Weird exception while using contains() method

Question

I'm building a web application using Spring MVC framework.

I have some controller which adds some attributes (users belonging to the same team) to my view, as follows:

@RequestMapping(value = "/friends", method = RequestMethod.GET)
    public ModelAndView showFriends(Principal principal) {
       ModelAndView mav = new ModelAndView("friends");

       User currentUser = userService.findUser(principal.getName());

       // this method returns a Collection<long> of userIds from users that belong to a given team
       Collection<long> userIds = findUsersFromTeam(currentUser.getTeam());

       mav.addObject("users", userIds);
       mav.addObject("currentUser", userService.findUsers();
       return mav;
    }

And, in my "friends.jsp" file, I do the following test:

<c:when test="${users.contains(currentUser.id)}">

Which throws the following exception:

java.lang.NoSuchMethodException: java.util.ArrayList.contains(java.lang.Long)

However, ArrayList class implements contains(Object o) method. What's wrong?

Answer 1

This is a just a result of how EL parses method expressions and how reflection works

${users.contains(currentUser.id)}

It gets the type of users , ArrayList , and the type of currentUser.id , Long . It then uses reflection to get a method named contains with a parameter of type Long on the type ArrayList . It doesn't find one because one doesn't exist. Remember, reflection does not apply inheritance hierarchy checking on parameter list elements.

So even though there is a ArrayList#contains(Object) , there is no ArrayList#contains(Long) . It therefore fails.

Don't use basic EL for this. Write your own EL function or do the logic in your handler method.