question: public String rewrite ( final String cssUri , final String imageUrl ) { notNull ( cssUri ) ; notNull ( imageUrl ) ; if ( StringUtils . isEmpty ( imageUrl ) ) { return imageUrl ; } if ( ServletContextUriLocator . isValid ( cssUri ) ) { if ( ServletContextUriLocator . isValid ( imageUrl ) ) { return prependContextPath ( imageUrl ) ; } if ( ServletContextUriLocator . isProtectedResource ( cssUri ) ) { return context . proxyPrefix + computeNewImageLocation ( cssUri , imageUrl ) ; } final String aggregatedPathPrefix = computeAggregationPathPrefix ( context . aggregatedFolderPath ) ; LOG . debug ( "computed aggregatedPathPrefix {}" , aggregatedPathPrefix ) ; String newImageLocation = computeNewImageLocation ( aggregatedPathPrefix + cssUri , imageUrl ) ; if ( newImageLocation . startsWith ( ServletContextUriLocator . PREFIX ) ) { newImageLocation = prependContextPath ( newImageLocation ) ; } LOG . debug ( "newImageLocation: {}" , newImageLocation ) ; return newImageLocation ; } if ( ClasspathUriLocator . isValid ( cssUri ) ) { final String proxyUrl = context . proxyPrefix + computeNewImageLocation ( cssUri , imageUrl ) ; final String contextRelativeUrl = prependContextPath ( imageUrl ) ; return ( ServletContextUriLocator . isValid ( imageUrl ) ? contextRelativeUrl : proxyUrl ) ; } if ( UrlUriLocator . isValid ( cssUri ) ) { final String computedCssUri = ServletContextUriLocator . isValid ( imageUrl ) ? computeCssUriForExternalServer ( cssUri ) : cssUri ; return computeNewImageLocation ( computedCssUri , imageUrl ) ; } throw new WroRuntimeException ( "Could not replace imageUrl: " + imageUrl + ", contained at location: " + cssUri ) ; }
target:  Computes the url of the image to be replaced in a css resource.