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Modul Stats4Lox::JSON

Objektklasse zum Laden und Speichern von JSON-Files.

Erkennt, ob Daten geändert wurden oder nicht - speichert nur, wenn sich Daten geändert haben.

Syntax

require "$lbpbindir/libs/S4LJson.pm";
 
# Will send debugging to STDERR
$Stats4Lox::JSON::DEBUG = 1;
# Will send dumps (Data::Dumper) of objects to STDERR
$Stats4Lox::JSON::DUMP = 1;
 
 
my $jsonparser = Stats4Lox::JSON->new();
my $config = $jsonparser->open(filename => "/tmp/nofile.json", writeonclose => 0, readonly => 0);
$jsonparser->write();
my $current_filename = $jsonparser->filename();
$jsonparser->find($object, $condition);
$jsonparser->dump($object, $comment);


Parameter

Parameter Optional Default Beschreibung
filename JSON-Datei, die geöffnet werden soll. Existiert die Datei nicht, wird sie erzeugt.
writeonclosex 0 Wenn 0, muss explizit write aufgerufen werden. Es kann auch mehrmals write aufgerufen werden.

Wenn 1, wird im Destruktor automatisch gespeichert.
readonly x 0 Wenn 1, wird niemals ein Schreibvorgang durchgeführt.

Grundsätzlich schreibt die Funktion nur, wenn tatsächlich Daten geändert wurden, auch bei explizitem Aufruf von write.

Bei writeonclose ⇒ 1 wird nicht sofort geschrieben, sondern, wenn der Destruktor aufgerufen wird, d.h. in der Regel 

  • beim Verlassen des Scopes des $jsonparser-Objekts (deswegen am besten $jsonparser im Hauptprogramm(weit oben definieren)
  • beim Beenden des Programms

Open and change JSON

#!/usr/bin/perl
use LoxBerry::System;
require "$lbpbindir/libs/S4LJson.pm";
 
$Stats4Lox::JSON::DEBUG = 1;
$Stats4Lox::JSON::DUMP = 1;
 
my $jsonparser = Stats4Lox::JSON->new();
my $config = $jsonparser->open(filename => "/tmp/nofile.json", writeonclose => 0);
if (!$config) {
    print "Error loading file\n";
} else {
    print "File loaded\n";
}
 
print "Version of the file: $config->{Version}\n";
 
# Simple values
$config->{Info} = "Write data to JSON";
$config->{Version} = $config->{Version} + 1;
 
# Creating  
$config->{MINISERVER_HASH}->{1}->{Name} = "MSOG";
$config->{MINISERVER_HASH}->{2}->{Name} = "MSUG";
 
my @colors = ( "red", "blue", "green");
$config->{Colors} = \@colors;
 
my %settings = ( "ip" => "192.168.0.1",
                 "port" => "8000",
                 "protocol" => "tcp"
                );
$config->{Server} = \%settings;
 
$jsonparser->write();

JSON Result 

{
   "Colors" : [
      "red",
      "blue",
      "green"
   ],
   "Info" : "Write data to JSON",
   "MINISERVERS" : {
      "1" : {
         "Name" : "MSOG"
      },
      "2" : {
         "Name" : "MSUG"
      }
   },
   "Server" : {
      "ip" : "192.168.0.1",
      "port" : "8000",
      "protocol" : "tcp"
   },
   "Version" : 1
}

Search in JSON

The module implements a find function to search for elements an hashes and arrays.

my @result = $jsonparser->find(@/%element_to_search, $condition);

Parameter Description
@/%element_to_searchThe element_to_search must be an ARRAY (@something) or a HASH (%something).

Most likely you would send an object of the readed JSON, e.g. $config→{colors}
$condition This must be a string that contains a valid Perl if condition, that is evaluated. \$_ is the current object in the condition.

Keep an eye on string interpolation:

* Non-escaped sequences are interpolated BEFORE of the function evaluation
* Escaped sequences are interpolated IN the funcation evaluation

Conditions must be able to be evaluated inside an if statement. Precisely it is evaluated as if ($perl_condition).

In the $condition, the $_ is the current evaluated object of the array/hash. Therefore, in your $condition you have to escape the element with \$_ .

In an ARRAY, \$_ therefore is the value of the array.

In an HASH, \$_ is the current evaluated object.

Both datatypes return an array with a list of the keys. In an ARRAY evaluation, the returning array holds the key number (0, 1, 2 etc). In an HASH evaluation, the returning array holds the key name of the found elements.

Double-check escaping in your condition!

my $house = "green";

my $condition_doublequotes = "\$_ eq \"$house\"";  → The function evaluates $_ eq "green" → OK

my $condition_doublequotes = "\$_ eq \$house"; → The function evaluates $_ eq $house. As $house is not defined in the function, it will raise an exception.

my $condition_singlequoutes = '$_ eq "' . $house . '"';  → The function evaluates $_ eq "green" → OK

my $condition_singlequoutes = '$_ eq "$house"';  → The function evaluates $_ eq "$house". As $house is not defined in the function, it will raise an exception.



See the examples. 

#!/usr/bin/perl
use LoxBerry::System;
require "$lbpbindir/libs/S4LJson.pm";
 
$Stats4Lox::JSON::DUMP = 1;
 
 
 
# Creating a hash (1, 2 are names, not array elements)
$config->{MINISERVER_HASH}->{1}->{Name} = "MSOG";
$config->{MINISERVER_HASH}->{2}->{Name} = "MSUG";
 
# HASH search
# Returns an array with the hash names
my @result = $jsonparser->find($config->{MINISERVER_HASH}, "\$_->{Name} eq 'MSUG'");
# Dump the result to STDERR
$jsonparser->dump(\@result, "Result of Hash search");
 
# ARRAY search
# Returns an array with the element indexes
my @result = $jsonparser->find($config->{Colors}, "\$_ eq 'red' or \$_ eq 'green'");
# Dump the result to STDERR
$jsonparser->dump(\@result, "Result of Array search");