public class ViewBaseServlet extends HttpServlet {

    private TemplateEngine templateEngine;

    @Override
    public void init() throws ServletException {

        // 1.获取ServletContext对象
        ServletContext servletContext = this.getServletContext();

        // 2.创建Thymeleaf解析器对象
        ServletContextTemplateResolver templateResolver = new ServletContextTemplateResolver(servletContext);

        // 3.给解析器对象设置参数
        // ①HTML是默认模式，明确设置是为了代码更容易理解
        templateResolver.setTemplateMode(TemplateMode.HTML);

        // ②设置前缀
        String viewPrefix = servletContext.getInitParameter("view-prefix");

        templateResolver.setPrefix(viewPrefix);

        // ③设置后缀
        String viewSuffix = servletContext.getInitParameter("view-suffix");

        templateResolver.setSuffix(viewSuffix);

        // ④设置缓存过期时间（毫秒）
        templateResolver.setCacheTTLMs(60000L);

        // ⑤设置是否缓存
        templateResolver.setCacheable(true);

        // ⑥设置服务器端编码方式
        templateResolver.setCharacterEncoding("utf-8");

        // 4.创建模板引擎对象
        templateEngine = new TemplateEngine();

        // 5.给模板引擎对象设置模板解析器
        templateEngine.setTemplateResolver(templateResolver);

    }

    protected void processTemplate(String templateName, HttpServletRequest req, HttpServletResponse resp) throws IOException {
        // 1.设置响应体内容类型和字符集
        resp.setContentType("text/html;charset=UTF-8");

        // 2.创建WebContext对象
        WebContext webContext = new WebContext(req, resp, getServletContext());

        // 3.处理模板数据
        templateEngine.process(templateName, webContext, resp.getWriter());
    }
}

<tr th:if="${#lists.isEmpty(session.bookList)}">
    <td colspan="4">库存为空</td>
</tr>

<tr th:unless="${#lists.isEmpty(session.bookList)}">
    <td>book1</td>
    td>200</td>
    td>30</td>
</tr>

@WebServlet("/add.do")
public class AddServlet extends ViewBaseServlet {

    private FruitDAO fruitDAO = new FruitDAOImpl();

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        request.setCharacterEncoding("UTF-8");

        String fname = request.getParameter("fname");
        Integer price = Integer.parseInt(request.getParameter("price")) ;
        Integer fcount = Integer.parseInt(request.getParameter("fcount"));
        String remark = request.getParameter("remark");

        Fruit fruit = new Fruit(0,fname , price , fcount , remark ) ;

        fruitDAO.addFruit(fruit);

        response.sendRedirect("index");

    }
}

@WebServlet("/fruit.do")
public class FruitServlet extends ViewBaseServlet {
    private FruitDAO fruitDAO = new FruitDAOImpl();

    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //设置编码
        request.setCharacterEncoding("UTF-8");

        String operate = request.getParameter("operate");
        if(StringUtil.isEmpty(operate)){
            operate = "index" ;
        }

        switch(operate){
            case "index":
                index(request,response);
                break;
            case "add":
                add(request,response);
                break;
            case "del":
                del(request,response);
                break;
            case "edit":
                edit(request,response);
                break;
            case "update":
                update(request,response);
                break;
            default:
                throw new RuntimeException("operate值非法!");
        }
    }

    private void update(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //1.设置编码
        request.setCharacterEncoding("utf-8");

        //2.获取参数
        String fidStr = request.getParameter("fid");
        Integer fid = Integer.parseInt(fidStr);
        String fname = request.getParameter("fname");
        String priceStr = request.getParameter("price");
        int price = Integer.parseInt(priceStr);
        String fcountStr = request.getParameter("fcount");
        Integer fcount = Integer.parseInt(fcountStr);
        String remark = request.getParameter("remark");

        //3.执行更新
        fruitDAO.updateFruit(new Fruit(fid,fname, price ,fcount ,remark ));

        //4.资源跳转
        //super.processTemplate("index",request,response);
        //request.getRequestDispatcher("index.html").forward(request,response);
        //此处需要重定向，目的是重新给IndexServlet发请求，重新获取furitList，然后覆盖到session中，这样index.html页面上显示的session中的数据才是最新的
        response.sendRedirect("fruit.do");
    }

    private void edit(HttpServletRequest request , HttpServletResponse response)throws IOException, ServletException {
        String fidStr = request.getParameter("fid");
        if(StringUtil.isNotEmpty(fidStr)){
            int fid = Integer.parseInt(fidStr);
            Fruit fruit = fruitDAO.getFruitByFid(fid);
            request.setAttribute("fruit",fruit);
            super.processTemplate("edit",request,response);
        }
    }

    private void del(HttpServletRequest request , HttpServletResponse response)throws IOException, ServletException {
        String fidStr = request.getParameter("fid");
        if(StringUtil.isNotEmpty(fidStr)){
            int fid = Integer.parseInt(fidStr);
            fruitDAO.delFruit(fid);

