spring mvc:控制层梳理

技术2022-05-19 17

言归正传，研究一下注解下的控制层。我习惯于使用JSTL展示页面，因此需要在原lib基础上增加jstl.jar和standard.jar，详细lib依赖如下：

引用 aopalliance-1.0.jar commons-logging-1.1.1.jar log4j-1.2.15.jar spring-beans-2.5.6.jar spring-context-2.5.6.jar spring-context-support-2.5.6.jar spring-core-2.5.6.jar spring-tx-2.5.6.jar spring-web-2.5.6.jar spring-webmvc-2.5.6.jar standard.jar jstl.jar

上一篇文中，我们定义了控制器AccountController： AccountController.java

Java代码 /** * 2010-1-23 */ package org.zlex.spring.controller; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.stereotype.Controller; import org.springframework.web.bind.ServletRequestUtils; import org.springframework.web.bind.annotation.RequestMapping; import org.springframework.web.bind.annotation.RequestMethod; import org.zlex.spring.service.AccountService; /** * * @author <a href="mailto:zlex.dongliang@gmail.com">梁栋</a> * @version 1.0 * @since 1.0 */ @Controller @RequestMapping("/account.do") public class AccountController { @Autowired private AccountService accountService; @RequestMapping(method = RequestMethod.GET) public void hello(HttpServletRequest request, HttpServletResponse response) throws Exception { String username = ServletRequestUtils.getRequiredStringParameter( request, "username"); String password = ServletRequestUtils.getRequiredStringParameter( request, "password"); System.out.println(accountService.verify(username, password)); } } /** * 2010-1-23 */ package org.zlex.spring.controller; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.stereotype.Controller; import org.springframework.web.bind.ServletRequestUtils; import org.springframework.web.bind.annotation.RequestMapping; import org.springframework.web.bind.annotation.RequestMethod; import org.zlex.spring.service.AccountService; /** * * @author <a href="mailto:zlex.dongliang@gmail.com">梁栋</a> * @version 1.0 * @since 1.0 */ @Controller @RequestMapping("/account.do") public class AccountController { @Autowired private AccountService accountService; @RequestMapping(method = RequestMethod.GET) public void hello(HttpServletRequest request, HttpServletResponse response) throws Exception { String username = ServletRequestUtils.getRequiredStringParameter( request, "username"); String password = ServletRequestUtils.getRequiredStringParameter( request, "password"); System.out.println(accountService.verify(username, password)); } }

先说注解@RequestMapping 这里使用注解@RequestMapping(method = RequestMethod.GET)指定这个方法为get请求时调用。同样，我们可以使用注解@RequestMapping(method = RequestMethod.POST)指定该方法接受post请求。

Java代码 @Controller @RequestMapping("/account.do") public class AccountController { @RequestMapping(method = RequestMethod.GET) public void get() { } @RequestMapping(method = RequestMethod.POST) public void post() { } } @Controller @RequestMapping("/account.do") public class AccountController { @RequestMapping(method = RequestMethod.GET) public void get() { } @RequestMapping(method = RequestMethod.POST) public void post() { } }

这与我们久别的Servlet很相像，类似于doGet()和doPost()方法！我们也可以将其改造为多动作控制器，如下代码所示：

Java代码 @Controller @RequestMapping("/account.do") public class AccountController { @RequestMapping(params = "method=login") public void login() { } @RequestMapping(params = "method=logout") public void logout() { } @Controller @RequestMapping("/account.do") public class AccountController { @RequestMapping(params = "method=login") public void login() { } @RequestMapping(params = "method=logout") public void logout() { }

这样，我们可以通过参数“method”指定不同的参数值从而通过请求（"/account.do?method=login"和"/account.do?method=logout"）调用不同的方法！注意：使用多动作控制器必须在配置文件中加入注解支持！

Xml代码 <bean class="org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter" /> <bean class="org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter" />

当然，我们也可以将注解@RequestMapping指定到某一个方法上，如：

Java代码 @Controller public class AccountController { @RequestMapping("/a.do") public void a() {} @RequestMapping("/b.do") public void b() {} } @Controller public class AccountController { @RequestMapping("/a.do") public void a() {} @RequestMapping("/b.do") public void b() {} }

