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Description
- -This is a implementation of the JSON specification -according to RFC 4627 www.ietf.org/rfc/rfc4627.txt -. Starting from version 1.0.0 on there will be two variants available:
--
-
A pure ruby variant, that relies on the iconv and the stringscan -extensions, which are both part of the ruby standard library.
- -
-
The quite a bit faster C extension variant, which is in parts implemented -in C and comes with its own unicode conversion functions and a parser -generated by the ragel state machine compiler www.cs.queensu.ca/~thurston/ragel -.
-
Both variants of the JSON generator generate UTF-8 -character sequences by default. If an :ascii_only option with a true value -is given, they escape all non-ASCII and control characters with uXXXX -escape sequences, and support UTF-16 surrogate pairs in order to be able to -generate the whole range of unicode code points.
- -All strings, that are to be encoded as JSON -strings, should be UTF-8 byte sequences on the Ruby side. To encode raw -binary strings, that aren’t UTF-8 encoded, please use the -to_json_raw_object method of String (which produces an object, that -contains a byte array) and decode the result on the receiving endpoint.
- -The JSON parsers can parse UTF-8, UTF-16BE, -UTF-16LE, UTF-32BE, and UTF-32LE JSON documents -under Ruby 1.8. Under Ruby 1.9 they take advantage of Ruby’s M17n features -and can parse all documents which have the correct String#encoding set. If -a document string has ASCII-8BIT as an encoding the parser attempts to -figure out which of the UTF encodings from above it is and trys to parse -it.
- -Installation
- -It’s recommended to use the extension variant of JSON, because it’s faster than the pure ruby variant. -If you cannot build it on your system, you can settle for the latter.
- -Just type into the command line as root:
- -# rake install- -
The above command will build the extensions and install them on your -system.
- -# rake install_pure- -
or
- -# ruby install.rb- -
will just install the pure ruby implementation of JSON.
- -If you use Rubygems you can type
- -# gem install json- -
instead, to install the newest JSON version.
- -There is also a pure ruby json only variant of the gem, that can be -installed with:
- -# gem install json_pure- -
Compiling the extensions yourself
- -If you want to build the extensions yourself you need rake:
- -You can get it from rubyforge: - http://rubyforge.org/projects/rake - -or just type - -# gem install rake - -for the installation via rubygems.- -
If you want to create the parser.c file from its parser.rl file or draw -nice graphviz images of the state machines, you need ragel from: www.cs.queensu.ca/~thurston/ragel
- -Usage
- -To use JSON you can
- -require 'json'- -
to load the installed variant (either the extension ‘json’ or the pure -variant ‘json_pure’). If you have installed the extension variant, you can -pick either the extension variant or the pure variant by typing
- -require 'json/ext'- -
or
- -require 'json/pure'- -
Now you can parse a JSON document into a ruby data -structure by calling
- -JSON.parse(document)- -
If you want to generate a JSON document from a ruby -data structure call
- -JSON.generate(data)- -
You can also use the pretty_generate method (which formats the output more -verbosely and nicely) or fast_generate (which doesn’t do any of the -security checks generate performs, e. g. nesting deepness checks).
- -To create a valid JSON document you have to make -sure, that the output is embedded in either a JSON -array [] or a JSON object {}. The easiest way to do -this, is by putting your values in a Ruby Array or Hash instance.
- -There are also the JSON and JSON[] methods which -use parse on a String or generate a JSON document -from an array or hash:
- -document = JSON 'test' => 23 # => "{\"test\":23}"
-document = JSON['test'] => 23 # => "{\"test\":23}"
-
-and
- -data = JSON '{"test":23}' # => {"test"=>23}
-data = JSON['{"test":23}'] # => {"test"=>23}
-
-You can choose to load a set of common additions to ruby core’s objects if -you
- -require 'json/add/core'- -
After requiring this you can, e. g., serialise/deserialise Ruby ranges:
- -JSON JSON(1..10) # => 1..10- -
To find out how to add JSON support to other or -your own classes, read the section “More Examples” below.
- -To get the best compatibility to rails’ JSON -implementation, you can
- -require 'json/add/rails'- -
Both of the additions attempt to require ‘json’ (like above) first, if it -has not been required yet.
