Apitomy Flow Engine

A lightweight, stateless workflow engine library for Java. Define workflows as graphs of typed nodes and conditional edges, then execute them with pluggable action handlers, error strategies, and event listeners.

Features

• Stateless execution -- the engine holds no internal state; all runtime state lives in an immutable WorkflowInstance snapshot, making the engine thread-safe and persistence-agnostic.
• Six node types -- START, END, ACTION, HUMAN_TASK, RECEIVE_EVENT, and WAIT.
• Conditional branching -- edges carry Jakarta EL expressions evaluated against the instance context, with priority ordering and default-edge support.
• Async / suspending nodes -- HUMAN_TASK, RECEIVE_EVENT, and WAIT nodes pause execution for external completion via completeCurrentNode().
• Event correlation -- match incoming events to RECEIVE_EVENT nodes by type and EL expressions.
• Pluggable SPI -- NodeExecutor for action execution, WorkflowErrorHandler for fail/retry/transition strategies, and WorkflowEventListener for lifecycle hooks.
• Validation -- structural correctness checks before execution.
• JSON serialization -- workflows and instances serialize to/from JSON via Jackson.

Installation

<dependency>
    <groupId>io.apitomy</groupId>
    <artifactId>apitomy-flow-engine</artifactId>
    <version>1.0.0</version>
</dependency>

Requirements

• Java 21+

License

Apache License 2.0