Disconnected mobile ad hoc networks (or D-MANETs) are partially or intermittently connected wireless networks, in which continuous end-to-end connectivity between mobile nodes is not guaranteed. The ability to self-form and self-manage brings great opportunities for D-MANETs, but developing distributed applications capable of running in such networks remains a major challenge. A middleware system is thus needed between network level and application level in order to ease application development, and help developers take advantage of D-MANETs' unique features. In this paper, we introduce JION (JavaSpaces Implementation for Opportunistic Networks), a coordination middleware specifically designed for D-MANETs, and with which pre-existing or new JavaSpaces-based applications can be easily deployed in such networks.