ftl页面下的forEach循环问题

来源：9-2 项目作业

importSharp

2021-04-02 11:10:56

在训练素材中给的category.html中，我需要把数据库中查询得到的数据返回到前端页面。我想到的是用request.setAttribute方法存到属性里，然后进一步在前端页面去显示。

问题一：原先的前后端作业中是用的jstl中的<%@taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>用 <c:forEach>方法进行循环，但现在mybatis中该用什么方法实现循环

问题二：老师有没有比较好的思路做数据返回，因为对ajax不太理解，是不是也可以用ajax，然后后台使用response.getWriter().println(json);去做前后交互

<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
        <title>分类列表</title>
        <link rel="stylesheet" href="/css/index.css">
        <link rel="stylesheet" href="/css/bootstrap.min.css">
    </head>

    <body>
       <header>
            <div class="container">

                    <nav>
                            <a href="/" >Java</a>
                    </nav>
                    <nav>
                            <a href="/forward/first" >前端</a>
                    </nav>
                    <nav>
                        <a href="/category" >分类</a>
                    </nav>

            </div>
        </header>
        <section class="banner">
            <div class="container">
                <div>
                    <h1>图书</h1>
                    <p>图书分类列表</p>
                </div>
            </div>
        </section>
        <section class="main">
            <div class="container">
                <table class="table table-striped">
                    <thead>
                    <tr>
                        <th>名称</th>
                        <th>创建时间</th>
                        <th>最后修改时间</th>
                    </tr>
                    </thead>
                    <tbody>
                            <tr>
                                <td>Java</td>
                                <td></td>
                                <td></td>
                            </tr>
                    </tbody>
                </table>
            </div>
        </section>
        <section class="page">
            <div class="container">
                <div id="fatie">
                    <a href="/forward/add_category"><button>新建</button></a>
                </div>
            </div>
        </section>
        <footer>
            copy@慕课网
        </footer>
    </body>
</html>

servlet

public class CategoryServlet extends HttpServlet {
    private CategoryService categoryService=new CategoryService();
    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request,response);
    }

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        request.setCharacterEncoding("utf-8");
        response.setContentType("text/html;charset=utf-8");
        List<Category> categoryList=categoryService.selectAll();
        request.setAttribute("categoryList",categoryList);
        request.getRequestDispatcher("/category.ftl").forward(request,response);
    }
}

dao

package library.dao;

import library.entity.Category;
import library.utils.MybatisUtils;

import java.util.List;

public class CategoryDao {

    /**
     * 无参数
     * 查询数据库中所有的类别
     * @return 数据库中的category
     */
    public List<Category> selectAll(){
        List<Category> categoryList=(List<Category>)MybatisUtils.executeQuery(sqlSession->{
            return sqlSession.selectList("categoryMapper.selectAll");
        });
        System.out.println(categoryList);
        return categoryList;
    }
}

工具类

package library.utils;


import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

import java.io.IOException;
import java.io.Reader;
import java.util.function.Function;

public class MybatisUtils {
    private static SqlSessionFactory sqlSessionFactory=null;

    static {
        Reader reader=null;

        try {
            reader=Resources.getResourceAsReader("mybatis-config.xml");
            sqlSessionFactory=new SqlSessionFactoryBuilder().build(reader);
        } catch (IOException e) {
            throw new ExceptionInInitializerError(e);
        }
    }

    public static Object executeQuery(Function<SqlSession,Object> func){
        SqlSession sqlSession=sqlSessionFactory.openSession();

        try{
            Object obj = func.apply(sqlSession);
            return obj;
        }finally {
            sqlSession.close();
        }

    }

    public static Object executeUpdate(Function<SqlSession,Object> func){
        SqlSession sqlSession=sqlSessionFactory.openSession(false);

        try{
            Object obj=func.apply(sqlSession);
            sqlSession.commit();
            return obj;
        }catch (RuntimeException e){
            sqlSession.rollback();
            throw e;
        }finally {
            sqlSession.close();
        }
    }
}

xml文件

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="categoryMapper">
    <select id="selectAll" resultType="library.entity.Category">
        select * from category
</select>
</mapper>