src/main/java/org/jivesoftware/smack/UserRoster.java
public RosterEntry getEntry(String user) {
        if (user == null) {
            return null;
        }
        return entries.get(user.toLowerCase());
    }
public RosterEntry getEntry(String user) {
        if (user == null) {
            return null;
        }
        return entries.get(user.toLowerCase());
    }
Returns the roster entry associated with the given XMPP address or
<tt>null</tt> if the user is not an entry in the roster.

@param user
the XMPP address of the user (eg "jsmith@example.com"). The
address could be in any valid format (e.g. "domain/resource",
"user@domain" or "user@domain/resource").
@return the roster entry or <tt>null</tt> if it does not exist.