正则表达式在ActionScript中解析iCalendar文件

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

该库使用我想要理解的这个正则表达式:

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

谢谢.

Answer 1

那是一个可怕的正则表达! .*并且.*?意味着匹配任何东西(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,不正确的使用将导致灾难性的回溯.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.

让我展示一下我将如何处理这个问题.显然,iCalendar文件格式是基于行的.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否定字符类的高效正则表达式:

([^\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所解释的那样:

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) «+»