SpringMVC之ModelAndView的⽤法（转）
（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 >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;
}
/**
springframework作用* 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() {
del;
/**
* Return the underlying <code>ModelMap</code> instance (never <code>null</code>).  */
public ModelMap getModelMap() {
if (del == null) {
}
del;
}
/
**
* 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.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.del));
}
/**
* 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 ").del);
String();
}
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.urt.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.urt.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.urt.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);

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