/*
* Copyright 2002-2007 the original author or authors.
*
* Licensed 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.springframework.web.servlet;
import javax.servlet.http.HttpServletRequest;
/**
* Interface to be implemented by objects that define a mapping between
* requests and handler objects.
*
* <p>This class can be implemented by application developers, although this is not
* necessary, as {@link org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping}
* and {@link org.springframework.web.servlet.handler.SimpleUrlHandlerMapping}
* are included in the framework. The former is the default if no
* HandlerMapping bean is registered in the application context.
*
* <p>HandlerMapping implementations can support mapped interceptors but do not
* have to. A handler will always be wrapped in a {@link HandlerExecutionChain}
* instance, optionally accompanied by some {@link HandlerInterceptor} instances.
* The DispatcherServlet will first call each HandlerInterceptor's
* <code>preHandle</code> method in the given order, finally invoking the handler
* itself if all <code>preHandle</code> methods have returned <code>true</code>.
*
* <p>The ability to parameterize this mapping is a powerful and unusual
* capability of this MVC framework. For example, it is possible to write
* a custom mapping based on session state, cookie state or many other
* variables. No other MVC framework seems to be equally flexible.
*
* <p>Note: Implementations can implement the {@link org.springframework.core.Ordered}
* interface to be able to specify a sorting order and thus a priority for getting
* applied by DispatcherServlet. Non-Ordered instances get treated as lowest priority.
*
* @author Rod Johnson
* @author Juergen Hoeller
* @see org.springframework.core.Ordered
* @see org.springframework.web.servlet.handler.AbstractHandlerMapping
* @see org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping
* @see org.springframework.web.servlet.handler.SimpleUrlHandlerMapping
*/
public interface HandlerMapping {
/**
* Name of the {@link HttpServletRequest} attribute that contains the path
* within the handler mapping, in case of a pattern match, or the full
* relevant URI (typically within the DispatcherServlet's mapping) else.
* <p>Note: This attribute is not required to be supported by all
* HandlerMapping implementations. URL-based HandlerMappings will
* typically support it, but handlers should not necessarily expect
* this request attribute to be present in all scenarios.
*/
String PATH_WITHIN_HANDLER_MAPPING_ATTRIBUTE = HandlerMapping.class.getName() + ".pathWithinHandlerMapping";
/**
* Return a handler and any interceptors for this request. The choice may be made
* on request URL, session state, or any factor the implementing class chooses.
* <p>The returned HandlerExecutionChain contains a handler Object, rather than
* even a tag interface, so that handlers are not constrained in any way.
* For example, a HandlerAdapter could be written to allow another framework's
* handler objects to be used.
* <p>Returns <code>null</code> if no match was found. This is not an error.
* The DispatcherServlet will query all registered HandlerMapping beans to find
* a match, and only decide there is an error if none can find a handler.
* @param request current HTTP request
* @return a HandlerExecutionChain instance containing handler object and
* any interceptors, or <code>null</code> if no mapping found
* @throws Exception if there is an internal error
*/
HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception;
}