这样，请求“a.do”和“b.do”将对应不同的方法a() 和b()。这使得一个控制器可以同时承载多个请求！ @RequestMapping("/account.do")是@RequestMapping(value="/account.do")的简写！再说输入参数！这里的方法名可以随意定义，但是参数和返回值却又要求！为什么？直接看源代码，我们就能找到答案！ AnnotationMethodHandlerAdapter.java部分源代码——有关参数部分：

Java代码 @Override protected Object resolveStandardArgument(Class parameterType, NativeWebRequest webRequest) throws Exception { HttpServletRequest request = (HttpServletRequest) webRequest.getNativeRequest(); HttpServletResponse response = (HttpServletResponse) webRequest.getNativeResponse(); if (ServletRequest.class.isAssignableFrom(parameterType)) { return request; } else if (ServletResponse.class.isAssignableFrom(parameterType)) { this.responseArgumentUsed = true; return response; } else if (HttpSession.class.isAssignableFrom(parameterType)) { return request.getSession(); } else if (Principal.class.isAssignableFrom(parameterType)) { return request.getUserPrincipal(); } else if (Locale.class.equals(parameterType)) { return RequestContextUtils.getLocale(request); } else if (InputStream.class.isAssignableFrom(parameterType)) { return request.getInputStream(); } else if (Reader.class.isAssignableFrom(parameterType)) { return request.getReader(); } else if (OutputStream.class.isAssignableFrom(parameterType)) { this.responseArgumentUsed = true; return response.getOutputStream(); } else if (Writer.class.isAssignableFrom(parameterType)) { this.responseArgumentUsed = true; return response.getWriter(); } return super.resolveStandardArgument(parameterType, webRequest); } @Override protected Object resolveStandardArgument(Class parameterType, NativeWebRequest webRequest) throws Exception { HttpServletRequest request = (HttpServletRequest) webRequest.getNativeRequest(); HttpServletResponse response = (HttpServletResponse) webRequest.getNativeResponse(); if (ServletRequest.class.isAssignableFrom(parameterType)) { return request; } else if (ServletResponse.class.isAssignableFrom(parameterType)) { this.responseArgumentUsed = true; return response; } else if (HttpSession.class.isAssignableFrom(parameterType)) { return request.getSession(); } else if (Principal.class.isAssignableFrom(parameterType)) { return request.getUserPrincipal(); } else if (Locale.class.equals(parameterType)) { return RequestContextUtils.getLocale(request); } else if (InputStream.class.isAssignableFrom(parameterType)) { return request.getInputStream(); } else if (Reader.class.isAssignableFrom(parameterType)) { return request.getReader(); } else if (OutputStream.class.isAssignableFrom(parameterType)) { this.responseArgumentUsed = true; return response.getOutputStream(); } else if (Writer.class.isAssignableFrom(parameterType)) { this.responseArgumentUsed = true; return response.getWriter(); } return super.resolveStandardArgument(parameterType, webRequest); }

也就是说，如果我们想要在自定义的方法中获得一些个“标准”输入参数，参数类型必须包含在以下类型中：

引用 ServletRequest ServletResponse HttpSession Principal Locale InputStream OutputStream Reader Writer

当然，上述接口其实都是对于HttpServletRequest和HttpServletResponse的扩展。此外，我们还可以定义自己的参数。注意：自定义参数必须是实现类，绝非接口！Spring容器将帮你完成对象初始化工作！比如说上文中，我们需要参数username和password。我们可以这么写：

Java代码 @RequestMapping(method = RequestMethod.GET) public void hello(String username,String password) { System.out.println(accountService.verify(username, password)); } @RequestMapping(method = RequestMethod.GET) public void hello(String username,String password) { System.out.println(accountService.verify(username, password)); }

