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 Pattern 类与 Pattern.MULTILINE 修饰符时，我能够匹配，但我无法使用（？m）进行此操作。

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).

与相同的模式（？m ）并使用 String.matches 似乎不起作用。

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

我肯定我错过了什么，但不知道是什么。我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.

这就是我试过的事情

String test = "User Comments: This is \t a\ta \n test \n\n message \n";

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，你在不正确的情况下使用修饰符假设。

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

Pattern.MULTILINE 或（？m）告诉Java接受锚点 ^ 和 $ 以匹配每行的开头和结尾（否则它们只是匹配整个字符串的开头/结尾。）

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，在你的情况下，正则表达式失败，因为你使用 matches（）方法，该方法要求正则表达式匹配整个字符串 - 由于存在一些字符，这当然不起作用在（\\ W）*（\\ S）* 匹配后离开。

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.

所以如果你只是想找一个以用户评论：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*(.*)

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 然后包含用户评论后的文字：

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