Elasticsearch : Can't get Native (Java) Script working

Question

I've been struggling with the Native (Java) script for some time now. I am writing custom score plugin and building with Maven. My java class looks like this

package org.elasticsearch.plugin.hw.customscore;

import java.util.Collections;
import java.util.List;
import java.util.Map;

import org.elasticsearch.plugins.Plugin;
import org.elasticsearch.plugins.ScriptPlugin;
import org.elasticsearch.common.Nullable;
import org.elasticsearch.script.*;

public class HW_NativeScriptPlugin extends Plugin implements ScriptPlugin {

 @Override
 public List<NativeScriptFactory> getNativeScripts() {
     return Collections.singletonList(new HW_NativeScriptFactory());
 }

 public static class HW_NativeScriptFactory implements NativeScriptFactory {
     @Override
     public ExecutableScript newScript(@Nullable Map<String, Object> params)     {
        return new HW_NativeScript();
     }
     @Override
     public boolean needsScores() {
         return false;
     }
     @Override
     public String getName() {
         return "HW_SCRIPT";
     }
 }

 public static class HW_NativeScript extends AbstractDoubleSearchScript {
     @Override
     public double runAsDouble() {
         double a = 1;
         double b = 2;
         return a * b;
     } 
}
}

pom.xml ->

<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/maven-    v4_0_0.xsd">
  <modelVersion>4.0.0</modelVersion>
  <groupId>org.elasticsearch.plugin.hirewand.customscore</groupId>
  <artifactId>NativeScriptPlugin</artifactId>
  <packaging>jar</packaging>
  <version>1.0-SNAPSHOT</version>
  <name>NativeScriptPlugin</name>
  <url>http://maven.apache.org</url>
  <properties>
    <jdk.version>1.8</jdk.version>
  </properties>
  <dependencies>
    <dependency>
      <groupId>org.elasticsearch</groupId>
      <artifactId>elasticsearch</artifactId>
      <version>5.2.1</version>
    </dependency>
   </dependencies>
</project>

plugin-descriptor.properties ->

description=Custom score script for peopleworld
version=0.1
name=NativeScriptPlugin
classname=org.elasticsearch.plugin.hw.customscore.NativeScriptPlugin
java.version=1.8
elasticsearch.version=5.2.1

I m getting the following error while building my project

[ERROR]

E:\ESPlugin\NativeScriptPlugin\src\main\java\org\elasticsearch\plugin\hw\customscore\HW_NativeScriptPlugin.java:[16,40] error: incompatible types: List<HW_NativeScriptFactory> cannot be converted to List<NativeScriptFactory>
[ERROR] -> [Help 1]

Can anybody point out what am i doing wrong here ?

Answer 1

This could be easily resolved if you will specify target version for maven as Java 8 like this:

<build>
    <pluginManagement>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.1</version>
                <configuration>
                    <source>${jdk.version}</source>
                    <target>${jdk.version}</target>
                </configuration>
            </plugin>
        </plugins>
    </pluginManagement>
</build>

I used ${jdk.version} property which you declared above just to control version in concise fashion.

Appending this xml-snippet right after dependencies section should resolve your compilation problem.