SpringMVC的 ModelAndView

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。

     public class ModelAndView {  

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

    /** 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();
    }  

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);
        }
    }  

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变量的方式${key}的方式进行获取值。

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)；

1）：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，使用下面这个版本的 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，

2）：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);