Besides bridging JMX to the HTTP/JSON world, the Jolokia agents also install their own MBeans which provide the extra services described in this chapter.
This MBean, which is registered under the name jolokia:type=Config, allows changing configuration parameters. Changes are non-persistent and get lost after a restart of the hosting application server. Debugging mode and the history store can be configured with this MBean.
Debugging can be switched on by setting the attribute
Debug. When debugging is switched on, the
Jolokia agent will store debug information in a ring buffer in
memory, whose size can be tuned with the attribute
MaxDebugEntries. The debug information can
be fetched by the operation
debugging output will contain the JSON responses (which in
turn contain their requests) sent to the client. Finally, the
resetDebugInfo clears the debug
The history store can be used to remember attribute and return values within the agent's memory. The Nagios check check_jmx4perl, for instance, uses this feature for its delta check, which measures changes in attribute values. In order to switch on history tracking, two operations are provided:
There are two kinds of limits which can be applied: Either by a
maximum number of historical values to remember or a maximum
duration for the values to keep. If both limits are given in a
configuration call on the MBean above, both limits are
applied. In any case, there are never more values remembered
than the global limit which can be set and retrieved with
The History store can be emptied with a call to the operation
resetHistoryEntries. This also
switches off all history tracking.
If for a request history tracking is switched on, the JSON
response will contain an extra field
history which contains a list with
historical values along with the timestamp when it was
recorded. This format is described in detail in Section 6.5, “Tracking historical values”.
The MBean jolokia:type=ServerHandler has a single
mBeanServersInfo with no
arguments. This operation can be used to dump out the name of
all registered MBeans on all found MBeanServers. It is helpful to
get a quick and condensed overview of the available JMX