SpringMVC之ModelAndView的用法（轉）

（一）使用ModelAndView類用來存儲處理完後的結果數據，以及顯示該數據的視圖。

從名字上看ModelAndView中的Model表明模型，View表明視圖，這個名字就很好地解釋了該類的做用。業務處理器調用模型層處理完用戶請求後，把結果數據存儲在該類的model屬性中，把要返回的視圖信息存儲在該類的view屬性中，而後讓該ModelAndView返回該Spring MVC框架。框架經過調用配置文件中定義的視圖解析器，對該對象進行解析，最後把結果數據顯示在指定的頁面上。 

具體做用：

一、返回指定頁面

ModelAndView構造方法能夠指定返回的頁面名稱，

也能夠經過setViewName()方法跳轉到指定的頁面 ,

二、返回所需數值

使用addObject()設置須要返回的值，addObject()有幾個不一樣參數的方法，能夠默認和指定返回對象的名字。

 

（二）【源碼】

1. 熟悉一個類的用法，最好從其源碼入手。

public class ModelAndView {  
  
    /** View instance or view name String */  
    private Object view  //該屬性用來存儲返回的視圖信息
/** Model Map */  
private ModelMap model;//<span style="color: rgb(0, 130, 0); font-family: Consolas, 'Courier New', Courier, mono, serif; line-height: 18px;">該屬性用來存儲處理後的結果數據</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();  
}

在源碼中有7個構造函數，如何用？是一個重點。

構造ModelAndView對象當控制器處理完請求時，一般會將包含視圖名稱或視圖對象以及一些模型屬性的ModelAndView對象返回到DispatcherServlet。

所以，常常須要在控制器中構造ModelAndView對象。

ModelAndView類提供了幾個重載的構造器和一些方便的方法，讓你能夠根據本身的喜愛來構造ModelAndView對象。這些構造器和方法以相似的方式支持視圖名稱和視圖對象。

經過ModelAndView構造方法能夠指定返回的頁面名稱，也能夠經過setViewName()方法跳轉到指定的頁面 , 使用addObject()設置須要返回的值，addObject()有幾個不一樣參數的方法，能夠默認和指定返回對象的名字。

2. 當你只有一個模型屬性要返回時，能夠在構造器中指定該屬性來構造ModelAndView對象

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);  
    }  
}

3. 若是有不止一個屬性要返回，能夠先將它們傳遞到一個Map中再來構造ModelAndView對象。

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);  
    }  
}

4. Spring也提供了ModelMap,這是java.util.Map實現，能夠根據模型屬性的具體類型自動生成模型屬性的名稱。 

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);  
    }  
}

這裏，我又想多說一句：ModelMap對象主要用於傳遞控制方法處理數據到結果頁面，

也就是說咱們把結果頁面上須要的數據放到ModelMap對象中便可，他的做用相似於request對象的setAttribute方法的做用，用來在一個請求過程當中傳遞處理的數據。

經過如下方法向頁面傳遞參數： 

addAttribute(String key,Object value); //modelMap的方法

在頁面上能夠經過el變量方式${key}或者bboss的一系列數據展現標籤獲取並展現modelmap中的數據。 

modelmap自己不能設置頁面跳轉的url地址別名或者物理跳轉地址，那麼咱們能夠經過控制器方法的返回值來設置跳轉url地址別名或者物理跳轉地址。 好比

public String xxxxmethod(String someparam,ModelMap model)  
{  
     //省略方法處理邏輯若干  
      //將數據放置到ModelMap對象model中,第二個參數能夠是任何java類型  
      model.addAttribute("key",someparam);  
     ......  
     //返回跳轉地址  
      return "path:handleok";  
}

在這些構造函數中最簡單的ModelAndView是持有View的名稱返回，以後View名稱被view resolver，也就是實做org.springframework.web.servlet.View接口的實例解析，

