JExten Processor

Annotation processor for compile-time validation of JExten extensions.

Overview

This module provides an annotation processor that validates @Extension and @ExtensionPoint usage at compile time. It ensures:

Correct annotation placement (classes for @Extension, interfaces for @ExtensionPoint)
Proper module-info.java declarations (exports, opens, provides, uses)
Valid semantic version formats
Type hierarchy correctness (extensions must implement their extension points)

The processor also generates META-INF metadata files for runtime extension discovery.

Installation

<dependency>
    <groupId>org.myjtools.jexten</groupId>
    <artifactId>jexten-processor</artifactId>
    <version>1.0.0</version>
    <scope>provided</scope>
</dependency>

The processor is automatically discovered via META-INF/services and runs during compilation.

Validations

Extension Validation

The processor validates that extensions:

Are applied to classes (not interfaces or enums)
Implement or extend the declared extension point
Have valid extensionPointVersion format
Are declared in module-info.java with provides

Extension Point Validation

The processor validates that extension points:

Are applied to interfaces
Have valid version format
Are exported in module-info.java
Are opened to org.myjtools.jexten for reflection
Are declared with uses directive

Error Messages

The processor provides helpful error messages with suggested fixes:

error: [jexten] Extension com.example.MyExtension implementing extension point
       com.example.MyExtensionPoint must be declared in the module-info.java file

Try to apply the following fixes to the module-info.java file:
    provides com.example.MyExtensionPoint with com.example.MyExtension;

Common Errors

Error	Cause	Solution
`Cannot find module definition`	Missing `module-info.java`	Create a `module-info.java` file
`@Extension ignored for X`	Applied to non-class	Move annotation to a class
`@ExtensionPoint not valid for X`	Applied to non-interface	Move annotation to an interface
`must be exported`	Package not exported	Add `exports package.name;`
`must be opened to org.myjtools.jexten`	Package not opened	Add `opens package.name to org.myjtools.jexten;`
`must be declared in module-info`	Missing `provides`	Add `provides ExtPoint with Impl;`
`must be a valid semantic version`	Invalid version format	Use format `major.minor[.patch]`

Generated Files

The processor generates metadata files in META-INF/:

`META-INF/extensions`

Lists all extensions and their extension points:

com.example.api.MyExtensionPoint=com.example.impl.MyExtensionImpl
com.example.api.OtherPoint=com.example.impl.OtherImpl1,com.example.impl.OtherImpl2

`META-INF/extension-points`

Lists all extension points defined in the module:

com.example.api.MyExtensionPoint
com.example.api.OtherPoint

IDE Integration

The processor integrates with IDEs that support annotation processing:

IntelliJ IDEA

Annotation processing is enabled by default. Errors appear in the editor and build output.

Eclipse

Enable annotation processing in: Project Properties > Java Compiler > Annotation Processing

VS Code (with Java Extension Pack)

Annotation processing works automatically with the Java Language Server.

Disabling the Processor

To disable the processor temporarily:

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-compiler-plugin</artifactId>
    <configuration>
        <compilerArgument>-proc:none</compilerArgument>
    </configuration>
</plugin>

Documentation

For complete documentation, see the main JExten README.

License

Apache License 2.0