spring mvc 3.0 ModelAndView模型视图类

见名知意，从名字上我们可以知道ModelAndView中的Model代表模型，View代表视图。即，这个类把要显示的数据存储到了Model属性中，要跳转的视图信息存储到了view属性。我们看一下ModelAndView的部分源码，即可知其中关系：

public class ModelAndView {

    /** View instance or view name String */
    private Object view;

    /** Model Map */
    private ModelMap model;

    /**
     * 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();
    }
}

测试代码：

package com.sxt.web;

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.servlet.mvc.multiaction.MultiActionController;

import com.sxt.po.User;

@Controller
@RequestMapping(value = "user")
public class UserController extends MultiActionController  {

    @RequestMapping(value = "/reg")
    public ModelAndView reg(@RequestParam("uname") String uname){
        ModelAndView mv = new ModelAndView();
        mv.setViewName("index");
//        mv.setView(new RedirectView("index"));

        User u = new User();
        u.setUname("高淇");
        mv.addObject(u);   //查看源代码，得知，直接放入对象。属性名为”首字母小写的类名”。 一般建议手动增加属性名称。
        mv.addObject("a", "aaaa");
        return mv;
    }

}

jsp代码：

<%@ page language="java" import="java.util.*" pageEncoding="utf-8"%>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
  <head>
  </head>
  <body>
       <h1>${requestScope.a}</h1>
       <h1>${requestScope.user.uname}</h1>
  </body>
</html>