Gemini LLM Plugin for Fess

Overview

This plugin provides Google Gemini integration for Fess's RAG (Retrieval-Augmented Generation) features. It enables Fess to use Google Gemini models for AI-powered search capabilities including intent detection, answer generation, document summarization, and FAQ handling.

Download

See Maven Repository.

Requirements

• Fess 15.x or later
• Java 21 or later
• Google Gemini API key

Installation

1. Download the plugin JAR from the Maven Repository
2. Place it in your Fess plugin directory
3. Restart Fess

For detailed instructions, see the Plugin Administration Guide.

Configuration

Configure the following properties in fess_config.properties:

Property	Default	Description
rag.llm.name	-	Set to gemini to use this plugin
rag.chat.enabled	false	Enable RAG chat feature
rag.llm.gemini.api.key	-	Google Gemini API key (required)
rag.llm.gemini.api.url	https://generativelanguage.googleapis.com/v1beta	Gemini API endpoint URL
rag.llm.gemini.model	gemini-3-flash-preview	Model name (e.g., gemini-2.5-flash, gemini-2.0-flash)
rag.llm.gemini.timeout	60000	HTTP request timeout in milliseconds
rag.llm.gemini.availability.check.interval	60	Interval (seconds) for checking API availability
rag.llm.gemini.chat.context.max.chars	4000	Maximum characters for context in chat
rag.llm.gemini.chat.evaluation.max.relevant.docs	3	Maximum number of relevant documents for evaluation

Extended Thinking (Gemini 3)

For models that support extended thinking, you can configure the thinking budget via thinkingConfig.thinkingBudget in the generation config. Thinking parts (marked with thought: true) are automatically filtered out from responses.

Features

• Intent Detection - Determines user intent (search, summary, FAQ, unclear) and generates Lucene queries
• Answer Generation - Generates answers based on search results with citation support
• Document Summarization - Summarizes specific documents
• FAQ Handling - Provides direct, concise answers to FAQ-type questions
• Relevance Evaluation - Identifies the most relevant documents for answer generation
• Streaming Support - Real-time response streaming via newline-delimited JSON
• Availability Checking - Validates API availability at configurable intervals
• Extended Thinking - Support for Gemini 3 thinking models with configurable thinking budget

Gemini API Endpoints Used

• GET /models?key={apiKey} - Lists available models for availability checking
• POST /models/{model}:generateContent?key={apiKey} - Performs chat completion
• POST /models/{model}:streamGenerateContent?key={apiKey} - Performs streaming chat completion

Development

Building from Source

mvn clean package

Running Tests

mvn test

License

Apache License 2.0