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社区首页 >问答首页 >JSTL消息:不知道如何使用forEach迭代提供的"items“

问JSTL消息:不知道如何使用forEach迭代提供的"items“
EN

Stack Overflow用户
提问于 2013-04-09 22:45:06
回答 2查看 24.6K关注 0票数 8

我正在向<c:forEach>传递一个列表，但我收到错误消息，指出它不知道如何遍历该列表。

代码语言：javascript
复制
@RequestMapping("/viewall")
public String viewAll(Model model) {

    // productService.findAllProducts() returns List<Product> 
    model.addAttribute("everything", productService.findAllProducts());

    // Also tried using iterator, but I get same error
    //model.addAtrribute("everything", productService.findAllProducts().iterator());

    ....
}

jsp页面：

代码语言：javascript
复制
<c:forEach items="${everything}" var="prod">
    <p> ${prod.name} </p>
</c:forEach>

错误：

代码语言：javascript
复制
javax.servlet.ServletException: javax.servlet.jsp.JspTagException: Don't know how to iterate over supplied "items" in &lt;forEach&gt;
    org.apache.jasper.runtime.PageContextImpl.doHandlePageException(PageContextImpl.java:912)
    org.apache.jasper.runtime.PageContextImpl.handlePageException(PageContextImpl.java:841)
    org.apache.jsp.WEB_002dINF.jsp.allprod_jsp._jspService(allprod_jsp.java:158)
    org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    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:722)
    org.springframework.web.servlet.view.InternalResourceView.renderMergedOutputModel(InternalResourceView.java:238)
    org.springframework.web.servlet.view.AbstractView.render(AbstractView.java:262)
    org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1180)
    org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:950)
    org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:852)
    org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:882)
    org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:778)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    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$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:183)
    org.springframework.security.web.FilterChainProxy$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)

root cause

javax.servlet.jsp.JspTagException: Don't know how to iterate over supplied "items" in &lt;forEach&gt;
    org.apache.taglibs.standard.tag.common.core.ForEachSupport.toForEachIterator(ForEachSupport.java:255)
    org.apache.taglibs.standard.tag.common.core.ForEachSupport.supportedTypeForEachIterator(ForEachSupport.java:219)
    org.apache.taglibs.standard.tag.common.core.ForEachSupport.prepare(ForEachSupport.java:137)
    javax.servlet.jsp.jstl.core.LoopTagSupport.doStartTag(LoopTagSupport.java:227)
    org.apache.jsp.WEB_002dINF.jsp.allprod_jsp._jspx_meth_c_005fforEach_005f0(allprod_jsp.java:180)
    org.apache.jsp.WEB_002dINF.jsp.allprod_jsp._jspService(allprod_jsp.java:137)
    org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    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:722)
    org.springframework.web.servlet.view.InternalResourceView.renderMergedOutputModel(InternalResourceView.java:238)
    org.springframework.web.servlet.view.AbstractView.render(AbstractView.java:262)
    org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1180)
    org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:950)
    org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:852)
    org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:882)
    org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:778)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:722)
    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$VirtualFilterChain.doFilter(FilterChainProxy.java:342)
    org.springframework.security.web.authentication.AbstractAuthenticationProcessingFilter.doFilter(AbstractAuthenticationProcessingFilter.java:183)
    org.springframework.security.web.FilterChainProxy$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)
jstl
el
java
jsp
spring-mvc
EN

回答 2

Stack Overflow用户

回答已采纳

发布于 2013-04-09 23:17:08

问题似乎是在Session或ServletContext (应用程序)中有另一个同名的属性。从JspContext#findAttribute (这是使用${something}时执行的方法)：

按顺序在页面、请求、会话(如果有效)和应用程序范围中搜索命名属性，并返回值关联或null。

它没有解释如何搜索属性的具体顺序，因此它可能是特定于供应商的。

为了避免问题，只需更改属性的名称即可。

票数 9
EN

Stack Overflow用户

发布于 2013-04-11 20:49:19

为了循环你的列表，你可以这样做，

代码语言：javascript
复制
<c:forEach var="prod" begin="1" end="5">
        <option value="${prod}" >${prod.name}</option>
    </c:forEach>

您可以通过添加一个可用作jstl apis的库来获取列表的长度。

代码语言：javascript
复制
<%@ taglib uri="http://java.sun.com/jsp/jstl/functions" prefix="fn" %>

然后在end属性中，您可以将end值设置为列表的大小，

代码语言：javascript
复制
${fn:length(everything)}

最终的代码应该是这样的，

代码语言：javascript
复制
<c:forEach var="prod" begin="1" end="${fn:length(everything)}">
        <option value="${prod.name}" >${l}</option>
    </c:forEach>

这段代码将循环变量设置为start，begin value为1，end value作为列表大小。

票数 3
EN
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：

https://stackoverflow.com/questions/15905055

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