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Monitor Service


One of the essential activities for a management application is monitoring.  JMX provides a set of monitoring services, each capable of observing attributes of specific Java types.  Any number of attributes can be monitored.  For each attribute, an instance of a monitor service has to be used.  If the specified condition satisfies, the monitor service triggers notification.  The manager application, in turn, receiving this notification can take appropriate actions (if required).  It is essential to know about these notifications (monitor notifications) so that each of the monitor services can be explained easily.

Monitor Notifications


MonitorNotification class is a sub-class of Notification class.  The MonitorNotification class provides definitions of the notifications sent by monitor MBeans, and all the monitoring services use this class.  

This notification is used to report one of the following cases:
  1. One of the trigger conditions of a monitor is detected.
  2. An error occurs during an observation of the attribute.
The list of notifications fired by the monitor MBeans is described below:

Notification Type
Reason for occurrence
Triggered By
jmx.monitor.error.mbean
Observed MBean is not registered in the MBean Server.
Counter, Gauge, and String Monitor
jmx.monitor.error.attribute Observed attribute is not present in the observed MBean.
Counter, Gauge, and String Monitor
jmx.monitor.error.type Type of the observed attribute is not correct.
Counter, Gauge, and String Monitor
jmx.monitor.error.runtime A non-predefined error type has occurred when trying to get the value of the observed attribute.
Counter, Gauge, and String Monitor
jmx.monitor.error.threshold Type of the threshold, offset, or modulus is not correct.
Counter and Gauge Monitor
jmx.monitor.counter.threshold
Observed attribute has exceeded the threshold value. Counter Monitor
jmx.monitor.gauge.high
Observed attribute has exceeded the high threshold value.
Gauge Monitor
jmx.monitor.gauge.low Observed attribute has exceeded the low threshold value. Gauge Monitor
jmx.monitor.string.matches
Observed attribute has matched the "string to compare" value.
String Monitor
jmx.monitor.string.differs Observed attribute has differed from the "string to compare" value. String Monitor
 

Types of Monitors

  1. Counter Monitor
  2. Gauge Monitor
  3. String Monitor
Each of the monitors is dealt with in separate topics.

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Timer Service Counter Monitor Service