java-actions

Mendix Java Actions Skill

This skill provides comprehensive guidance for creating and using custom Java actions in Mendix projects.

Reference files

SKILL.md covers declaring a Java action in MDL and calling it from a microflow — the parts that touch the model. The Java side is next door:

• reference/writing-java.md — creating the action in Studio Pro, writing the executeAction body, the Core API surface you have, and the recurring patterns (HTTP calls, file handling, batch work).
• reference/best-practices.md — error handling, transactions and rollback, logging, threading, security, and performance. Read it before shipping a Java action that touches data or an external system.

When to Use This Skill

Use this skill when:

• You need to extend Mendix with custom Java logic
• Building integrations with external Java libraries
• Implementing complex algorithms not feasible in microflows
• Calling Java actions from MDL microflows
• Debugging Java action calls

Overview

Java actions allow you to extend Mendix with custom Java code. The workflow is:

1. Define the Java action in Studio Pro (parameters, return type)
2. Implement the Java code in Eclipse/IDE
3. Call the Java action from microflows using MDL

Part 2.5: Creating Java Actions in MDL

MDL supports defining Java actions with inline Java code using create java action.

Basic Syntax

create java action Module.ActionName(param1: type, param2: type) returns ReturnType
as $$
// java code here
return result;
$$;

AS $$ ... $$ is mandatory. The body cannot be omitted even for placeholder or stub actions. Omitting it causes a parse error: no viable alternative at input '...'. Use a minimal body if the real implementation is not yet written:

create java action Module.Stub() returns boolean
as $$
return false;
$$;

Type Parameters (Generics)

Type parameters let Java actions accept any entity type dynamically. Use entity <pEntity> in a parameter type to declare the type parameter inline. That parameter becomes the entity type selector (receives the entity type name, e.g., 'Module.Entity'). Bare pEntity parameters become parameterized entity params (receive entity instances, e.g., $Variable).