Spring mvc 使用多种viewResolver的问题

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Spring mvc 使用多种viewResolver的问题5

问题大概是这样的：我配置了两个viewResovler：

 <bean id="velocityConfigurer" class="org.springframework.web.servlet.view.velocity.VelocityConfigurer">
	  	<property name="resourceLoaderPath" value="/WEB-INF/velo/"/>
	  	<property name= "velocityProperties">      
            <props>      
                 <prop key="input.encoding">utf-8</prop>      
                 <prop key="output.encoding">utf-8</prop>          
            </props>      
        </property>               
</bean>
<bean id="viewResolver" class="org.springframework.web.servlet.view.velocity.VelocityViewResolver">
		  <property name="cache" value="false"/>
		  <property name="prefix" value=""/>
		  <property name="suffix" value=".vm"/>
		  <property name="contentType"><value>text/html;charset=UTF-8</value></property>
		  <property name="exposeSpringMacroHelpers" value="true"/>
		  <property name="order"><value>0</value></property>
	</bean>
	 <bean id="JSPviewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver">
		  <property name="cache" value="false"/>
		  <property name="prefix" value="/WEB-INF/jsp/"/>
		  <property name="suffix" value=".jsp"/>
		  <property name="contentType"><value>text/html;charset=UTF-8</value></property>
		  <property name="order"><value>1</value></property>
	</bean>

目的是为了，请求多种视图，viewResovler的order如上图使用

@RequestMapping(value ="/welcome/user")
	public ModelAndView welcome(HttpServletRequest request,HttpServletResponse response,
			ModelMap modelMap) {
		return new ModelAndView("welcome",modelMap);
		//普通转向
	}

第一次http://localhost:8080/Prj/welcome/user 请求/WEB-INF/velo/目录底下的welcome.vm文件可以正常访问
当我把java代码修改成这样

@RequestMapping(value ="/welcome/user")
	public ModelAndView welcome(HttpServletRequest request,HttpServletResponse response,
			ModelMap modelMap) {
		return new ModelAndView("welcome",modelMap);
		//普通转向
	}

并且把jspresovler的order改成0，把velocity的resovler改成1
目的就是为了在/WEB-INF/jsp/目录下找不到welcome.jsp文件，按理说servlet会继续在另外一个resovler里面来查找.vm文件
应该是去找 /WEB-INF/veclo/目录底下寻找 welcome.vm文件，但是
当我请求上面的请求的时候，tomcat提示404错误，后台打印说找不到welcome.jsp文件
是什么原因？
各位大虾？

补充：当我把两个order都设为0的时候，也是可以找到的

Spring

2011年12月01日 16:41

successfulroof
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3个答案按时间排序按投票排序

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采纳的答案

public boolean checkResource(Locale locale) throws Exception {
		return true;
	}

罪魁祸首就是spring实现该方法时返回true，这样相当于view总是存在，从而导致其余视图解析器无法得到解析机会。

覆盖该方法，应该就可以了。

public class IcomJstlView extends JstlView {

	public boolean checkResource(Locale locale) throws Exception {
		File file = new File(this.getServletContext().getRealPath("/")+getUrl());
		return file.exists();//判断该jsp页面是否存在
	}
}

2011年12月10日 00:23

gglu
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不错

2014年8月14日 10:37

java_frog
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我没有用过两个视图，所以看了一下源码，看代码：

DispatchServlet.java中 doDispatch最后是调用render方法做视图渲染的：
protected void render(ModelAndView mv, HttpServletRequest request, HttpServletResponse response)
			throws Exception {

	// Determine locale for request and apply it to the response.
	Locale locale = this.localeResolver.resolveLocale(request);
	response.setLocale(locale);

	View view = null;

	if (mv.isReference()) {
		// We need to resolve the view name.
		view = resolveViewName(mv.getViewName(), mv.getModelInternal(), locale, request);
		if (view == null) {
			throw new ServletException("Could not resolve view with name '" + mv.getViewName() +
					"' in servlet with name '" + getServletName() + "'");
		}
	}
	else {
		// No need to lookup: the ModelAndView object contains the actual View object.
		view = mv.getView();
		if (view == null) {
			throw new ServletException("ModelAndView [" + mv + "] neither contains a view name nor a " +
					"View object in servlet with name '" + getServletName() + "'");
		}
	}

