Java正则表达式:否定前瞻 [英] Java regex: Negative lookahead
问题描述
我正在尝试制作两个匹配URI的正则表达式。这些URI的格式为: / foo / someVariableData
和 / foo / someVariableData / bar / someOtherVariableData
I'm trying to craft two regular expressions that will match URIs. These URIs are of the format: /foo/someVariableData
and /foo/someVariableData/bar/someOtherVariableData
我需要两个正则表达式。每个都需要匹配一个而不是另一个。
I need two regexes. Each needs to match one but not the other.
我最初提出的正则表达式是:
/ foo /.+
和 / foo /.+/ bar /.+
。
The regexes I originally came up with are:
/foo/.+
and /foo/.+/bar/.+
respectively.
我认为第二个正则表达式很好。它只匹配第二个字符串。然而,第一个正则表达式匹配两者。所以,我开始玩(第一次)负向前瞻。我设计了正则表达式 / foo /.+(?!bar)
并设置以下代码进行测试
I think the second regex is fine. It will only match the second string. The first regex, however, matches both. So, I started playing around (for the first time) with negative lookahead. I designed the regex /foo/.+(?!bar)
and set up the following code to test it
public static void main(String[] args) {
String shouldWork = "/foo/abc123doremi";
String shouldntWork = "/foo/abc123doremi/bar/def456fasola";
String regex = "/foo/.+(?!bar)";
System.out.println("ShouldWork: " + shouldWork.matches(regex));
System.out.println("ShouldntWork: " + shouldntWork.matches(regex));
}
当然,两者都解析为真
。
And, of course, both of them resolve to true
.
有谁知道我做错了什么?我不需要使用Negative lookahead,我只需要解决问题,我认为负面的预测可能是一种方法。
Anybody know what I'm doing wrong? I don't need to use Negative lookahead necessarily, I just need to solve the problem, and I think that negative lookahead might be one way to do it.
谢谢,
推荐答案
尝试
String regex = "/foo/(?!.*bar).+";
或可能
String regex = "/foo/(?!.*\\bbar\\b).+";
以避免路径失败,例如 / foo / baz / crowbars
我认为你确实希望正则表达式匹配。
to avoid failures on paths like /foo/baz/crowbars
which I assume you do want that regex to match.
说明:(没有Java字符串所需的双反斜杠)
Explanation: (without the double backslashes required by Java strings)
/foo/ # Match "/foo/"
(?! # Assert that it's impossible to match the following regex here:
.* # any number of characters
\b # followed by a word boundary
bar # followed by "bar"
\b # followed by a word boundary.
) # End of lookahead assertion
.+ # Match one or more characters
\b
,单词边界锚,匹配字母数字字符和非字母数字字符之间的空格(或字符串的开头/结尾之间)和一个alnum角色)。因此,它在 b
之前或在bar中的
,但在 r
之后匹配crowbar中
。 w
和 b
之间无法匹配
\b
, the "word boundary anchor", matches the empty space between an alphanumeric character and a non-alphanumeric character (or between the start/end of the string and an alnum character). Therefore, it matches before the b
or after the r
in "bar"
, but it fails to match between w
and b
in "crowbar"
.
Protip:看看 http:/ /www.regular-expressions.info - 一个很棒的正则表达式教程。
Protip: Take a look at http://www.regular-expressions.info - a great regex tutorial.
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