Java Management Extensions

Counter Monitors

As mentioned in the first part of this chapter, a counter monitor is used to observe an MBean attribute that is:

• Greater than or equal to zero

• Continually increasing (i.e., never decreasing)

• One of the Java integer types (byte, short, int, or long) or one of the corresponding JDK wrapper classes (Byte, Short, Int, or Long)

In this section, we will look at the agent code that shows how to use a counter monitor. When using a counter monitor, the first thing to do is to create a new instance of the CounterMonitor class:

CounterMonitor monitor = new CounterMonitor(  );

After that, the following attributes of the monitor must be set:

• ObservedObject

• ObservedAttribute

• Notify (must be set to true if a notification is to be sent)

• Threshold

• GranularityPeriod

• Offset (optional)

• DifferenceMode (optional)

• Modulus (optional)

We discussed some of these attributes earlier in this chapter. If the Offset attribute is set, each time the derived gauge exceeds the threshold value, the current value of the MBean attribute is incremented by the value of Offset until the MBean attribute value is greater than the derived gauge (to prevent multiple notifications should the derived gauge spike well beyond the current MBean attribute value). When the counter monitor determines that a notification should be sent to all interested listeners, a single notification is sent, regardless of how many multiples of the threshold value the derived gauge is calculated to be.

In other words, if the previous ...