Manual Conversion of 3rd Party Class With Morphia

问题:

Long story short: Is it possible to write a type converter for a 3rd party library class with Morphia?

Long story: I'm new to Morphia. I have an entity class which contains a field typed javax.activation.MimeType. When I try to save instances of my class, Morphia complains it "can't serialize class javax.activation.MimeType". I tried writing a TypeConverter and adding it to the list of converters but it didn't work. Here are the code pieces:

Entity.class

@Entity
@Converters(MimeTypeConverter.class)
public class Entity {
    @Id ObjectId id;
    String name;
    javax.activation.MimeType mimeType;
}

MimeTypeConverter.class

public class MimeTypeConverter extends TypeConverter {

    @Override
    public Object decode(Class targetClass, 
                         Object fromDBObject, 
                         MappedField optionalExtraInfo) {
        MimeType mimetype;

        BasicDBObject dbObject = (BasicDBObject) fromDBObject;
        String mimeString = dbObject.getString("mimeType");
        try{
            mimetype = new MimeType(mimeString);
        } catch(MimeTypeParseException ex){
            mimetype = new MimeType();
        }

        return mimetype;
    }

    @Override
    public Object encode(Object value, MappedField optionalExtraInfo) {
        MimeType mimetype = (MimeType) value;
        return mimetype.getBaseType();
    }

    @Override
    public Class[] getSupportTypes() {
        return new Class[]{MimeType.class};
    }
}

Test Case

Morphia morphia = new Morphia().map(Entity.class);
morphia.getMapper().getConverters().addConverter(new MimeTypeConverter());
Datastore ds = morphia.createDatastore(new MongoClient(), "test"); //UnknownHostException

Entity entity = new Entity();
entity.name = "test name";
entity.mimeType = new MimeType("text/plain"); //MimeTypeParseException

ds.save(entity); // FAILS WITH ERROR HERE

I want MimeType class to serialize in "foo/bar" style, and deserialize from it. Is that possible?

回答1:

This actually works for me using 0.107 code. I'm using a slightly modified converter which might have contributed to my success. The converter i'm using is below as well as the test.

@Entity
@Converters(MimeTypeConverter.class)
public static class MimeTyped {
    @Id
    private ObjectId id;
    private String name;
    private javax.activation.MimeType mimeType;
}

public class MimeTypeConverter extends TypeConverter {
     public MimeTypeConverter() {
          super(MimeType.class);
     }

     @Override
     public Object decode(final Class targetClass, final Object fromDBObject, final MappedField optionalExtraInfo) {
          try {
                return new MimeType(((BasicDBObject) fromDBObject).getString("mimeType"));
          } catch (MimeTypeParseException ex) {
                return new MimeType();
          }
     }

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

@Test
public void mimeType() throws UnknownHostException, MimeTypeParseException {
     getMorphia().getMapper().getConverters().addConverter(new MimeTypeConverter());
     MimeTyped entity = new MimeTyped();
     entity.name = "test name";
     entity.mimeType = new MimeType("text/plain"); //MimeTypeParseException
     final DBObject dbObject = getMorphia().toDBObject(entity);
     assertEquals("text/plain", dbObject.get("mimeType"));
     getDs().save(entity);
}