java regex , extract a line?

Question

given 3 lines , how can I extract 2nd line using regular expression ?

line1
line2
line3 

I used

pattern = Pattern.compile("line1.*(.*?).*line3");

But nothing appears

Answer 1

You can use Pattern.DOTALL flag like this:

String str = "line1\nline2\nline3";
Pattern pt = Pattern.compile("line1\n(.+?)\nline3", Pattern.DOTALL);
Matcher m = pt.matcher(str);
while (m.find())
    System.out.printf("Matched - [%s]%n", m.group(1)); // outputs [line2]

Answer 2

This won't work, since your first .* matches everything up to line3. Your reluctant match gets lost, as does the second .* . Try to specify the line breaks (^ and $) after line1 / before line3.

Answer 3

尝试pattern = Pattern.compile("line1.*?(.*?).*?line3", Pattern.DOTALL | Pattern.MULTILINE);

Answer 4

您可以提取两条非空行之间的所有内容：

(?<=.+\n).+(?=\n.+)