如果参数名不能与这里的变量名保持一致，那么我们可以使用注解@RequestParam进行强制绑定，代码如下所示：

Java代码 @RequestMapping(method = RequestMethod.GET) public void hello(@RequestParam("username") String u, @RequestParam("password") String p) { System.out.println(accountService.verify(u, p)); } @RequestMapping(method = RequestMethod.GET) public void hello(@RequestParam("username") String u, @RequestParam("password") String p) { System.out.println(accountService.verify(u, p)); }

这比起我们之前写的代码有所简洁：

Java代码 @RequestMapping(method = RequestMethod.GET) public void hello(HttpServletRequest request, HttpServletResponse response) throws Exception { String username = ServletRequestUtils.getRequiredStringParameter( request, "username"); String password = ServletRequestUtils.getRequiredStringParameter( request, "password"); System.out.println(accountService.verify(username, password)); } @RequestMapping(method = RequestMethod.GET) public void hello(HttpServletRequest request, HttpServletResponse response) throws Exception { String username = ServletRequestUtils.getRequiredStringParameter( request, "username"); String password = ServletRequestUtils.getRequiredStringParameter( request, "password"); System.out.println(accountService.verify(username, password)); }

ServletRequestUtils类的工作已经由Spring底层实现了，我们只需要把参数名定义一致即可，其内部取参无需关心！除了传入参数，我们还可以定义即将传出的参数，如加入ModelMap参数：

Java代码 @SuppressWarnings("unchecked") @RequestMapping(method = RequestMethod.GET) public Map hello(String username, String password, ModelMap model) { System.out.println(accountService.verify(username, password)); model.put("msg", username); return model; } @SuppressWarnings("unchecked") @RequestMapping(method = RequestMethod.GET) public Map hello(String username, String password, ModelMap model) { System.out.println(accountService.verify(username, password)); model.put("msg", username); return model; }

这时，我们没有定义页面名称，Spring容器将根据请求名指定同名view，即如果是jap页面，则account.do->account.jsp！不得不承认，这样写起来的确减少了代码量！接着说输出参数！通过ModelMap，我们可以绑定输出到的页面的参数，但最终我们将要返回到何种页面呢？再次查看AnnotationMethodHandlerAdapter源代码！ AnnotationMethodHandlerAdapter.java部分源代码——有关返回值部分：

Java代码 @SuppressWarnings("unchecked") public ModelAndView getModelAndView(Method handlerMethod, Class handlerType, Object returnValue, ExtendedModelMap implicitModel, ServletWebRequest webRequest) { if (returnValue instanceof ModelAndView) { ModelAndView mav = (ModelAndView) returnValue; mav.getModelMap().mergeAttributes(implicitModel); return mav; } else if (returnValue instanceof Model) { return new ModelAndView().addAllObjects(implicitModel).addAllObjects(((Model) returnValue).asMap()); } else if (returnValue instanceof Map) { return new ModelAndView().addAllObjects(implicitModel).addAllObjects((Map) returnValue); } else if (returnValue instanceof View) { return new ModelAndView((View) returnValue).addAllObjects(implicitModel); } else if (returnValue instanceof String) { return new ModelAndView((String) returnValue).addAllObjects(implicitModel); } else if (returnValue == null) { // Either returned null or was 'void' return. if (this.responseArgumentUsed || webRequest.isNotModified()) { return null; } else { // Assuming view name translation... return new ModelAndView().addAllObjects(implicitModel); } } else if (!BeanUtils.isSimpleProperty(returnValue.getClass())) { // Assume a single model attribute... ModelAttribute attr = AnnotationUtils.findAnnotation(handlerMethod, ModelAttribute.class); String attrName = (attr != null ? attr.value() : ""); ModelAndView mav = new ModelAndView().addAllObjects(implicitModel); if ("".equals(attrName)) { Class resolvedType = GenericTypeResolver.resolveReturnType(handlerMethod, handlerType); attrName = Conventions.getVariableNameForReturnType(handlerMethod, resolvedType, returnValue); } return mav.addObject(attrName, returnValue); } else { throw new IllegalArgumentException("Invalid handler method return value: " + returnValue); } } @SuppressWarnings("unchecked") public ModelAndView getModelAndView(Method handlerMethod, Class handlerType, Object returnValue, ExtendedModelMap implicitModel, ServletWebRequest webRequest) { if (returnValue instanceof ModelAndView) { ModelAndView mav = (ModelAndView) returnValue; mav.getModelMap().mergeAttributes(implicitModel); return mav; } else if (returnValue instanceof Model) { return new ModelAndView().addAllObjects(implicitModel).addAllObjects(((Model) returnValue).asMap()); } else if (returnValue instanceof Map) { return new ModelAndView().addAllObjects(implicitModel).addAllObjects((Map) returnValue); } else if (returnValue instanceof View) { return new ModelAndView((View) returnValue).addAllObjects(implicitModel); } else if (returnValue instanceof String) { return new ModelAndView((String) returnValue).addAllObjects(implicitModel); } else if (returnValue == null) { // Either returned null or was 'void' return. if (this.responseArgumentUsed || webRequest.isNotModified()) { return null; } else { // Assuming view name translation... return new ModelAndView().addAllObjects(implicitModel); } } else if (!BeanUtils.isSimpleProperty(returnValue.getClass())) { // Assume a single model attribute... ModelAttribute attr = AnnotationUtils.findAnnotation(handlerMethod, ModelAttribute.class); String attrName = (attr != null ? attr.value() : ""); ModelAndView mav = new ModelAndView().addAllObjects(implicitModel); if ("".equals(attrName)) { Class resolvedType = GenericTypeResolver.resolveReturnType(handlerMethod, handlerType); attrName = Conventions.getVariableNameForReturnType(handlerMethod, resolvedType, returnValue); } return mav.addObject(attrName, returnValue); } else { throw new IllegalArgumentException("Invalid handler method return value: " + returnValue); } } }