            //super.processTemplate("index",request,response);
            response.sendRedirect("fruit.do");
        }
    }

    private void add(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        request.setCharacterEncoding("UTF-8");

        String fname = request.getParameter("fname");
        Integer price = Integer.parseInt(request.getParameter("price")) ;
        Integer fcount = Integer.parseInt(request.getParameter("fcount"));
        String remark = request.getParameter("remark");

        Fruit fruit = new Fruit(0,fname , price , fcount , remark ) ;

        fruitDAO.addFruit(fruit);

        response.sendRedirect("fruit.do");

    }

    private void index(HttpServletRequest request , HttpServletResponse response)throws IOException, ServletException {
        HttpSession session = request.getSession() ;

        // 设置当前页，默认值1
        Integer pageNo = 1 ;

        String oper = request.getParameter("oper");

        //如果oper!=null 说明 通过表单的查询按钮点击过来的
        //如果oper是空的，说明 不是通过表单的查询按钮点击过来的
        String keyword = null ;
        if(StringUtil.isNotEmpty(oper) && "search".equals(oper)){
            //说明是点击表单查询发送过来的请求
            //此时，pageNo应该还原为1 ， keyword应该从请求参数中获取
            pageNo = 1 ;
            keyword = request.getParameter("keyword");
            //如果keyword为null，需要设置为空字符串""，否则查询时会拼接成 %null% , 我们期望的是 %%
            if(StringUtil.isEmpty(keyword)){
                keyword = "" ;
            }
            //将keyword保存（覆盖）到session中
            session.setAttribute("keyword",keyword);
        }else{
            //说明此处不是点击表单查询发送过来的请求（比如点击下面的上一页下一页或者直接在地址栏输入网址）
            //此时keyword应该从session作用域获取
            String pageNoStr = request.getParameter("pageNo");
            if(StringUtil.isNotEmpty(pageNoStr)){
                pageNo = Integer.parseInt(pageNoStr);   //如果从请求中读取到pageNo，则类型转换。否则，pageNo默认就是1
            }
            //如果不是点击的查询按钮，那么查询是基于session中保存的现有keyword进行查询
            Object keywordObj = session.getAttribute("keyword");
            if(keywordObj!=null){
                keyword = (String)keywordObj ;
            }else{
                keyword = "" ;
            }
        }

        // 重新更新当前页的值
        session.setAttribute("pageNo",pageNo);

        FruitDAO fruitDAO = new FruitDAOImpl();
        List<Fruit> fruitList = fruitDAO.getFruitList(keyword , pageNo);
        session.setAttribute("fruitList",fruitList);

        //总记录条数
        int fruitCount = fruitDAO.getFruitCount(keyword);
        //总页数
        int pageCount = (fruitCount+5-1)/5 ;
        /*
        总记录条数       总页数
        1               1
        5               1
        6               2
        10              2
        11              3
        fruitCount      (fruitCount+5-1)/5
         */
        session.setAttribute("pageCount",pageCount);

        //此处的视图名称是 index
        //那么thymeleaf会将这个 逻辑视图名称 对应到 物理视图 名称上去
        //逻辑视图名称 ：   index
        //物理视图名称 ：   view-prefix + 逻辑视图名称 + view-suffix
        //所以真实的视图名称是：      /       index       .html
        super.processTemplate("index",request,response);
    }
}

@WebServlet("/fruit.do")
public class FruitServlet extends ViewBaseServlet {
    private FruitDAO fruitDAO = new FruitDAOImpl();

    @Override
    protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        //设置编码
        request.setCharacterEncoding("UTF-8");

        String operate = request.getParameter("operate");
        if(StringUtil.isEmpty(operate)){
            operate = "index" ;
        }

        // 获取当前类中所有方法
        Method[] methods = this.getClass().getDeclareMethods();

        for (Method m : methods) {
            String methodName = m.getName();
            if (operate.equals(methodName)) {
                try {
                    // 找到和 operate 同名的方法， 那么通过反射技术调用它
                    m.invoke(this, request, response);
                    return;
                } catch(IllegalAcc....)
                e.printS
            }
        }

        throw new RuntimeException("operate值非法!");
    }

        // switch(operate){
        //     case "index":
        //         index(request,response);
        //         break;
        //     case "add":
        //         add(request,response);
        //         break;
        //     case "del":
        //         del(request,response);
        //         break;
        //     case "edit":
        //         edit(request,response);
        //         break;
        //     case "update":
        //         update(request,response);
        //         break;
        //     default:
                //  throw new RuntimeException("operate值非法!");
        // }
    }

    private void update(HttpServletRequest request, HttpServletResponse response) throws