在哪里验证String参数

Question

I have a Student class that has to have a property of a String ID, which has to be validated. I'm not sure whether to validate it inside the student class or the class that I'm implementing the Student class in. Does that make sense?

Answer 1

Assuming ID is final and immutable, then one approach is to have Student constructor throw an exception, probably new IllegalArgumentException("Invalid student ID");

You may additionally provide static method in Student class, which verifies if string is valid, in case you need to check it without creating Student object.

But the logic of determining if ID is valid or not should be in the Student class, I think.

If there are (or can be in future) different kind of student IDs, you could also consider abstract factory pattern, but sounds like that is bit of an overkill.

Answer 2

If Student already has any business inside use validate inside else use second one

Class Student
{
 public boolean  validate ()
  {
   //some logic to validation
  }
}

Inside of Model or controller or Action

 public boolean  validate ()
  {
   //some logic to validation
  }

Answer 3

One of the approach is to use validation object. For instance see the Validation approach uses in the Spring Framework. You create an object which implements the interface Validator with two methods: one to detect if the Validator can validate the instance to validate, and another one which validate it.

public class StudentValidator implements Validator<Student> {

  public boolean supports(Student student) {
   // ...
  }

  public void validate(Object target, Errors errors) {
   // ...
  }
}

This approach leads to separation of the code of the object and the way to validate it, offering more flexibility when combining validator:

• you can combine several Validator even if the class hierarchy is not respected (POJO principle).
• when you need to validate field with data from other system (for instance a database), this approach avoid to mix database / persistence code in the POJO domain class.

Please see the documentation of Spring about Validation .