匹配器不包含所有匹配的组

Question

我有一个RegEx，它将匹配如下模式：

• @Mike Hello Mike, how are you doing today?
• Hello, I'm Mike.

My RegEx如下所示：^(?:@(w|-|_|)*)?s*(.*)$

然而，在我的代码中，Matcher不知何故只识别Hello Mike ......。无法识别@Mike。

代码：

public static void main(String[] args) {
String withAt = "@Mike Hello Mike, how are you doing today?";
String withoutAt = "Hello, I'm Mike.";
matchString(withAt);
matchString(withoutAt);
} 
private static void matchString(String messageString) {
System.out.println("Maching String: " + messageString);

Pattern messagePattern = Pattern.compile( "^(?:@(\w|-|_|)*)?\s*(.*)$" );
Matcher matcher = messagePattern.matcher(messageString);
if (matcher.find()) {
System.out.println("@: " +  matcher.group(1));
System.out.println("Message: " + matcher.group(2));
}
}

运行这种代码将产生以下输出：

Maching String: @Mike Hello Mike, how are you doing today?
@:                
Message: Hello Mike, how are you doing today?

Maching String: Hello, I'm Mike.
@: null
Message: Hello, I'm Mike.

问题：

为什么withAt-字符串不将@: Mike打印到控制台？这种信息的平静在哪里？

Answer 1

您没有捕获@Mike。使用

Pattern.compile( "^(?:@([\w-]*))?\s*(.*)$" )

请参阅正则表达式证明。

解释

--------------------------------------------------------------------------------
^                        the beginning of the string
--------------------------------------------------------------------------------
(?:                      group, but do not capture (optional
(matching the most amount possible)):
--------------------------------------------------------------------------------
@                        '@'
--------------------------------------------------------------------------------
(                        group and capture to 1:
--------------------------------------------------------------------------------
[w-]*                   any character of: word characters (a-
z, A-Z, 0-9, _), '-' (0 or more times
(matching the most amount possible))
--------------------------------------------------------------------------------
)                        end of 1
--------------------------------------------------------------------------------
)?                       end of grouping
--------------------------------------------------------------------------------
s*                      whitespace (n, r, t, f, and " ") (0 or
more times (matching the most amount
possible))
--------------------------------------------------------------------------------
(                        group and capture to 2:
--------------------------------------------------------------------------------
.*                       any character except n (0 or more times
(matching the most amount possible))
--------------------------------------------------------------------------------
)                        end of 2
--------------------------------------------------------------------------------
$                        before an optional n, and the end of the
string