Java正则表达式返回完整字符串而不是捕获

Question

Java Code:

String imagesArrayResponse = xmlNode.getChildText("files");
Matcher m = Pattern.compile("path\":\"([^\"]*)").matcher(imagesArrayResponse);

while (m.find()) {
    String path = m.group(0);
}

String:

[{"path":"upload\/files\/56727570aaa08922_0.png","dir":"files","name":"56727570aaa08922_0","original_name":"56727570aaa08922_0.png"}{"path":"upload\/files\/56727570aaa08922_0.png","dir":"files","name":"56727570aaa08922_0","original_name":"56727570aaa08922_0.png"}{"path":"upload\/files\/56727570aaa08922_0.png","dir":"files","name":"56727570aaa08922_0","original_name":"56727570aaa08922_0.png"}{"path":"upload\/files\/56727570aaa08922_0.png","dir":"files","name":"56727570aaa08922_0","original_name":"56727570aaa08922_0.png"}]

m.group returns

path":"upload\/files\/56727570aaa08922_0.png"

instead of captured value of path. Where I am wrong?

Answer 1

See the documentation of group( int index ) method

When called with 0, it returns the entire string. Group 1 is the first.

To avoid such a trap, you should use named group with syntax : "path\\":\\"(?<mynamegroup>[^\\"]*)"

javadoc :

Capturing groups are indexed from left to right, starting at one. Group zero denotes the entire pattern, so the expression m.group(0) is equivalent to m.group().

Answer 2

m.group(1) will give you the Match. If there are more than one matchset (), it will be m.group(2), m.group(3),...

Answer 3

By convention, AFAIK in regex engines the 0th group is always the whole matched string. Nested groups start at 1.

Answer 4

Check out the grouping options in Matcher .

 Matcher m = 
   Pattern.compile(
    //<-     (0)     ->  that's group(0)
    //          <-(1)->  that's group(1)
     "path\":\"([^\"]*)").matcher(imagesArrayResponse);

Change your code to

while (m.find()) {
  String path = m.group(1);
}

And you should be okay. This is also worth checking out: What is a non-capturing group? What does a question mark followed by a colon (?:) mean?