Question

我使用库来解析iCalendar文件，但我不明白要拆分属性的正则表达式。
iCalendar属性有3种不同的风格：

BEGIN:VEVENT
DTSTART;VALUE=DATE:20080402
RRULE:FREQ=YEARLY;WKST=MO

库使用我想要了解的正则表达式：

var matches:Array = data.match(/(.+?)(;(.*?)=(.*?)((,(.*?)=(.*?))*?))?:(.*)$/);
p.name = matches[1];
p.value = matches[9];                   
p.paramString = matches[2];

感谢。

Answer 1

这是一个可怕的正则表达式！ .*和.*?意味着匹配任意数量（贪婪）或少数（懒惰）。这些只应作为最后的手段。当正则表达式与输入文本不匹配时，使用不当将导致catastrophic backtracking。所有你需要了解的这个正则表达式，你不想写这样的正则表达式。

让我说明一下我将如何处理这个问题。显然iCalendar File Format是基于行的。每行都有一个属性和一个用冒号分隔的值。该属性可以具有以分号分隔的参数。这意味着属性不能包含换行符，分号或冒号，可选参数不能包含换行符或冒号，并且该值不能包含换行符。这些知识允许我们编写一个使用negated character classes的有效正则表达式：

([^\r\n;:]+)(;[^\r\n:]+)?:(.+)

或者在ActionScript中：

var matches:Array = data.match(/([^\r\n;:]+)(;[^\r\n:]+)?:(.+)/);  
p.name = matches[1];
p.value = matches[3];
p.paramString = matches[2];

正如RegexBuddy所说：

Match the regular expression below and capture its match into backreference number 1 «([^\r\n;:]+)»
   Match a single character NOT present in the list below «[^\r\n;:]+»
      Between one and unlimited times, as many times as possible, giving back as needed (greedy) «+»
      A carriage return character «\r»
      A line feed character «\n»
      One of the characters “;:” «;:»
Match the regular expression below and capture its match into backreference number 2 «(;[^\r\n:]+)?»
   Between zero and one times, as many times as possible, giving back as needed (greedy) «?»
   Match the character “;” literally «;»
   Match a single character NOT present in the list below «[^\r\n:]+»
      Between one and unlimited times, as many times as possible, giving back as needed (greedy) «+»
      A carriage return character «\r»
      A line feed character «\n»
      The character “:” «:»
Match the character “:” literally «:»
Match the regular expression below and capture its match into backreference number 3 «(.+)»
   Match any single character that is not a line break character «.+»
      Between one and unlimited times, as many times as possible, giving back as needed (greedy) «+»

正则表达式在ActionScript中解析iCalendar文件

1 个答案: