SpringMVC(十)：SpringMVC 處理輸出模型數據之Map及Model

Spring MVC提供了以下幾種途徑輸出模型數據：

1）ModelAndView：處理方法返回值類型為ModelAndView時，方法體即可通過該對象添加模型數據；

2）Map及Model：處理方法入參為org.springframework.ui.Model、org.springframework.ui.ModelMap或java.util.Map時，處理方法返回時，Map中的數據會自動被添加到模型中；

3）@SessionAttributes：將模型中的某個屬性暫存到HttpSeession中，以便多個請求之間可以共享這個屬性；

4）@ModelAttribute：方法入參標注該注解后，入參的對象就會放到數據模型中。

Map及Model

使用示例：

在TestModelData.java類中追加方法：

    @RequestMapping("/testMap")
    public String testMap(Map<String, Object> map) {
        map.put("mapTestKey", "mapTestValue");
        return SUCCESS;
    }

修改/WEB-INF/views/success.jsp頁面，中

測試地址：http://localhost:8080/SpringMVC_02/testMap

返回頁面打印信息：

SUCCESS PAGE 
current time: 
testMap mapTestKey:mapTestValue 

查看此時入參Map實際什么類型，修改TestModelData.java代碼：

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

打印結果：

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

從打印結果發現，實際上入參Map是BildingAwareModelMap

public class BindingAwareModelMap extends ExtendedModelMap 

public class ExtendedModelMap extends ModelMap implements Model 

由於BildingAwareModelMap繼承了ExtendedModelMap，而ExtendedModelMap又繼承了ModeMap和實現了Model接口，因此，這里Map入參可以替換為ModelMap和Model。

調試：設置斷點在“   map.put("mapTestKey", "mapTestValue");”行處

從調試跟蹤發現，入參map最終被解析的類是MapMethodProcessor.java

MapMethodProcessor.java

/*
 * Copyright 2002-2017 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.method.annotation;

import java.util.Map;

import org.springframework.core.MethodParameter;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.web.bind.support.WebDataBinderFactory;
import org.springframework.web.context.request.NativeWebRequest;
import org.springframework.web.method.support.HandlerMethodArgumentResolver;
import org.springframework.web.method.support.HandlerMethodReturnValueHandler;
import org.springframework.web.method.support.ModelAndViewContainer;

/**
 * Resolves {@link Map} method arguments and handles {@link Map} return values.
 *
 * <p>A Map return value can be interpreted in more than one ways depending
 * on the presence of annotations like {@code @ModelAttribute} or
 * {@code @ResponseBody}. Therefore this handler should be configured after
 * the handlers that support these annotations.
 *
 * @author Rossen Stoyanchev
 * @since 3.1
 */
public class MapMethodProcessor implements HandlerMethodArgumentResolver, HandlerMethodReturnValueHandler {

    @Override
    public boolean supportsParameter(MethodParameter parameter) {
        return Map.class.isAssignableFrom(parameter.getParameterType());
    }

    @Override
    @Nullable
    public Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,
            NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception {

        Assert.state(mavContainer != null, "ModelAndViewContainer is required for model exposure");
        return mavContainer.getModel();
    }

    @Override
    public boolean supportsReturnType(MethodParameter returnType) {
        return Map.class.isAssignableFrom(returnType.getParameterType());
    }

    @Override
    @SuppressWarnings({ "unchecked", "rawtypes" })
    public void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,
            ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception {

        if (returnValue instanceof Map){
            mavContainer.addAllAttributes((Map) returnValue);
        }
        else if (returnValue != null) {
            // should not happen
            throw new UnsupportedOperationException("Unexpected return type: " +
                    returnType.getParameterType().getName() + " in method: " + returnType.getMethod());
        }
    }

}

當頁面返回時，該入參會被加載到Request請求域。