question: public static boolean doCacheHeaderValidation ( final SolrQueryRequest solrReq , final HttpServletRequest req , final Method reqMethod , final HttpServletResponse resp ) { if ( Method . POST == reqMethod || Method . OTHER == reqMethod ) { return false ; } final long lastMod = HttpCacheHeaderUtil . calcLastModified ( solrReq ) ; final String etag = HttpCacheHeaderUtil . calcEtag ( solrReq ) ; resp . setDateHeader ( "Last-Modified" , lastMod ) ; resp . setHeader ( "ETag" , etag ) ; if ( checkETagValidators ( req , resp , reqMethod , etag ) ) { return true ; } if ( checkLastModValidators ( req , resp , lastMod ) ) { return true ; } return false ; }
target:  Sets HTTP Response cache validator headers appropriately and validates the HTTP Request against these using any conditional request headers. If the request contains conditional headers, and those headers indicate a match with the current known state of the system, this method will return "true" indicating that a 304 Status code can be returned, and no further processing is needed.