Question

i have pattern:

host=([a-z0-9./:]*)

it’s find for me host address. And i have content

host=http//:sdf3452.domain.com/

And my code is:

    Matcher m;
    Pattern hostP = Pattern.compile("host=([a-z0-9./:]*)");
    m=hostP.matcher(content);//string 1
    String match = m.group();//string 2 
    Log.i("host", ""+hostP.matcher(content).find());

if i delete string 1 and 2 i see true in logcat. If left as is I got exception nothing found.
I’ve tried all kinds of pattern. Through debug looked m variable, finds no match. Please teach me use reg exp!

Answer 1

Before you group() a match, you need to invoke find().

Try it like this:

Pattern hostP = Pattern.compile("host=([a-z0-9./:]*)");
Matcher m = hostP.matcher(content);

if(m.find()) {
  String match = m.group();
  // ... 
}

EDIT

and a little demo that shows what each match-group contains:

Pattern p = Pattern.compile("host=([a-z0-9./:]*)");
Matcher m = p.matcher("host=http://sdf3452.domain.com/");
if (m.find()) {
  for(int i = 0; i <= m.groupCount(); i++) {
    System.out.printf("m.group(%d) = '%s'\n", i, m.group(i));
  }
}

which will print:

m.group(0) = 'host=http://sdf3452.domain.com/'
m.group(1) = 'http://sdf3452.domain.com/'

As you can see, group(0), which is the same as group(), contains what the entire pattern matches.

But realize that a URL can contain much more than what your defined in [a-z0-9./:]*!