JSTL消息：不知道如何迭代提供的「項目」與forEach

我傳遞一個列表到<c:forEach>，但我得到的錯誤，指出它不知道如何遍歷它。JSTL消息：不知道如何迭代提供的「項目」與forEach

@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頁面：

<c:forEach items="${everything}" var="prod"> 
    <p> ${prod.name} </p> 
</c:forEach>

錯誤：

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)

來源

2013-04-09 user1636922

'productService.findAllProducts（）'返回什麼？ – BobTheBuilder 2013-04-09 14:47:16

他說'列表' – 2013-04-09 14:47:39

看起來像另一個屬性（會話，servletcontext）具有與List不同的同名。 – 2013-04-09 14:48:41

這個問題似乎是存在具有相同名稱的會話或ServletContext中（應用程序）的另一個屬性。從JspContext#findAttribute（這是使用${something}時執行的方法）：

Searches for the named attribute in page, request, session (if valid), and application scope(s) in order and returns the value associated or null.

它沒有解釋有關屬性如何搜索特定的順序，因此它可能是供應商特定的。

爲了避免問題，只需更改屬性的名稱即可。

來源

2013-04-09 15:17:07

對於循環您的列表，你可以做這樣的事情，

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

，你可以通過添加可作爲JSTL的API庫讓你列表的長度，

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

然後在結束屬性中，您可以將最終值設置爲列表的大小，

${fn:length(everything)}

the final co德會是這樣的，

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

這個代碼將循環變量入手開始值爲1和最終值列表規模。

來源

2013-04-11 12:49:19 VPK

不好意思，但OP的問題不是關於如何迭代循環，原因是它存在session或ServletContext中另一個具有相同名稱的屬性。重命名屬性解決了問題（正如我的答案中所述）。 – 2013-04-11 12:54:12

JSTL消息：不知道如何迭代提供的「項目」與forEach

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