求助，关于以下错误：Cannot create iterator for this collection

Question

我用的JBuilder2005；出错的过程是这样的
首先跳转到一个action里面，这个action的作用是读数据库的值，然后跳转到一个jsp页面显示出那些值，显示的时候用的是struts的logic和bean标签。经过调试发现，错误是在从action跳转到jsp页面的时候发生的，也就是在return actionmapping.findforward("XXXX")；这条语句之后；
请明白的大侠帮忙看看！~谢谢！！~~~

Answer 1

return actionmapping.findforward("XXXX")；返回后还执行

Answer 2

下面是出错的提示：
javax.servlet.ServletException: Cannot create iterator for this collection
org.apache.jasper.runtime.PageContextImpl.doHandlePageException(PageContextImpl.java:825)
org.apache.jasper.runtime.PageContextImpl.handlePageException(PageContextImpl.java:758)
org.apache.jsp.typeAdd_jsp._jspService(typeAdd_jsp.java:374)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:94)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:324)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:292)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:236)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
org.apache.struts.action.RequestProcessor.doForward(RequestProcessor.java:1069)
org.apache.struts.action.RequestProcessor.processForwardConfig(RequestProcessor.java:455)
org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:279)
org.apache.struts.action.ActionServlet.process(ActionServlet.java:1482)
org.apache.struts.action.ActionServlet.doGet(ActionServlet.java:507)
javax.servlet.http.HttpServlet.service(HttpServlet.java:689)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
root cause javax.servlet.jsp.JspException: Cannot create iterator for this collection
org.apache.struts.taglib.logic.IterateTag.doStartTag(IterateTag.java:310)
org.apache.jsp.typeAdd_jsp._jspService(typeAdd_jsp.java:286)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:94)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:324)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:292)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:236)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
org.apache.struts.action.RequestProcessor.doForward(RequestProcessor.java:1069)
org.apache.struts.action.RequestProcessor.processForwardConfig(RequestProcessor.java:455)
org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:279)
org.apache.struts.action.ActionServlet.process(ActionServlet.java:1482)
org.apache.struts.action.ActionServlet.doGet(ActionServlet.java:507)
javax.servlet.http.HttpServlet.service(HttpServlet.java:689)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)

Answer 3

取出来的数据是存入actionform，然后再放入数组中，然后把数组存入session。

Answer 4

以下是action的代码：
public class TypeShowAction extends Action {    public ActionForward execute(ActionMapping mapping,
                                 ActionForm actionForm,
                                 HttpServletRequest request,
                                 HttpServletResponse response) throws
            IOException {
//        TypeForm tf = (TypeForm) actionForm;
        ConnectionBean cb = new ConnectionBean();
        ResultSet rs = null;
        ArrayList arr = new ArrayList();
        HttpSession session = request.getSession(true);
        String state = request.getParameter("state");
        if (state=="add" || state.equals("add")) {            rs = cb.dbSelect("select * from cy_articleclass order by cy_Order ");            try {
                while (rs.next()) {
                    TypeForm tf = new TypeForm();
                    tf.setTypeId(rs.getInt(1));
                    String nbsp = "";
                    for (int i = 0; i < rs.getInt(5); i++) {
                        nbsp += "&nbsp;&nbsp;";
                    }                    tf.setTypeName(nbsp + rs.getString(2));
                    tf.setTypeRootID(rs.getInt(3));
                    tf.setTypePID(rs.getInt(4));
                    tf.setTypeLevel(rs.getInt(5));
                    tf.setTypeChild(rs.getInt(6));
                    tf.setTypeOrder(rs.getInt(7));
                    tf.setTypePath(rs.getString(8));
                    tf.setTypeDir(rs.getString(9));
                    tf.setTypePageNum(rs.getInt(10));
                    tf.setTypeSummary(rs.getString(11));
                    tf.setTypeMetaSummary(rs.getString(12));                    arr.add(tf);                }                session.setAttribute("type", arr);
                rs.close();
                cb.close();
            } catch (Exception e) {
                e.printStackTrace();
            }            return mapping.findForward("showParentType");
        } else {
            if (state=="show" || state.equals("show")) {
                rs = cb.dbSelect(
                        "select * from cy_articleclass order by cy_Order");                try {
                    while (rs.next()) {
                        TypeForm tf = new TypeForm();
                        tf.setTypeId(rs.getInt(1));
                        String nbsp = "";
                        for (int i = 0; i < rs.getInt(5); i++) {
                            nbsp += "&nbsp;&nbsp;";
                        }
                        tf.setTypeName(nbsp + rs.getString(2));
                        tf.setTypeRootID(rs.getInt(3));
                        tf.setTypePID(rs.getInt(4));
                        tf.setTypeLevel(rs.getInt(5));
                        tf.setTypeChild(rs.getInt(6));
                        tf.setTypeOrder(rs.getInt(7));
                        tf.setTypePath(rs.getString(8));
                        tf.setTypeDir(rs.getString(9));
                        tf.setTypePageNum(rs.getInt(10));
                        tf.setTypeSummary(rs.getString(11));
                        tf.setTypeMetaSummary(rs.getString(12));                        arr.add(tf);                    }                    session.setAttribute("type", arr);
                    rs.close();
                    cb.close();
                } catch (Exception e) {
                    e.printStackTrace();
                }            }
            return mapping.findForward("showAllType");
        }
    }    
}

