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// *  http://www.apache.org/licenses/LICENSE-2.0                                                                             *
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package org.apache.juneau.http.header;

import java.util.function.*;

import org.apache.juneau.http.annotation.*;

/**
 * Represents a parsed <l>Pragma</l> HTTP request/response header.
 *
 * <p>
 * Implementation-specific fields that may have various effects anywhere along the request-response chain.
 *
 * <h5 class='figure'>Example</h5>
 * <p class='bcode'>
 *    Pragma: no-cache
 * </p>
 *
 * <h5 class='topic'>RFC2616 Specification</h5>
 *
 * The Pragma general-header field is used to include implementation- specific directives that might apply to any
 * recipient along the request/response chain.
 * All pragma directives specify optional behavior from the viewpoint of the protocol; however, some systems MAY
 * require that behavior be consistent with the directives.
 *
 * <p class='bcode'>
 *    Pragma            = "Pragma" ":" 1#pragma-directive
 *    pragma-directive  = "no-cache" | extension-pragma
 *    extension-pragma  = token [ "=" ( token | quoted-string ) ]
 * </p>
 *
 * <p>
 * When the no-cache directive is present in a request message, an application SHOULD forward the request toward the
 * origin server even if it has a cached copy of what is being requested.
 * This pragma directive has the same semantics as the no-cache cache-directive (see section 14.9) and is defined here
 * for backward compatibility with HTTP/1.0.
 * Clients SHOULD include both header fields when a no-cache request is sent to a server not known to be HTTP/1.1
 * compliant.
 *
 * <p>
 * Pragma directives MUST be passed through by a proxy or gateway application, regardless of their significance to that
 * application, since the directives might be applicable to all recipients along the request/response chain.
 * It is not possible to specify a pragma for a specific recipient; however, any pragma directive not relevant to a
 * recipient SHOULD be ignored by that recipient.
 *
 * <p>
 * HTTP/1.1 caches SHOULD treat "Pragma: no-cache" as if the client had sent "Cache-Control: no-cache".
 * No new Pragma directives will be defined in HTTP.
 *
 * <p>
 * Note: because the meaning of "Pragma: no-cache as a response header field is not actually specified, it does not
 * provide a reliable replacement for "Cache-Control: no-cache" in a response.
 *
 * <h5 class='section'>See Also:</h5><ul>
 *    <li class='link'><a class="doclink" href="../../../../../index.html#juneau-rest-common">juneau-rest-common</a>
 *    <li class='extlink'><a class="doclink" href="https://www.w3.org/Protocols/rfc2616/rfc2616.html">Hypertext Transfer Protocol -- HTTP/1.1</a>
 * </ul>
 *
 * @serial exclude
 */
@Header("Pragma")
public class Pragma extends BasicStringHeader {

   //-----------------------------------------------------------------------------------------------------------------
   // Static
   //-----------------------------------------------------------------------------------------------------------------

   private static final long serialVersionUID = 1L;
   private static final String NAME = "Pragma";

   /**
    * Static creator.
    *
    * @param value
    *    The header value.
    *    <br>Can be <jk>null</jk>.
    * @return A new header bean, or <jk>null</jk> if the value is <jk>null</jk>.
    */
   public static Pragma of(String value) {
      return value == null ? null : new Pragma(value);
   }

   /**
    * Static creator with delayed value.
    *
    * <p>
    * Header value is re-evaluated on each call to {@link #getValue()}.
    *
    * @param value
    *    The supplier of the header value.
    *    <br>Can be <jk>null</jk>.
    * @return A new header bean, or <jk>null</jk> if the value is <jk>null</jk>.
    */
   public static Pragma of(Supplier<String> value) {
      return value == null ? null : new Pragma(value);
   }

   //-----------------------------------------------------------------------------------------------------------------
   // Instance
   //-----------------------------------------------------------------------------------------------------------------

   /**
    * Constructor.
    *
    * @param value
    *    The header value.
    *    <br>Can be <jk>null</jk>.
    */
   public Pragma(String value) {
      super(NAME, value);
   }

   /**
    * Constructor with delayed value.
    *
    * <p>
    * Header value is re-evaluated on each call to {@link #getValue()}.
    *
    * @param value
    *    The supplier of the header value.
    *    <br>Can be <jk>null</jk>.
    */
   public Pragma(Supplier<String> value) {
      super(NAME, value);
   }
}