/*
 * Copyright 2002-2018 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
 *
 *      https://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;
import javax.servlet.http.HttpServletResponse;

import org.springframework.lang.Nullable;

MVC framework SPI, allowing parameterization of the core MVC workflow.
Interface that must be implemented for each handler type to handle a request. This interface is used to allow the DispatcherServlet to be indefinitely extensible. The DispatcherServlet accesses all installed handlers through this interface, meaning that it does not contain code specific to any handler type. 
Note that a handler can be of type Object. This is to enable handlers from other frameworks to be integrated with this framework without custom coding, as well as to allow for annotation-driven handler objects that do not obey any specific Java interface. 
This interface is not intended for application developers. It is available
to handlers who want to develop their own web workflow.
Note: HandlerAdapter implementors may implement the Ordered interface to be able to specify a sorting order (and thus a priority) for getting applied by the DispatcherServlet. Non-Ordered instances get treated as lowest priority. 
Author:
Rod Johnson, Juergen Hoeller
See Also:
SimpleControllerHandlerAdapter
SimpleServletHandlerAdapter/**
 * MVC framework SPI, allowing parameterization of the core MVC workflow.
 *
 * <p>Interface that must be implemented for each handler type to handle a request.
 * This interface is used to allow the {@link DispatcherServlet} to be indefinitely
 * extensible. The {@code DispatcherServlet} accesses all installed handlers through
 * this interface, meaning that it does not contain code specific to any handler type.
 *
 * <p>Note that a handler can be of type {@code Object}. This is to enable
 * handlers from other frameworks to be integrated with this framework without
 * custom coding, as well as to allow for annotation-driven handler objects that
 * do not obey any specific Java interface.
 *
 * <p>This interface is not intended for application developers. It is available
 * to handlers who want to develop their own web workflow.
 *
 * <p>Note: {@code HandlerAdapter} implementors may implement the {@link
 * org.springframework.core.Ordered} interface to be able to specify a sorting
 * order (and thus a priority) for getting applied by the {@code DispatcherServlet}.
 * Non-Ordered instances get treated as lowest priority.
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @see org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter
 * @see org.springframework.web.servlet.handler.SimpleServletHandlerAdapter
 */
public interface HandlerAdapter {

	
Given a handler instance, return whether or not this HandlerAdapter can support it. Typical HandlerAdapters will base the decision on the handler type. HandlerAdapters will usually only support one handler type each. 
A typical implementation:

return (handler instanceof MyHandler);
 
Params:
handler – the handler object to check
Returns:
whether or not this object can use the given handler/**
	 * Given a handler instance, return whether or not this {@code HandlerAdapter}
	 * can support it. Typical HandlerAdapters will base the decision on the handler
	 * type. HandlerAdapters will usually only support one handler type each.
	 * <p>A typical implementation:
	 * <p>{@code
	 * return (handler instanceof MyHandler);
	 * }
	 * @param handler the handler object to check
	 * @return whether or not this object can use the given handler
	 */
	boolean supports(Object handler);

	
Use the given handler to handle this request.
The workflow that is required may vary widely.
Params:
request – current HTTP request
response – current HTTP response
handler – the handler to use. This object must have previously been passed to the supports method of this interface, which must have returned true.
Throws:
Exception – in case of errors
Returns:
a ModelAndView object with the name of the view and the required model data, or null if the request has been handled directly/**
	 * Use the given handler to handle this request.
	 * The workflow that is required may vary widely.
	 * @param request current HTTP request
	 * @param response current HTTP response
	 * @param handler the handler to use. This object must have previously been passed
	 * to the {@code supports} method of this interface, which must have
	 * returned {@code true}.
	 * @throws Exception in case of errors
	 * @return a ModelAndView object with the name of the view and the required
	 * model data, or {@code null} if the request has been handled directly
	 */
	@Nullable
	ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception;

	
Same contract as for HttpServlet's getLastModified method. Can simply return -1 if there's no support in the handler class. 
Params:
request – current HTTP request
handler – the handler to use
See Also:
getLastModified.getLastModified
LastModified.getLastModified
Returns:
the lastModified value for the given handler/**
	 * Same contract as for HttpServlet's {@code getLastModified} method.
	 * Can simply return -1 if there's no support in the handler class.
	 * @param request current HTTP request
	 * @param handler the handler to use
	 * @return the lastModified value for the given handler
	 * @see javax.servlet.http.HttpServlet#getLastModified
	 * @see org.springframework.web.servlet.mvc.LastModified#getLastModified
	 */
	long getLastModified(HttpServletRequest request, Object handler);

}