Class: Oj::ScHandler

Inherits:
Object
  • Object
show all
Defined in:
lib/oj/schandler.rb

Overview

A Simple Callback Parser (SCP) for JSON. The Oj::ScHandler class should be subclassed and then used with the Oj.sc_parse() method. The Scp methods will then be called as the file is parsed. The handler does not have to be a subclass of the ScHandler class as long as it responds to the desired methods.

To make the desired methods active while parsing the desired method should be made public in the subclasses. If the methods remain private they will not be called during parsing.

def hash_start(); end
def hash_end(); end
def hash_key(key); end
def hash_set(h, key, value); end
def array_start(); end
def array_end(); end
def array_append(a, value); end
def add_value(value); end

As certain elements of a JSON document are reached during parsing the callbacks are called. The parser helps by keeping track of objects created by the callbacks but does not create those objects itself.

hash_start

When a JSON object element starts the hash_start() callback is called if public. It should return what ever Ruby Object is to be used as the element that will later be included in the hash_set() callback.

  hash_end

At the end of a JSON object element the hash_end() callback is called if
public.

  hash_key

When a hash key is encountered the hash_key() method is called with the parsed hash value key. The return value from the call is then used as the key in the key-value pair that follows.

hash_set

When a key value pair is encountered during parsing the hash_set() callback is called if public. The first element will be the object returned from the enclosing hash_start() callback. The second argument is the key and the last is the value.

array_start

When a JSON array element is started the array_start() callback is called if public. It should return what ever Ruby Object is to be used as the element that will later be included in the array_append() callback.

array_end

At the end of a JSON array element the array_end() callback is called if public.

array_append

When a element is encountered that is an element of an array the array_append() callback is called if public. The first argument to the callback is the Ruby object returned from the enclosing array_start() callback.

add_value

The handler is expected to handle multiple JSON elements in one stream, file, or string. When a top level JSON has been read completely the add_value() callback is called. Even if only one element was ready this callback returns the Ruby object that was constructed during the parsing.

Examples:


require 'oj'

class MyHandler < ::Oj::ScHandler
  def hash_start
    {}
  end

  def hash_set(h,k,v)
    h[k] = v
  end

  def array_start
    []
  end

  def array_append(a,v)
    a << v
  end

  def add_value(v)
    p v
  end

  def error(message, line, column)
    p "ERROR: #{message}"
  end
end

File.open('any.json', 'r') do |f|
  Oj.sc_parse(MyHandler.new, f)
end

Instance Method Summary collapse

Constructor Details

#initialize ⇒ ScHandler

Create a new instance of the ScHandler class.



109
110
 
# File 'lib/oj/schandler.rb', line 109

def initialize()
end