什么时候'。'在正则表达式中不匹配？ [英] When does '.' not match in a Regex?

问题描述

我遇到了以下问题（简化）。我写了以下内容

I encountered the following problem (simplified). I wrote the following

Pattern pattern = Pattern.compile("Fig.*");
String s = readMyString();
Matcher matcher = pattern.matcher(s);

在读取一个字符串时，匹配器无法匹配，即使它以Fig开头。我将问题跟踪到字符串下一部分中的流氓角色。它的代码点值为1633来自

In reading one string the matcher failed to match even though it started with "Fig". I tracked the problem down to a rogue character in the next part of the string. It had codePoint value 1633 from

(int) charAt(i)

但与正则表达式不匹配。我认为这是由于输入过程中某处的非UTF-8编码。

but did not match the regex. I think it is due to a non-UTF-8 encoding somewhere in the input process.

Javadocs 说：

预定义的字符类
。任何字符（可能与行终止符匹配也可能不匹配）

Predefined character classes . Any character (may or may not match line terminators)

据推测，这不是严格意义上的字符，而是仍然是String的一部分。如何检测此问题？

Presumably this is not a character in the strict sense of the word, but is is still part of the String. How do I detect this problem?

更新：这是由于（char）10不容易发现。我上面的诊断是错误的，下面的所有答案都与问题相关并且很有用。

UPDATE: It was due to a (char)10 which was not easy to spot. My diagnosis above is wrong and all answers below are relevant to the question as asked and are useful.

推荐答案

。 Java正则表达式中的字符匹配除行终止符之外的任何字符，除非您使用标志 Pattern.DOTALL 在编译你的模式时。

The . character in a Java regex matches any character except line terminators, unless you use the flag Pattern.DOTALL when compiling your pattern.

为此，你可以使用这样的模式：

To do so, you would use a Pattern like this:

Pattern p = Pattern.compile("somepattern", Pattern.DOTALL);

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