springmvc中常见的非注解开发的处理器适配器

处理器映射器：根据请求URL查找对应的Handler（处理器）

处理器适配器：根据请求URL执行对应的Handler（处理器）

处理器适配器能调用并执行符合要求的handler，其中，适配器的support方法表明了符合该适配器要求的handler需要实现什么接口，下面，我介绍两种常见的非注解开发的处理器适配器

1、SimpleControllerHandlerAdapter（org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter）

源码：

public class SimpleControllerHandlerAdapter implements HandlerAdapter {

	public boolean supports(Object handler) {
		return (handler instanceof Controller);
	}

	public ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
			throws Exception {

		return ((Controller) handler).handleRequest(request, response);
	}

	public long getLastModified(HttpServletRequest request, Object handler) {
		if (handler instanceof LastModified) {
			return ((LastModified) handler).getLastModified(request);
		}
		return -1L;
	}

}

support方法表明：符合该适配器的handler必须实现Controller接口，该接口源码：

/*
 * Copyright 2002-2008 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.mvc;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.web.servlet.ModelAndView;

/**
 * Base Controller interface, representing a component that receives
 * <code>HttpServletRequest</code> and <code>HttpServletResponse</code>
 * instances just like a <code>HttpServlet</code> but is able to
 * participate in an MVC workflow. Controllers are comparable to the
 * notion of a Struts <code>Action</code>.
 *
 * <p>Any implementation of the Controller interface should be a
 * <i>reusable, thread-safe</i> class, capable of handling multiple
 * HTTP requests throughout the lifecycle of an application. To be able to
 * configure a Controller easily, Controller implementations are encouraged
 * to be (and usually are) JavaBeans.
 * </p>
 *
 * <p><b><a name="workflow">Workflow</a></b></p>
 *
 * <p>
 * After a <cde>DispatcherServlet</code> has received a request and has
 * done its work to resolve locales, themes and suchlike, it then tries
 * to resolve a Controller, using a
 * {@link org.springframework.web.servlet.HandlerMapping HandlerMapping}.
 * When a Controller has been found to handle the request, the
 * {@link #handleRequest(HttpServletRequest, HttpServletResponse) handleRequest}
 * method of the located Controller will be invoked; the located Controller
 * is then responsible for handling the actual request and - if applicable -
 * returning an appropriate
 * {@link org.springframework.web.servlet.ModelAndView ModelAndView}.
 * So actually, this method is the main entrypoint for the
 * {@link org.springframework.web.servlet.DispatcherServlet DispatcherServlet}
 * which delegates requests to controllers.</p>
 *
 * <p>So basically any <i>direct</i> implementation of the Controller interface
 * just handles HttpServletRequests and should return a ModelAndView, to be further
 * interpreted by the DispatcherServlet. Any additional functionality such as
 * optional validation, form handling, etc should be obtained through extending
 * one of the abstract controller classes mentioned above.</p>
 *
 * <p><b>Notes on design and testing</b></p>
 *
 * <p>The Controller interface is explicitly designed to operate on HttpServletRequest
 * and HttpServletResponse objects, just like an HttpServlet. It does not aim to
 * decouple itself from the Servlet API, in contrast to, for example, WebWork, JSF or Tapestry.
 * Instead, the full power of the Servlet API is available, allowing Controllers to be
 * general-purpose: a Controller is able to not only handle web user interface
 * requests but also to process remoting protocols or to generate reports on demand.</p>
 *
 * <p>Controllers can easily be tested by passing in mock objects for the
 * HttpServletRequest and HttpServletResponse objects as parameters to the
 * {@link #handleRequest(HttpServletRequest, HttpServletResponse) handleRequest}
 * method. As a convenience, Spring ships with a set of Servlet API mocks
 * that are suitable for testing any kind of web components, but are particularly
 * suitable for testing Spring web controllers. In contrast to a Struts Action,
 * there is no need to mock the ActionServlet or any other infrastructure;
 * HttpServletRequest and HttpServletResponse are sufficient.</p>
 *
 * <p>If Controllers need to be aware of specific environment references, they can
 * choose to implement specific awareness interfaces, just like any other bean in a
 * Spring (web) application context can do, for example:</p>
 * <ul>
 * <li><code>org.springframework.context.ApplicationContextAware</code></li>
 * <li><code>org.springframework.context.ResourceLoaderAware</code></li>
 * <li><code>org.springframework.web.context.ServletContextAware</code></li>
 * </ul>
 *
 * <p>Such environment references can easily be passed in testing environments,
 * through the corresponding setters defined in the respective awareness interfaces.
 * In general, it is recommended to keep the dependencies as minimal as possible:
 * for example, if all you need is resource loading, implement ResourceLoaderAware only.
 * Alternatively, derive from the WebApplicationObjectSupport base class, which gives
 * you all those references through convenient accessors - but requires an
 * ApplicationContext reference on initialization.
 *
 * <p>Controllers can optionally implement the {@link LastModified} interface.
 *
 * @author Rod Johnson
 * @author Juergen Hoeller
 * @see LastModified
 * @see SimpleControllerHandlerAdapter
 * @see AbstractController
 * @see org.springframework.mock.web.MockHttpServletRequest
 * @see org.springframework.mock.web.MockHttpServletResponse
 * @see org.springframework.context.ApplicationContextAware
 * @see org.springframework.context.ResourceLoaderAware
 * @see org.springframework.web.context.ServletContextAware
 * @see org.springframework.web.context.support.WebApplicationObjectSupport
 */
public interface Controller {

