SpringMVC ModelAndView的用法使用詳解
(一)使用ModelAndView類用來儲存處理完後的結果資料,以及顯示該資料的檢視。從名字上看ModelAndView中的Model代表模型,View代表檢視,這個名字就很好地解釋了該類的作用。業務處理器呼叫模型層處理完使用者請求後,把結果資料儲存在該類的model屬性中,把要返回的檢視資訊儲存在該類的view屬性中,然後讓該ModelAndView返回該Spring MVC框架。框架通過呼叫配置檔案中定義的檢視解析器,對該物件進行解析,最後把結果資料顯示在指定的頁面上。
具體作用:
1、返回指定頁面
ModelAndView構造方法可以指定返回的頁面名稱,
也可以通過setViewName()方法跳轉到指定的頁面,
2、返回所需數值
使用addObject()設定需要返回的值,addObject()有幾個不同引數的方法,可以預設和指定返回物件的名字。
1、【其原始碼】:熟悉一個類的用法,最好從其原始碼入手。
public class ModelAndView { /** View instance or view name String */ private Object view //該屬性用來儲存返回的檢視資訊 /** Model Map */ private ModelMap model;//<span style="color: rgb(0,130,0); font-family: Consolas,'Courier New',Courier,mono,serif; line-height: 18px;">該屬性用來儲存處理後的結果資料</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,?> 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,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(); }
在原始碼中有7個建構函式,如何用?是一個重點。
構造ModelAndView物件當控制器處理完請求時,通常會將包含檢視名稱或檢視物件以及一些模型屬性的ModelAndView物件返回到DispatcherServlet。
因此,經常需要在控制器中構造ModelAndView物件。
ModelAndView類提供了幾個過載的構造器和一些方便的方法,讓你可以根據自己的喜好來構造ModelAndView物件。這些構造器和方法以類似的方式支援檢視名稱和檢視物件。
通過ModelAndView構造方法可以指定返回的頁面名稱,也可以通過setViewName()方法跳轉到指定的頁面,使用addObject()設定需要返回的值,addObject()有幾個不同引數的方法,可以預設和指定返回物件的名字。
(1)當你只有一個模型屬性要返回時,可以在構造器中指定該屬性來構造ModelAndView物件:
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)如果有不止一個屬性要返回,可以先將它們傳遞到一個Map中再來構造ModelAndView物件。
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,這是java.util.Map實現,可以根據模型屬性的具體型別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",model); } }
這裡,我又想多說一句:ModelMap物件主要用於傳遞控制方法處理資料到結果頁面,
也就是說我們把結果頁面上需要的資料放到ModelMap物件中即可,他的作用類似於request物件的setAttribute方法的作用,用來在一個請求過程中傳遞處理的資料。
通過以下方法向頁面傳遞引數:
addAttribute(String key,Object value); //modelMap的方法
在頁面上可以通過el變數方式${key}或者bboss的一系列資料展示標籤獲取並展示modelmap中的資料。
modelmap本身不能設定頁面跳轉的url地址別名或者物理跳轉地址,那麼我們可以通過控制器方法的返回值來設定跳轉url地址別名或者物理跳轉地址。 比如:
public String xxxxmethod(String someparam,ModelMap model) { //省略方法處理邏輯若干 //將資料放置到ModelMap物件model中,第二個引數可以是任何java型別 model.addAttribute("key",someparam); ...... //返回跳轉地址 return "path:handleok"; }
在這些建構函式中最簡單的ModelAndView是持有View的名稱返回,之後View名稱被view resolver,也就是實作org.springframework.web.servlet.View介面的例項解析,
例如: InternalResourceView或JstlView等等:ModelAndView(String viewName);
如果您要返回Model物件,則可以使用Map來收集這些Model物件,然後設定給ModelAndView,使用下面這個版本:
ModelAndView:ModelAndView(String viewName,Map model),Map物件中設定好key與value值,之後可以在檢視中取出
如果您只是要返回一個Model物件,則可以使用下面這個 ModelAndView版本:
ModelAndView(String viewName,Object modelObject),其中modelName,您可以在檢視中取出Model並顯示
ModelAndView類別提供實作View介面的物件來作View的引數:
ModelAndView(View view) ModelAndView(View view,Map model) ModelAndView(View view,Object modelObject)
2【方法使用】:給ModelAndView例項設定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物件。其中前者比較常用。事實上View是一個介面,而不是一個可以構造的具體類,我們只能通過其他途徑來獲取View的例項。對於viewName,它既可以是jsp的名字,也可以是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的例項以後再研究。
而對應如何給ModelAndView例項設定model則比較複雜。有三個方法可以使用:
addObject(Object modelObject); addObject(String modelName,Object modelObject); addAllObjects(Map modelMap);
3【作用簡介】:
ModelAndView物件有兩個作用:
作用一: 設定轉向地址,如下所示(這也是ModelAndView和ModelMap的主要區別)
ModelAndView view = new ModelAndView("path:ok");
作用二 :用於傳遞控制方法處理結果資料到結果頁面,也就是說我們把需要在結果頁面上需要的資料放到ModelAndView物件中即可,
他的作用類似於request物件的setAttribute方法的作用,用來在一個請求過程中傳遞處理的資料。通過以下方法向頁面傳遞引數:
addObject(String key,Object value);
以上就是本文的全部內容,希望對大家的學習有所幫助,也希望大家多多支援我們。