Java lang Plugin for ElasticSearch

The Java language plugin enables the use of java as the language of scripts to execute. It is simple, lightweight and requires no additional classpath dependencies.

Motivation

The main value add of this plugin is that it allows users to create fast native Java based scripts inside of a query, without having to distribute the scripts to each node as a configuration step. This greatly simplifies the operational concerns associated with using the alternative: native scripts.

Installation

To install the latest development version:

• git clone [email protected]:btiernay/elasticsearch-lang-java.git
• cd elasticsearch-lang-java/
• mvn clean package -DskipTests=true
• bin/plugin -url file:./target/releases/elasticsearch-lang-java-<VERSION>.zip -install lang-java

For more information, see http://www.elasticsearch.org/guide/reference/modules/plugins/.

Configuration

In elasticsearch.yml you may configure plugin.script.java.imports to have a ;,: or , delimited list of imports:

script.java.imports: "com.company.*;foo.bar.Baz"

You may also dynamically define imports using the Cluster Update Settings API:

curl -XPUT "http://localhost:9200/_cluster/settings" -d'
{
   "persistent": {
      "script.java.imports": "org.elasticsearch.*"
   }
}'

The two settings are completely independent of one another and get concatenated at runtime.

Scripts

Scripts are written using Java method fragments that are inlined into a class template before being compiled with the standard jdk JavaCompiler class. As such, it is required that you provide a return value in each control path of your script.

Be warned that calling methods such as System.exit() will succeed in terminating the host JVM.

Variables

Script variables may be accessed via the Object var(String name) method. Depending on the script context, the following members will also be available:

• lookup of type SearchLookup
• doc() of type DocLookup
• fields() of type FieldsLookup
• source() of type SourceLookup
• score() of type float

Not that with var, casting the return value is required in order to access object members. This is because compilation occurs before the variable types are supplied / known at runtime.

Examples

Script Fields

The following example shows how to execute a Java script without parameters:

{
    "script_fields" : {
        "result" : {
            "script" : "return 1 + 2;"
            "lang": "java"
        }
    }
}

The following example shows how to execute a Java script using parameters:

{
    "script_fields" : {
        "result" : {
            "script" : "return (Integer)var(\"x\") + (Integer)var(\"y\");",
            "params": {
                "x": 1,
                "y": 2
            }, 
            "lang": "java"
        }
    }
}

If your variables consist of a single character, you can simplify the above using:

{
    "script_fields" : {
        "result" : {
            "script" : "return (Integer)var('x') + (Integer)var('y');",
            "params": {
                "x": 1,
                "y": 2
            }, 
            "lang": "java"
        }
    }
}

Disclaimer

This plugin has not been tested in a production environment and is currently for development purposes only.

License

This software is licensed under the Apache 2 license, quoted below.

Copyright 2013 Bob Tiernay

Licensed under the Apache License, Version 2.0 (the "License"); you may not
use this file except in compliance with the License. You may obtain a copy of
the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
License for the specific language governing permissions and limitations under
the License.