下面是根据@gertas的回答修改的中间件解决方案。这个解决方案不是Rails特有的——它应该适用于任何Rack应用程序。

这里使用的中间件技术，使用#each，由Eifion Bedford在ASCIIcasts 151: Rack middleware中进行了解释。

这段代码放在app/middleware/pretty_json_response.rb中:

class PrettyJsonResponse

  def initialize(app)
    @app = app
  end

  def call(env)
    @status, @headers, @response = @app.call(env)
    [@status, @headers, self]
  end

  def each(&block)
    @response.each do |body|
      if @headers["Content-Type"] =~ /^application\/json/
        body = pretty_print(body)
      end
      block.call(body)
    end
  end

  private

  def pretty_print(json)
    obj = JSON.parse(json)  
    JSON.pretty_unparse(obj)
  end

end

要打开它，将其添加到config/environments/test中。config/environments/development.rb:

config.middleware.use "PrettyJsonResponse"

正如@gertas在他的解决方案版本中警告的那样，避免在生产中使用它。有点慢。

使用Rails 4.1.6测试。

看看Awesome Print吧。将JSON字符串解析为Ruby Hash，然后用ap显示它，如下所示:

require "awesome_print"
require "json"

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

ap(JSON.parse(json))

通过以上，你会看到:

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

Awesome Print还会添加一些Stack Overflow无法显示的颜色。

# example of use:
a_hash = {user_info: {type: "query_service", e_mail: "my@email.com", phone: "+79876543322"}, cars_makers: ["bmw", "mitsubishi"], car_models: [bmw: {model: "1er", year_mfc: 2006}, mitsubishi: {model: "pajero", year_mfc: 1997}]}
pretty_html = a_hash.pretty_html

# include this module to your libs:
module MyPrettyPrint
    def pretty_html indent = 0
        result = ""
        if self.class == Hash
            self.each do |key, value|
                result += "#{key}: #{[Array, Hash].include?(value.class) ? value.pretty_html(indent+1) : value}"
            end
        elsif self.class == Array
            result = "[#{self.join(', ')}]"
        end
        "#{result}"
    end

end

class Hash
    include MyPrettyPrint
end

class Array
    include MyPrettyPrint
end

我能想到的最简单的例子:

my_json = '{ "name":"John", "age":30, "car":null }'
puts JSON.pretty_generate(JSON.parse(my_json))

Rails控制台示例:

core dev 1555:0> my_json = '{ "name":"John", "age":30, "car":null }'
=> "{ \"name\":\"John\", \"age\":30, \"car\":null }"
core dev 1556:0> puts JSON.pretty_generate(JSON.parse(my_json))
{
  "name": "John",
  "age": 30,
  "car": null
}
=> nil

如果你想要处理active_record对象，puts就足够了。

例如:

没有了

2.6.0 (main):0 > User.first.to_json
  User Load (0.4ms)  SELECT  "users".* FROM "users" ORDER BY "users"."id" ASC LIMIT $1  [["LIMIT", 1]]
=> "{\"id\":1,\"admin\":true,\"email\":\"admin@gmail.com\",\"password_digest\":\"$2a$10$TQy3P7NT8KrdCzliNUsZzuhmo40LGKoth2hwD3OI.kD0lYiIEwB1y\",\"created_at\":\"2021-07-20T08:34:19.350Z\",\"updated_at\":\"2021-07-20T08:34:19.350Z\",\"name\":\"Arden Stark\"}"

与使

2.6.0 (main):0 > puts User.first.to_json
  User Load (0.3ms)  SELECT  "users".* FROM "users" ORDER BY "users"."id" ASC LIMIT $1  [["LIMIT", 1]]
{"id":1,"admin":true,"email":"admin@gmail.com","password_digest":"$2a$10$TQy3P7NT8KrdCzliNUsZzuhmo40LGKoth2hwD3OI.kD0lYiIEwB1y","created_at":"2021-07-20T08:34:19.350Z","updated_at":"2021-07-20T08:34:19.350Z","name":"Arden Stark"}
=> nil

如果你处理json数据，json。Pretty_generate是一个很好的替代方案

例子:

obj = {foo: [:bar, :baz], bat: {bam: 0, bad: 1}}
json = JSON.pretty_generate(obj)
puts json

输出:

{
  "foo": [
    "bar",
    "baz"
  ],
  "bat": {
    "bam": 0,
    "bad": 1
  }
}

如果是在ROR项目中，我总是喜欢使用gem pry-rails在rails控制台中格式化我的代码，而不是awesome_print，这太冗长了。

撬轨的例子:

它还有语法高亮显示。

使用<pre> HTML代码和pretty_generate是一个好技巧:

<%
  require 'json'

  hash = JSON[{hey: "test", num: [{one: 1, two: 2, threes: [{three: 3, tthree: 33}]}]}.to_json] 
%>

<pre>
  <%=  JSON.pretty_generate(hash) %>
</pre>