jsp中c:foreach标签遍历问题

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本文介绍了一种在使用JSP进行网页开发时遇到的错误：在<forEach>标签中遍历集合时发生的异常。该异常通常是因为传入的集合类型不正确或未被正确初始化。

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HTTP Status 500 - javax.servlet.ServletException: javax.servlet.jsp.JspTagException: Don't know how to iterate over supplied "items" in <forEach>

type Exception report

message javax.servlet.ServletException: javax.servlet.jsp.JspTagException: Don't know how to iterate over supplied "items" in <forEach>

description The server encountered an internal error that prevented it from fulfilling this request.

exception

org.apache.jasper.JasperException: javax.servlet.ServletException: javax.servlet.jsp.JspTagException: Don't know how to iterate over supplied "items" in &lt;forEach&gt;
	org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:556)
	org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:462)
	org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:395)
	org.apache.jasper.servlet.JspServlet.service(JspServlet.java:339)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
	org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
	org.springframework.web.servlet.view.InternalResourceView.renderMergedOutputModel(InternalResourceView.java:168)
	org.springframework.web.servlet.view.AbstractView.render(AbstractView.java:303)
	org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1257)
	org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1037)
	org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:980)
	org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:897)
	org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970)
	org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:872)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:650)
	org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
	org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
	org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:197)
	org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)

root cause

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:916)
	org.apache.jasper.runtime.PageContextImpl.handlePageException(PageContextImpl.java:845)
	org.apache.jsp.WEB_002dINF.views.studentlogin_jsp._jspService(studentlogin_jsp.java:112)
	org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
	org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:439)
	org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:395)
	org.apache.jasper.servlet.JspServlet.service(JspServlet.java:339)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
	org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
	org.springframework.web.servlet.view.InternalResourceView.renderMergedOutputModel(InternalResourceView.java:168)
	org.springframework.web.servlet.view.AbstractView.render(AbstractView.java:303)
	org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1257)
	org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1037)
	org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:980)
	org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:897)
	org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970)
	org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:872)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:650)
	org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
	org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
	org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:197)
	org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)

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:274)
	org.apache.taglibs.standard.tag.common.core.ForEachSupport.supportedTypeForEachIterator(ForEachSupport.java:238)
	org.apache.taglibs.standard.tag.common.core.ForEachSupport.prepare(ForEachSupport.java:155)
	javax.servlet.jsp.jstl.core.LoopTagSupport.doStartTag(LoopTagSupport.java:256)
	org.apache.jsp.WEB_002dINF.views.studentlogin_jsp._jspx_meth_c_005fforEach_005f0(studentlogin_jsp.java:134)
	org.apache.jsp.WEB_002dINF.views.studentlogin_jsp._jspService(studentlogin_jsp.java:95)
	org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
	org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:439)
	org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:395)
	org.apache.jasper.servlet.JspServlet.service(JspServlet.java:339)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
	org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
	org.springframework.web.servlet.view.InternalResourceView.renderMergedOutputModel(InternalResourceView.java:168)
	org.springframework.web.servlet.view.AbstractView.render(AbstractView.java:303)
	org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1257)
	org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1037)
	org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:980)
	org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:897)
	org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970)
	org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:872)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:650)
	org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
	org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
	org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:197)
	org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)

note The full stack trace of the root cause is available in the Apache Tomcat/7.0.69 logs.

此处出现的异常是：foreach标签中的遍历值与后台传的值存在差异，导致foreach不知如何遍历。