SpringMVC ModelAndView的用法使用详解

(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

* <span>after</span> 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:

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)。

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);

以上是 SpringMVC ModelAndView的用法使用详解 的全部内容, 来源链接: utcz.com/z/350735.html

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