During the period of my internship at WSO2 I had the oppotunity of working on Apache Axis2 project. I implemented JSON support in Apache Axis2 after some research to understand the architecture of the Axis2 engine.
Apache Axis2 is a Web services stack that delivers incoming messages into target applications. In other words it is basically a SOAP processing engine. In most cases, these messages are SOAP messages. In addition, it is also possible to send REST messages through Axis2. Both types of messages use XML as their data exchangeable format. So if we can use XML as a format, JSON is also a good replacement for XML in some applications.
To read more on this implementation, read the article, JSON Support for Apache Axis2 in the WSO2 Oxygen Tank.