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/*
 * Request.java
 *
 * Created on September 27, 2007, 5:39 PM
 *
 */

package javax.ws.rs.core;

import java.util.Date;
import java.util.List;
import javax.ws.rs.core.Response.ResponseBuilder;

/**
 * An injectable helper for request processing, all methods throw
 * java.lang.IllegalStateException if called outside the scope of a request
 * (e.g. from a provider constructor).
 * 
 * Precondition processing (see the <code>evaluatePreconditions</code> methods)
 * can result in either a <code>null</code> return value to indicate that
 * preconditions have been met and that the request should continue, or
 * a non-null return value to indicate that preconditions were not met. In the
 * event that preconditions were not met, the returned <code>ResponseBuilder</code>
 * instance will have an appropriate status and will also include a <code>Vary</code>
 * header if the {@link #selectVariant} method was called prior to to calling
 * <code>evaluatePreconditions</code>. It is the responsibility of the caller
 * to check the status and add additional metadata if required. E.g., see
 * <a href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html#sec10.3.5">HTTP/1.1, section 10.3.5</a>
 * for details of the headers that are expected to accompany a <code>304 Not Modified</code>
 * response.
 */
public interface Request {
    
    /**
     * Get the request method, e.g. GET, POST, etc.
     * @return the request method
     * @see javax.ws.rs.HttpMethod
     */
    String getMethod();

    /**
     * Select the representation variant that best matches the request. More
     * explicit variants are chosen ahead of less explicit ones. A vary header
     * is computed from the supplied list and automatically added to the 
     * response.
     * 
     * @param variants a list of Variant that describe all of the
     * available representation variants.
     * @return the variant that best matches the request.
     * @see Variant.VariantListBuilder
     * @throws java.lang.IllegalArgumentException if variants is empty or null
     * @throws java.lang.IllegalStateException if called outside the scope of a request
     */
    Variant selectVariant(List<Variant> variants) throws IllegalArgumentException;
    
    /**
     * Evaluate request preconditions based on the passed in value. 
     * 
     * @param eTag an ETag for the current state of the resource
     * @return null if the preconditions are met or a ResponseBuilder set with
     * the appropriate status if the preconditions are not met. A returned
     * ResponseBuilder will include an ETag header set with the value of eTag.
     * @throws java.lang.IllegalArgumentException if eTag is null
     * @throws java.lang.IllegalStateException if called outside the scope of a request
     */
    ResponseBuilder evaluatePreconditions(EntityTag eTag);

    /**
     * Evaluate request preconditions based on the passed in value.
     * 
     * @param lastModified a date that specifies the modification date of the resource
     * @return null if the preconditions are met or a ResponseBuilder set with
     * the appropriate status if the preconditions are not met.
     * @throws java.lang.IllegalArgumentException if lastModified is null
     * @throws java.lang.IllegalStateException if called outside the scope of a request
     */
    ResponseBuilder evaluatePreconditions(Date lastModified);
    
    /**
     * Evaluate request preconditions based on the passed in value.
     * 
     * @param lastModified a date that specifies the modification date of the resource
     * @param eTag an ETag for the current state of the resource
     * @return null if the preconditions are met or a ResponseBuilder set with
     * the appropriate status if the preconditions are not met.  A returned
     * ResponseBuilder will include an ETag header set with the value of eTag.
     * @throws java.lang.IllegalArgumentException if lastModified or eTag is null
     * @throws java.lang.IllegalStateException if called outside the scope of a request
     */
    ResponseBuilder evaluatePreconditions(Date lastModified, EntityTag eTag);
    
    /**
     * Evaluate request preconditions for a resource that does not currently
     * exist. The primary use of this method is to support the {@link <a
     * href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.24">
     * If-Match: *</a>} and {@link <a
     * href="http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.26">
     * If-None-Match: *</a>} preconditions.
     *
     * <p>Note that both preconditions <code>If-None-Match: *</code> and
     * <code>If-None-Match: <i>something</i></code> will always be considered to
     * have been met and it is the applications responsibility
     * to enforce any additional method-specific semantics. E.g. a
     * <code>PUT</code> on a resource that does not exist might succeed whereas
     * a <code>GET</code> on a resource that does not exist would likely result
     * in a 404 response. It would be the responsibility of the application to
     * generate the 404 response.</p>
     *
     * @return null if the preconditions are met or a ResponseBuilder set with
     * the appropriate status if the preconditions are not met.
     * @throws java.lang.IllegalStateException if called outside the scope of
     * a request
     */
    ResponseBuilder evaluatePreconditions();
}