[英]Java Regex,Empty String be matched
I wrote a regex in Java to match sentences containing some string like this: 我用Java写了一个正则表达式来匹配包含以下字符串的句子:
String regex = "((^|([.!?:] ))" + "[^!.?:]*?" + queryStr + ".*?" + "([!.?])|$)+?";
Then I use the regex to match my String, see below: 然后,我使用正则表达式来匹配我的String,如下所示:
Pattern pattern = Pattern.compile(regex);
String content = "Hello World!!!";
Matcher match = pattern.matcher(content);
int index = 0;
while(match.find(index))
{
index = match.end() -1;
System.out.println(match.group());
}
But the loop never ends, I suspect, because the regex matches empty string. 但是我怀疑循环永远不会结束,因为正则表达式匹配空字符串。 Apparently, my regex includes the String queryStr.
显然,我的正则表达式包含字符串queryStr。 So, I am confused with this.
所以,我对此感到困惑。 Can anyone help me to slove this?
谁能帮助我解决这个问题?
Your regex pattern looks like 您的正则表达式模式看起来像
((^|([.!?:] ))[^!.?:]*?Hello.*?([!.?])|$)+?
It contains 2 alternatives: 它包含2个替代方案:
(^|([.!?:] ))[^!.?:]*?Hello.*?([!.?])
$
So, the problem was that you were matching the end of string all the time in a loop. 因此,问题在于您一直在循环中匹配字符串的结尾。
Make this change: 进行以下更改:
String regex = "(^|[.!?:] )" + "[^!.?:]*?" + queryStr + ".*?" + "([!.?]+?|$)";
Now, it will look like 现在,它看起来像
(^|[.!?:] )[^!.?:]*?Hello.*?([!.?]+?|$)
And $
will be an alternative to [!.?]+?
$
将替代[!.?]+?
only. 只要。
See demo on regex101.com . 请参阅regex101.com上的演示 。
Every term of your regex is optional. 正则表达式的每个术语都是可选的。
To prevent matching blank input, add this to the front of your regex: 为防止匹配空白输入,请将其添加到正则表达式的前面:
(?!$)
This is a look ahead that asserts the current position is not followed by end of input (ie "something" is following) 这是一个向前看的断言,断言当前位置后面没有输入结束(即紧跟着“某物”)
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