Application Cache Buster
The Application Cache Buster (short AppCacheBuster) is similar to the Cache Buster but is used for application resources.
SAPUI5 supports the application cache buster on SAP NetWeaver AS for ABAP only.
For Java apps on the SAP HANA Cloud Platform you can enable it by including server-side components which are not available externally.
For Java apps on SAP NetWeaver AS for Java and SAP HANA XS the application cache buster concept is not supported.
Applications provide an index file (created on the fly) containing the last modified timestamps of all included files (scripts, properties – files which we load via XHR programmatically). Technically this file is a mapping between the request path (below the context path of the application) and the last modified timestamp.
The server in general caches all the above resources (not using the 304/not modified mechanism). For the index file we are using the 304/not modified mechanism to avoid to load when it has not been changed.
On the client-side we initially load this file of the application when enabled via configuration option sap-ui-appcachebuster and use this for the XHR requests. If the request path is contained in the above mentioned index file we simply add the timestamp as leading path segment to this request. If the timestamp doesn’t change the URL is unique and therefore it will be taken from cache. Once the file is modified the URL parameter will be changed and therefore loaded again from the backend.
The server has to delete the timestamp from this URL to lookup the file properly. For ABAP, the logic is implemented in the ICF handler. Both backend implementations, Java and ABAP, also generate the index file on-the-fly.