You can extend the RESTful Web Service Using JSON sample in the following way:
By default, the back-end message flow, MqXmlApp.msgflow, stores data in a shared variable, see Long-lived variables in the IBM Integration Bus documentation. However, the lifetime of a shared variable is the same as the length of time that the flow is deployed, therefore, if the back-end flow is undeployed or redeployed, the variable is reset, and its content is lost.
The data can be persisted by the inclusion of a database, see Working with databases in the IBM Integration Bus documentation.