- -More Examples
- -To create a JSON document from a ruby data -structure, you can call JSON.generate like that:
- -json = JSON.generate [1, 2, {"a"=>3.141}, false, true, nil, 4..10]
-# => "[1,2,{\"a\":3.141},false,true,null,\"4..10\"]"
-
-To get back a ruby data structure from a JSON -document, you have to call JSON.parse on it:
- -JSON.parse json
-# => [1, 2, {"a"=>3.141}, false, true, nil, "4..10"]
-
-Note, that the range from the original data structure is a simple string -now. The reason for this is, that JSON doesn’t -support ranges or arbitrary classes. In this case the json library falls -back to call Object#to_json, which is the same as to_s.to_json.
- -It’s possible to add JSON support serialization to -arbitrary classes by simply implementing a more specialized version of the -to_json method, that should return a JSON object (a -hash converted to JSON with to_json) like this -(don’t forget the *a for all the arguments):
- -class Range
- def to_json(*a)
- {
- 'json_class' => self.class.name, # = 'Range'
- 'data' => [ first, last, exclude_end? ]
- }.to_json(*a)
- end
-end
-
-The hash key ‘json_class’ is the class, that will be asked to deserialise -the JSON representation later. In this case it’s -‘Range’, but any namespace of the form ‘A::B’ or ‘::A::B’ will do. All -other keys are arbitrary and can be used to store the necessary data to -configure the object to be deserialised.
- -If a the key ‘json_class’ is found in a JSON -object, the JSON parser checks if the given class -responds to the json_create class method. If so, it is called with the JSON object converted to a Ruby hash. So a range can -be deserialised by implementing Range.json_create like this:
- -class Range - def self.json_create(o) - new(*o['data']) - end -end- -
Now it possible to serialise/deserialise ranges as well:
- -json = JSON.generate [1, 2, {"a"=>3.141}, false, true, nil, 4..10]
-# => "[1,2,{\"a\":3.141},false,true,null,{\"json_class\":\"Range\",\"data\":[4,10,false]}]"
-JSON.parse json
-# => [1, 2, {"a"=>3.141}, false, true, nil, 4..10]
-
-JSON.generate always creates the -shortest possible string representation of a ruby data structure in one -line. This is good for data storage or network protocols, but not so good -for humans to read. Fortunately there's also JSON.pretty_generate (or JSON.pretty_generate) that -creates a more readable output:
- -puts JSON.pretty_generate([1, 2, {"a"=>3.141}, false, true, nil, 4..10])
-[
- 1,
- 2,
- {
- "a": 3.141
- },
- false,
- true,
- null,
- {
- "json_class": "Range",
- "data": [
- 4,
- 10,
- false
- ]
- }
-]
-
-There are also the methods Kernel#j for generate, and Kernel#jj for -pretty_generate output to the console, that work analogous to Core Ruby’s p -and the pp library’s pp methods.
- -The script tools/server.rb contains a small example if you want to test, -how receiving a JSON object from a webrick server -in your browser with the javasript prototype library www.prototypejs.org works.
- -Speed Comparisons
- -I have created some benchmark results (see the benchmarks/data-p4-3Ghz -subdir of the package) for the JSON-parser to estimate the speed up in the -C extension:
- -Comparing times (call_time_mean): - 1 ParserBenchmarkExt#parser 900 repeats: - 553.922304770 ( real) -> 21.500x - 0.001805307 - 2 ParserBenchmarkYAML#parser 1000 repeats: - 224.513358139 ( real) -> 8.714x - 0.004454078 - 3 ParserBenchmarkPure#parser 1000 repeats: - 26.755020642 ( real) -> 1.038x - 0.037376163 - 4 ParserBenchmarkRails#parser 1000 repeats: - 25.763381731 ( real) -> 1.000x - 0.038814780 - calls/sec ( time) -> speed covers - secs/call- -
In the table above 1 is JSON::Ext::Parser, 2 is YAML.load with YAML -compatbile JSON document, 3 is is JSON::Pure::Parser, and 4 is -ActiveSupport::JSON.decode. The ActiveSupport JSON-decoder converts the -input first to YAML and then uses the YAML-parser, the conversion seems to -slow it down so much that it is only as fast as the JSON::Pure::Parser!
