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

1. public class ModelAndView {
3. /** View instance or view name String */
4. private Object view;//<span style=”color: rgb(0, 130, 0); font-family: Consolas, ‘Courier New’, Courier, mono, serif; line-height: 18px;”>该属性用来存储返回的视图信息</span>

[java] view plain copy

1. /** Model Map */
2. 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>
4. /**
5. * Indicates whether or not this instance has been cleared with a call to {@link #clear()}.
6. */
7. private boolean cleared = false;
10. /**
11. * Default constructor for bean-style usage: populating bean
12. * properties instead of passing in constructor arguments.
13. * @see #setView(View)
14. * @see #setViewName(String)
15. */
16. public ModelAndView() {
17. }
19. /**
20. * Convenient constructor when there is no model data to expose.
21. * Can also be used in conjunction with <code>addObject</code>.
22. * @param viewName name of the View to render, to be resolved
23. * by the DispatcherServlet’s ViewResolver
24. * @see #addObject
25. */
26. public ModelAndView(String viewName) {
27. this.view = viewName;
28. }
30. /**
31. * Convenient constructor when there is no model data to expose.
32. * Can also be used in conjunction with <code>addObject</code>.
33. * @param view View object to render
34. * @see #addObject
35. */
36. public ModelAndView(View view) {
37. this.view = view;
38. }
40. /**
41. * Creates new ModelAndView given a view name and a model.
42. * @param viewName name of the View to render, to be resolved
43. * by the DispatcherServlet’s ViewResolver
44. * @param model Map of model names (Strings) to model objects
45. * (Objects). Model entries may not be <code>null</code>, but the
46. * model Map may be <code>null</code> if there is no model data.
47. */
48. public ModelAndView(String viewName, Map<String, ?> model) {
49. this.view = viewName;
50. if (model != null) {
51. getModelMap().addAllAttributes(model);
52. }
53. }
55. /**
56. * Creates new ModelAndView given a View object and a model.
57. * <emphasis>Note: the supplied model data is copied into the internal
58. * storage of this class. You should not consider to modify the supplied
59. * Map after supplying it to this class</emphasis>
60. * @param view View object to render
61. * @param model Map of model names (Strings) to model objects
62. * (Objects). Model entries may not be <code>null</code>, but the
63. * model Map may be <code>null</code> if there is no model data.
64. */
65. public ModelAndView(View view, Map<String, ?> model) {
66. this.view = view;
67. if (model != null) {
68. getModelMap().addAllAttributes(model);
69. }
70. }
72. /**
73. * Convenient constructor to take a single model object.
74. * @param viewName name of the View to render, to be resolved
75. * by the DispatcherServlet’s ViewResolver
76. * @param modelName name of the single entry in the model
77. * @param modelObject the single model object
78. */
79. public ModelAndView(String viewName, String modelName, Object modelObject) {
80. this.view = viewName;
81. addObject(modelName, modelObject);
82. }
84. /**
85. * Convenient constructor to take a single model object.
86. * @param view View object to render
87. * @param modelName name of the single entry in the model
88. * @param modelObject the single model object
89. */
90. public ModelAndView(View view, String modelName, Object modelObject) {
91. this.view = view;
92. addObject(modelName, modelObject);
93. }
96. /**
97. * Set a view name for this ModelAndView, to be resolved by the
98. * DispatcherServlet via a ViewResolver. Will override any
99. * pre-existing view name or View.
100. */
101. public void setViewName(String viewName) {
102. this.view = viewName;
103. }
105. /**
106. * Return the view name to be resolved by the DispatcherServlet
107. * via a ViewResolver, or <code>null</code> if we are using a View object.
108. */
109. public String getViewName() {
110. return (this.view instanceof String ? (String) this.view : null);
111. }
113. /**
114. * Set a View object for this ModelAndView. Will override any
115. * pre-existing view name or View.
116. */
117. public void setView(View view) {
118. this.view = view;
119. }
121. /**
122. * Return the View object, or <code>null</code> if we are using a view name
123. * to be resolved by the DispatcherServlet via a ViewResolver.
124. */
125. public View getView() {
126. return (this.view instanceof View ? (View) this.view : null);
127. }
129. /**
130. * Indicate whether or not this <code>ModelAndView</code> has a view, either
131. * as a view name or as a direct {@link View} instance.
132. */
133. public boolean hasView() {
134. return (this.view != null);
135. }
137. /**
138. * Return whether we use a view reference, i.e. <code>true</code>
139. * if the view has been specified via a name to be resolved by the
140. * DispatcherServlet via a ViewResolver.
141. */
142. public boolean isReference() {
143. return (this.view instanceof String);
144. }
146. /**
147. * Return the model map. May return <code>null</code>.
148. * Called by DispatcherServlet for evaluation of the model.
149. */
150. protected Map<String, Object> getModelInternal() {
151. return this.model;
152. }
154. /**
155. * Return the underlying <code>ModelMap</code> instance (never <code>null</code>).
156. */
157. public ModelMap getModelMap() {
158. if (this.model == null) {
159. this.model = new ModelMap();
160. }
161. return this.model;
162. }
164. /**
165. * Return the model map. Never returns <code>null</code>.
166. * To be called by application code for modifying the model.
167. */
168. public Map<String, Object> getModel() {
169. return getModelMap();
170. }
173. /**
174. * Add an attribute to the model.
175. * @param attributeName name of the object to add to the model
176. * @param attributeValue object to add to the model (never <code>null</code>)
177. * @see ModelMap#addAttribute(String, Object)
178. * @see #getModelMap()
179. */
180. public ModelAndView addObject(String attributeName, Object attributeValue) {
181. getModelMap().addAttribute(attributeName, attributeValue);
182. return this;
183. }
185. /**
186. * Add an attribute to the model using parameter name generation.
187. * @param attributeValue the object to add to the model (never <code>null</code>)
188. * @see ModelMap#addAttribute(Object)
189. * @see #getModelMap()
190. */
191. public ModelAndView addObject(Object attributeValue) {
192. getModelMap().addAttribute(attributeValue);
193. return this;
194. }
196. /**
197. * Add all attributes contained in the provided Map to the model.
198. * @param modelMap a Map of attributeName -> attributeValue pairs
199. * @see ModelMap#addAllAttributes(Map)
200. * @see #getModelMap()
201. */
202. public ModelAndView addAllObjects(Map<String, ?> modelMap) {
203. getModelMap().addAllAttributes(modelMap);
204. return this;
205. }
208. /**
209. * Clear the state of this ModelAndView object.
210. * The object will be empty afterwards.
211. * <p>Can be used to suppress rendering of a given ModelAndView object
212. * in the <code>postHandle</code> method of a HandlerInterceptor.
213. * @see #isEmpty()
214. * @see HandlerInterceptor#postHandle
215. */
216. public void clear() {
217. this.view = null;
218. this.model = null;
219. this.cleared = true;
220. }
222. /**
223. * Return whether this ModelAndView object is empty,
224. * i.e. whether it does not hold any view and does not contain a model.
225. */
226. public boolean isEmpty() {
227. return (this.view == null && CollectionUtils.isEmpty(this.model));
228. }
230. /**
231. * Return whether this ModelAndView object is empty as a result of a call to {@link #clear}
232. * i.e. whether it does not hold any view and does not contain a model.
233. * <p>Returns <code>false</code> if any additional state was added to the instance
234. * <strong>after</strong> the call to {@link #clear}.
235. * @see #clear()
236. */
237. public boolean wasCleared() {
238. return (this.cleared && isEmpty());
239. }
242. /**
243. * Return diagnostic information about this model and view.
244. */
245. @Override
246. public String toString() {
247. StringBuilder sb = new StringBuilder(“ModelAndView: “);
248. if (isReference()) {
249. sb.append(“reference to view with name ‘”).append(this.view).append(“‘”);
250. }
251. else {
252. sb.append(“materialized View is [“).append(this.view).append(‘]’);
253. }
254. sb.append(“; model is “).append(this.model);
255. return sb.toString();
256. }

