Is it possible to write a generic enum converter for JPA?

Question

I wanted to write a Converter for JPA that stores any enum as UPPERCASE. Some enums we encounter do not follow yet the convention to use only Uppercase letters so until they

Answer 1

Based on @scottb solution I made this, tested against hibernate 4.3: (no hibernate classes, should run on JPA just fine)

Interface enum must implement:

public interface PersistableEnum {
    public T getValue();
}

Base abstract converter:

@Converter
public abstract class AbstractEnumConverter & PersistableEnum, E> implements AttributeConverter {
    private final Class clazz;

    public AbstractEnumConverter(Class clazz) {
        this.clazz = clazz;
    }

    @Override
    public E convertToDatabaseColumn(T attribute) {
        return attribute != null ? attribute.getValue() : null;
    }

    @Override
    public T convertToEntityAttribute(E dbData) {
        T[] enums = clazz.getEnumConstants();

        for (T e : enums) {
            if (e.getValue().equals(dbData)) {
                return e;
            }
        }

        throw new UnsupportedOperationException();
    }
}

You must create a converter class for each enum, I find it easier to create static class inside the enum: (jpa/hibernate could just provide the interface for the enum, oh well...)

public enum IndOrientation implements PersistableEnum {
    LANDSCAPE("L"), PORTRAIT("P");

    private final String value;

    @Override
    public String getValue() {
        return value;
    }

    private IndOrientation(String value) {
        this.value= value;
    }

    public static class Converter extends AbstractEnumConverter {
        public Converter() {
            super(IndOrientation.class);
        }
    }
}

And mapping example with annotation:

...
@Convert(converter = IndOrientation.Converter.class)
private IndOrientation indOrientation;
...

With some changes you can create a IntegerEnum interface and generify for that.