环境

基于maven，至多须要援用如下两个包

<dependency>  <groupId>org.elasticsearch</groupId>  <artifactId>elasticsearch</artifactId>  <version>${elasticsearch.version}</version>  <scope>provided</scope></dependency><dependency>  <groupId>org.elasticsearch.test</groupId>  <artifactId>framework</artifactId>  <version>${elasticsearch.version}</version>  <scope>test</scope></dependency>

开发es插件，必定是要援用es的依赖，而且es还提供了测试框架，不便测试。这里要留神两点：

elasticsearch.version须要依据你的指标es版本在指定
设置为provided防止打包时将es作为依赖打进来

打包插件举荐这么配置：

<plugin>    <artifactId>maven-assembly-plugin</artifactId>    <version>3.1.1</version>    <configuration>      <appendAssemblyId>false</appendAssemblyId>      <descriptors>        <descriptor>src/assembly/release.xml</descriptor>      </descriptors>    </configuration>    <executions>      <execution>        <id>make-assembly</id>        <phase>package</phase>        <goals>          <goal>single</goal>        </goals>      </execution>    </executions>  </plugin>  <plugin>    <artifactId>maven-resources-plugin</artifactId>    <version>3.1.0</version>    <executions>      <execution>        <id>copy-resources</id>        <!-- here the phase you need -->        <phase>validate</phase>        <goals>          <goal>copy-resources</goal>        </goals>        <configuration>          <outputDirectory>${basedir}/target/extra-resources</outputDirectory>          <resources>            <resource>              <directory>src/main/resources</directory>              <filtering>true</filtering>            </resource>          </resources>        </configuration>      </execution>    </executions>  </plugin>

resources下减少文件：

src/main/resources/plugin-descriptor.propertiessrc/main/resources/plugin-security.policy

同时plugin-descriptor.properties内容如下，留神其中的变量：

java.version=1.8name=${project.artifactId}version=${version}description=${project.description}.elasticsearch.version=${elasticsearch.version}classname=com.eoi.nacos.elasticsearch.NacosPlugin

maven-resources-plugin会将src/main/resources下的资源文件复制到target/extra-resources目录，并替换文件中的变量。

maven-assembly-plugin依据src/assembly/release.xml的配置进行打包。src/assembly/release.xml如下：

<assembly xmlns="http://maven.apache.org/ASSEMBLY/2.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"          xsi:schemaLocation="http://maven.apache.org/ASSEMBLY/2.0.0 http://maven.apache.org/xsd/assembly-2.0.0.xsd">    <!-- Assembles a packaged version targeting OS installation. -->    <id>${build.timestamp}</id>    <formats>        <format>zip</format>    </formats>    <includeBaseDirectory>false</includeBaseDirectory>    <fileSets>        <fileSet>            <!-- maven-resources-plugin will filter the file and copy into the following directory -->            <directory>${project.basedir}/target/extra-resources</directory>            <outputDirectory>.</outputDirectory>            <includes>                <include>plugin-descriptor.properties</include>                <include>plugin-security.policy</include>            </includes>        </fileSet>    </fileSets>    <dependencySets>        <dependencySet>            <excludes>                <!-- exclude dependency that elasticsearch already contains -->                <exclude>org.joda:joda-convert</exclude>                <exclude>joda-time:joda-time</exclude>                <exclude>org.yaml:snakeyaml</exclude>                <exclude>com.fasterxml.jackson.dataformat:jackson-dataformat-yaml</exclude>                <exclude>jackson-core</exclude>                <!-- the following jar is duplicated in plugin repository-hdfs -->                <exclude>commons-collections:commons-collections</exclude>                <exclude>commons-logging:commons-logging</exclude>            </excludes>            <outputDirectory>.</outputDirectory>            <useProjectArtifact>true</useProjectArtifact>            <useTransitiveFiltering>true</useTransitiveFiltering>        </dependencySet>    </dependencySets></assembly>

这里设置打包次要申明了生成zip包（es插件的规范公布形式），并把替换好的plugin-descriptor.properties和plugin-security.policy打到zip包中。同时设置排除一些包，这些包是与es有抵触的，在最终测试时，依据插件依赖的复杂度，这块很可能要调整。

根底类

创立一个继承自org.elasticsearch.plugins.Plugin的类NacosPlugin，这个类就是插件的入口：

public class NacosPlugin extends Plugin {    protected final Settings settings;    public NacosPlugin(final Settings settings) {        this.settings = settings;    }        @Override    public List<Setting<?>> getSettings() {        ...    }        @Override    public Collection<Object> createComponents(...) {        ...    }}

简直所有的插件都须要配置，在插件的实现中，通过重写getSettings办法，裸露插件对外反对的配置。用户在elasticsearch.yml中配置的相干信息，会通过构造函数传给插件类。
createComponents是返回插件实例化的“组件”。常见的组件能够是org.elasticsearch.common.component.AbstractLifecycleComponent，该组件需实现doStart和doStop，对应es的启动和进行事件。createComponents参数如下：

Client client: 罕用。通过client拜访es的各种接口，同时能够衍生出ClusterAdminClient。Nacos插件中须要通过ClusterAdminClient获取节点的拜访点信息
ClusterService clusterService
ThreadPool threadPool: 罕用。es提供的线程池入口，能够通过threadPool来启动定时工作线程等异步操作
ResourceWatcherService resourceWatcherService
ScriptService scriptService
NamedXContentRegistry xContentRegistry
Environment environment: es环境相干信息
NodeEnvironment nodeEnvironment: 节点环境相干信息，例如获取nodeId
NamedWriteableRegistry namedWriteableRegistry

插件与es的交互，简直都是通过上述参数传来的对象进行的。因而大多数状况下createComponents才是真正的入口，咱们返回的“组件”必须保留须要的对象援用从而发展工作。