例如： InternalResourceView或JstlView等等：ModelAndView(String viewName)；若是您要返回Model對象，則可使用Map來收集這些Model對象，而後設定給ModelAndView，使用下面這個版本：

ModelAndView：ModelAndView(String viewName, Map model)，Map對象中設定好key與value值，以後能夠在視圖中取出

若是您只是要返回一個Model對象，則可使用下面這個 ModelAndView版本：

ModelAndView(String viewName, String modelName, Object modelObject)，其中modelName，您能夠在視圖中取出Model並顯示

ModelAndView類別提供實做View接口的對象來做View的參數：

ModelAndView(View view)

ModelAndView(View view, Map model)

ModelAndView(View view, String modelName, Object modelObject)

5. 【方法使用】：給ModelAndView實例設置view的方法有兩個：setViewName(String viewName) 和 setView(View view)。

前者是使用viewName，後者是使用預先構造好的View對象。其中前者比較經常使用。事實上View是一個接口，而不是一個能夠構造的具體類，咱們只能經過其餘途徑來獲取View的實例。對於viewName，它既能夠是jsp的名字，也能夠是tiles定義的名字，取決於使用的ViewNameResolver如何理解這個view name。如何獲取View的實例之後再研究。

而對應如何給ModelAndView實例設置model則比較複雜。有三個方法可使用：

addObject(Object modelObject);
addObject(String modelName, Object modelObject);
addAllObjects(Map modelMap);

6.【做用簡介】：

ModelAndView對象有兩個做用： 
做用一： 設置轉向地址,以下所示（這也是ModelAndView和ModelMap的主要區別） 

ModelAndView view = new ModelAndView("path:ok");

做用二 ：用於傳遞控制方法處理結果數據到結果頁面，也就是說咱們把須要在結果頁面上須要的數據放到ModelAndView對象中便可，

他的做用相似於request對象的setAttribute方法的做用，用來在一個請求過程當中傳遞處理的數據。經過如下方法向頁面傳遞參數： 

addObject(String key,Object value);

7. ModelAndView重定向

spring web framework利用ModelAndView也能實現forward、redirec

public ModelAndView getPage404MV() {        
    ModelAndView mv = new ModelAndView("redirect:/404.htm");
    return mv;
}

//第三個參數（UserModel user）默認爲綁定對象  
    @RequestMapping(value = "/user/save", method = RequestMethod.POST)  
    public ModelAndView saveUser(HttpServletRequest request, HttpServletResponse response,UserModel user) throws Exception {  
        ModelAndView mv = new ModelAndView("/user/save/result");//默認爲forward模式  
//      ModelAndView mv = new ModelAndView("redirect:/user/save/result");//redirect模式  
        mv.addObject("message","保存用戶成功！");  
        return mv;  
    }

map返回數據

@RequestMapping("/demo2/show") 
public Map<String, String> getMap() { 
    Map<String, String> map = new HashMap<String, String>(); 
    map.put("key1", "value-1"); 
    map.put("key2", "value-2"); 
    return map; 
}

8.SpringMVC：處理器方法返回值——返回ModelAndView以及String

(1) 返回ModelAndView：

應用場景：

若處理器對請求處理事後，不只要進行跳轉，並且在跳轉過程當中還要傳遞數據，此時使用ModelAndView較爲方便。

---

(2) 返回String：

a、返回物理視圖名稱：

這樣在地址欄裏輸入xxx/some.do就能夠跳轉到welcome.jsp頁面。

b、返回邏輯視圖名稱：

 (1)、在spring容器註冊視圖解析器：

(2)、處理器：

這個return的welcome和註冊的視圖解析器能夠拼接出WEB-INF/jsp/welcome.jsp的地址。

c、spring容器裏註冊視圖對象：

(1)、在spring容器裏註冊視圖對象：

(2)、處理器：

注意：視圖解析器，會按照註冊前後順序進行匹配，爲此有必要添加優先級。