Events are used in distributed systems for monitoring purposes since internal states are often hidden from the observer. Composite events are recursively defined events upon conditions involving other events and occur whenever those conditions are satisfied. In systems where conditions on the occurrences of multiple events need to be monitored, composite events are extremely useful for clarifying the se-mantics of the conditions to be monitored and the corre-lation of simpler events. In this paper, we present a com-posite event package in Java called JEM, which accepts and monitors the composite events specified in a Java Event Specification Language(JESL). JESL is developed based on a unified formalism presented in [14] for composite event and timing constraint specification. The system structure of JEM and its major components, i.e. Event Subscrip-tion Server, Composite Event Compiler and Monitor, are de-scribed in the paper. Some performance experiment results and the scalability issue of JEM are also discussed. The pa-per also demonstrates the practicality of JEM by explaining how a network event correlation application is built using JEM.