Hard to find a clear answer from the Oracle site. The following is from javax.ws.rs.core.HttpHeaders.java:
/**
* See {@link <a href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.1">HTTP/1.1 documentation</a>}.
*/
public static final String ACCEPT = "Accept";
/**
* See {@link <a href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.2">HTTP/1.1 documentation</a>}.
*/
public static final String ACCEPT_CHARSET = "Accept-Charset";