Another possibility using split's:

use 5.010;
use strict;
use warnings;

while (<DATA>){
  chomp;
  my %ps = map {my @k = split /=/; $k[0] => $k[1]} split /&/,(split /\
+?/)[1];
  say "username = $ps{username}; id=$ps{id}"
}

__DATA__
http://beta.websitename.com/tool/view/mb/file?username=anirudh007&id=4
+3242342
http://beta.websitename.com/tool/view/mb/file?id=3323213&username=anir
+udh007
[download]

username = anirudh007; id=43242342
username = anirudh007; id=3323213
[download]