Technical data

6 Using Log Messages to Manage WebLogic Servers
6-2 Administration Guide
n WebLogic Server component subsystems generate messages that are logged to a
local file, that is, a file that resides on the machine where the server is running.
If there are multiple servers on a machine, each server has its own log file.
Applications deployed on your WebLogic Servers may also log messages to the
server’s local log file.
n In addition, a subset of messages logged locally are stored in a central
domain-wide log file maintained by the Administration Server.
Java Management Extension (JMX) facilities, embedded in the WebLogic Server, are
used to transmit log messages from WebLogic Servers to the Administration Server.
A message forwarded to other entities on the initiative of a local WebLogic Server is
called a notification in JMX terminology.
When a WebLogic server starts, the Administration Server’s message handler registers
with that server to receive log messages. At the time of registration, a user-modifiable
filter is provided that is used by the local server to select the messages to be forwarded
to the Administration Server. These messages are collected in the domain log.
If the Administration Server is unavailable, Managed Servers continue to write
messages to their local log files, but they do not keep track of which messages they
generate while the Administration Server is unavailable. For example, if the
Administration Server is unavailable for two hours and then is restored, the domain log
will not contain any messages that were generated during the two hours.
By default, only the most important log messages (as determined by Message Severity)
are forwarded from the local servers to the domain log. The domain log gives you an
overall view of the entire domain while focusing on just the most critical messages.
If you want to modify the filter, to receive a different subset of logged messages from
a local server, you can do so dynamically, using the Administration Console. You do
not need to restart the local server for your changes to take effect. (See Creating
Domain Log Filters.)
Developers can also build custom message handlers that can register with a WebLogic
Server to receive log messages via JMX notifications.