使用正则表达式匹配多行文本 [英] Match multiline text using regular expression

问题描述

我正在尝试使用 java 匹配多行文本.当我使用带有 Pattern.MULTILINE 修饰符的 Pattern 类时，我能够匹配，但我不能使用 (?m) 匹配.

I am trying to match a multi line text using java. When I use the Pattern class with the Pattern.MULTILINE modifier, I am able to match, but I am not able to do so with (?m).

使用 (?m) 和使用 String.matches 的相同模式似乎不起作用.

The same pattern with (?m) and using String.matches does not seem to work.

我确定我遗漏了一些东西，但不知道是什么.不太擅长正则表达式.

I am sure I am missing something, but no idea what. Am not very good at regular expressions.

这是我试过的

String test = "User Comments: This is 	 a	a 
 test 

 message 
";

String pattern1 = "User Comments: (\W)*(\S)*";
Pattern p = Pattern.compile(pattern1, Pattern.MULTILINE);
System.out.println(p.matcher(test).find());  //true

String pattern2 = "(?m)User Comments: (\W)*(\S)*";
System.out.println(test.matches(pattern2));  //false - why?

推荐答案

首先，您在错误的假设下使用了修饰符.

First, you're using the modifiers under an incorrect assumption.

Pattern.MULTILINE 或 (?m) 告诉 Java 接受锚 ^ 和 $ 来匹配在每行的开头和结尾处(否则它们只会在整个字符串的开头/结尾处匹配).

Pattern.MULTILINE or (?m) tells Java to accept the anchors ^ and $ to match at the start and end of each line (otherwise they only match at the start/end of the entire string).

Pattern.DOTALL 或 (?s) 告诉 Java 也允许点匹配换行符.

Pattern.DOTALL or (?s) tells Java to allow the dot to match newline characters, too.

其次，在您的情况下，正则表达式失败，因为您使用的是 matches() 方法，该方法期望正则表达式匹配 整个 字符串 - 这当然不会'不工作，因为在 (\W)*(\S)* 匹配后还有一些字符.

Second, in your case, the regex fails because you're using the matches() method which expects the regex to match the entire string - which of course doesn't work since there are some characters left after (\W)*(\S)* have matched.

因此，如果您只是在寻找以 User Comments: 开头的字符串，请使用正则表达式

So if you're simply looking for a string that starts with User Comments:, use the regex

^s*User Comments:s*(.*)

使用 Pattern.DOTALL 选项:

Pattern regex = Pattern.compile("^\s*User Comments:\s+(.*)", Pattern.DOTALL);
Matcher regexMatcher = regex.matcher(subjectString);
if (regexMatcher.find()) {
    ResultString = regexMatcher.group(1);
} 

ResultString 然后将包含 User Comments:

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