When both LastModifiedDate and ETag are passed to evaluatePreconditions(java.util.Date lastModified, EntityTag eTag) method, RestEasy will return NotModifies status code if any of them match with request headers.

However ETag should have higher priority.

Extract from RFC 7232:

A recipient must ignore If-Modified-Since if the request contains an If-None-Match header field; the condition in If-None-Match is considered to be a more accurate replacement for the condition in If-Modified-Since, and the two are only combined for the sake of interoperating with older intermediaries that might not implement If-None-Match.

A recipient MUST ignore If-Unmodified-Since if the request contains an If-Match header field; the condition in If-Match is considered to be a more accurate replacement for the condition in If-Unmodified-Since, and the two are only combined for the sake of interoperating with older intermediaries that might not implement If-Match.