如何在JSP中将null变量传递给Spring表达式

时间：2013-04-29 22:33:24

标签： jsp spring-el

我在JSP中使用<spring:eval>标记：

<spring:eval expression="'today is ' + today" />

其中today是java.util.Date。只要今天的变量不为null，一切正常。当today为空时，我得到

org.springframework.expression.spel.SpelEvaluationException: EL1007E:(pos 0): Field or property 'today' cannot be found on null
    org.springframework.expression.spel.ast.PropertyOrFieldReference.readProperty(PropertyOrFieldReference.java:243)
    org.springframework.expression.spel.ast.PropertyOrFieldReference.getValueInternal(PropertyOrFieldReference.java:112)
    org.springframework.expression.spel.ast.PropertyOrFieldReference.getValueInternal(PropertyOrFieldReference.java:107)
    org.springframework.expression.spel.ast.OpPlus.getValueInternal(OpPlus.java:70)
    org.springframework.expression.spel.ast.SpelNodeImpl.getTypedValue(SpelNodeImpl.java:102)
    org.springframework.expression.spel.standard.SpelExpression.getValue(SpelExpression.java:98)
    org.springframework.web.servlet.tags.EvalTag.doEndTag(EvalTag.java:126)
    org.apache.jsp.WEB_002dINF.views.admin.inbox_jsp._jspx_meth_s_005feval_005f1(inbox_jsp.java:195)
    org.apache.jsp.WEB_002dINF.views.admin.inbox_jsp._jspService(inbox_jsp.java:120)
    org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
    org.apache.jasper.runtime.JspRuntimeLibrary.include(JspRuntimeLibrary.java:954)
    org.apache.jasper.runtime.PageContextImpl.doInclude(PageContextImpl.java:684)
    org.apache.jasper.runtime.PageContextImpl.include(PageContextImpl.java:678)
    org.apache.tiles.request.jsp.JspRequest.doInclude(JspRequest.java:123)
    org.apache.tiles.request.AbstractViewRequest.dispatch(AbstractViewRequest.java:47)
    org.apache.tiles.request.render.DispatchRenderer.render(DispatchRenderer.java:45)
    org.apache.tiles.request.render.ChainedDelegateRenderer.render(ChainedDelegateRenderer.java:68)
    org.apache.tiles.impl.BasicTilesContainer.render(BasicTilesContainer.java:259)
    org.apache.tiles.template.InsertAttributeModel.renderAttribute(InsertAttributeModel.java:188)
    org.apache.tiles.template.InsertAttributeModel.execute(InsertAttributeModel.java:132)
    org.apache.tiles.jsp.taglib.InsertAttributeTag.doTag(InsertAttributeTag.java:299)
    org.apache.jsp.WEB_002dINF.views.common.main_002dlayout_jsp._jspx_meth_tiles_005finsertAttribute_005f2(main_002dlayout_jsp.java:243)
    org.apache.jsp.WEB_002dINF.views.common.main_002dlayout_jsp._jspService(main_002dlayout_jsp.java:103)
    org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
    org.apache.tiles.request.servlet.ServletRequest.forward(ServletRequest.java:265)
    org.apache.tiles.request.servlet.ServletRequest.doForward(ServletRequest.java:228)
    org.apache.tiles.request.AbstractClientRequest.dispatch(AbstractClientRequest.java:57)
    org.apache.tiles.request.render.DispatchRenderer.render(DispatchRenderer.java:45)
    org.apache.tiles.impl.BasicTilesContainer.render(BasicTilesContainer.java:259)
    org.apache.tiles.impl.BasicTilesContainer.render(BasicTilesContainer.java:397)
    org.apache.tiles.impl.BasicTilesContainer.render(BasicTilesContainer.java:238)
    org.apache.tiles.impl.BasicTilesContainer.render(BasicTilesContainer.java:221)
    org.apache.tiles.renderer.DefinitionRenderer.render(DefinitionRenderer.java:59)
    org.springframework.web.servlet.view.tiles3.TilesView.renderMergedOutputModel(TilesView.java:145)
    org.springframework.web.servlet.view.AbstractView.render(AbstractView.java:264)
    org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1208)
    org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:992)
    org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:939)
    org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:856)
    org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:936)
    org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:827)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
    org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:812)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
    org.springframework.orm.hibernate4.support.OpenSessionInViewFilter.doFilterInternal(OpenSessionInViewFilter.java:152)
    org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:330)
    org.springframework.security.web.access.intercept.FilterSecurityInterceptor.invoke(FilterSecurityInterceptor.java:118)
    org.springframework.security.web.access.intercept.FilterSecurityInterceptor.doFilter(FilterSecurityInterceptor.java:84)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    org.springframework.security.web.access.ExceptionTranslationFilter.doFilter(ExceptionTranslationFilter.java:113)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    org.springframework.security.web.session.SessionManagementFilter.doFilter(SessionManagementFilter.java:103)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    org.springframework.security.web.authentication.AnonymousAuthenticationFilter.doFilter(AnonymousAuthenticationFilter.java:113)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    org.springframework.security.web.servletapi.SecurityContextHolderAwareRequestFilter.doFilter(SecurityContextHolderAwareRequestFilter.java:54)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    org.springframework.security.web.savedrequest.RequestCacheAwareFilter.doFilter(RequestCacheAwareFilter.java:45)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    org.springframework.security.web.authentication.www.BasicAuthenticationFilter.doFilter(BasicAuthenticationFilter.java:150)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:183)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    org.springframework.security.web.authentication.logout.LogoutFilter.doFilter(LogoutFilter.java:105)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    org.springframework.security.web.context.SecurityContextPersistenceFilter.doFilter(SecurityContextPersistenceFilter.java:87)
    org.springframework.security.web.FilterChainProxy$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    org.springframework.security.web.FilterChainProxy.doFilterInternal(FilterChainProxy.java:192)
    org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:160)
    org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:346)
    org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:259)

所以我尝试用Elvis运算符检查null：

<spring:eval expression="'today is ' + (today ?: 'null date!') " />

但是它给出了完全相同的表达式。在使用调试器进入Spring PropertyOrFieldReference代码之后，我发现它似乎无法处理空变量。

普通的旧JSTL代码通过不打印来处理null，这很好：

today is ${today}

如果today是bean的属性，它也适用于SPeL：

<spring:eval expression="'today is ' + myBean.today" />

这会产生预期的字符串“today is null”。在这个简单的例子中，当变量为null时，我可以使用JSTL分支我的<spring:eval>标签，但我真正需要做的是使用<spring:eval>来执行一个静态函数几个变量，其中任何变量都可以合法地为空。问题是，如果变量为null，则SPeL似乎无法正确解析变量。

1 个答案:

答案 0 :(得分：1)

EL还可以。范围不明确。春天甚至找不到变量。

将此用于请求范围：

<spring:eval expression="'today is ' + requestScope['today']" />

将此用于会话范围：

<spring:eval expression="'today is ' + sessionScope['today']" />
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