Java正则表达式：积极前瞻和后瞻的多重匹配

Question

I have some strings like this

• my {test} value
• my { test } value
• my { test } value

I need to create a regex that will get everything inside {} without spaces.

With the next pattern (?<=\\{)\\s*[a-zA-Z]+\\s*(?=}) I get the content of curly brackets but with spaces

If I put \\s* to positive lookahead like this (?<=\\{\\s*)[a-zA-Z]+(?=\\s*}) I see next error

Unable to execute regular expression. java.util.regex.PatternSyntaxException: Look-behind group does not have an obvious maximum length near index 8 (?<={\\s*)[a-zA-Z]+(?=\\s*}) ^

Is it possible to achieve this without trim() of every regex match?

Answer 1

You don't need look ahead or look behind. Simple regex like this is enough,

\{\s*(.*?)\s*\}

Demo, https://regex101.com/r/REDmDT/2 (included some more sample strings)

Like you said, "I need to create a regex that will get everything inside {} without spaces"

This regex gives you everything within curley braces while excluding right /left spaces and preserving any spaces inside as it is.

Here is a java code demonstrating same.

public static void main(String[] args) throws IOException {
    List<String> list = Arrays.asList("my  {test} value", "my  {   test     } value", "my  { test  } value",
            "my  { test hello I am  } value", "my  { testing 10 times  } value");
    Pattern p = Pattern.compile("\\{\\s*(.*?)\\s*\\}");

    list.forEach(x -> {
        Matcher m = p.matcher(x);
        if (m.find()) {
            System.out.println(x + " --> " + m.group(1));
        }
    });
}

This outputs,

my  {test} value --> test
my  {   test     } value --> test
my  { test  } value --> test
my  { test hello I am  } value --> test hello I am
my  { testing 10 times  } value --> testing 10 times