Question

I have the following class:

class UserValidator{

     // no constructor , default is fine. 

     void Validate(Request request, Response response){
        // some validation logic on request
        // if fails, add the message to response.
     }

}

Similarly I can do the same as follows:

class UserValidator{

     private Request request;
     private Response response;

     UserValidator(Request _request, Response _response)
     {
         request = _request;
         response = _response;
     }

     void Validate(){
        // some validation logic for request
        // if fails, add the message to response.
     }

}

For Testing which one is more preferable? Can i say that the second UserValidator class has a state and thus easier to test, whereas first one doesnt have a state and harder to test? Matter of the fact the first one can be a static class as well, which can not be passed to other methods, but if called statically it doest work.

Which one is better in terms of testability? which one contains state? which is more ideal?

Answer 1

Only the second one contains state.

Personally, I would use the first one statically, like

class UserValidator{

     private UserValidator() { } // no constructor

     public static void Validate(Request request, Response response){
        // some validation logic on request
        // if fails, add the message to response.
     }

}

However, there is an advantage to storing the result – you can run it again and again without needing to actually run it.

class UserValidator {
    public static enum ValidatorState { NOT_RUN, PASSED, FAILED }
    private ValidatorState state = NOT_RUN;
    private final Request request;
    private final Response response;
    public UserValidator(Request request, Response response) {
        this.request = request;
        this.response = response;
    }
    public ValidatorState validate() {
        if(state != NOT_RUN) return state;
        if(blah blah)
            state = PASSED;
        else
            state = FAILED;
        return state;
    }
}

To have a list of various validators, you will need some kind of interface to perform that.

public interface Validator {
    boolean validate(Request request, Response response);
}

Then you would create a static method library with all your validation. Note that these are made up examples, but contain some real-world-ish kind of logic.

public class ValidationLibrary {
    private ValidationLibrary() { }
    public boolean validateUsername(Request request, Response response) {
        String name = request.getProperty("username");
        if(name.length() < 3) return false;
        if(name.length() > 12) return false;
        if(name.equals(name.reverse()) return false; // who knows?
        return true;
    }
    public boolean validateSecurity(Request request, Response response) {
        // what page is the user trying to reach?
        SecurityRealm realm = SecurityRealm.realmForPage(request.getProperty("page"));
        String username = request.getProperty("name");
        return realm.allows(username);
    }
}

Later if you need multiple validators, you can simply do this

List<Validator> validators = new ArrayList<Validator>();
validators.add(new Validator(){ 
    public boolean validate(Request req, Response res) { ValidationLibrary.validateUsername(req,res); } 
});
validators.add(new Validator(){ 
    public boolean validate(Request req, Response res) { ValidationLibrary.validateSecurity(req,res); } 
});

Then when you get a request, you simply do this to validate it:

for(Validator v : validators) if(!v.validate(request,response)) return false;