	/**
	 * Process the request and return a ModelAndView object which the DispatcherServlet
	 * will render. A <code>null</code> return value is not an error: It indicates that
	 * this object completed request processing itself, thus there is no ModelAndView
	 * to render.
	 * @param request current HTTP request
	 * @param response current HTTP response
	 * @return a ModelAndView to render, or <code>null</code> if handled directly
	 * @throws Exception in case of errors
	 */
	ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) throws Exception;

}

下面给出一个handler的例子：

package com.js.springmvc01;

import java.util.ArrayList;
import java.util.List;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.servlet.mvc.Controller;

import com.js.po.Items;

/**
 * 第一个controller
 * 入门程序：商品列表的查询
 * @author jiangs
 *
 */
public class ItemController01 implements Controller{

	@Override
	public ModelAndView handleRequest(HttpServletRequest request,
			HttpServletResponse response) throws Exception {
		//使用静态数据把商品列表显示在jsp页面
		List<Items> itemsList = new ArrayList<Items>();
		Items items_1 = new Items();
		items_1.setName("联想笔记本");
		items_1.setPrice(6000f);
		items_1.setDetail("ThinkPad T430联想笔记本电脑");
		
		Items items_2 = new Items();
		items_2.setName("苹果手机");
		items_2.setPrice(5000f);
		items_2.setDetail("iphone6苹果手机！");
		
		itemsList.add(items_1);
		itemsList.add(items_2);
		//将list传到页面
//		原来的做法，是set到request域中，现在使用modelandview来做
//		request.setAttribute("itemsList", itemsList);
		//定义modelandview对象
		ModelAndView modelAndView = new ModelAndView();
		//将数据填充到request域
		modelAndView.addObject("itemsList", itemsList);
		//指定转发的jsp页面
		//指定jsp的路径
		modelAndView.setViewName("/WEB-INF/jsp/itemsList.jsp");
		return modelAndView;
	}
	
}

其中，ModelAndView对象是springmvc封装的模型视图对象。

2、HttpRequestHandlerAdapter（org.springframework.web.servlet.mvc.HttpRequestHandlerAdapter）

源码：

public class HttpRequestHandlerAdapter implements HandlerAdapter {

	public boolean supports(Object handler) {
		return (handler instanceof HttpRequestHandler);
	}

	public ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler)
			throws Exception {

		((HttpRequestHandler) handler).handleRequest(request, response);
		return null;
	}

	public long getLastModified(HttpServletRequest request, Object handler) {
		if (handler instanceof LastModified) {
			return ((LastModified) handler).getLastModified(request);
		}
		return -1L;
	}

