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Example text analysis plugin

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Example text analysis plugin

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This example shows how to create a simple "Hello world" text analysis plugin using the stable plugin API. The plugin provides a custom Lucene token filter that strips all tokens except for "hello" and "world".

Elastic provides a Grade plugin, elasticsearch.stable-esplugin, that makes it easier to develop and package stable plugins. The steps in this guide assume you use this plugin. However, you don’t need Gradle to create plugins.

Create a new directory for your project.
In this example, the source code is organized under the main and test directories. In your project’s home directory, create src/ src/main/, and src/test/ directories.

Create the following build.gradle build script in your project’s home directory:

ext.pluginApiVersion = '8.7.0'
ext.luceneVersion = '9.5.0'

buildscript {
  ext.pluginApiVersion = '8.7.0'
  repositories {
    mavenCentral()
  }
  dependencies {
    classpath "org.elasticsearch.gradle:build-tools:${pluginApiVersion}"
  }
}

apply plugin: 'elasticsearch.stable-esplugin'
apply plugin: 'elasticsearch.yaml-rest-test'

esplugin {
  name 'my-plugin'
  description 'My analysis plugin'
}

group 'org.example'
version '1.0-SNAPSHOT'

repositories {
  mavenLocal()
  mavenCentral()
}

dependencies {

  //TODO transitive dependency off and plugin-api dependency?
  compileOnly "org.elasticsearch.plugin:elasticsearch-plugin-api:${pluginApiVersion}"
  compileOnly "org.elasticsearch.plugin:elasticsearch-plugin-analysis-api:${pluginApiVersion}"
  compileOnly "org.apache.lucene:lucene-analysis-common:${luceneVersion}"

  //TODO for testing this also have to be declared
  testImplementation "org.elasticsearch.plugin:elasticsearch-plugin-api:${pluginApiVersion}"
  testImplementation "org.elasticsearch.plugin:elasticsearch-plugin-analysis-api:${pluginApiVersion}"
  testImplementation "org.apache.lucene:lucene-analysis-common:${luceneVersion}"

  testImplementation ('junit:junit:4.13.2'){
    exclude group: 'org.hamcrest'
  }
  testImplementation 'org.mockito:mockito-core:4.4.0'
  testImplementation 'org.hamcrest:hamcrest:2.2'

}

In src/main/java/org/example/, create HelloWorldTokenFilter.java. This file provides the code for a token filter that strips all tokens except for "hello" and "world":

package org.example;

import org.apache.lucene.analysis.FilteringTokenFilter;
import org.apache.lucene.analysis.TokenStream;
import org.apache.lucene.analysis.tokenattributes.CharTermAttribute;

import java.util.Arrays;

public class HelloWorldTokenFilter extends FilteringTokenFilter {
    private final CharTermAttribute term = addAttribute(CharTermAttribute.class);

    public HelloWorldTokenFilter(TokenStream input) {
        super(input);
    }

    @Override
    public boolean accept() {
        if (term.length() != 5) return false;
        return Arrays.equals(term.buffer(), 0, 4, "hello".toCharArray(), 0, 4)
                || Arrays.equals(term.buffer(), 0, 4, "world".toCharArray(), 0, 4);
    }
}

This filter can be provided to Elasticsearch using the following HelloWorldTokenFilterFactory.java factory class. The @NamedComponent annotation is used to give the filter the hello_world name. This is the name you can use to refer to the filter, once the plugin has been deployed.

package org.example;

import org.apache.lucene.analysis.TokenStream;
import org.elasticsearch.plugin.analysis.TokenFilterFactory;
import org.elasticsearch.plugin.NamedComponent;

@NamedComponent(value = "hello_world")
public class HelloWorldTokenFilterFactory implements TokenFilterFactory {

    @Override
    public TokenStream create(TokenStream tokenStream) {
        return new HelloWorldTokenFilter(tokenStream);
    }

}

Unit tests may go under the src/test directory. You will have to add dependencies for your preferred testing framework.
Run:
```
gradle bundlePlugin
```
This builds the JAR file, generates the metadata files, and bundles them into a plugin ZIP file. The resulting ZIP file will be written to the build/distributions directory.
Install the plugin.

You can use the _analyze API to verify that the hello_world token filter works as expected:

GET /_analyze
{
  "text": "hello to everyone except the world",
  "tokenizer": "standard",
  "filter":  ["hello_world"]
}

YAML REST tests

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If you are using the elasticsearch.stable-esplugin plugin for Gradle, you can use Elasticsearch’s YAML Rest Test framework. This framework allows you to load your plugin in a running test cluster and issue real REST API queries against it. The full syntax for this framework is beyond the scope of this tutorial, but there are many examples in the Elasticsearch repository. Refer to the example analysis plugin in the Elasticsearch Github repository for an example.

Create a yamlRestTest directory in the src directory.
Under the yamlRestTest directory, create a java folder for Java sources and a resources folder.

In src/yamlRestTest/java/org/example/, create HelloWorldPluginClientYamlTestSuiteIT.java. This class implements ESClientYamlSuiteTestCase.

import com.carrotsearch.randomizedtesting.annotations.Name;
import com.carrotsearch.randomizedtesting.annotations.ParametersFactory;
import org.elasticsearch.test.rest.yaml.ClientYamlTestCandidate;
import org.elasticsearch.test.rest.yaml.ESClientYamlSuiteTestCase;

public class HelloWorldPluginClientYamlTestSuiteIT extends ESClientYamlSuiteTestCase {

    public HelloWorldPluginClientYamlTestSuiteIT(
            @Name("yaml") ClientYamlTestCandidate testCandidate
    ) {
        super(testCandidate);
    }

    @ParametersFactory
    public static Iterable<Object[]> parameters() throws Exception {
        return ESClientYamlSuiteTestCase.createParameters();
    }
}

In src/yamlRestTest/resources/rest-api-spec/test/plugin, create the 10_token_filter.yml YAML file:

## Sample rest test
---
"Hello world plugin test - removes all tokens except hello and world":
  - do:
      indices.analyze:
        body:
          text: hello to everyone except the world
          tokenizer: standard
          filter:
            - type: "hello_world"
  - length: { tokens: 2 }
  - match:  { tokens.0.token: "hello" }
  - match:  { tokens.1.token: "world" }

Run the test with:
```
gradle yamlRestTest
```

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