SpringMVC之ModelAndView的用法「建议收藏」

大家好，又见面了，我是你们的朋友全栈君。

（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。

[java] view plain copy

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

[java] view plain copy

/** Model Map */
private ModelMap model;//该属性用来存储处理后的结果数据
/**
* 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.
* 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.
* Returns <code>false</code> if any additional state was added to the instance
* after 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：

[java] view plain copy

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。

[java] view plain copy

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。

[java] view plain copy

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：

[java] view plain copy

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，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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