Match Braces in Java

Asked Nov 16 '20 at 21:53

Active Nov 16 '20 at 22:16

Viewed 39 times

I'm trying to match the inner content of the first braces in Java only if the template with braces occurs first. For instance:

{FOO}/bar/{BAR} -> "FOO"
/{FOO}/bar/{BAR} -> null
{BAR}/foo/{FOO} -> "BAR"

I was tested the following regex which seemed to work ^{(.*?)} in the online regex testers; however, when I try to do this in Java as ^\\{(.*?)} it fails. I suspect it has something to do with the braces being misinterpreted. Currently, the Java regex doesn't match any of the above strings.

protected Optional<String> getHostVariableNameFromTemplate(String template) {
    final String REGEX = "^\\{([^}]*)}";

    Pattern pattern = Pattern.compile(REGEX);
    Matcher matcher = pattern.matcher(template);

    return (matcher.matches()) ? Optional.of(matcher.group(0)) : Optional.empty();
}

@Test // fails
public void getHostVariableNameFromTemplate_shouldReturnFirstVariable() {
    String template = "{SOME_HOST}/foo/{fooId}/bar/{barId}?filter=foobar";
    Optional<String> host = testObj.getHostVariableNameFromTemplate(template);
    assertTrue(host.isPresent());
    assertEquals("SOME_HOST", host.get());
}

edited Nov 16 '20 at 22:16

asked Nov 16 '20 at 21:53

scriptkiddie

Is it run in Android? Then you need to escape `}`. – Wiktor Stribiżew Nov 16 '20 at 21:54
No its Spring and I tried escaping } – scriptkiddie Nov 16 '20 at 21:58
1

Ok, what do you mean by "it fails"? – Wiktor Stribiżew Nov 16 '20 at 21:58
1

Don't *only* describe your code. Show it (preferably as [mcve]) so we could debug it properly. – Pshemo Nov 16 '20 at 22:00
2

Can't reproduce the problem: https://ideone.com/le0JRt – Pshemo Nov 16 '20 at 22:04
2

@scriptkiddie Have you been probably confused with `match` and `find`? – terrorrussia-keeps-killing Nov 16 '20 at 22:15
I updated the question with an example. – scriptkiddie Nov 16 '20 at 22:17
1

`matcher.matches()` checks if regex matches *entire* string. If you want to allow for *fragment* of text to be matched by regex use `matcher.find()`. – Pshemo Nov 16 '20 at 22:22
1

Yeah I was also using the wrong group I think. I should have been using `.group(1)` instead of `.group(0)`. Thanks Pshemo! – scriptkiddie Nov 16 '20 at 22:28

Match Braces in Java

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