how to customize JSON output to finer details

Question

This is for all the JSON brains out there.

Let's say I have an interface like:

public interface Model {
  String getName();
  String getDateCreated();
  String getTimeCreated();
  String getLastUpdated();
  String getLastUpdatedTime();
}

Then let's say I have an Item object:

public class Item {

  private String name;
  private Date created;
  private Date updated;

  ..setters and getters
}

Then let's say I have an model wrapper:

public class ItemModel implements Model {

  private final Item item;

  public ItemModel(Item item){
      this.item = item;
  }

  public String getName(){
      return item.getName();
  }

  public String getDateCreated(){
      Date created = item.getCreated();
      //format the date nicely and return a date string
  }

  public String getTimeCreated(){
      Date created = item.getCreated();
      //format the date nicely and return a time string
  }

  ...you get the gyst, right?
}

Question is:

1. How do I serialize ItemModel so that the json output will reflect the getter names on the model interface?
2. Specifically, which library does this most easily? How do you achieve this using a specific library?
3. Finally, I DO NOT want to serialize the Item object wrapped inside the ItemModel

I want the output to be something like this:

{item : {name: '', dateCreated : '', timeCreated : '', lastUpdated : '', lastUpdatedTime : ''}

Thanks in advance!

---

I thought I should share what I have been able to come with so far, and get your feedback. It's almost meeting my requirements, but I'm not sure if it's the right way:

I was pointed to genson by a user here, and I find it very interesting.

First I created a Serializer

public class ModelSerializer implements Serializer {

@Override
public void serialize(T target, ObjectWriter writer, Context cntxt) throws TransformationException, IOException {
    writer.beginObject();
    for (Method method : target.getClass().getMethods()) {
        String methodName = method.getName();
        if (methodName.startsWith("get")) {
            int index = "get".length();
            String valueName = Character.toLowerCase(methodName.charAt(index)) + method.getName().substring(index + 1);
            try {
                String valueString = (String) method.invoke(target, new Object[]{});
                writer.writeName(valueName).writeValue(valueString);
            } catch (IllegalArgumentException ex) {
                Logger.getLogger(ModelSerializer.class.getName()).log(Level.SEVERE, null, ex);
                throw new TransformationException(ex.getMessage());
            } catch (IllegalAccessException ex) {
                Logger.getLogger(ModelSerializer.class.getName()).log(Level.SEVERE, null, ex);
                throw new TransformationException(ex.getMessage());
            } catch (InvocationTargetException ex) {
                Logger.getLogger(ModelSerializer.class.getName()).log(Level.SEVERE, null, ex);
                throw new TransformationException(ex.getMessage());
            }
        }
    }
    writer.endObject();
}

}

Next, I created Genson and passed the Serializer

Genson genson = new Genson.Builder().withSerializer(new ModelSerializer(), Model.class).create();

Now when I pass the ViewModel, I get the fields formatted as I expected

Model viewModel = new ItemModel(domainModel); where domainModel is an instance of Item System.out.println(genson.serialize(viewModel));

Answer 1

I would refactor your code a bit. First you want a POCO class as your data carrier, which would be your Item Class. Then you would want a Repository to do the CRUD operations for you.

public interface IItemModelRepository {
 Item getItemByName();
 Item getItemByDateCreated();
}

You would implement the interface as:

public class ItemModelRepository : IItemModelRepository {

private IEnumerable<Item> _items;

public ItemModelRepository()
{
   this._items = /// Logic to load all items from database or from in memory cache
} 

public Item getItemByName(string name){
  return this._items.First(i => i.Name.Equals(name);
}

public Item getItemByDateCreated(DateTime dateCreated){
  return this._items.First(i => i.DateCreated == dateCreated);     
}

....
}

Then you can use this Repository (not a good idea to use Repository directly in Controller. You would rather want to return a ViewModel, which is a POCO class containing the properties required by your view) as:

var item = ItemModelRespository.GetByName("enter name here");
var viewModel = new ViewModel();
var serializer = new JavaScriptSerializer();
viewModel.JsonData = serializer.Serialize(item );

And on client side, you can use:

<%= Model.JsonData %>

have a look here as well: ASP.NET MVC: How to convert View Model into Json object

--edit

Sorry, missed the bit that you are using Java. As mentioned here:

http://flax.ie/flax-engine-gwt-client-side-json-serialization-and-deserialization/

you could just modify your existing Item Class as:

public class Item implements JsonSerializable {

  private String name;
  private Date created;
  private Date updated;

 ..setters and getters

/**
* Pass this method JSON and it gives you back an object which you can
* then assign to your object via MyObject x = JsonToObject(String Json);
*
* @param JSON
* @return
*/
public static Item JsonToObject(String Json) {
    Serializer serializer = (Serializer) GWT.create(Serializer.class);
    return (Item)serializer.deSerialize(Json,"your fully qualified Item assembly name");
}

/**
* Creates a JSON string from the current object
*
* @return String of JSON
*/
public String toJson() {
    Serializer serializer = (Serializer) GWT.create(Serializer.class);
    return serializer.serialize(this);
}
}

And then in your code that consumes IItemModelRepository, you can use:

var item = ItemModelRepository.GetItemByName("name");
var jsonString = item.ToJson();

What I do not get is, why do you want to serialize ItemModel when you want the JSON output to be serialized representation of the Item object?

Answer 2

You could try genson library it provides a couple of ways to solve your problem http://code.google.com/p/genson/.

If the desired output is {name: '', dateCreated : '', timeCreated : '', lastUpdated : '', lastUpdatedTime : ''} without "item :" :

public class ItemModel implements Model {    
    @JsonIgnore private final Item item; 
    ....
}

new Genson().serialize(myItemModel);

If you want the "item" key you could also implement a custom Serializer or Converter like in the wiki.

Answer 3

You can define your own JSON mappings manually with a library like Jettison so you don't have to contort yourself with POJOS and POCOs and wrappers and other silly things. It really doesn't take much time to set up the mappings.