A simple example plugin demonstrating how to create custom script engines for Fess, the open-source enterprise search server.

A Fess script engine turns a template plus a parameter map into a value. Fess uses script engines wherever an administrator can enter a small script or expression — for example to compute a document boost, derive a field value during crawling, or run logic in a scheduled job. The built-in groovy engine evaluates full Groovy scripts; this example shows the minimal shape of a custom one.

This plugin provides a minimal implementation of a custom script engine for Fess. The ExampleEngine serves as a template and starting point for developers who want to create their own script engines with custom template processing logic.

• Real, Minimal Evaluation: Performs simple ${key} placeholder substitution from the parameter map
• Idiomatic Structure: Demonstrates the standard structure of a Fess script engine
• Self-Registration: Registers itself with the script engine factory via the DI container
• Focused Tests: Meaningful tests covering substitution, missing keys, null/blank input, and factory lookup

The plugin extends Fess's AbstractScriptEngine class and implements:

• Template Evaluation (evaluate): Substitutes ${key} placeholders with values from the parameter map. A blank template returns null; a missing or null value leaves the placeholder untouched.
• Engine Identification (getName): Provides the unique name ("example") used to register and look up the engine
• DI Integration: fess_se++.xml registers the engine into Fess's scriptEngineFactory at startup via a register postConstruct (the ++ suffix means the fragment is additively merged into the core fess_se.xml)

• Fess 15.7.0 or later
• Java 21 or later

You can download the plugin JAR from Maven Central.

1. Download the latest fess-script-example-{version}.jar from the releases
2. Copy the JAR file to your Fess plugin directory ($FESS_HOME/app/WEB-INF/plugin/)
3. Restart Fess server
4. The "example" script engine will be available for use

For detailed installation instructions, see the Fess Plugin Guide.

There is no extra configuration to "use" the engine — the plugin self-registers via fess_se++.xml when Fess starts. Once installed, the engine is available by its registered name, example, anywhere Fess lets you pick a script type, including:

• Data store crawling — field-mapping scripts that compute index field values
• Document boost — boost expressions evaluated per document during crawling
• Scheduled jobs — jobs whose Script Type is set to an engine name
• Path mappings / replacements — value transformations that accept a script type

In those places, select or enter example as the script type and provide a template such as Hello ${name}. Internally Fess resolves the engine through the factory:

ComponentUtil.getScriptEngineFactory().getScriptEngine("example").evaluate(template, paramMap);

This example engine substitutes ${key} placeholders with values from the parameter map, which makes it a useful starting point for learning the API and for building richer engines.

git clone https://github.com/codelibs/fess-script-example.git
cd fess-script-example
mvn clean package

mvn test

The test suite includes focused test cases covering:

• Placeholder substitution (single, multiple, and non-string values)
• Missing-key and null-value behavior (placeholder left untouched)
• Blank/null template handling (returns null)
• Engine name and factory registration/lookup by name

# Format code
mvn formatter:format

# Check license headers
mvn license:check

# Generate Javadoc
mvn javadoc:javadoc

src/
├── main/java/
│   └── org/codelibs/fess/script/example/
│       └── ExampleEngine.java          # Script engine implementation (${key} substitution)
├── main/resources/
│   └── fess_se++.xml                    # DI fragment that registers the engine (additive merge)
└── test/
    ├── java/
    │   └── org/codelibs/fess/script/example/
    │       ├── ExampleEngineTest.java   # Engine tests + factory lookup
    │       └── UnitScriptTestCase.java  # Minimal UTFlute test base for the plugin
    └── resources/
        └── test_app.xml                 # Test DI container (includes scriptEngineFactory)

This project serves as a template for creating custom script engines. To create your own:

1. Fork this repository
2. Rename the ExampleEngine class
3. Implement your custom template processing logic in the evaluate method
4. Update the getName method to return your engine's unique identifier
5. Update the DI configuration in fess_se++.xml
6. Add appropriate tests

• Fess Framework: Core search server functionality (provided scope)
• LastaFlute: Web application framework with DI container
• DBFlute: Database access framework
• OpenSearch: Search engine integration (provided scope)
• UTFlute: Testing framework for LastaFlute applications

We welcome contributions! Please feel free to submit issues, feature requests, or pull requests.

• Follow the existing code style and formatting
• Add comprehensive tests for new functionality
• Update documentation as needed
• Ensure all tests pass before submitting PRs

This project is licensed under the Apache License 2.0 - see the LICENSE file for details.

• Documentation: Fess Official Documentation
• Issues: GitHub Issues
• Community: Fess Community Forum

• Fess - The main Fess search server
• Fess Plugins - Other Fess plugins

Developed by CodeLibs Project