WAS v8.5 > Troubleshoot > Add logging and tracing to the application > Use Java logging in an application > Use a logger

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 that is 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.

WAS uses the following set of log handlers 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 dmgr console.

IBM recommends using the HPEL log and trace infrastructure. With HPEL, one views logs using the LogViewer command-line tool in PROFILE/bin.

Related concepts:

Loggers
Log filters
Log formatters

Related

Use a logger
Configure Java logging
Troubleshoot applications with HPEL

Reference:

Log levels

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