Spring Web Socket Session throws Jackson Exception - json

Question

In chat application, there are many rooms(Map type), which consist of Strings, boolean, and List<WebSocketSession>.
I think the problem is List<WebSocketSession> can't be written to JSON.
#RequestMapping(value = "/api/v1/lobby/roomList", method = RequestMethod.GET)
public ResponseEntity<Object> getRooms(
HttpServletRequest request,
HttpServletResponse response) {
logger.debug("RoomCtrl - getRooms");
Map<Integer, Room> rooms = roomService.getRooms();
Map<String, Object> returnMap = new HashMap<>();
returnMap.put("rooms", rooms);
return new ResponseEntity<>(
returnMap,
HttpStatus.OK);
}
This is my method to get rooms from roomService. What I have to do to receive that response correctly?
For giving more information to you, I post Room Class.
public class Room {
private String host, title;
private List<WebSocketSession> members = new ArrayList<>();
private boolean status;
public String getHost() {
return host;
}
public void setHost(String host) {
this.host = host;
}
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
public List<WebSocketSession> getMembers() {
return members;
}
public void setMembers(List<WebSocketSession> members) {
this.members = members;
}
public boolean isStatus() {
return status;
}
public void setStatus(boolean status) {
this.status = status;
}
}

Answer 1

A WebSocketSession is an abstraction to send messages over a WebSocket.
In the backend you can maintain WebSocketSession instances (while generally you maintain some specific values of WebSocketSession such as id) to perform some matching (who does the request and so for...) but you will never expose and send them in a JSON object to the clients.
Why send such a payload to the clients ? Why should they know the network details of the other users (IP, sessionID and so for) ? It will just create an overhead and decrease the security level of your application.
So WebSocketSession doesn't implement Serializable and so is defacto not serializable by Jackson (that requires that as most of JSON processing API in Java).
To resolve your issue :
Since the users need to know the name of the other chat room users you should
create a mapping between WebSocketSession.id and their unique pseudo/username with a Map<String, String> for example.
And now expose List<String> users in the JSON object returned.

Answer 2

Yes, you are right, WebSocketSession not json serializable, and anyway you better dont send this info to clientside.
You can use json ignore annotation here
#JsonIgnore
private List<WebSocketSession> members
so Jackson will ignore this field, when trying to serialize Room object