playframework .json template List-Ojects with foreach? - json

Question

My Problem is: I don't want to return the whole model object structure and datas in a json response. renderJSON() returns everything from the model in the response.
So I thought the best way would be to use *.json templates. Ok and now I have a List and I don't now how the syntax in the *.json-template must be.
Part of Controller:
List<User> users = User.find("byActive", true).fetch();
if (users != null) {
render(users);
}
"User/showAll.json" (template):
//something like foreach( User currentUser in users )
{
"username": "${currentUser.name}",
"userdescr": "${currentUser.description}"
}
For a single user it's no problem, I got it, but how does it look like for a List of users inside the json template?

Answer 1

There is another solution to your problem without using .json template.
"renderJSON()" has a variation takes JsonSerializer as parameter, so you can define your own serializer which implements JsonSerializer, and decide what part of model object to be sent in the response. Then you could invoke renderJSON() to return JSON object in the controller.
Example:
public class UserSerializer implements JsonSerializer<User> {
public JsonElement serialize(User src, Type typeOfSrc, JsonSerializationContext context) {
Gson gson = new GsonBuilder()
.setExclusionStrategies(new LocalExclusionStrategy()).create();
return gson.toJsonTree(src);
}
public static class LocalExclusionStrategy implements ExclusionStrategy {
public boolean shouldSkipClass(Class<?> clazz) {
return false;
}
public boolean shouldSkipField(FieldAttributes f) {
// add exlusion rules here:
// exclude all fields whose name is not "name" or "description"
return !f.getName().toLowerCase().equals("name")
&& !f.getName().toLowerCase().equals("description");
}
}
}
In your controller:
List<User> users = User.find("byActive", true).fetch();
renderJSON(users, new UserSerializer());
Play framework utilizes Google's GSON library for json serialization/deserialization
You can find more info of GSON here

Answer 2

[
#{list users}
{
"username": "${_.name}",
"userdescr": "${_.description}"
} #{if !_isLast},#{/if}
#{/list}
]
Check http://www.playframework.org/documentation/1.2.4/tags#list for more information