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

1. package com.apress.springrecipes.court.web;
2. …
3. import org.springframework.web.servlet.ModelAndView;
4. import org.springframework.web.servlet.mvc.AbstractController;
5. public class WelcomeController extends AbstractController{
6. public ModelAndView handleRequestInternal(HttpServletRequest request,
7. HttpServletResponse response)throws Exception{
8. Date today = new Date();
9. return new ModelAndView(“welcome”,“today”,today);
10. }
11. }

（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

1. package com.apress.springrecipes.court.web;
2. …
3. import org.springframework.web.servlet.ModelAndView;
4. import org. springframework.web.servlet.mvc.AbstractController;
5. public class ReservationQueryController extends AbstractController{
6. …
7. public ModelAndView handleRequestInternal(HttpServletRequest request,
8. HttpServletResponse response)throws Exception{
9. …
10. Map<String,Object> model = new HashMap<String,Object>();
11. if(courtName != null){
12. model.put(“courtName”,courtName);
13. model.put(“reservations”,reservationService.query(courtName));
14. }
15. return new ModelAndView(“reservationQuery”,model);
16. }
17. }

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

1. package com.apress.springrecipes.court.web;
2. …
3. import org.springframework.ui.ModelMap;
4. import org.springframework.web.servlet.ModelAndView;
5. import org.springframework.web.servlet.mvc.AbstractController;
6. public class ReservationQueryController extends AbstractController{
7. …
8. public ModelAndView handleRequestInternal(HttpServletRequest request,
9. HttpServletResponse response)throws Exception{
10. …
11. ModelMap model = new ModelMap();
12. if(courtName != null){
13. model.addAttribute(“courtName”,courtName);
14. model.addAttribute(“reservations”,reservationService.query(courtName));
15. }
16. return new ModelAndView(“reservationQuery”,model);
17. }
18. }

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

1. public String xxxxmethod(String someparam,ModelMap model)
2. {
3. //省略方法处理逻辑若干
4. //将数据放置到ModelMap对象model中,第二个参数可以是任何java类型
5. model.addAttribute(“key”,someparam);
6. ……
7. //返回跳转地址
8. return “path:handleok”;
9. }

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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