SpringMVC之ModelAndView的用法（转）

原文地址：https://blog.csdn.net/qq30211478/article/details/78016155

（一）使用ModelAndView类用来存储处理完后的结果数据，以及显示该数据的视图。从名字上看ModelAndView中的Model代表模型，View代表视图，这个名字就很好地解释了该类的作用。业务处理器调用模型层处理完用户请求后，把结果数据存储在该类的model属性中，把要返回的视图信息存储在该类的view属性中，然后让该ModelAndView返回该Spring MVC框架。框架通过调用配置文件中定义的视图解析器，对该对象进行解析，最后把结果数据显示在指定的页面上。

具体作用：

1、返回指定页面

ModelAndView构造方法可以指定返回的页面名称，

也可以通过setViewName()方法跳转到指定的页面 ,

2、返回所需数值

使用addObject()设置需要返回的值，addObject()有几个不同参数的方法，可以默认和指定返回对象的名字。

1、【其源码】：熟悉一个类的用法，最好从其源码入手。

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();
} 

在源码中有7个构造函数，如何用？是一个重点。

构造ModelAndView对象当控制器处理完请求时，通常会将包含视图名称或视图对象以及一些模型属性的ModelAndView对象返回到DispatcherServlet。

因此，经常需要在控制器中构造ModelAndView对象。

ModelAndView类提供了几个重载的构造器和一些方便的方法，让你可以根据自己的喜好来构造ModelAndView对象。这些构造器和方法以类似的方式支持视图名称和视图对象。

通过ModelAndView构造方法可以指定返回的页面名称，也可以通过setViewName()方法跳转到指定的页面 , 使用addObject()设置需要返回的值，addObject()有几个不同参数的方法，可以默认和指定返回对象的名字。

（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);
    }
}  

Spring也提供了ModelMap,这是java.util.Map实现，可以根据模型属性的具体类型自动生成模型属性的名称。

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);
    }
}  

这里，我又想多说一句：ModelMap对象主要用于传递控制方法处理数据到结果页面，

也就是说我们把结果页面上需要的数据放到ModelMap对象中即可，他的作用类似于request对象的setAttribute方法的作用，用来在一个请求过程中传递处理的数据。

通过以下方法向页面传递参数：

addAttribute(String key,Object value); //modelMap的方法

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。

modelmap本身不能设置页面跳转的url地址别名或者物理跳转地址，那么我们可以通过控制器方法的返回值来设置跳转url地址别名或者物理跳转地址。 比如：

public String xxxxmethod(String someparam,ModelMap model)
{
     //省略方法处理逻辑若干
      //将数据放置到ModelMap对象model中,第二个参数可以是任何java类型
      model.addAttribute("key",someparam);
     ......
     //返回跳转地址
      return "path:handleok";
}  

在这些构造函数中最简单的ModelAndView是持有View的名称返回，之后View名称被view resolver，也就是实作org.springframework.web.servlet.View接口的实例解析，

例如： InternalResourceView或JstlView等等：ModelAndView(String viewName)；

如果您要返回Model对象，则可以使用Map来收集这些Model对象，然后设定给ModelAndView，使用下面这个版本：

ModelAndView：ModelAndView(String viewName, Map model)，Map对象中设定好key与value值，之后可以在视图中取出

如果您只是要返回一个Model对象，则可以使用下面这个 ModelAndView版本：

ModelAndView(String viewName, String modelName, Object modelObject)，其中modelName，您可以在视图中取出Model并显示 

ModelAndView类别提供实作View接口的对象来作View的参数：

ModelAndView(View view)

ModelAndView(View view, Map model)

ModelAndView(View view, String modelName, Object modelObject)

2【方法使用】：给ModelAndView实例设置view的方法有两个：setViewName(String viewName) 和 setView(View view)。

前者是使用viewName，后者是使用预先构造好的View对象。其中前者比较常用。事实上View是一个接口，而不是一个可以构造的具体类，我们只能通过其他途径来获取View的实例。对于viewName，它既可以是jsp的名字，也可以是tiles定义的名字，取决于使用的ViewNameResolver如何理解这个view name。如何获取View的实例以后再研究。

而对应如何给ModelAndView实例设置model则比较复杂。有三个方法可以使用：

addObject(Object modelObject);
addObject(String modelName, Object modelObject);
addAllObjects(Map modelMap);

3【作用简介】：

ModelAndView对象有两个作用： 
作用一： 设置转向地址,如下所示（这也是ModelAndView和ModelMap的主要区别）

ModelAndView view = new ModelAndView("path:ok"); 

作用二 ：用于传递控制方法处理结果数据到结果页面，也就是说我们把需要在结果页面上需要的数据放到ModelAndView对象中即可，

他的作用类似于request对象的setAttribute方法的作用，用来在一个请求过程中传递处理的数据。通过以下方法向页面传递参数：

addObject(String key,Object value);