正则表达式问题模式匹配

Question

I am trying to write a regular expression for below string pattern

String str = "<name>{f:<one>,l:<two>,t:<three>} )";

this pattern ends with "?" so below code works

String result = str.replaceAll(pattern, "abc");
System.out.println(result);

and the output is

<name> ( abc abc)

But if the input string changes

where next pattern doesn't end with ?, Java hung.....

String result = str.replaceAll(pattern, "abc"); 
System.out.println(result);

Equivalent Scala code is

pattern.replaceAllIn(str,"abc")

Where am I wrong, thanks in advance

Answer 1

From you example it is hard to tell what you try to achieve here are some remarks how the regex could be improved:

There are several strange things in your regex

• (.)* could create an infinite number of relatively expensive catching groups if you do not want to use the result later use (?:) or at least change to (.*)
• <\\\\S+?> is better expressed as <[^>]+>

As with most of your matchers you use the non-greedy approach you may run in a bad backtracking issue which could be avoided by changing the regex.

Answer 2

it should work, if you change your regex to ie * at end

String pattern = "\\{(((.)*?(<\\S+?>)?)+?)\\}\\?*";

or simply

String pattern = "\\{.*?(\\})(\\?)*";