Missing Elements in HTTP Request - Null or Empty?

Question

I have a HTTP Request javax.servlet.http.HttpServletRequest that is passing in a value to be used in some code being handled in a Java web service using JAX-RS. The POST function in Java is consuming application/json. There are two possible values to be passed into the request, call one X and the other Y, assume both are Strings. The request requires at least one of the two possible values to be considered 'valid'.

When the request comes in, if X is provided and Y is left out of the request entirely, what is the proper way to check to see if Y is there? Would you check to see if Y.isEmpty() or Y == null? Providing X doesn't guarantee Y is present, and vice versa.

Solution 1

If a parameter is not specified at all like so,

http://example.com/context/servlet?x=foo

then it will return null:

String x = request.getParameter("x"); // "foo"
String y = request.getParameter("y"); // null

If a parameter is specified, but does not have a value like so,

http://example.com/context/servlet?x=foo&y

then it will return an empty string:

String x = request.getParameter("x"); // "foo"
String y = request.getParameter("y"); // ""

Makes sense, right?

Solution 2

Tests if a parameter is present in the request

httpServletRequest.getParameter( "Y" ) == null

The following code tests the value of the parameter if it is present

if ( httpServletRequest.getParameter( "Y" ) != null )
{
    String value = httpServletRequest.getParameter( "Y" );

    // Put your test code here.  Include a empty value check
}

Comments

[G. Bach]

You should move the line String value = httpServletRequest.getParameter( "Y" ); before the if-clause so the request doesn't have to be evaluated twice.

[mightyrick]

The code isn't intended to be a single block of code. I'm only pointing out how to check whether a parameter is passed. And then also how to use that to check the value of a parameter.

[Walls]

Thanks for the clarification, this answer is exactly what I needed. Thanks again and I'll remember the servlets tag in the future. (will accept when it lets me)

[G. Bach]

Oh I see, so requesting the parameter twice is more an didactic choice to show what to do with it; I agree, this makes the purpose of each line clearer.

[Haagenti]

@G.Bach +1 for the condescending sarcasm

[G. Bach]

@ScareCrow This was more than two years ago so I may be wrong, but I actually don't think I was being sarcastic. Doing superfluous stuff to elucidate something is sometimes a valid didactic approach.