Spring中Model、ModelMap、ModelAndView理解和具体使用总结

大家好，又见面了，我是你们的朋友全栈君。

在了解这三者之前，需要知道一点：SpringMVC在调用方法前会创建一个隐含的数据模型，作为模型数据的存储容器，成为”隐含模型”。
也就是说在每一次的前后台请求的时候会随带这一个背包，不管你用没有，这个背包确实是存在的，用来盛放我们请求交互传递的值；关于这一点，spring里面有一个注解：
@ModelAttribute ：被该注解修饰的方法，会在每一次请求时优先执行，用于接收前台jsp页面传入的参数
例子：

@Controller
public class User1Controller{

    private static final Log logger = LogFactory.getLog(User1Controller.class);

    // @ModelAttribute修饰的方法会先于login调用，该方法用于接收前台jsp页面传入的参数
    @ModelAttribute
    public void userModel(String loginname,String password,
             Model model){
        logger.info("userModel");
        // 创建User对象存储jsp页面传入的参数
        User2 user = new User2();
        user.setLoginname(loginname);
        user.setPassword(password);
        // 将User对象添加到Model当中
        model.addAttribute("user", user);
    }

    @RequestMapping(value="/login1")
     public String login(Model model){
        logger.info("login");
        // 从Model当中取出之前存入的名为user的对象
        User2 user = (User2) model.asMap().get("user");
        System.out.println(user);
        // 设置user对象的username属性
        user.setUsername("测试");
        return "result1";
    }

在前端向后台请求时，spring会自动创建Model与ModelMap实例，我们只需拿来使用即可；
这里写图片描述
无论是Mode还是ModelMap底层都是使用BindingAwareModelMap，所以两者基本没什么区别；
我们可以简单看一下两者区别：

①Model

Model是一个接口，它的实现类为ExtendedModelMap，继承ModelMap类

public class ExtendedModelMap extends ModelMap implements Model

②ModelMap

ModelMap继承LinkedHashMap，spring框架自动创建实例并作为controller的入参，用户无需自己创建

public class ModelMap extends LinkedHashMap

而是对于ModelAndView顾名思义，ModelAndView指模型和视图的集合，既包含模型又包含视图；ModelAndView的实例是开发者自己手动创建的，这也是和ModelMap主要不同点之一；ModelAndView其实就是两个作用，一个是指定返回页面，另一个是在返回页面的同时添加属性；它的源码：

public class ModelAndView { 
     

    /** View instance or view name String */  
    private Object view  //该属性用来存储返回的视图信息
/** Model Map */  
private ModelMap model;//<span style="color: rgb(0, 130, 0); font-family: Consolas, 'Courier New', Courier, mono, serif; line-height: 18px;">该属性用来存储处理后的结果数据</span> 

/** * Indicates whether or not this instance has been cleared with a call to {@link #clear()}. */  
private boolean cleared = false;  


/** * Default constructor for bean-style usage: populating bean * properties instead of passing in constructor arguments. * @see #setView(View) * @see #setViewName(String) */  
public ModelAndView() {  
}  

/** * Convenient constructor when there is no model data to expose. * Can also be used in conjunction with <code>addObject</code>. * @param viewName name of the View to render, to be resolved * by the DispatcherServlet's ViewResolver * @see #addObject */  
public ModelAndView(String viewName) {  
    this.view = viewName;  
}  

/** * Convenient constructor when there is no model data to expose. * Can also be used in conjunction with <code>addObject</code>. * @param view View object to render * @see #addObject */  
public ModelAndView(View view) {  
    this.view = view;  
}  

/** * Creates new ModelAndView given a view name and a model. * @param viewName name of the View to render, to be resolved * by the DispatcherServlet's ViewResolver * @param model Map of model names (Strings) to model objects * (Objects). Model entries may not be <code>null</code>, but the * model Map may be <code>null</code> if there is no model data. */  
public ModelAndView(String viewName, Map<String, ?> model) {  
    this.view = viewName;  
    if (model != null) {  
        getModelMap().addAllAttributes(model);  
    }  
}  

/** * Creates new ModelAndView given a View object and a model. * <emphasis>Note: the supplied model data is copied into the internal * storage of this class. You should not consider to modify the supplied * Map after supplying it to this class</emphasis> * @param view View object to render * @param model Map of model names (Strings) to model objects * (Objects). Model entries may not be <code>null</code>, but the * model Map may be <code>null</code> if there is no model data. */  
public ModelAndView(View view, Map<String, ?> model) {  
    this.view = view;  
    if (model != null) {  
        getModelMap().addAllAttributes(model);  
    }  
}  

/** * Convenient constructor to take a single model object. * @param viewName name of the View to render, to be resolved * by the DispatcherServlet's ViewResolver * @param modelName name of the single entry in the model * @param modelObject the single model object */  
public ModelAndView(String viewName, String modelName, Object modelObject) {  
    this.view = viewName;  
    addObject(modelName, modelObject);  
}  

