NullpointerException when testing a controller method

Question

Here is a controller method I'm about to test with JUnit and JMock.

public String myMethod(ModelMap model, Principal principal,
                        @PathVariable MyObject obj) {
  if (obj != null) {
    Student student = getStudent(principal);
    if (check(obj, student)) {
      model.addAttribute(student).addAttribute(obj);
      return "page";
    }
  }
  return REDIR;
}


private boolean check(MyObject obj, Student student) {
  return student.getStudentNumber().longValue() == obj.getStudent().getStudentNumber().longValue();
}

My test

final StudentService studentService = context.mock(StudentService.class);

public void test() throws Exception {
  ModelMap model = new ModelMap();
  final MyObject = new myObject();

  context.checking(new Expectations() {
    {
      oneOf(studentService).getByNumber(SecurityHelper.getStudentNumberOf(Helper.getTestPrincipal()));
      will(returnValue(mockStudent));
    }
  });

  controller.myMethod(model, Helper.getTestPrincipal(), obj);
}

When running test, I get a NullPointerExeption which points to check-method. Any idea where that comes from? Is it because I lack some expectation? Student and obj are not interfaces to be mockable. I'm new with this. Which is the best way to track these kind of testing errors?

Please post your stacktrace. Also, please show the code in your test where you mock the `studentService`. — Duncan Jones, Nov 29 '12 at 08:24
I added the mocking. Tracktrace points to line number on controller method where is the if clause and on test where I call controller.test-method — mjgirl, Nov 29 '12 at 09:01
One way to pinpoint null pointer is to split statement up to use temp variables. That is, when you have `method1(methdo2()).method3()...`, change that to `temp2 = method2(); temp1 = method1(temp2); temp1.method3()...`. — hyde, Nov 29 '12 at 09:08

score 1 · Answer 1 · edited Nov 29 '12 at 11:12

If i understand you correctly, this is the line that throws an exception:

return student.getStudentNumber().longValue() == obj.getStudent()
    .getStudentNumber().longValue();

So the exception can come from several places:

studen or obj are null.
student.getStudentNumber() returns null.
obj.getStudent() returns null
obj.getStudent().getStudentNumber() returns null.

Do a System.out on all of these statements and see which is null.

NullpointerException when testing a controller method

1 Answers1