Datasheet

The Formatter Class

The Formatter class is used to perform some custom processing on a log record. This formatting

might be localization, adding additional program information (such as adding the time and date to log

records), or any other processing needed. The

Formatter returns a string that is the processed log

record. The

Formatter class also has support for head and tail strings that come before and after all

log records. An example that will be implemented later in this section is a custom

Formatter that

writes log records to an HTML table. For this formatter, the head string would be the

<table> tag, and

the tail string is the

</table> tag. The methods defined in the Formatter class are listed in the follow-

ing table.

Method Description

abstract String format(LogRecord Performs specific formatting of the log record and

record) returns the formatted string.

String formatMessage(LogRecord The message string in the LogRecord is localized using

record) the record’s ResourceBundle, and formatted accord-

ing to

java.text style formatting (replacing strings

such as

{0}).

String getHead(Handler h) Returns the header string for a specified handler, which

can be null.

String getTail(Handler h) Returns the tail string for a specified handler, which

can be null.

Stock Formatters

The logging package comes already equipped with a couple of useful formatters. The SimpleFormatter

provides a basic implementation of a formatter. The XMLFormatter outputs log records in a predefined

XML format. These two stock formatters will cover a variety of basic logging scenarios, but if you need

behavior not supplied by either of these formatters, you can write your own.

SimpleFormatter

The SimpleFormatter does a minimal level of work to format log messages. The format method of the

SimpleFormatter returns a one- or two-line summary of the log record that is passed in. Logging a

simple log message, such as

test 1, using the SimpleFormatter will issue the following output:

Apr 18, 2004 12:18:25 PM LoggingTest main

INFO: test 1

The SimpleFormatter formats the message with the date, time, originating class name, originating

method name, and on the second line, the level of the log message and the log message itself.

XMLFormatter

The XMLFormatter formats the log records according to an XML DTD. You can use the XMLFormatter

with any character encoding, but it is suggested that it be used only with “UTF-8”. The getHead() and

Part I: Thinking Like a Java Developer

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