In the Java Logging API, formatters are used to control the format of log messages. A formatter is an object that implements the java.util.logging.Formatter interface and is associated with a Handler object.

The Formatter interface has a single method, String format(LogRecord record), which is called by a handler to format a given log record. The method returns a String that represents the formatted log message.

Here is an example of how to use a SimpleFormatter to format log messages:

Logger logger = Logger.getLogger(MyClass.class.getName());
Handler handler = new ConsoleHandler();
handler.setFormatter(new SimpleFormatter());
logger.addHandler(handler);

In this example, we create a ConsoleHandler object and set its formatter to the SimpleFormatter. We then add the ConsoleHandler to the logger.

The SimpleFormatter formats log messages in a simple format that includes the log level, the logger name, and the message itself.

There are several other built-in formatters provided by the Java Logging API, including:

• XMLFormatter: formats log messages in XML format
• HTMLFormatter: formats log messages in HTML format
• PatternFormatter: formats log messages using a customizable pattern

You can also create custom formatters to suit your specific needs.

Formatters can be configured using a variety of properties, such as the date format, the output pattern, and the locale. For example, you can set the date format of a SimpleFormatter using the setDateFormat() method:

SimpleFormatter formatter = new SimpleFormatter();
formatter.setDateFormat("yyyy-MM-dd HH:mm:ss.SSS");
handler.setFormatter(formatter);

In this example, we create a SimpleFormatter and set its date format to a custom format. We then set the formatter of the ConsoleHandler to the new SimpleFormatter.