This is a backport of QJson from Qt5.2.1 to Qt4.8.
It is based on the initial backport from https://github.com/5in4/qjson-backport
Just add all *.cpp and *.h files to your project and add includepath. Not need to build as separate external library.
You can use standart Qt5 include syntax, like:
#include <QJsonDocument>
#include <QJsonObject>
#include <QJsonArray>
The license is the same, obviously, as for the library in Qt itself, LGPL 2.1. All sources include details.