正则表达式和转义和未转义的分隔符 [英] Regex and escaped and unescaped delimiter

问题描述

与此相关的问题

我有一个字符串

  a\; b \\; c; d 
  

在Java中看起来像

  String s =a\ \; b \\\\\; c; d
  

我需要拆分它分号符合以下规则：

1. 如果分号前面加上反斜杠，则不应将其视为分隔符（




2. 如果反斜杠本身被转义，因此不能自行转义分号，该分号应该是分隔符（在 b 和 c 之间）。

所以分号应该被当作分隔符，如果在它之前有一个零或偶数的反斜杠。

例如上面的例子，我想获取以下的字符串（双反斜杠java编译器）：

  a\; b \\ 
c 
d 
  

解决方案

您可以使用正则表达式

 （?: \\。 \\\] ++）* 
  

匹配非转义分号之间的所有文本：

 列表< String> matchList = new ArrayList< String>（）; 
尝试{
模式regex = Pattern.compile（（？：\\\\。| [^; \\\\] ++）*）; 
 Matcher regexMatcher = regex.matcher（subjectString）; 
 while（regexMatcher.find（））{
 matchList.add（regexMatcher.group（））; 
} 
  

说明：

 （?:＃匹配... 
 \\。＃任意转义的字符
 |＃或... 
 [^; \\] ++＃除分号或反斜杠之外的任何字符;占有性匹配
）*＃重复任意次数。 
  

所有权匹配（ ++ ）是重要的是避免由于嵌套量词而造成的灾难性回溯。

question related to this

I have a string

a\;b\\;c;d

which in Java looks like

String s = "a\\;b\\\\;c;d"

I need to split it by semicolon with following rules:

1. If semicolon is preceded by backslash, it should not be treated as separator (between a and b).

2. If backslash itself is escaped and therefore does not escape itself semicolon, that semicolon should be separator (between b and c).

So semicolon should be treated as separator if there is either zero or even number of backslashes before it.

For example above, I want to get following strings (double backslashes for java compiler):

a\;b\\
c
d

解决方案

You can use the regex

(?:\\.|[^;\\]++)*

to match all text between unescaped semicolons:

List<String> matchList = new ArrayList<String>();
try {
    Pattern regex = Pattern.compile("(?:\\\\.|[^;\\\\]++)*");
    Matcher regexMatcher = regex.matcher(subjectString);
    while (regexMatcher.find()) {
        matchList.add(regexMatcher.group());
    } 

Explanation:

(?:        # Match either...
 \\.       # any escaped character
|          # or...
 [^;\\]++  # any character(s) except semicolon or backslash; possessive match
)*         # Repeat any number of times.

The possessive match (++) is important to avoid catastrophic backtracking because of the nested quantifiers.

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