/target/releases/elasticsearch-plugin-1.0-SNAPSHOT.zip
-> Downloading file:Users/liuxg/java/plugins/elasticsearch-plugin/target/releases/elasticsearch-plugin-1.0-SNAPSHOT.zip
[=================================================] 100%   
-> Installed rest_handler
-> Please restart Elasticsearch to activate any plugins installed
$ ./bin/elasticsearch-plugin list
rest_handler

从上面的显示中，我们可以看出来 rest_handler 插件已经被成功地安装。我们接下来需要重新启动 Elasticsearch。这个非常重要！

我们打开 Kibana，并打入如下的命令：

我们也可以直接在 terminal 中打入如下的命令：

curl -k --user elastic:V_USqc1cWM40W_pIHnni https://localhost:9200/_cat/example

$ curl -k --user elastic:V_USqc1cWM40W_pIHnni https://localhost:9200/_cat/example
Hello from Cat Example action

整个项目的代码可以在地址下载：GitHub - liu-xiao-guo/rest_handler_plugin

参考：

【1】elasticsearch/plugins/examples at main · elastic/elasticsearch · GitHub

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