wicket-request/src/main/java/org/apache/wicket/request/IRequestMapper.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.wicket.request;


/**
 * Maps {@link IRequestHandler}(s) into {@link Url}(s) and {@link Request}(s) to
 * {@link IRequestHandler}(s). For {@link IRequestHandler}s and {@link Request}s the implementation
 * doesn't recognize, the {@link #mapHandler(IRequestHandler)} and {@link #mapRequest(Request)}
 * methods must return {@code null}.
 * 
 * The workflow is: the Application class collects a set of {@link IRequestMapper}s and for each
 * request the {@link IRequestCycle request cycle} asks these mappers whether any of them knows how
 * to handle the current {@link Request}’s {@link Url url}. Wicket pre-configures several mappers
 * which are used for the basic application functionality like a mapper for the home page, a mapper
 * for Wicket resources, for bookmarkable pages, etc. The user application can add additional
 * mappers with the various WebApplication#mountXYZ() methods.
 * 
 * The mapper has two main tasks:
 * 
 * <ol>
 * <li>To create {@link IRequestHandler} that will produce the response. When a request comes Wicket
 * uses {@link #getCompatibilityScore(Request)} to decide which mapper should be asked first to
 * process the request. If two mappers have the same score then the one added later is asked first.
 * This way user’s mappers have precedence than the system ones. If a mapper knows how to handle the
 * request’s url then it should return non-{@code null} {@link IRequestHandler}.</li>
 * <li>
 * The second task is to produce {@link Url} for an {@link IRequestHandler}. This is needed at
 * markup rendering time to create the urls for links, forms' action attribute, etc.</li>
 * </ol>
 * 
 * @author Matej Knopp
 */
public interface IRequestMapper
{
	/**
	 * Returns {@link IRequestHandler} for the request or <code>null</code> if the {@link Url} is
	 * not recognized.
	 * 
	 * @param request
	 *            provides access to request data (i.e. Url and Parameters)
	 * 
	 * @return RequestHandler instance or <code>null</code>
	 */
	IRequestHandler mapRequest(Request request);

	/**
	 * Returns the score representing how compatible this request mapper is to processing the given
	 * request. When a request comes in all mappers are scored and are tried in order from highest
	 * score to lowest.
	 * <p>
	 * A good criteria for calculating the score is the number of matched url segments. For example
	 * when there are two mappers for a mounted page, one mapped to <code>/foo</code> another to
	 * <code>/foo/bar</code> and the incoming request URL is </code>/foo/bar/baz</code>, the mapping
	 * to <code>/foo/bar</code> should probably handle the request first as it has matching segments
	 * count of 2 while the first one has only matching segments count of 1.
	 * <p>
	 * Note that the method can return value greater then zero even if the mapper does not recognize
	 * the request.
	 * 
	 * @param request
	 * @return the compatibility score, e.g. count of matching segments
	 */
	int getCompatibilityScore(Request request);

	/**
	 * Returns the {@link Url} for given {@link IRequestHandler} or <code>null</code> if the request
	 * handler is not recognized.
	 * 
	 * @param requestHandler
	 * @return Url instance or <code>null</code>.
	 */
	Url mapHandler(IRequestHandler requestHandler);
}