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SpringMVC之ModelAndView的用法

(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)。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: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:

```java
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);

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

后端
  • 泽泽泽
  • 2020-11-13 09:16:04.034

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