JExten Core

Core API module for the JExten extension framework.

Overview

This module provides the fundamental API for defining and discovering extensions in modular Java applications. It contains:

• @Extension and @ExtensionPoint annotations
• ExtensionManager for discovering and retrieving extensions
• Scope and Priority enums for lifecycle and ordering control
• InjectionProvider and ExtensionLoader for DI integration

Installation

<dependency>
    <groupId>org.myjtools.jexten</groupId>
    <artifactId>jexten-core</artifactId>
    <version>1.0.0</version>
</dependency>

Quick Start

Define an Extension Point

@ExtensionPoint(version = "1.0")
public interface MessageFormatter {
    String format(String message);
}

Implement an Extension

@Extension
public class UpperCaseFormatter implements MessageFormatter {
    @Override
    public String format(String message) {
        return message.toUpperCase();
    }
}

Discover Extensions

ExtensionManager manager = ExtensionManager.create();

// Get highest priority extension
Optional<MessageFormatter> formatter = manager.getExtension(MessageFormatter.class);

// Get all extensions
manager.getExtensions(MessageFormatter.class)
    .forEach(f -> System.out.println(f.format("hello")));

Module Configuration

Your module-info.java must declare the extension point and implementations:

module my.application {
    requires org.myjtools.jexten;

    exports com.example.api;  // Package containing extension point
    opens com.example.api to org.myjtools.jexten;

    uses com.example.api.MessageFormatter;
    provides com.example.api.MessageFormatter
        with com.example.impl.UpperCaseFormatter;
}

Extension Configuration

Priority

Control which extension is selected when multiple exist:

@Extension(priority = Priority.HIGHEST)
public class PreferredFormatter implements MessageFormatter { }

Priority levels: LOWEST, LOW, NORMAL (default), HIGH, HIGHEST

Scope

Control instance lifecycle:

@Extension(scope = Scope.SINGLETON)  // Single shared instance
@Extension(scope = Scope.LOCAL)      // One per context (default)
@Extension(scope = Scope.TRANSIENT)  // New instance per request

Named Extensions

Identify extensions by name:

@Extension(name = "json")
public class JsonFormatter implements MessageFormatter { }

// Retrieve by name
manager.getExtensionByName(MessageFormatter.class, "json");

Dependency Injection

Inject dependencies into extensions using @Inject:

@Extension
public class LoggingFormatter implements MessageFormatter {
    @Inject
    private Logger logger;

    @Override
    public String format(String message) {
        logger.info("Formatting: {}", message);
        return message;
    }
}

Custom Injection Provider

Integrate with external DI frameworks:

ExtensionManager manager = ExtensionManager.create()
    .withInjectionProvider(new SpringInjectionProvider(applicationContext));

Documentation

For complete documentation, see the main JExten README.

License

Apache License 2.0