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How to "pretty" format JSON output in Ruby on Rails


Question

I would like my JSON output in Ruby on Rails to be "pretty" or nicely formatted.

Right now, I call to_json and my JSON is all on one line. At times this can be difficult to see if there is a problem in the JSON output stream.

Is there way to configure to make my JSON "pretty" or nicely formatted in Rails?

2020/03/02
1
642
3/2/2020 3:16:42 AM

Accepted Answer

Use the pretty_generate() function, built into later versions of JSON. For example:

require 'json'
my_object = { :array => [1, 2, 3, { :sample => "hash"} ], :foo => "bar" }
puts JSON.pretty_generate(my_object)

Which gets you:

{
  "array": [
    1,
    2,
    3,
    {
      "sample": "hash"
    }
  ],
  "foo": "bar"
}
2016/07/25
1019
7/25/2016 10:33:27 PM

The <pre> tag in HTML, used with JSON.pretty_generate, will render the JSON pretty in your view. I was so happy when my illustrious boss showed me this:

<% if @data.present? %>
   <pre><%= JSON.pretty_generate(@data) %></pre>
<% end %>
2019/05/29

Thanks to Rack Middleware and Rails 3 you can output pretty JSON for every request without changing any controller of your app. I have written such middleware snippet and I get nicely printed JSON in browser and curl output.

class PrettyJsonResponse
  def initialize(app)
    @app = app
  end

  def call(env)
    status, headers, response = @app.call(env)
    if headers["Content-Type"] =~ /^application\/json/
      obj = JSON.parse(response.body)
      pretty_str = JSON.pretty_unparse(obj)
      response = [pretty_str]
      headers["Content-Length"] = pretty_str.bytesize.to_s
    end
    [status, headers, response]
  end
end

The above code should be placed in app/middleware/pretty_json_response.rb of your Rails project. And the final step is to register the middleware in config/environments/development.rb:

config.middleware.use PrettyJsonResponse

I don't recommend to use it in production.rb. The JSON reparsing may degrade response time and throughput of your production app. Eventually extra logic such as 'X-Pretty-Json: true' header may be introduced to trigger formatting for manual curl requests on demand.

(Tested with Rails 3.2.8-5.0.0, Ruby 1.9.3-2.2.0, Linux)

2016/09/10

If you want to:

  1. Prettify all outgoing JSON responses from your app automatically.
  2. Avoid polluting Object#to_json/#as_json
  3. Avoid parsing/re-rendering JSON using middleware (YUCK!)
  4. Do it the RAILS WAY!

Then ... replace the ActionController::Renderer for JSON! Just add the following code to your ApplicationController:

ActionController::Renderers.add :json do |json, options|
  unless json.kind_of?(String)
    json = json.as_json(options) if json.respond_to?(:as_json)
    json = JSON.pretty_generate(json, options)
  end

  if options[:callback].present?
    self.content_type ||= Mime::JS
    "#{options[:callback]}(#{json})"
  else
    self.content_type ||= Mime::JSON
    json
  end
end
2014/04/11

Check out Awesome Print. Parse the JSON string into a Ruby Hash, then display it with ap like so:

require "awesome_print"
require "json"

json = '{"holy": ["nested", "json"], "batman!": {"a": 1, "b": 2}}'

ap(JSON.parse(json))

With the above, you'll see:

{
  "holy" => [
    [0] "nested",
    [1] "json"
  ],
  "batman!" => {
    "a" => 1,
    "b" => 2
  }
}

Awesome Print will also add some color that Stack Overflow won't show you.

2019/11/30

If you find that the pretty_generate option built into Ruby's JSON library is not "pretty" enough, I recommend my own NeatJSON gem for your formatting.

To use it:

gem install neatjson

and then use

JSON.neat_generate

instead of

JSON.pretty_generate

Like Ruby's pp it will keep objects and arrays on one line when they fit, but wrap to multiple as needed. For example:

{
  "navigation.createroute.poi":[
    {"text":"Lay in a course to the Hilton","params":{"poi":"Hilton"}},
    {"text":"Take me to the airport","params":{"poi":"airport"}},
    {"text":"Let's go to IHOP","params":{"poi":"IHOP"}},
    {"text":"Show me how to get to The Med","params":{"poi":"The Med"}},
    {"text":"Create a route to Arby's","params":{"poi":"Arby's"}},
    {
      "text":"Go to the Hilton by the Airport",
      "params":{"poi":"Hilton","location":"Airport"}
    },
    {
      "text":"Take me to the Fry's in Fresno",
      "params":{"poi":"Fry's","location":"Fresno"}
    }
  ],
  "navigation.eta":[
    {"text":"When will we get there?"},
    {"text":"When will I arrive?"},
    {"text":"What time will I get to the destination?"},
    {"text":"What time will I reach the destination?"},
    {"text":"What time will it be when I arrive?"}
  ]
}

It also supports a variety of formatting options to further customize your output. For example, how many spaces before/after colons? Before/after commas? Inside the brackets of arrays and objects? Do you want to sort the keys of your object? Do you want the colons to all be lined up?

2019/11/30

Source: https://stackoverflow.com/questions/86653
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