servlet取到值后传到jsp输出却是空值，哪里出错了？

Question

jsp的商城系统，在后台servlet取数据库的商品数据后，转发到jsp渲染出来，但是前台渲染始终是空白的，找了好久都没找到问题，也不报错，下面是代码：

ListProductServlet.java

package sh.shop.web.servlet.manager;
import java.io.IOException;
import java.util.List;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import sh.shop.domain.Product;
import sh.shop.exception.ListProductException;
import sh.shop.service.ProductService;

@WebServlet("/listProduct")
/**
 * 后台
 * 查询所有商品信息的servlet
 */
public class ListProductServlet extends HttpServlet {
    public void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
            try {
                // 1.创建service层的对象
                ProductService service = new ProductService();
                // 2.调用service层的listAll()
                List<Product> list = service.listAll();
                // 3.将查询出的所有商品放进request域中
                request.setAttribute("list", list);
                // 4.将请求转发到list.jsp
                request.getRequestDispatcher("/admin/products/list.jsp").forward(
                                request, response);
                return;
            } catch (ListProductException e) {
                    e.printStackTrace();
                    response.getWriter().write(e.getMessage());
                    return;
            }
    }
    public void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        doGet(request,response);
    }
}

ProductService.java

package sh.shop.service;

import java.io.IOException;
import java.sql.SQLException;
import java.util.List;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import sh.shop.exception.AddProductException;
import sh.shop.dao.ProductDao;
import sh.shop.domain.Product;
import sh.shop.exception.ListProductException;


@WebServlet("/ProductService")
public class ProductService {
    private ProductDao dao = new ProductDao();

    public List<Product> listAll() throws ListProductException {
        try {
            List<Product> list = dao.listAll();
            return list;
        } catch (SQLException e) {
            e.printStackTrace();
            throw new ListProductException("查询商品失败");
        }
    }
    
    public void addProduct(Product p) throws AddProductException {
        try {
            dao.addProduct(p);
        } catch (SQLException e) {
            e.printStackTrace();
            throw new AddProductException("添加商品失败");
        }
    }
    
}

ProductDao.java

package sh.shop.dao;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;
import org.apache.commons.dbutils.QueryRunner;
import org.apache.commons.dbutils.handlers.ArrayListHandler;
import org.apache.commons.dbutils.handlers.BeanHandler;
import org.apache.commons.dbutils.handlers.BeanListHandler;
import org.apache.commons.dbutils.handlers.ScalarHandler;
import sh.shop.domain.Product;
import sh.shop.utils.DataSourceUtils;

public class ProductDao {
    // 查询所有商品
    public List<Product> listAll() throws SQLException {
        String sql = "select * from products";
        QueryRunner runner = new QueryRunner(DataSourceUtils.getDataSource());
        List<Product> list = runner.query(sql, new BeanListHandler<Product>(Product.class));
        return list;
    }
    
    //添加商品
    public void addProduct(Product p) throws SQLException {

        String sql = "insert into products values(?,?,?,?,?,?,?)";
        QueryRunner runner = new QueryRunner(DataSourceUtils.getDataSource());
        runner.update(sql, p.getId(), p.getName(), p.getPrice(),
                null, p.getImgurl(), p.getDescription());
    }
}

list.jsp

<tbody>
<c:forEach items="${list}" var="p">
    <tr class="text-c va-m">
        <td><input name="" type="checkbox" value=""></td>
        <td>${p.id }</td>
        <td><a onClick="" href="javascript:;"><img width="60" class="product-thumb" src=""></a></td>
        <td class="text-l"><a style="text-decoration:none" onClick="" href="javascript:;">${p.name }</a></td>
        <td class="text-l">${p.description }</td>
        <td>${p.price }</td>
        <td>${p.category }</td>
        <td class="td-manage"><a style="text-decoration:none" class="ml-5" onClick="product_edit('产品编辑','product-add.html','10001')" href="javascript:;" title="编辑"><i class="Hui-iconfont">&#xe6df;</i></a> <a style="text-decoration:none" class="ml-5" onClick="product_del(this,'10001')" href="javascript:;" title="删除"><i class="Hui-iconfont">&#xe6e2;</i></a></td>
    </tr>
</c:forEach>
</tbody>

后台取到的值是有数据的：

Answer 1

${requestScope.list} 试一下? 一楼的意思应该是在浏览器debug一下看看吧...

Answer 2

放session吧周期长

Answer 3

用debug标签看下前端值栈里面的list呢，是null就是传值问题，否则就是前端取值的问题

Answer 4

@鸟德大师 是这个吗？看不懂哦