/** * Convenient constructor to take a single model object. * @param view View object to render * @param modelName name of the single entry in the model * @param modelObject the single model object */  
public ModelAndView(View view, String modelName, Object modelObject) {  
    this.view = view;  
    addObject(modelName, modelObject);  
}  


/** * Set a view name for this ModelAndView, to be resolved by the * DispatcherServlet via a ViewResolver. Will override any * pre-existing view name or View. */  
public void setViewName(String viewName) {  
    this.view = viewName;  
}  

/** * Return the view name to be resolved by the DispatcherServlet * via a ViewResolver, or <code>null</code> if we are using a View object. */  
public String getViewName() {  
    return (this.view instanceof String ? (String) this.view : null);  
}  

/** * Set a View object for this ModelAndView. Will override any * pre-existing view name or View. */  
public void setView(View view) {  
    this.view = view;  
}  

/** * Return the View object, or <code>null</code> if we are using a view name * to be resolved by the DispatcherServlet via a ViewResolver. */  
public View getView() {  
    return (this.view instanceof View ? (View) this.view : null);  
}  

/** * Indicate whether or not this <code>ModelAndView</code> has a view, either * as a view name or as a direct {@link View} instance. */  
public boolean hasView() {  
    return (this.view != null);  
}  

/** * Return whether we use a view reference, i.e. <code>true</code> * if the view has been specified via a name to be resolved by the * DispatcherServlet via a ViewResolver. */  
public boolean isReference() {  
    return (this.view instanceof String);  
}  

/** * Return the model map. May return <code>null</code>. * Called by DispatcherServlet for evaluation of the model. */  
protected Map<String, Object> getModelInternal() {  
    return this.model;  
}  

/** * Return the underlying <code>ModelMap</code> instance (never <code>null</code>). */  
public ModelMap getModelMap() {  
    if (this.model == null) {  
        this.model = new ModelMap();  
    }  
    return this.model;  
}  

/** * Return the model map. Never returns <code>null</code>. * To be called by application code for modifying the model. */  
public Map<String, Object> getModel() {  
    return getModelMap();  
}  


/** * Add an attribute to the model. * @param attributeName name of the object to add to the model * @param attributeValue object to add to the model (never <code>null</code>) * @see ModelMap#addAttribute(String, Object) * @see #getModelMap() */  
public ModelAndView addObject(String attributeName, Object attributeValue) {  
    getModelMap().addAttribute(attributeName, attributeValue);  
    return this;  
}  

/** * Add an attribute to the model using parameter name generation. * @param attributeValue the object to add to the model (never <code>null</code>) * @see ModelMap#addAttribute(Object) * @see #getModelMap() */  
public ModelAndView addObject(Object attributeValue) {  
    getModelMap().addAttribute(attributeValue);  
    return this;  
}  

/** * Add all attributes contained in the provided Map to the model. * @param modelMap a Map of attributeName -> attributeValue pairs * @see ModelMap#addAllAttributes(Map) * @see #getModelMap() */  
public ModelAndView addAllObjects(Map<String, ?> modelMap) {  
    getModelMap().addAllAttributes(modelMap);  
    return this;  
}  


/** * Clear the state of this ModelAndView object. * The object will be empty afterwards. * <p>Can be used to suppress rendering of a given ModelAndView object * in the <code>postHandle</code> method of a HandlerInterceptor. * @see #isEmpty() * @see HandlerInterceptor#postHandle */  
public void clear() {  
    this.view = null;  
    this.model = null;  
    this.cleared = true;  
}  

/** * Return whether this ModelAndView object is empty, * i.e. whether it does not hold any view and does not contain a model. */  
public boolean isEmpty() {  
    return (this.view == null && CollectionUtils.isEmpty(this.model));  
}  

/** * Return whether this ModelAndView object is empty as a result of a call to {@link #clear} * i.e. whether it does not hold any view and does not contain a model. * <p>Returns <code>false</code> if any additional state was added to the instance * <strong>after</strong> the call to {@link #clear}. * @see #clear() */  
public boolean wasCleared() {  
    return (this.cleared && isEmpty());  
}  


/** * Return diagnostic information about this model and view. */  
@Override  
public String toString() {  
    StringBuilder sb = new StringBuilder("ModelAndView: ");  
    if (isReference()) {  
        sb.append("reference to view with name '").append(this.view).append("'");  
    }  
    else {  
        sb.append("materialized View is [").append(this.view).append(']');  
    }  
    sb.append("; model is ").append(this.model);  
    return sb.toString();  
}

a 它有很多构造方法，对应会有很多使用方法：
例子：
（1）当你只有一个模型属性要返回时，可以在构造器中指定该属性来构造ModelAndView对象：

package com.apress.springrecipes.court.web;  
...  
import org.springframework.web.servlet.ModelAndView;  
import org.springframework.web.servlet.mvc.AbstractController;  
public class WelcomeController extends AbstractController{ 
     
    public ModelAndView handleRequestInternal(HttpServletRequest request,  
        HttpServletResponse response)throws Exception{  
        Date today = new Date();  
        return new ModelAndView("welcome","today",today);  
    }  
}