}

通过support方法可知，符合该适配器要求的handler必须实现HttpRequestHandler接口，该接口源码：

/*
 * 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;

import java.io.IOException;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

/**
 * Plain handler interface for components that process HTTP requests,
 * analogous to a Servlet. Only declares {@link javax.servlet.ServletException}
 * and {@link java.io.IOException}, to allow for usage within any
 * {@link javax.servlet.http.HttpServlet}}. This interface is essentially the
 * direct equivalent of an HttpServlet, reduced to a central handle method.
 *
 * <p>The easiest way to expose an HttpRequestHandler bean in Spring style
 * is to define it in Spring's root web application context and define
 * an {@link org.springframework.web.context.support.HttpRequestHandlerServlet}
 * in <code>web.xml</code>, pointing at the target HttpRequestHandler bean
 * through its <code>servlet-name</code> which needs to match the target bean name.
 *
 * <p>Supported as a handler type within Spring's
 * {@link org.springframework.web.servlet.DispatcherServlet}, being able
 * to interact with the dispatcher's advanced mapping and interception
 * facilities. This is the recommended way of exposing an HttpRequestHandler,
 * while keeping the handler implementations free of direct dependencies
 * on a DispatcherServlet environment.
 *
 * <p>Typically implemented to generate binary responses directly,
 * with no separate view resource involved. This differentiates it from a
 * {@link org.springframework.web.servlet.mvc.Controller} within Spring's Web MVC
 * framework. The lack of a {@link org.springframework.web.servlet.ModelAndView}
 * return value gives a clearer signature to callers other than the
 * DispatcherServlet, indicating that there will never be a view to render.
 *
 * <p>As of Spring 2.0, Spring's HTTP-based remote exporters, such as
 * {@link org.springframework.remoting.httpinvoker.HttpInvokerServiceExporter}
 * and {@link org.springframework.remoting.caucho.HessianServiceExporter},
 * implement this interface rather than the more extensive Controller interface,
 * for minimal dependencies on Spring-specific web infrastructure.
 *
 * <p>Note that HttpRequestHandlers may optionally implement the
 * {@link org.springframework.web.servlet.mvc.LastModified} interface,
 * just like Controllers can, <i>provided that they run within Spring's
 * DispatcherServlet</i>. However, this is usually not necessary, since
 * HttpRequestHandlers typically only support POST requests to begin with.
 * Alternatively, a handler may implement the "If-Modified-Since" HTTP
 * header processing manually within its <code>handle</code> method.
 *
 * @author Juergen Hoeller
 * @since 2.0
 * @see org.springframework.web.context.support.HttpRequestHandlerServlet
 * @see org.springframework.web.servlet.DispatcherServlet
 * @see org.springframework.web.servlet.ModelAndView
 * @see org.springframework.web.servlet.mvc.Controller
 * @see org.springframework.web.servlet.mvc.LastModified
 * @see org.springframework.web.servlet.mvc.HttpRequestHandlerAdapter
 * @see org.springframework.remoting.httpinvoker.HttpInvokerServiceExporter
 * @see org.springframework.remoting.caucho.HessianServiceExporter
 * @see org.springframework.remoting.caucho.BurlapServiceExporter
 */
public interface HttpRequestHandler {

	/**
	 * Process the given request, generating a response.
	 * @param request current HTTP request
	 * @param response current HTTP response
	 * @throws ServletException in case of general errors
	 * @throws IOException in case of I/O errors
	 */
	void handleRequest(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException;

}

下面就是一个handler的例子：

package com.js.springmvc01;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.web.HttpRequestHandler;
import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.servlet.mvc.Controller;

import com.js.po.Items;

/**
 * 第2个controller
 * 适配：HttpRequestHandlerAdapter，
 * 该适配器要求实现HttpRequestHandler接口
 * 入门程序：商品列表的查询
 * @author jiangs
 *
 */
public class ItemController02 implements HttpRequestHandler{

	@Override
	public void handleRequest(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		//使用静态数据把商品列表显示在jsp页面
		List<Items> itemsList = new ArrayList<Items>();
		Items items_1 = new Items();
		items_1.setName("联想笔记本");
		items_1.setPrice(6000f); 
		items_1.setDetail("ThinkPad T430联想笔记本电脑");
		
		Items items_2 = new Items();
		items_2.setName("苹果手机");
		items_2.setPrice(5000f);
		items_2.setDetail("iphone6苹果手机！");
		
		itemsList.add(items_1);
		itemsList.add(items_2);
		request.setAttribute("itemsList", itemsList);
		//转发到jsp页面
		request.getRequestDispatcher("/WEB-INF/jsp/itemsList.jsp").forward(request, response);
	}
	
}

比较可知，HttpRequestHandler接口中没有ModelAndView对象，所以我们使用requet对象来进行请求转发。