JSON path - extract all maps - json

Question

I am trying to write a JSON path expression to extract all maps and submaps from a JSON structure. Considering the JSON:
{
"k1":"v1",
"arr": ["1","2","3" ,["7","8"] ],
"submap":
{
"a":"b",
"c":"d"
},
"submap_2":
{
"a_2":"b",
"c_2":"d",
"nested": { "x":"y" }
}
}
I would want to extract the elements "submap", "submap_2", "nested".
I've tried JSONPath expressions like:
$..*[?(#.length()>0 && #.*[0] empty true)]
This returns the structures I want, but also returns [ "7","8" ]. Is there any way to do this with JSONPath or is this better done in code?
(A neat JSONPath testing tools is here: http://jsonpath.herokuapp.com/)
(The specific implementation that I'm using is this one: https://github.com/jayway/JsonPath )

Answer 1

jq queries are often very similar to JSONPath queries, and I would strongly recommend that if at all possible you consider using jq.
Assuming the example data is in a file named example.json, the following invocation of jq produces the result you requested:
$ jq 'path(.. | select(type=="object")) | .[-1] | select(.)' example.json
"submap"
"submap_2"
"nested"
The output of the first filter (path(....)) consists of the full path expressions of the paths to all the JSON objects, including the top-level object itself. The remaining filters are needed to produce the exact output you requested. In practice, though, the full path expressions are probably more useful, so it might be helpful for you to see the output produced by the first filter:
$ jq -c 'path(.. | select(type=="object"))' example.json
[]
["submap"]
["submap_2"]
["submap_2","nested"]