Chapter 6. Monitors and Monitoring

Monitoring is an essential activity for a management application. Instrumentation provides raw information about the status of an application or device. Administrators specify acceptable values, or ranges of values, for the status information the instrumentation provides. In many cases the administrator would also like to specify an action to take if the status information indicates a problem. For example, an important aspect of managing a database is ensuring that the file system that holds the database's tables has sufficient space; if the file system begins to fill up, an e-mail or a page needs to be sent to the administrator so that the appropriate action ”for example, extending the file system or archiving data ”can be taken.

Management applications use monitors to automate administration; they configure their monitors to check an application's status information periodically and send notifications if the values don't meet the administrator's specifications. The management application reacts to those notifications, perhaps by taking some prearranged corrective action or by sending e-mail to, or even paging, a human administrator.

Because monitoring plays such a central role in management applications, JMX provides a set of monitor services that simplify the task of building sophisticated management applications.