morphia - 使用 Morphia 手动转换第 3 方类

Question

长话短说:是否可以使用 Morphia 为第三方库类编写类型转换器？

长话短说:我是 Morphia 的新手。我有一个实体类，其中包含一个类型为 javax.activation.MimeType 的字段。当我尝试保存类的实例时，Morphia 提示它“无法序列化类 javax.activation.MimeType”。我尝试编写一个 TypeConverter 并将其添加到转换器列表中，但它不起作用。以下是代码片段:

实体.类

@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};
    }
}

测试用例

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

我希望 MimeType 类以“foo/bar”样式序列化，并从中反序列化。这可能吗？

Answer 1

这实际上对我使用 0.107 代码有效。我正在使用一个稍微修改过的转换器，这可能有助于我的成功。我正在使用的转换器以及测试如下。

@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);
}