Answer 5

jsp就这一个地方用了标签：
<TR>
    <TD>所属分类：</TD>
    <TD><SELECT size=1 name="typePID" onchange="find(this.value);">
      <option value="0">无（作为第一类）</option>
      <logic:present name="type">
          <logic:iterate id="type" name="type">
            <logic:present name="type">
              <option value="<bean:write name="type" property="typeId"/>">
                <bean:write name="type" property="typeName" filter="false"/>
              </option>
            </logic:present>
          </logic:iterate>
        </logic:present>
        </SELECT></TD>
    <TD><SPAN class=red></SPAN><SPAN class=gray></SPAN></TD></TR>

Answer 6

我记得在html:itrator得源码中看见过这个错误,导致这个错误的原因是itrator枚举的时候引用到了ActionForm中的容器,一般我们会用List，它用这个接口产生一个Itrator来枚举数据，但是如果你用了其它的容器，就会出现不能枚举的错误，楼主食不是用了html:itrator标签？

Answer 7

简化一下你的html先测试一下<SELECT size=1 name="typePID" onchange="find(this.value);">
<option value="0">无（作为第一类）</option>
<logic:iterate id="type" name="type">
<option value="<bean:write name="type" property="typeId"/>">
<bean:write name="type" property="typeName" filter="false"/>
</option>
</logic:iterate>
</SELECT>

Answer 8

源码是这样写的，你看一下：
      if (collection.getClass().isArray()) {
            try {
                // If we're lucky, it is an array of objects
                // that we can iterate over with no copying
                iterator = Arrays.asList((Object[]) collection).iterator();
            } catch (ClassCastException e) {
                // Rats -- it is an array of primitives
                int length = Array.getLength(collection);
                ArrayList c = new ArrayList(length);
                for (int i = 0; i < length; i++) {
                    c.add(Array.get(collection, i));
                }
                iterator = c.iterator();
            }
        } else if (collection instanceof Collection) {
            iterator = ((Collection) collection).iterator();
        } else if (collection instanceof Iterator) {
            iterator = (Iterator) collection;
        } else if (collection instanceof Map) {
            iterator = ((Map) collection).entrySet().iterator();
        } else if (collection instanceof Enumeration) {
            iterator = new IteratorAdapter((Enumeration) collection);
        } else {
            JspException e = new JspException(messages.getMessage("iterate.iterator"));
            TagUtils.getInstance().saveException(pageContext, e);
            throw e;
        }messages.getMessage("iterate.iterator")输出的信息就是楼主看见的Cannot create iterator for this collection

Answer 9

html:itrator标签  这个标签我没用过阿

Answer 10

刚才用了最笨也是最彻底的方法，把html代码一个个加进原来做的jsp页面了，结果一切正常了，不再报错，也能读数据库里的值了，我猜想问题就出在html代码里，因为美工不是我来负责，原来的jsp页面在功能测试时是好使的，加上了美工给的html代码（复制-->粘贴）后就出了问题了，所以我把美工给的代码一段一段对应我的jsp页面加了进去，结果，错误消失了。
美中不足就是到最好也没真正找到错误的根源，只是排除了错误而已。

Answer 11

html:itrator我写错了，是logic:itrator