（2）如果有不止一个属性要返回，可以先将它们传递到一个Map中再来构造ModelAndView对象。

package com.apress.springrecipes.court.web;  
...  
import org.springframework.web.servlet.ModelAndView;  
import org. springframework.web.servlet.mvc.AbstractController;  
public class ReservationQueryController extends AbstractController{  
    ...  
    public ModelAndView handleRequestInternal(HttpServletRequest request,  
        HttpServletResponse response)throws Exception{  
        ...  
        Map<String,Object> model = new HashMap<String,Object>();  
        if(courtName != null){  
            model.put("courtName",courtName);  
            model.put("reservations",reservationService.query(courtName));  
        }  
        return new ModelAndView("reservationQuery",model);  
    }  
}

当然也可以使用spring提供的Model或者ModelMap,这是java.util.Map实现；

package com.apress.springrecipes.court.web;  
...  
import org.springframework.ui.ModelMap;  
import org.springframework.web.servlet.ModelAndView;  
import org.springframework.web.servlet.mvc.AbstractController;  
public class ReservationQueryController extends AbstractController{  
    ...  
    public ModelAndView handleRequestInternal(HttpServletRequest request,  
        HttpServletResponse response)throws Exception{  
        ...  
        ModelMap model = new ModelMap();  
        if(courtName != null){  
            model.addAttribute("courtName",courtName);  
            model.addAttribute("reservations",reservationService.query(courtName));  
        }  
        return new ModelAndView("reservationQuery",model);  
    }  
}

在页面上可以通过el变量方式${key}或者bboss的一系列数据展示标签获取并展示modelmap中的数据；上面主要讲了ModelAndView的使用，其实Model与ModelMap使用方法都是一致；

下面我通过一个下例子展示一下：
在spring项目中，在配置文件中配置好视图解析器：

<!-- 视图解析器 -->
    <bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <!-- 前缀 -->
        <property name="prefix" value="/WEB-INF/jsp/"/>
        <!-- 后缀 -->
        <property name="suffix" value=".jsp"/>
    </bean>

在后台写：

    @RequestMapping("/test1")
    public ModelAndView test1(ModelMap mm ,HttpServletRequest request){
        ModelAndView mv = new ModelAndView("mytest");
        mv.addObject("key1","123");
        mm.addAttribute("key1","1234");
        return mv;
    }//前端为 123 123

    @RequestMapping("/test2")
    public String test2(ModelMap mm ,HttpServletRequest request){
        mm.addAttribute("key1", "1234");
        return "mytest";
    }//前端为 1234 1234 

    @RequestMapping("/test3")
    public String test3(Model mm ,HttpServletRequest request){
        mm.addAttribute("key1", "12345");
        return "mytest";
    }

    @RequestMapping("/test4")
    public String test4(Model mm ,HttpServletRequest request){
        mm.addAttribute("key1", "12345");
        request.setAttribute("key1", "123456");
        return "mytest";
    }//前端为 12345 12345

    @RequestMapping("/test5")
    public String test5(Model mm ,ModelMap mmp,HttpServletRequest request){
        request.setAttribute("key1", "123456");
        mm.addAttribute("key1", "12345");
        mmp.addAttribute("key1", "1234567");
        return "mytest";
    }//前端为 1234567 1234567

对应前端：

<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%>
<!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>Insert title here</title>

<% String test = String.valueOf(request.getAttribute("key1")); %>
</head>
<body>
<%=test %>

${key1 }

</body>
</html>

从上面测试可以看到Model，ModelMap与ModelAndView的具体使用；同时可以看出Model与ModelMap的值是能够替换的；并且两者赋值后作用比request.setAttribute()要大；这点在使用时需要注意；具体为啥，估计是最终解析时还是放在request上，最终还是替换了；我们知道

        request.setAttribute("key1", "123456");
        request.setAttribute("key1", "123457");

这样的代码最终得到的是“123457”；具体原因这里不看了，先学会熟练使用；

终上所述，我们知道了Model与ModelMap其实都是实现了hashMap,并且用法都是一样的；两者都是spring在请求时自动生成，拿来用便可；ModelAndView就是在两者的基础上可以指定返回页面；
赋值能力 ModelAndView > Model/ModelMap>request ;

附加：转发与重定向：
a 原始servlet：

转发时可以将页面的资源传给另一个页面，使用相对路径!
 重定向只是单纯的进行页面跳转。使用绝对路径



if(username.equals("123")&&password.equals("123")){  
            request.getRequestDispatcher("/success.html").forward(request, response); 

        }else{  
            //在sendRedict中url前必须加上当前web程序的路径名.....  
            response.sendRedirect(request.getContextPath()+"/fail.html"); 
        }

springMVC中，默认转发，重定向的话使用如下：

@RequestMapping("filesUpload")
    public String filesUpload(@RequestParam("files") MultipartFile[] files) {
        //判断file数组不能为空并且长度大于0
        if(files!=null&&files.length>0){
            //循环获取file数组中得文件
            for(int i = 0;i<files.length;i++){
                MultipartFile file = files[i];
                //保存文件
                saveFile(file);
            }
        }
        // 重定向
        return "redirect:/list.html";
    }