Scala：没有找到Object类型的Json序列化器。 尝试为此类型实现隐式的Writes或Format

Question

I have two functions, one returns a single user based on his id and the second returns multiple users based on their ids,

The first function return this array : User[id=1, name="name1", lastName= "lastname1"]

The second function return this: [User [id=1, name="name1", lastName= "lastname1"], User [id=2, name="name2", lastName= "lastname2"]]

My first scala function is as follow and the json is well returned and i have no error:

 Option(Try(id.toLong) match {
     case Success(id) => User.getUserById(1)
    }) match {  
      case Some(user) => Ok(Json.toJson(user) )
      case None => NotFound
    }

But my second scala function returns an error (see my title) :

Option(Try(id.toList) match {
     case Success(id) => User.getUsersByIds(id) // id list is 1,2
    }) match {  
      case Some(users) => Ok(Json.toJson(users) )
      case None => NotFound
    }

My getUsersByIds function :

 public static synchronized ArrayList<User> getUsersByIds(List usersIDs) {


        String strSQL = "SELECT * FROM User WHERE ID IN" + usersIDs) ;

        ArrayList<User> userList = getArrayList(strSQL);

    return userList
    }

How can i return the right json format to get all my users ? I need to add a map ? if so, how ?

thank you

Answer 1

By default, Play only has serializers for the Scala collection. This should make it work:

import scala.collection.JavaConverters._

Json.toJson(users.asScala)

Answer 2

好的，我找到了：.asScala解决了这个问题