Static Metamodel Generator

Introduction

Sometimes you'd like to have a real, typesafe metamodel of your java classes. This library (metamodel-generator) provides an annotation-processor that will create such a metamodel.

Setup

First you'll need to include the api-artifact as a compile-time dependency and the processor as a provided dependency into your project:

    <dependency>
        <groupId>de.hilling.lang.metamodel</groupId>
        <artifactId>api</artifactId>
        <version>1.5</version>
    </dependency>
    <dependency>
        <groupId>de.hilling.lang.metamodel</groupId>
        <artifactId>processor</artifactId>
        <version>1.5</version>
        <scope>provided</scope>
    </dependency>

This will automatically run the annotation-process during compilation. You may also want to read this Blog Post (in German) and refer to the examples in the integration-tests module.

Usage

Just annotate the classes that need a metamodel with the @GenerateModel annotation:

@GenerateModel
public class Car {
    private       String model;
    private final int    year;

    public Car(int year) {
        this.year = year;
    }
    public String getModel() {
        return model;
    }
    public void setModel(String model) {
        this.model = model;
    }
    public int getYear() {
        return year;
    }
}

For the above example the following metamodel class will be generated:

public abstract class Car__Metamodel {
    private static final List<Attribute> ATTRIBUTES;

    public static final Attribute<Car, Integer> year;

    public static final MutableAttribute<Car, String> model;

    static {
        [...]
    }

    public static List<Attribute> attributes() {
        return ATTRIBUTES;
    }
}

And you can query as follows (snippet from CarTest.java:

    @Test
    public void readAttributes() {
        car = new Car(1974);
        car.setModel("Golf");

        assertEquals("Golf", Car__Metamodel.model.readAttribute(car));
        assertEquals((Integer) 1974, Car__Metamodel.year.readAttribute(car));

        Car__Metamodel.model.writeAttribute(car, "Polo");
        assertEquals("Polo", car.getModel());
    }

You can also inspect dynamically using the getAttributes() method which is kind of the point of the whole processor! The original order of the attributes is retained in the returned attributes list.

Possible enhancements

• Better support for primites: They are just auto-boxed.
• Access attributes via map.
• Support for generic method-inspection.
• General infos about class structure.

Most of these things would be easy to do. Feel free to create a pull request!