- -If you look at the benchmark data you can see that this is mostly caused by -the frequent high outliers - the median of the Rails-parser runs is still -overall smaller than the median of the JSON::Pure::Parser runs:
- -Comparing times (call_time_median): - 1 ParserBenchmarkExt#parser 900 repeats: - 800.592479481 ( real) -> 26.936x - 0.001249075 - 2 ParserBenchmarkYAML#parser 1000 repeats: - 271.002390644 ( real) -> 9.118x - 0.003690004 - 3 ParserBenchmarkRails#parser 1000 repeats: - 30.227910865 ( real) -> 1.017x - 0.033082008 - 4 ParserBenchmarkPure#parser 1000 repeats: - 29.722384421 ( real) -> 1.000x - 0.033644676 - calls/sec ( time) -> speed covers - secs/call- -
I have benchmarked the JSON-Generator as well. This generated a few more -values, because there are different modes that also influence the achieved -speed:
- -Comparing times (call_time_mean): - 1 GeneratorBenchmarkExt#generator_fast 1000 repeats: - 547.354332608 ( real) -> 15.090x - 0.001826970 - 2 GeneratorBenchmarkExt#generator_safe 1000 repeats: - 443.968212317 ( real) -> 12.240x - 0.002252414 - 3 GeneratorBenchmarkExt#generator_pretty 900 repeats: - 375.104545883 ( real) -> 10.341x - 0.002665923 - 4 GeneratorBenchmarkPure#generator_fast 1000 repeats: - 49.978706968 ( real) -> 1.378x - 0.020008521 - 5 GeneratorBenchmarkRails#generator 1000 repeats: - 38.531868759 ( real) -> 1.062x - 0.025952543 - 6 GeneratorBenchmarkPure#generator_safe 1000 repeats: - 36.927649925 ( real) -> 1.018x 7 (>=3859) - 0.027079979 - 7 GeneratorBenchmarkPure#generator_pretty 1000 repeats: - 36.272134441 ( real) -> 1.000x 6 (>=3859) - 0.027569373 - calls/sec ( time) -> speed covers - secs/call- -
In the table above 1-3 are JSON::Ext::Generator methods. 4, 6, and 7 are JSON::Pure::Generator methods and 5 is -the Rails JSON generator. It is now a bit faster -than the generator_safe and generator_pretty methods of the pure variant -but slower than the others.
- -To achieve the fastest JSON document output, you -can use the fast_generate method. Beware, that this will disable the -checking for circular Ruby data structures, which may cause JSON to go into an infinite loop.
- -Here are the median comparisons for completeness’ sake:
- -Comparing times (call_time_median): - 1 GeneratorBenchmarkExt#generator_fast 1000 repeats: - 708.258020939 ( real) -> 16.547x - 0.001411915 - 2 GeneratorBenchmarkExt#generator_safe 1000 repeats: - 569.105020353 ( real) -> 13.296x - 0.001757145 - 3 GeneratorBenchmarkExt#generator_pretty 900 repeats: - 482.825371244 ( real) -> 11.280x - 0.002071142 - 4 GeneratorBenchmarkPure#generator_fast 1000 repeats: - 62.717626652 ( real) -> 1.465x - 0.015944481 - 5 GeneratorBenchmarkRails#generator 1000 repeats: - 43.965681162 ( real) -> 1.027x - 0.022745013 - 6 GeneratorBenchmarkPure#generator_safe 1000 repeats: - 43.929073409 ( real) -> 1.026x 7 (>=3859) - 0.022763968 - 7 GeneratorBenchmarkPure#generator_pretty 1000 repeats: - 42.802514491 ( real) -> 1.000x 6 (>=3859) - 0.023363113 - calls/sec ( time) -> speed covers - secs/call- -
Author
- -Florian Frank <flori@ping.de>
- -License
- -Ruby License, see the COPYING file included in the source distribution. The -Ruby License includes the GNU General Public License (GPL), Version 2, so -see the file GPL as well.
- -Download
- -The latest version of this library can be downloaded at
- - -Online Documentation should be located at
- - -