I want to read .json file by http api

Any of them will allow you to fetch the file...

Richard's correct, both the Dropbox API v1 (a.k.a. Core API) and API v2 allow you to access file content. We recommend using an SDK whenever possible (in which case, you should refer to the specific documentation/tutorial), but the relevant HTTP endpoints are:

for v1, /files (GET): https://www.dropbox.com/developers-v1/core/docs#files-GET
for v2, /files/download: https://www.dropbox.com/developers/documentation/http/documentation#files-download