question: private static DateTimeFormatter createFormatterForPattern ( String pattern ) { if ( pattern == null || pattern . length ( ) == 0 ) { throw new IllegalArgumentException ( "Invalid pattern specification" ) ; } DateTimeFormatter formatter = null ; synchronized ( cPatternedCache ) { formatter = cPatternedCache . get ( pattern ) ; if ( formatter == null ) { DateTimeFormatterBuilder builder = new DateTimeFormatterBuilder ( ) ; parsePatternTo ( builder , pattern ) ; formatter = builder . toFormatter ( ) ; cPatternedCache . put ( pattern , formatter ) ; } } return formatter ; }
target:  Select a format from a custom pattern.