question: public static Properties prefixProperties ( Properties props , String prefix ) { Properties prefixProps = new Properties ( ) ; for ( String key : props . stringPropertyNames ( ) ) { if ( key . startsWith ( prefix ) ) { String keyWithoutPrefix = key . substring ( prefix . length ( ) ) ; prefixProps . setProperty ( keyWithoutPrefix , props . getProperty ( key ) ) ; } } return prefixProps ; }
target:  Extract only the properties that match a prefix, and with the prefix removed.