最近登陆tomcat总是报

org.springframework.web.util.NestedServletException: Request processing failed; nested exception is org.mybatis.spring.MyBatisSystemException: nested exception is org.apache.ibatis.exceptions.PersistenceException: 
### Error querying database.  Cause: org.springframework.jdbc.CannotGetJdbcConnectionException: Could not get JDBC Connection; nested exception is com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.
### The error may exist in com/how2java/mapper/CategoryMapper.java (best guess)
### The error may involve com.how2java.mapper.CategoryMapper.total
### The error occurred while executing a query
### Cause: org.springframework.jdbc.CannotGetJdbcConnectionException: Could not get JDBC Connection; nested exception is com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.
	org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:973)
	org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:852)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:624)
	org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:837)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
	org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
	org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:88)
	org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:108)

实际原因是因为我这边网络太差，总是连接不到服务器数据库的缘故

今天完成的任务

完成了增删改查操作

// 告诉spring mvc这是一个控制器类
@Controller
@RequestMapping("")
public class CategoryController {
    @Autowired
    CategoryService categoryService;

    @RequestMapping("listCategory")//这个分页查询就是调用的sql关于某段的某几个数列的查询
    public ModelAndView listCategory(Page page){

        ModelAndView mav = new ModelAndView();//构造方法
        List<Category> cs= categoryService.list(page);//怕不是自动装配的
        //int total = categoryService.total();//得到数据库数据总量
       // page.caculateLast(total);//调用caculateLast方法，但是没卵用啊，这句话 根本就没被返回
        // 放入转发参数
        mav.addObject("cs", cs);
        // 放入jsp路径
        mav.setViewName("listCategory");
        return mav;
    }

    @RequestMapping("addCategory")//增加
    public ModelAndView addCategory(Category category){
        categoryService.add(category);
        ModelAndView mav = new ModelAndView("redirect:/listCategory");
        return mav;
    }

    @RequestMapping("deleteCategory")//删除
    public ModelAndView deleteCategory(Category category){
        categoryService.delete(category);
        ModelAndView mav = new ModelAndView("redirect:/listCategory");
        return mav;
    }

    @RequestMapping("editCategory")//查询id，有点特殊
    public ModelAndView editCategory(Category category){
        Category c= categoryService.get(category.getId());
        ModelAndView mav = new ModelAndView("editCategory");
        mav.addObject("c", c);
        return mav;
    }

    @RequestMapping("updateCategory")//改
    public ModelAndView updateCategory(Category category){
        categoryService.update(category);
        ModelAndView mav = new ModelAndView("redirect:/listCategory");
        return mav;
    }

}

 ModelAndView mav = new ModelAndView("redirect:/listCategory");

保证都能映射在地址为listCategory上

其实很简单

就是

jsp-程序-数据库的交互

用户在网页上输入内容-通过java调用相关的sql语句-sql返回信息-打印在网页上

关于分页查询所使用的sql语句

<select id="list" resultType="Category">
    select * from   category_ 
    <if test="start!=null and count!=null">
        limit #{start},#{count}
    </if>

</select>

实际上为select * from   category_ limit #{start},#{count}

即查询category_表中自start行开始共计count行的数据

分页查询就是通过用户的操作改变start的数值返回数据并打印出来

修改和删除都是通过获得的id，通过sql语句进行操作，本质上讲和任务一的对数据库进行增删改查几乎一样

因为修改和增加涉及到了jsp对用户输入的一个接受，对这部分我理解还不深刻，仅在下面附录

<%@ page language="java" contentType="text/html; charset=UTF-8"
         pageEncoding="UTF-8" import="java.util.*"%>

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>

<div style="width:500px;margin:0px auto;text-align:center">
    <table align='center' border='1' cellspacing='0'>
        <tr>
            <td>id</td>
            <td>name</td>
            <td>编辑</td>
            <td>删除</td>
        </tr>
        <c:forEach items="${cs}" var="c" varStatus="st">
            <tr>
                <td>${c.id}</td>
                <td>${c.name}</td>
                <td><a href="editCategory?id=${c.id}">编辑</a></td>
                <td><a href="deleteCategory?id=${c.id}">删除</a></td>
            </tr>
        </c:forEach>
    </table>
    <div style="text-align:center">
        <a href="?start=0">首  页</a>
        <a href="?start=${page.start-page.count}">上一页</a>
        <a href="?start=${page.start+page.count}">下一页</a>
        <a href="?start=${page.last}">末  页</a>
    </div>


    <div style="text-align:center;margin-top:40px">

        <form method="post" action="addCategory">
            分类名称： <input name="name" value="" type="text"> <br><br>
            <input type="submit" value="增加分类">
        </form>

    </div>
</div>

<%@ page language="java" contentType="text/html; charset=UTF-8"
         pageEncoding="UTF-8" import="java.util.*"%>

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%>

<div style="width:500px;margin:0px auto;text-align:center">


    <div style="text-align:center;margin-top:40px">

        <form method="post" action="updateCategory">
            分类名称： <input name="name" value="${c.name}" type="text"> <br><br>
            <input type="hidden" value="${c.id}" name="id">
            <input type="submit" value="增加分类">
        </form>

    </div>
</div>

明天要做的事

学习jsp做出一个符合修真院特色的网页格式

观看师兄的日报，找出自己对REST风格的接口理解是否有问题

遇到的问题

收获