adding variables in a regular expression to make it dynamic in java

Question

I need to form a regular expression in order to check the outputs of a response log. The log file will always be different based on the input. Thus, I want to create a dynamic regular expression based on the input to the function. I may need to pass variable number of variables at a time for comparison, so how can that 'or' factor be inserted in the regex?

Is it possible to create such a regular expression in Java, and how should I go about it?

Answer 1

Yes, the regex is only a string, you can concatenate your user input to constant parts and then create a pattern from it.

If you want to match the user input literally, you should use Pattern.quote("UserString") to regex escape it.

Example:

String UserInput = "Bar()";
String Prefix = "Foo";

Pattern p = Pattern.compile(Prefix + Pattern.quote(UserInput));

String s1 = "FooBar()";
String s2 = "FooBarNo";

String[] s = { s1, s2};

for (String a : s) {
    Matcher m = p.matcher(a);
    if (m.find())
        System.out.println(a + " ==> Success");
    else
        System.out.println(a + " ==> Failure");
}

Output:

FooBar() ==> Success
FooBarNo ==> Failure

Answer 2

I think you can do that by concatenating. eg: "your regex" + "{" + input + "}".