Log handlers
Log handlers write log record objects to output devices like log files, sockets, and notification mechanisms.
Loggers can have zero or more attached handlers. All objects that are logged to the logger are passed to the attached handlers, if handlers are supplied. We can configure handlers with a level. The handler compares the level specified in the logged object to the level specified for the handler. If the level of the logged object is less severe than the level set in the handler, the object is ignored by the handler. The default level for handlers is ALL.
Handlers can have a filter. If a filter is supplied, the filter is invoked for each incoming object to tell the handler whether or not to ignore it.
Handlers can have a formatter. If a formatter is supplied, the formatter controls how the logged objects are formatted. For example, the formatter can decide to first include the time stamp, followed by a string representation of the level, followed by the message included in the logged object. The handler writes this formatted representation to the output device.
Both loggers and handlers can have levels and filters, and a logged object must pass all of these elements to be output. For example, we can set the logger level to FINE, but if the handler level is set at WARNING, only WARNING level messages are displayed in the output for that handler. Conversely, if the log handler is set to output all messages (level=All), but the logger level is set to WARNING, the logger never sends messages beneath the WARNING to the log handler.
(dist) WAS uses the following set of log handlers that are available to all loggers:
- Diagnostic trace
- JMX notification object
- Service log
- SystemErr
- SystemOut
For instructions on how to configure these log handlers, see Configuring Java logging using the administrative console.
This topic references one or more of the application server log files. As a recommended alternative, we can configure the server to use the High Performance Extensible Logging (HPEL) log and trace infrastructure instead of using SystemOut.log , SystemErr.log, trace.log, and activity.log files on distributed and IBM i systems. We can also use HPEL in conjunction with the native z/OS logging facilities. If we are using HPEL, we can access all of the log and trace information using the LogViewer command-line tool from the server profile bin directory. See the information about using HPEL to troubleshoot applications for more information on using HPEL.
Related concepts
Loggers Log filters Log formatters
Related tasks
Use a logger Configure Java logging using the administrative console Use High Performance Extensible Logging to troubleshoot applications
Log levels