abstract public String format(LoggingEvent event)
Implement this method to create your own layout format.

 public String getContentType() 
{
    return "text/plain";
}

Returns the content type output by this layout. The base class returns "text/plain".

 public String getFooter() 
{
    return null;
}

Returns the footer for the layout format. The base class returns null.

 public String getHeader() 
{
    return null;
}

Returns the header for the layout format. The base class returns null.

 abstract public boolean ignoresThrowable()
If the layout handles the throwable object contained within
LoggingEvent , then the layout should return
false. Otherwise, if the layout ignores throwable
object, then the layout should return true.
If ignoresThrowable is true, the appender is responsible for
rendering the throwable.

The SimpleLayout , TTCCLayout , PatternLayout  all return true. The org.apache.log4j.xml.XMLLayout  returns false.