正则表达式用嵌套引号解析csv

这个正则表达式将在Java(或.NET和其他支持占有量词和冗长正则表达式的实现)中工作：

^            # Start of string
(?:          # Match the following:
 (?:         #  Either match
  [^",n]*+  #   0 or more characters except comma,quote or newline
 |           #  or
  "          #   an opening quote
  (?:        #   followed by either
   [^"]*+    #    0 or more non-quote characters
  |          #   or
   ""        #    an escaped quote ("")
  )*         #   any number of times
  "          #   followed by a closing quote
 )           #  End of alternation,#  Match a comma (separating the CSV columns)
)*           # Do this zero or more times.
(?:          # Then match
 (?:         #  using the same rules as above
  [^",n]*+  #  an unquoted CSV field
 |           #  or a quoted CSV field
  "(?:[^"]*+|"")*"
 )           #  End of alternation
)            # End of non-capturing group
$           # End of string

Java代码：

boolean foundMatch = subjectString.matches(
    "(?x)^         # Start of stringn" +
    "(?:           # Match the following:n" +
    " (?:          #  Either matchn" +
    "  [^",n]*+ #   0 or more characters except comma,quote or newlinen" +
    " |            #  orn" +
    "  "          #   an opening quoten" +
    "  (?:         #   followed by eithern" +
    "   [^"]*+    #    0 or more non-quote charactersn" +
    "  |           #   orn" +
    "   ""       #    an escaped quote ("")n" +
    "  )*          #   any number of timesn" +
    "  "          #   followed by a closing quoten" +
    " )            #  End of alternationn" +
    ",#  Match a comma (separating the CSV columns)n" +
    ")*            # Do this zero or more times.n" +
    "(?:           # Then matchn" +
    " (?:          #  using the same rules as aboven" +
    "  [^",n]*+ #  an unquoted CSV fieldn" +
    " |            #  or a quoted CSV fieldn" +
    "  "(?:[^"]*+|"")*"n" +
    " )            #  End of alternationn" +
    ")             # End of non-capturing groupn" +
    "$            # End of string");

请注意,您不能假设CSV文件中的每一行都是完整的行.您可以在CSV行中包含换行符(只要包含换行符的列用引号括起来).这个正则表达式知道这一点,但如果你只给它一个部分行,它就会失败.这是您真正需要CSV解析器来验证CSV文件的另一个原因.这就是解析器的作用.如果您控制输入并且知道在CSV字段中永远不会有换行符,那么您可能会放弃它,但只有这样.