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### A.11.14 Log Window

Log Window

The log window can be obtained using the View Log () option on the File menu of the Control Window.

This window displays any log messages which the application has generated. These messages are not required reading for users, but they can be useful for debugging in case of problems, and they can also tell you some useful information about what the application is doing, for instance external URLs that are being accessed or ADQL query text. These messages can be useful if you want to reproduce some parts of TOPCAT's behaviour outside the application, e.g. using `curl` or a web browser.

The messages are colour-coded to some extent. WARNING- and SEVERE-level messages, which generally indicate some kind of problem that may cause trouble, are displayed in red and black respectively. INFO- and CONFIG-level messages, which generally just provide information about what's going on under the hood, are assigned an arbitrary colour based on the code subsystem (the Source value) that has generated them. These colours are not really significant, they are just intended as a visual aid.

The Level selector at the bottom can be used as a filter so that only messages beyond a certain severity are displayed.

Depending on whether the `-verbose` flag has been specified, some or all of the displayed messages may have been written to the console as well (if there is a console - this depends on how you have invoked TOPCAT).

There is a limit (currently 1000) to the number of logging messages retained, so for long-running instances the older ones may be discarded.

The following toolbar/menu items are available:

Clear
  Clears all the existing messages from the display.
Auto-scroll
  When this toggle is on (the default), the display will scroll to the bottom any time a new log message is added, so you can always see the latest ones. That can be annoying if you're trying to examine messages earlier in the list however, so by turning it off you can prevent this behaviour.
Pause logging
  While this toggle is on, no more messages will be added to the display.
Export to file
  Writes all the current content of the logging buffer to a text file. Even those messages currently filtered out by level from the display are included. The output is in a somewhat different format than what's displayed. This output may be a useful accompaniment to (certain kinds of) bug reports.

Note: the messages displayed here are those written through Java's logging system. Although it tries not to disturb things too much, TOPCAT's manipulation of the logging infrastructure affects how it is set up, so if you have customised your logging setup using, e.g., the `java.util.logging.config.*` system properties, you may find that it's not behaving exactly as you expected. Sorry.

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Next: Algebraic Functions
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TOPCAT - Tool for OPerations on Catalogues And Tables
Starlink User Note253
TOPCAT web page: http://www.starlink.ac.uk/topcat/
Author email: m.b.taylor@bristol.ac.uk
Mailing list: topcat-user@jiscmail.ac.uk