SpringMVC(十)：SpringMVC 处理输出模型数据之Map及Model-白红宇

SpringMVC(十)：SpringMVC 处理输出模型数据之Map及Model

阅读量：5955 次

发布时间：2019-06-19

本文共 4704 字，大约阅读时间需要 15 分钟。

Spring MVC提供了以下几种途径输出模型数据：

1）ModelAndView：处理方法返回值类型为ModelAndView时，方法体即可通过该对象添加模型数据；

2）Map及Model：处理方法入参为org.springframework.ui.Model、org.springframework.ui.ModelMap或java.util.Map时，处理方法返回时，Map中的数据会自动被添加到模型中；

3）@SessionAttributes：将模型中的某个属性暂存到HttpSeession中，以便多个请求之间可以共享这个属性；

4）@ModelAttribute：方法入参标注该注解后，入参的对象就会放到数据模型中。

Map及Model

使用示例：

在TestModelData.java类中追加方法：

1     @RequestMapping("/testMap")2     public String testMap(Map
     
       map) {3         map.put("mapTestKey", "mapTestValue");4         return SUCCESS;5     }

修改/WEB-INF/views/success.jsp页面，中

测试地址：http://localhost:8080/SpringMVC_02/testMap

返回页面打印信息：

SUCCESS PAGE
current time:
testMap mapTestKey:mapTestValue

查看此时入参Map实际什么类型，修改TestModelData.java代码：

@RequestMapping("/testMap")    public String testMap(Map
     
       map) {        map.put("mapTestKey", "mapTestValue");        System.out.println(map);        System.out.println(map.getClass());        return SUCCESS;    }

打印结果：

{mapTestKey=mapTestValue}class org.springframework.validation.support.BindingAwareModelMap

从打印结果发现，实际上入参Map是BildingAwareModelMap

public class BindingAwareModelMap extends ExtendedModelMap

public class ExtendedModelMap extends ModelMap implements Model

由于BildingAwareModelMap继承了ExtendedModelMap，而ExtendedModelMap又继承了ModeMap和实现了Model接口，因此，这里Map入参可以替换为ModelMap和Model。

调试：设置断点在“ map.put("mapTestKey", "mapTestValue");”行处

从调试跟踪发现，入参map最终被解析的类是MapMethodProcessor.java

MapMethodProcessor.java

1 /* 2  * Copyright 2002-2017 the original author or authors. 3  * 4  * Licensed under the Apache License, Version 2.0 (the "License"); 5  * you may not use this file except in compliance with the License. 6  * You may obtain a copy of the License at 7  * 8  *      http://www.apache.org/licenses/LICENSE-2.0 9  *10  * Unless required by applicable law or agreed to in writing, software11  * distributed under the License is distributed on an "AS IS" BASIS,12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.13  * See the License for the specific language governing permissions and14  * limitations under the License.15  */16 17 package org.springframework.web.method.annotation;18 19 import java.util.Map;20 21 import org.springframework.core.MethodParameter;22 import org.springframework.lang.Nullable;23 import org.springframework.util.Assert;24 import org.springframework.web.bind.support.WebDataBinderFactory;25 import org.springframework.web.context.request.NativeWebRequest;26 import org.springframework.web.method.support.HandlerMethodArgumentResolver;27 import org.springframework.web.method.support.HandlerMethodReturnValueHandler;28 import org.springframework.web.method.support.ModelAndViewContainer;29 30 /**31  * Resolves {
     @link Map} method arguments and handles {
     @link Map} return values.32  *33  * A Map return value can be interpreted in more than one ways depending34  * on the presence of annotations like {
     @code @ModelAttribute} or35  * {
     @code @ResponseBody}. Therefore this handler should be configured after36  * the handlers that support these annotations.37  *38  * @author Rossen Stoyanchev39  * @since 3.140  */41 public class MapMethodProcessor implements HandlerMethodArgumentResolver, HandlerMethodReturnValueHandler {42 43     @Override44     public boolean supportsParameter(MethodParameter parameter) {45         return Map.class.isAssignableFrom(parameter.getParameterType());46     }47 48     @Override49     @Nullable50     public Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,51             NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception {52 53         Assert.state(mavContainer != null, "ModelAndViewContainer is required for model exposure");54         return mavContainer.getModel();55     }56 57     @Override58     public boolean supportsReturnType(MethodParameter returnType) {59         return Map.class.isAssignableFrom(returnType.getParameterType());60     }61 62     @Override63     @SuppressWarnings({ "unchecked", "rawtypes" })64     public void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,65             ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {66 67         if (returnValue instanceof Map){68             mavContainer.addAllAttributes((Map) returnValue);69         }70         else if (returnValue != null) {71             // should not happen72             throw new UnsupportedOperationException("Unexpected return type: " +73                     returnType.getParameterType().getName() + " in method: " + returnType.getMethod());74         }75     }76 77 }

View Code

当页面返回时，该入参会被加载到Request请求域。

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