mjCoAP: An open-source lightweight java CoAP library for internet of things applications

The Internet of Things (IoT) is expected to pervasively interconnect more than 50 billion devices, denoted as "smart objects", by 2020 in an Internet-like structure, which will extend the current Internet, enabling new forms of interaction between physical objects and people. The IoT will be made up of heterogeneous devices, featuring extremely diverse capabilities, in terms of computational power, connectivity, availability, and mobility. In such a scenario, characterized by the heterogeneity and large number of involved devices, in order to effectively allow and foster the growth of new applications and services, it is necessary to provide appropriate standards that can guarantee full interoperability among existing hosts and IoT nodes. Standardization organizations, such as the Internet Engineering Task Force (IETF), and research projects are chartered to bring IP to smart objects and to define suitable application-layer and security protocols for IoT scenarios. In order to cope with the limitations of smart objects, the IETF CoRE Working Group has defined the Constrained Application Protocol (CoAP), a standard application-layer protocol for use with constrained nodes and constrained networks. In this work, we present mjCoAP, an open source lightweight Java-based implementation of CoAP, which aims at simplifying the development of CoAP-based IoT applications. The mjCoAP library is fully RFC-compliant and integrates several IETF CoRE WG specifications, such as blockwise transfers, resource observing, and HTTP/CoAP mapping. We also present some application scenarios and we describe how they can be easily implemented based on mjCoAP.