Struggling with regex logic: how do I remove a param from a url query string? - regex

Question

I'm comparing 2 URL query strings to see if they're equal; however, I want to ignore a specific query parameter (always with a numeric value) if it exists. So, these 2 query strings should be equal:
firstName=bobby&lastName=tables&paramToIgnore=2
firstName=bobby&lastName=tables&paramToIgnore=5
So, I tried to use a regex replace using the REReplaceNoCase function:
REReplaceNoCase(myQueryString, "&paramToIgnore=[0-9]*", "")
This works fine for the above example. I apply the replace to both strings and then compare. The problem is that I can't be sure that the param will be the last one in the string... the following 2 query strings should also be equal:
firstName=bobby&lastName=tables&paramToIgnore=2
paramToIgnore=5&firstName=bobby&lastName=tables
So, I changed the regex to make the preceding ampersand optional... "&?paramToIgnore=[0-9]*". But - these strings will still not be equal as I'll be left with an extra ampersand in one of the strings but not the other:
firstName=bobby&lastName=tables
&firstName=bobby&lastName=tables
Similarly, I can't just remove preceding and following ampersands ("&?paramToIgnore=[0-9]*&?") as if the query param is in the middle of the string I'll strip one ampersand too many in one string and not the other - e.g.
firstName=bobby&lastName=tables&paramToIgnore=2
firstName=bobby&paramToIgnore=5&lastName=tables
will become
firstName=bobby&lastName=tables
firstName=bobbylastName=tables
I can't seem to get my head around the logic of this... Can anyone help me out with a solution?

Answer 1

If you can't be sure of the order the parameters appear i would recommend, that you don't compare them by the string itsself.
I recommend splitting the string up like this:
String stringA = "firstName=bobby&lastName=tables&paramToIgnore=2";
String stringB = "firstName=bobby&lastName=tables&paramToIgnore=5";
String[] partsA = stringA.split("&");
String[] partsB = stringB.split("&");
Then go through arrays and make the paramToIgnore somehow euqal:
for(int i = 0; i < partsA.length; i++)
{
if(partsA[i].startsWith("paramToIgnore"){
partsA[i] = "IgnoreMePlease";
}
}
for(int j = 0; j < partsB.length; j++)
{
if(partsB[i].startsWith("paramToIgnore"){
partsB[i] = "IgnoreMePlease";
}
}
Then you can sort and compare the arrays to see if they are equal:
Arrays.sort(partsA);
Arrays.sort(partsB);
boolean b = Arrays.equals(partsA, partsB);
I'm pretty sure it's possible to make this more compact and give it a better performance. But with comparing strings like you do, you somehow alsways have to care about the order of your parameters.

Answer 2

You can use the QueryStringDeleteVar UDF on cflib to remove the query string variables you want to ignore from both strings, then compare them.

Answer 3

Make it in two steps:
first remove your param, as you described in example
then remove ampersand which is left at the begining or the end of query with separate regex, or any double/triple/... ampersands in the middle of the query

Answer 4

How about having an 'or' in the RegEx to match an ampersand at the start or the end?
&paramToIgnore=[0-9]*|paramToIgnore=[0-9]*&
Seems to do the job when testing in regexpal.com

Answer 5

try changing it to:
REReplaceNoCase(myQueryString, "&?paramToIgnore=[0-9]+", "")
plus instead of star should capture 1 or more of the preceding matched characters. It won't match anything but 0-9 so if there is another parameter after that it'll stop when it can't match any more digits.
Alternatively, you could use:
REReplaceNoCase(myQueryString, "&?paramToIgnore=[^&]", "")
This will match anything but an ampersand. It will cover the case if the parameter exists but there is no value; which is probably something you'd want to account for.