没找到问题在哪！！大神帮忙看一下代码（JSP使用JSTL的c:forEach标签显示数据怎么不管用

Question

<form name="myform" method="post" action="newstypeservlet?op=batchDelete">
        <table border="1">
            <tr>
                <th>编号</th>
                <th>类型名</th>
                <th>编辑</th>
                <th>删除</th>
            </tr>
            <c:forEach items="${requestScope.newsTypeList }"  var="newsType" varStatus="status">
            <tr style="background-color: ${status.index%2==0?'red':'green' } ">
                <td>
                    <input type="checkbox" name="ids" value="${newsType.id }"/>
                    ${newsType.id }
                </td>
                <td>${newsType.typeName }</td>
                <td><a href="newstypeservlet?op=toEdit&id=${newsType.id }">编辑</a></td>
                <td><a href="newstypeservlet?op=delete&id=${newsType.id }">删除</a></td>
            </tr>
        </c:forEach>
        <tr>
            <td colspan="4" >
                <input type="button" value="批量删除" onclick="checkSelected()"/>
            </td>
        </tr>
        </table>
    </form>

Servlet里的代码：

 protected void doPost(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {

        // System.out.println("进入sevlet");
        request.setCharacterEncoding("UTF-8");// 解决Post提交时的乱码问题
        String op = request.getParameter("op");// 注意：此处的JSP页面不放在根目录下，Servlet就无法接收到页面传来的数据，因为web.xml配置信息无法覆盖
        if ("add".equals(op)) {
            addNewsType(request, response);
        } else if ("list".equals(op)) {
            listNewsType(request, response);
        } else if ("batchDelete".equals(op)) {
            batchDelete(request, response);
        } else if ("delete".equals(op)) {
            deleteById(request, response);
        }
    }

    // 新闻列表
    private void listNewsType(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {
        NewsTypeService newsTypeService = new NewsTypeService();
        List<NewsType> newsTypeList = newsTypeService.findAll();
        request.setAttribute("newsTypeList", newsTypeList);
        request.getRequestDispatcher("../listNewsType.jsp").forward(request,
                response);
    }

    private void deleteById(HttpServletRequest request,
            HttpServletResponse response) throws IOException, ServletException {
        PrintWriter out = response.getWriter();
        String idStr = request.getParameter("id");
        if (idStr == null || "".equals(idStr)) {
            out.write("<script>alert('密码不能为空');history.back();</script>");
            return;
        }
        int id = Integer.parseInt(idStr);
        NewsTypeService newsTypeService = new NewsTypeService();
        newsTypeService.delete(id);
        // 删除数据后，返回列表
        listNewsType(request, response);
    }

    private void batchDelete(HttpServletRequest request,
            HttpServletResponse response) throws ServletException, IOException {
        String[] ids = request.getParameterValues("ids");
        NewsTypeService newsTypeService = new NewsTypeService();
        newsTypeService.batchDelete(ids);
        // 删除数据后，返回列表
        listNewsType(request, response);

    }

service代码：

public class NewsTypeService {

    public int save(NewsType newsType) {

        return new NewsTypeDao().save(newsType);
    }

    public int batchDelete(String[] ids) {
        return new NewsTypeDao().batchDelete(ids);
    }

    public List<NewsType> findAll() {
        return new NewsTypeDao().findAll();
    }

    public int delete(int id) {
        return new NewsTypeDao().delete(id);
    }

DAO里的代码

 public class NewsTypeDao {

    DBUtil dbUtil = new DBUtil();

    // 保存新闻类型
    public int save(NewsType newsType) {
        String sql = "insert into newstype(typeName) values (?)";
        Object[] params = { newsType.getTypeName() };
        return dbUtil.executeUpdate(sql, params);
        // executeUpdate的返回值是一个整数，指示受影响的行数（即更新计数）
    }

    public List<NewsType> findAll() {
        List<NewsType> newsTypeList = new ArrayList<NewsType>();
        String sql = "select * from newstype";
        ResultSet rs = dbUtil.executeQuery(sql, null);
        try {
            while (rs.next()) {
                NewsType newsType = new NewsType(rs.getInt("id"),
                        rs.getString("typeName"));
                newsTypeList.add(newsType);
            }
        } catch (SQLException e) {
            e.printStackTrace();
            return newsTypeList;
        } finally {
            dbUtil.closeAll();
        }
        return newsTypeList;
    }

    /**
     * 批量删除
     * 
     * @param ids
     *            指定的ID集合
     * @return
     */
    public int batchDelete(String[] ids) {
        // TODO Auto-generated method stub
        String sql = "delete from newstype where id in(?)";
        Object[] params = { ArrayUtil.array2String(ids, ",") };

        return dbUtil.executeUpdate(sql, params);
    }

    /**
     * 根据Id进行删除
     * 
     * @param id
     * @return
     */
    public int delete(int id) {
        String sql = "delete from newsType where id=?";
        Object[] params = { id };
        return dbUtil.executeUpdate(sql, params);
    }

## # }谢谢大神****

Answer 1

先自己调试，查询封装数据的list中是否有数据，缩小出现错误的范围