返回值的定义十分庞大，或者说可怕的if-else多少有点让我觉得厌恶！我们可以定义以下类型的返回值：

引用 ModelAndView Model View Map String null

ModelAndView、Model和View都是Spring之前版本所特有的元素，Map对应于传入参数ModelMap，String定义页面名称，null即对应void类型方法！最常用的实现方式如下：

Java代码 @SuppressWarnings("unchecked") @RequestMapping(method = RequestMethod.GET) public String hello(String username, String password, ModelMap model) { System.out.println(accountService.verify(username, password)); model.put("msg", username); return "account"; } @SuppressWarnings("unchecked") @RequestMapping(method = RequestMethod.GET) public String hello(String username, String password, ModelMap model) { System.out.println(accountService.verify(username, password)); model.put("msg", username); return "account"; }

当然，对于我来说在返回值中写入这么一个字符串多少有点不能接受，于是我还是乐于使用输入参数ModelMap+输出参数Map的方式。给出一个完整的AccountController实现： AccountController.java

Java代码 /** * 2010-1-23 */ package org.zlex.spring.controller; import java.util.Map; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.stereotype.Controller; import org.springframework.ui.ModelMap; import org.springframework.web.bind.annotation.RequestMapping; import org.springframework.web.bind.annotation.RequestMethod; import org.zlex.spring.service.AccountService; /** * * @author <a href="mailto:zlex.dongliang@gmail.com">梁栋</a> * @version 1.0 * @since 1.0 */ @Controller @RequestMapping("/account.do") public class AccountController { @Autowired private AccountService accountService; @SuppressWarnings("unchecked") @RequestMapping(method = RequestMethod.GET) public Map hello(String username, String password, ModelMap model) { System.out.println(accountService.verify(username, password)); model.put("msg", username); return model; } } /** * 2010-1-23 */ package org.zlex.spring.controller; import java.util.Map; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.stereotype.Controller; import org.springframework.ui.ModelMap; import org.springframework.web.bind.annotation.RequestMapping; import org.springframework.web.bind.annotation.RequestMethod; import org.zlex.spring.service.AccountService; /** * * @author <a href="mailto:zlex.dongliang@gmail.com">梁栋</a> * @version 1.0 * @since 1.0 */ @Controller @RequestMapping("/account.do") public class AccountController { @Autowired private AccountService accountService; @SuppressWarnings("unchecked") @RequestMapping(method = RequestMethod.GET) public Map hello(String username, String password, ModelMap model) { System.out.println(accountService.verify(username, password)); model.put("msg", username); return model; } }

