More agent services: monitors and timers - JMX in Action - page 298

to a value different than the value in the String monitor. You should eventually
see the following notification type appear in the agent output:

jmx.monitor.string.differs
Play around with the different attributes of the String monitor before moving on
the next section, which discusses the GaugeMonitor MBean.

12.2.3 Testing the Gauge monitor

The GaugeMonitor MBean operates over the Gauge attribute of the ObservableOb-
ject MBean. Table 12.7 lists the attributes of the GaugeMonitor MBean that you
need to set, along with appropriate values.

Table 12.7 The attributes you need to configure in the GaugeMonitor MBean in order to monitor
the Gauge attribute of the ObservableObject MBean.

Monitor attribute Value Description

Tells the MBean to send a notification if
the observed attribute reaches or
exceeds the high threshold

NotifyHigh true

Tells the MBean to send a notification if
the observed attribute reaches or
moves below the low threshold

NotifyLow true

Name of the observed attribute from
the subject MBean

ObservedAttribute Gauge

Object name of the subject MBean that
will be monitored by this Gauge monitor

ObservedObject JMXBookAgent:name=subject

High threshold value

HighThreshold 4.1

Low threshold value

LowThreshold 2.1

You will test this monitor just like the previous MBean. Select the GaugeMonitor
in the HTML adapter and set the attributes as described in table 12.7, and then
invoke the start() method by clicking the Start button. Now go back to the
ObservableObject and set the Gauge attribute to a value above the high threshold
of the Gauge monitor. You should see the following appear in the agent output:

jmx.monitor.gauge.high
Once again, go back to the ObservableObject MBean and change the Gauge
attribute to a value below the low threshold value of the GaugeMonitor MBean.
The agent will receive the following notification type:

jmx.monitor.gauge.low