elasticsearch使用x-pack插件后javaapi访问出现的问题及解决方法。

es装了x-pack权限工具以后，java(maven项目)访问es也需要相应的调整。按照官网给的教程：
首先，pom.xml增加

<project ...>
   <repositories>
      <!-- add the elasticsearch repo -->
      <repository>
         <id>elasticsearch-releases</id>
         <url>https://artifacts.elastic.co/maven</url>
         <releases>
            <enabled>true</enabled>
         </releases>
         <snapshots>
            <enabled>false</enabled>
         </snapshots>
      </repository>
      ...
   </repositories>
   ...
   <dependencies>
      <!-- add the x-pack jar as a dependency -->
      <dependency>
         <groupId>org.elasticsearch.client</groupId>
         <artifactId>x-pack-transport</artifactId>
         <version>{version}</version>
      </dependency>
      ...
   </dependencies>
   ...
 </project>

很多人发现，在这步的时候x-pack-transport依赖根本下载不下来，会报找不到类。

比如：

Caused by: java.lang.ClassNotFoundException: org.elasticsearch.xpack.XPackPlugin

解决办法：
查看maven的settings.xml文件
把mirrorOf标签里的内容改成*,!elasticsearch-releases（与pom.xml的repository id同名）。
配置成*表示所有的依赖都只会在配置的这个url找。加!elasticsearch-releases表示除了elasticsearch-releases的依赖其他依赖都在这个url找。

    <mirror> 
      <id>central</id>
      <mirrorOf>*,!elasticsearch-releases</mirrorOf>
      <name>Human Readable Name for this Mirror</name>
       <url>http://192.168.3.18:9096/nexus/content/groups/public/</url>
    </mirror>

还有另一种办法就是修改settings.xml的profile(推荐)。
修改settings.xml如下：

 <mirrors>
    <mirror> 
      <id>central</id>
      <mirrorOf>central</mirrorOf><!-- 修改此处 -->
      <name>Human Readable Name for this Mirror</name>
       <url>http://192.168.3.18:9096/nexus/content/groups/public/</url>
    </mirror>
 </mirrors>
 <profiles>
    <profile>
      <id>central-repos</id>
      <repositories>
        ...
         <repository>  <!-- 增加elastic仓库 -->
             <id>elasticsearch-releases</id>
             <url>https://artifacts.elastic.co/maven</url>
             <releases>
                <enabled>true</enabled>
             </releases>
             <snapshots>
                <enabled>false</enabled>
             </snapshots>
          </repository>
      </repositories>
      <pluginRepositories>
        ...
       </pluginRepositories>
    </profile>
  </profiles>
  <activeProfiles>
   <activeProfile>central-repos</activeProfile> <!-- 激活 -->
  </activeProfiles>

然后就可以把pom.xml文件里的repositories代码删掉。

接着是官网的Java代码：

import org.elasticsearch.xpack.client.PreBuiltXPackTransportClient;
...

TransportClient client = new PreBuiltXPackTransportClient(Settings.builder()
        .put("cluster.name", "myClusterName")
        .put("xpack.security.user", "transport_client_user:changeme")
        ...
        .build())
    .addTransportAddress(new InetSocketTransportAddress("localhost", 9300))
    .addTransportAddress(new InetSocketTransportAddress("localhost", 9301));

本来以为这次完美了，结果跑起来以后报了底下这个错误。

Caused by: java.lang.IllegalArgumentException: unknown setting [xpack.security.transport.ssl.enabled] please check that any required plugins are installed, or check the breaking changes documentation for removed settings

粗心啊！要用x-pack插件就不能用PreBuiltTransportClient来实例化client了，把PreBuiltTransportClient换成PreBuiltXPackTransportClient就搞定了。