A hello world that shows how to use morphia with an immutable id type

HelloMorphia.java

import java.net.UnknownHostException;

import org.apache.commons.lang.builder.ToStringBuilder;

import com.google.code.morphia.Datastore;
import com.google.code.morphia.Morphia;
import com.google.code.morphia.annotations.Entity;
import com.google.code.morphia.annotations.Id;
import com.google.code.morphia.converters.SimpleValueConverter;
import com.google.code.morphia.converters.TypeConverter;
import com.google.code.morphia.mapping.MappedField;
import com.google.code.morphia.mapping.MappingException;
import com.mongodb.Mongo;
import com.mongodb.MongoException;

/**
 * Hello morphia, can we use immutable id user types? Yes, we can.
 */
public class HelloMorphia {


    public static void main( final String[] args ) throws UnknownHostException, MongoException {

        final Morphia morphia = new Morphia();
        final Datastore ds = morphia.createDatastore( new Mongo( "localhost" ), "myDB" );
        morphia.getMapper().getConverters().addConverter( new MyIdConverter() );

        final MyClass myClass = new MyClass( new MyId( 42L ), "HelloMorphia" );
        ds.save( myClass );

        final MyClass found = ds.get(MyClass.class, myClass.id);
        System.out.println( "found " + ToStringBuilder.reflectionToString( found ));
    }

    /**
     * The converter for the immutable id must implement {@link SimpleValueConverter}
     * so that <code>Mapper.readMappedField</code> uses this converter during
     * updateKeyInfo/postSaveAction. Alternatively the id field could be annotated with
     * {@link com.google.code.morphia.annotations.Property}.
     */
    static class MyIdConverter extends TypeConverter implements SimpleValueConverter {

        public MyIdConverter() {
            super( MyId.class );
        }

        @Override
        public Object decode( final Class targetClass, final Object fromDBObject, final MappedField optionalExtraInfo ) throws MappingException {
            return new MyId( Long.parseLong( (String )fromDBObject ) );
        }

        @Override
        public Object encode( final Object value, final MappedField optionalExtraInfo ) {
            return value.toString();
        }

    }

    public static class MyId {
        private final Long _id;
        public MyId(final long id) {
            _id = Long.valueOf( id );
        }

        @Override
        public String toString() {
            return _id.toString();
        }

        @Override
        public int hashCode() {
            final int prime = 31;
            int result = 1;
            result = prime * result + ( ( _id == null ) ? 0 : _id.hashCode() );
            return result;
        }

        @Override
        public boolean equals( final Object obj ) {
            if ( this == obj ) {
                return true;
            }
            if ( obj == null ) {
                return false;
            }
            if ( getClass() != obj.getClass() ) {
                return false;
            }
            final MyId other = (MyId) obj;
            if ( _id == null ) {
                if ( other._id != null ) {
                    return false;
                }
            }
            else if ( !_id.equals( other._id ) ) {
                return false;
            }
            return true;
        }
    }

    @Entity
    public static class MyClass {
        @Id MyId id;
        String name;
        public MyClass() {
        }
        public MyClass( final MyId id, final String name ) {
            super();
            this.id = id;
            this.name = name;
        }
    }

}