Struts2 validation expression sample

What does this [D][C][M])[-]*[a-zA-z0-9]*$开发者_开发知识库 mean? What do *,^,$ [-] all mean? Please explain.

That looks like part of a regular expression validator -

• * - match the previous item 0 or more times
• ^ - the beginning of a line
• $ - the end of a line
• [-] - the character class that contains "-"
• [1-5] - the character class that contains the range of "1" to "5" inclusive
• [a-z] - the character class that contains the range of "a" to "z" inclusive

[D][C][M])[-]*[a-zA-Z0-9]*$:

• [D][C][M]) - some capture group ending with the characters "DCM"
• [-]* - 0 or more "-"s
• [a-zA-Z0-9]*$ - 0 or more alphanumeric characters at the end of the line