最后说注解@Session 如果想将某个ModelMap中的参数指定到Session中，可以使用@Session注解，将其绑定为Session熟悉，代码如下所示：

Java代码 @Controller @RequestMapping("/account.do") @SessionAttributes("msg") public class AccountController { @Autowired private AccountService accountService; @SuppressWarnings("unchecked") @RequestMapping(method = RequestMethod.GET) public Map hello(String username, String password, ModelMap model) { System.out.println(accountService.verify(username, password)); model.put("msg", username); return model; } } @Controller @RequestMapping("/account.do") @SessionAttributes("msg") public class AccountController { @Autowired private AccountService accountService; @SuppressWarnings("unchecked") @RequestMapping(method = RequestMethod.GET) public Map hello(String username, String password, ModelMap model) { System.out.println(accountService.verify(username, password)); model.put("msg", username); return model; } }

当然，我们还需要配置一下对应的视图解析器，给出完整配置： servelt.xml

Xml代码 <?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:p="http://www.springframework.org/schema/p" xmlns:context="http://www.springframework.org/schema/context" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd"> <context:component-scan base-package="org.zlex.spring.controller" /> <bean id="urlMapping" class="org.springframework.web.servlet.mvc.annotation.DefaultAnnotationHandlerMapping" /> <bean class="org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter" /> <bean id="jstlViewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver" p:viewClass="org.springframework.web.servlet.view.JstlView" p:prefix="/WEB-INF/page/" p:suffix=".jsp" /> </beans> <?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:p="http://www.springframework.org/schema/p" xmlns:context="http://www.springframework.org/schema/context" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd"> <context:component-scan base-package="org.zlex.spring.controller" /> <bean id="urlMapping" class="org.springframework.web.servlet.mvc.annotation.DefaultAnnotationHandlerMapping" /> <bean class="org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter" /> <bean id="jstlViewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver" p:viewClass="org.springframework.web.servlet.view.JstlView" p:prefix="/WEB-INF/page/" p:suffix=".jsp" /> </beans>

这里使用了JstlView作为视图解析器。同时，指定前缀路径为"/WEB-INF/page/"，后缀路径为".jsp"。也就是说，Spring容器将会在这个路径中寻找匹配的jsp文件！注意加入xmlns:p="http://www.springframework.org/schema/p"命名空间！再给出页面内容： taglib.jsp

Jsp代码 <%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%> <%@ taglib prefix="fmt" uri="http://java.sun.com/jsp/jstl/fmt"%> <%@ taglib prefix="sql" uri="http://java.sun.com/jsp/jstl/sql"%> <%@ taglib prefix="x" uri="http://java.sun.com/jsp/jstl/xml"%> <%@ taglib prefix="fn" uri="http://java.sun.com/jsp/jstl/functions"%> <%@ taglib prefix="spring" uri="http://www.springframework.org/tags"%> <%@ taglib prefix="form" uri="http://www.springframework.org/tags/form"%> <%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%> <%@ taglib prefix="fmt" uri="http://java.sun.com/jsp/jstl/fmt"%> <%@ taglib prefix="sql" uri="http://java.sun.com/jsp/jstl/sql"%> <%@ taglib prefix="x" uri="http://java.sun.com/jsp/jstl/xml"%> <%@ taglib prefix="fn" uri="http://java.sun.com/jsp/jstl/functions"%> <%@ taglib prefix="spring" uri="http://www.springframework.org/tags"%> <%@ taglib prefix="form" uri="http://www.springframework.org/tags/form"%>

account.jap

Jsp代码 <%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%> <%@ include file="/WEB-INF/page/taglib.jsp"%> <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> <title>Account</title> </head> <body> <c:out value="${msg}"></c:out> </body> </html> <%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%> <%@ include file="/WEB-INF/page/taglib.jsp"%> <!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <html> <head> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> <title>Account</title> </head> <body> <c:out value="${msg}"></c:out> </body> </html>

目录结构如图所示：启动应用，最后将得到一个带有内容的页面，如图：代码见附件！

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