Java Regex: Look behind group does not have an "obvious maximum length"

Question

I have a service running that uses regex sent to it and uses it to retrieve a value from a string.

I can create a main method inside the class and debug the regex (?<=\\().+?(?=\\){1}) and it works perfectly.

However, as soon as I deploy it in tomcat to test remotely, I get the following exception:

Look-behind group does not have an obvious maximum length near index 19
(?<=\\().+?(?=\\){1})
                   ^

Here is the function for parsing out a value that is being called:

private String parsePattern(String value, String pattern)
{
    String ret = "";

    Matcher m = Pattern.compile(pattern).matcher(value);
    while (m.find())
    {
        ret = m.group(0);
    }

    return ret;
}

What is going on that is causing it to compile in an app, but not work in a webapp?

EDIT:

This fails with any string, but the string currently being checked is: "(Group Camp Renovation)"

When called from main, the method returns "Group Camp Renovation", when called via webapp, it throws the exception.

Answer 1

The problem is - once again - quoting of strings in the Java code vs no quoting when read via some kind of input.

When you paste the string (?<=\\().+?(?=\\){1}) like this:

String s1 = "(?<=\\().+?(?=\\){1})";
System.out.println(s1);

you will get this output

(?<=\().+?(?=\){1})

and this is what the regexp parser sees.

But when the same string is read via an InputStream (just as an example), nothing is altered:

String s1 = new BufferedReader(new InputStreamReader(System.in)).readLine();
System.out.println(s1);

will print

(?<=\\().+?(?=\\){1})

Which means, that the {1} is attributed to the (?=\\) part and not to the (?<= part.

Answer 2

I have entered your pattern into ideone and the result is the same as your Tomcat's result:

System.out.println("aoeu".matches("(?<=\\\\().+?(?=\\\\){1})"));

Note how I have doubled all the backslashes in the string literal in order to have Pattern.compile receive the string you have in your error message.