An easy, streaming way to generate JSON.
gem install json-write-stream
require 'json-write-stream'
There are two types of JSON write stream: one that uses blocks and yield
to delimit arrays and objects, and one that's purely stateful. Here are two examples that produce the same output:
Yielding:
stream = StringIO.new
JsonWriteStream.from_stream(stream) do |writer|
writer.write_object do |obj_writer|
obj_writer.write_key_value('foo', 'bar')
obj_writer.write_array('baz') do |arr_writer|
arr_writer.write_element('goo')
end
end
end
Stateful:
stream = StringIO.new
writer = JsonWriteStream.from_stream(stream)
writer.write_object
writer.write_key_value('foo', 'bar')
writer.write_array('baz')
writer.write_element('goo')
writer.close # automatically adds closing punctuation for all nested types
Output:
stream.string # => {"foo":"bar","baz":["goo"]}
As far as yielding writers go, the example above contains everything you need. The stream will be automatically closed when the outermost block terminates.
Stateful writers have a number of additional methods:
stream = StringIO.new
writer = JsonWriteStream.from_stream(stream)
writer.write_object
writer.in_object? # => true, currently writing an object
writer.in_array? # => false, not currently writing an array
writer.eos? # => false, the stream is open and the outermost object hasn't been closed yet
writer.close_object # explicitly close the current object
writer.eos? # => true, the outermost object has been closed
writer.write_array # => raises JsonWriteStream::EndOfStreamError
writer.close_array # => raises JsonWriteStream::NotInArrayError
writer.closed? # => false, the stream is still open
writer.close # close the stream
writer.closed? # => true, the stream has been closed
JsonWriteStream also supports streaming to a file via the open
method:
Yielding:
JsonWriteStream.open('path/to/file.json') do |writer|
writer.write_object do |obj_writer|
...
end
end
Stateful:
writer = JsonWriteStream.open('path/to/file.json')
writer.write_object
...
writer.close
JsonWriteStream supports generating "pretty" JSON, i.e. JSON formatted in a more human-readable way. Currently only the stateful writer supports pretty generation. Example:
stream = StringIO.new
writer = JsonWriteStream.from_stream(stream, pretty: true)
writer.write_object
writer.write_key_value('foo', 'bar')
writer.write_array('baz')
writer.write_element('goo')
writer.close
Now stream.string
will contain
{
"foo": "bar",
"baz": [
"goo"
]
}
No external requirements.
bundle exec rake
should do the trick. Alternatively you can run bundle exec rspec
, which does the same thing.
- Cameron C. Dutro: http://github.com/camertron