	// Delegate to the View object for rendering.
	if (logger.isDebugEnabled()) {
		logger.debug("Rendering view [" + view + "] in DispatcherServlet with name '" + getServletName() + "'");
	}
	view.render(mv.getModelInternal(), request, response);
}

mv.isReference() 是说你是不是用名字代替传递一个View实例给ModelAndView对象，你传递的都是名字，所以再看
protected View resolveViewName(String viewName, Map model, Locale locale, HttpServletRequest request)
			throws Exception {

	for (Iterator it = this.viewResolvers.iterator(); it.hasNext();) {
		ViewResolver viewResolver = (ViewResolver) it.next();
		View view = viewResolver.resolveViewName(viewName, locale);
		if (view != null) {
			return view;
		}
	}
	return null;
}

this.viewResolvers 这个就是你配的两个viewResolvers，分别试着去创建View，再看看创建View的代码
public View resolveViewName(String viewName, Locale locale) throws Exception {
	if (!isCache()) {
		logger.warn("View caching is SWITCHED OFF -- DEVELOPMENT SETTING ONLY: This can severely impair performance");
		return createView(viewName, locale);
	}
	else {
		Object cacheKey = getCacheKey(viewName, locale);
		synchronized (this.viewCache) {
			View view = (View) this.viewCache.get(cacheKey);
			if (view == null) {
				// Ask the subclass to create the View object.
				view = createView(viewName, locale);
				this.viewCache.put(cacheKey, view);
				if (logger.isTraceEnabled()) {
					logger.trace("Cached view [" + cacheKey + "]");
				}
			}
			return view;
		}
	}
}
最终落实到 createView，因为你的两个viewResolvers都是实现的 UrlBasedViewResolver，所以看UrlBasedViewResolver这里面的buildView方法就行了
protected AbstractUrlBasedView buildView(String viewName) throws Exception {
	AbstractUrlBasedView view = (AbstractUrlBasedView) BeanUtils.instantiateClass(getViewClass());
	view.setUrl(getPrefix() + viewName + getSuffix());
	String contentType = getContentType();
	if (contentType != null) {
		view.setContentType(contentType);
	}
	view.setRequestContextAttribute(getRequestContextAttribute());
	view.setAttributesMap(getAttributesMap());
	return view;
}
并没有看到有试图去找(getPrefix() + viewName + getSuffix())对应的文件，所以并不会返回null，所以只查找了jsp就没有查找fm了

Spring并不会去检查你这个文件（welcome.jsp）是否存在，只是最后渲染的时候交给给自处理 VelocityViewResolver交给Velocity处理，
InternalResourceViewResolver交给 servlet request 处理

也可以说UrlBasedViewResolver找出来的View没有被Spring容器管理，所以他不知道有没有

如果想实现你的功能，可以扩展DispatchServlet的resolveViewName方法，例如：
class MyDispatcherServlet extends DispatcherServlet {
	private List viewResolvers;
	
	@Override
	protected View resolveViewName(String viewName, Map model, Locale locale,
			HttpServletRequest request) throws Exception {
		WebApplicationContext context = getWebApplicationContext();
		for (Iterator it = this.viewResolvers.iterator(); it.hasNext();) {
			ViewResolver viewResolver = (ViewResolver) it.next();
			View view = viewResolver.resolveViewName(viewName, locale);
			if (view != null) {
				
				if (view instanceof AbstractUrlBasedView) {
					try {
						Resource resource = context.getResource(((AbstractUrlBasedView) view).getUrl());
						if (resource == null) {
							// log
							continue;
						}
					} catch (Exception e) {
						// log
						continue;
					}
				}
				
				return view;
			}
		}
		return null;
	}
}
当然你要初始化viewResolvers 因为DispatchServlet中该属性为私有的

网上找到的：
如果为DispatcherServlet指定多个ViewResolver的话，不要给予InternalResour- ceViewResolver以及其他UrlBasedViewResolver子类过高的优先级，因为这些ViewResolver即使找不到相应的视图，也不会返回null以给我们轮询下一个ViewResolver的机会，这样，我们所指定的其他ViewResolver实际上就形同虚设。合理的处理方式是，给予ResourceBundleView- Resolver或者XmlViewResolver这种能够通过返回null以表明无法找到相应视图的ViewResolver较高的优先级，而只是将InternalResourceViewResolver（或者其他类似行为的ViewResolver）添加为最低优先级ViewResolver，以作为DispatcherServlet的后备查找对象。

2011年12月08日 16:53