$ cat t.pl 
use strict;
use warnings;
use Data::Dumper;
use JSON;

my $text; { local $/;$text= <DATA> };

my $junk = decode_json($text);

print Dumper($junk);

__DATA__
{ "1": { "subject1": "value", "subject2": [ { "subject3": "value", "subject4": "value" } ], "subject5": "value", "subject6": "value", "subject7": "value" } }

$ perl t.pl
$VAR1 = {
          '1' => {
                   'subject7' => 'value',
                   'subject2' => [
                                   {
                                     'subject4' => 'value',
                                     'subject3' => 'value'
                                   }
                                 ],
                   'subject5' => 'value',
                   'subject1' => 'value',
                   'subject6' => 'value'
                 }
        };