Java regex help needed to split string please! How to ignore an empty line?

Question

Hi,

I'm a complete noob to regex and I need help with splitting a string. I am inputing the following data

665  11% R     1    908K    388K  fg root     top
 61   1% S    42 152404K  29716K  fg system   system_server
 38   0% S     1    840K    340K  fg root     /system/bin/qemud
114   0% S    16 120160K  19156K  fg radio    com.android.phone

which is nothing but your regular top output. What I intend to do is select on entries like

655 11% R 1 fg root top

Now the code which I use to do the following is

while ((inputLine = in.readLine()) != null) 
{
  String[] segs= inputLine.split("[ ]+");
  str[i] = segs[0]+" "+segs[1]+" "+segs[2]+" "+
           segs[3]+" "+segs[6]+" "+segs[7]+" "+segs[8];
  Log.v("TOP Output", str[i]);
  i++; j++;
}

But the problem I face is, that I get on logcat is

java.lang.ArrayIndexOutOfBoundsException

Where am I going wrong, and what could I do different to prevent this. Thanks for helping.

EDIT: After reading the comments I realize i have a couple of empty line in my output. So in such a case how am I supposed to ignore those line. I know I am supposed to match a case, but I am not sure about the expression or syntax!

Answer 1

Forget about it... I'm too dump to count to 9. :-(

Answer 2

be careful at str instantiation, how big is it, because it's an array. You should use a list or anything else, because you don't know how many lines you have in your input.

Answer 3

Use the following regexp, and check for array's length, every line! And also consider using a StringBuilder or StringBuffer instead of concatenating.

 String[] s = inputLine.split("[\\s\\t]+");

Answer 4

You don't need the character class (square brackets). Space is a regular character in regex, so:

String[] segs = inputLine.split(" +");

Other than that, assuming array indices are there without range checking is bad style and an ArrayIndexOutOfBoundsException is just what you've asked for.

Better do it explicitly:

String re = "^\\s*(\\S+)\\s+(\\S+)\\s+(\\S+)\\s+(\\S+)\\s+(\\S+)\\s+(\\S+)\\s+(\\S+)\s+(\\S+)\\s+(\\S+)\\s*$";
Pattern p = Pattern.compile(re, Pattern.MULTILINE);
Matcher m = p.matcher(yourInputString);

while (m.find())
{
   // do stuff with m.group(1) through m.group(9)
}

This way it is guaranteed that every line you match fulfills your expectations and every matcher group contains what you expect, too.

Disclaimer: I'm not especially proud of that regex. It's quite an ugly one, actually, but it illustrates the point that explicit is more reliable and predictable than implicit. And it has the potential to be improved into a version that matches the desired parts even more accurately than a string split ever could.

Answer 5

How consistent is this output? Is there always a value in every column? If so, try this:

line = line.replaceFirst("(?:\s+\d+[KM]?){3}", "");

You don't have to worry about blank lines with this approach, because the regex doesn't match them.