Class IfHeader

  • All Implemented Interfaces:

    public class IfHeader
    extends Object
    implements Header
    The IfHeader class represents the state lists defined through the HTTP If header, which is specified in RFC 2518 as follows :
         If = "If" ":" ( 1*No-tag-list | 1*Tagged-list)
         No-tag-list = List
         Tagged-list = Resource 1*List
         Resource = Coded-URL
         List = "(" 1*(["Not"](State-etag | "[" entity-tag "]")) ")"
         State-etag = Coded-URL
         Coded-URL = "<" absoluteURI ">"

    Reformulating this specification into proper EBNF as specified by N. Wirth we get the following productions, which map to the parse METHODS of this class. Any whitespace is ignored except for white space surrounding and within words which is considered significant.

         If = "If:" ( Tagged | Untagged ).
         Tagged = { "<" Word ">" Untagged } .
         Untagged = { "(" IfList ")" } .
         IfList = { [ "Not" ] ( ("<" Word ">" ) | ( "[" Word "]" ) ) } .
         Word = characters .

    An If header either contains untagged IfList entries or tagged IfList entries but not a mixture of both. An If header containing tagged entries is said to be of tagged type while an If header containing untagged entries is said to be of untagged type.

    An IfList is a list of tokens - words enclosed in < > - and etags - words enclosed in [ ]. An IfList matches a (token, etag) tuple if all entries in the list match. If an entry in the list is prefixed with the word Not (parsed case insensitively) the entry must not match the concrete token or etag.

    Example: The ifList (<token> [etag]) only matches if the concret token has the value token and the conrete etag has the value etag. On the other hand, the ifList (Not <notoken>) matches any token which is not notoken (in this case the concrete value of the etag is not taken into consideration).

    Felix Meschberger
    • Constructor Detail

      • IfHeader

        public IfHeader​(String[] tokens)
        Create a Untagged IfHeader if the given lock tokens.
        tokens -
      • IfHeader

        public IfHeader​(javax.servlet.http.HttpServletRequest req)
        Parses the If header and creates and internal representation which is easy to query.
        req - The request object
    • Method Detail

      • getHeaderValue

        public String getHeaderValue()
        Return the String representation of the If header present on the given request or null.
        Specified by:
        getHeaderValue in interface Header
        If header value as String or null.
      • hasValue

        public boolean hasValue()
        Returns true if an If header was present in the given request. False otherwise.
        true if an If header was present.
      • matches

        public boolean matches​(String tag,
                               String token,
                               String etag)
        Tries to match the contents of the If header with the given token and etag values with the restriction to only check for the tag.

        If the If header is of untagged type, the untagged IfList is matched against the token and etag given: A match of the token and etag is found if at least one of the IfList entries match the token and etag tuple.

        tag - The tag to identify the IfList to match the token and etag against.
        token - The token to compare.
        etag - The ETag value to compare.
        If the If header is of untagged type the result is true if any of the IfList entries matches the token and etag values. For tagged type If header the result is true if either no entry for the given tag exists in the If header or if the IfList for the given tag matches the token and etag given.
      • getAllTokens

        public Iterator<String> getAllTokens()
        an iterator over all tokens present in the if header, that were not denied by a leading NOT statement.
      • getAllNotTokens

        public Iterator<String> getAllNotTokens()
        an iterator over all NOT tokens present in the if header, that were explicitly denied.