笔记66 Spring Boot快速入门（六）

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SpringBoot中使用Mybatis

一、注解方式

1.创建映射文件CategoryMapper.java

使用注解@Mapper 表示这是一个Mybatis Mapper接口。
使用@Select注解表示调用findAll方法会去执行对应的sql语句。

package com.example.springbootmybatisdemo.mapper; import com.example.springbootmybatisdemo.pojo.Category;
import org.apache.ibatis.annotations.Mapper;
import org.apache.ibatis.annotations.Select; import java.util.List; @Mapper
public interface CategoryMapper {
@Select("select * from category")
List<Category> findAll();
}

2.创建CategoryController.java

有问题：无法自动加载mapper，显示有错误，但是运行结果正确。

package com.example.springbootmybatisdemo.controller; import com.example.springbootmybatisdemo.mapper.CategoryMapper;
import com.example.springbootmybatisdemo.pojo.Category;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.RequestMapping; import java.util.List; @Controller
public class CategoryController {
@Autowired
private CategoryMapper categoryMapper; @RequestMapping("/listCategory")
public String listCategory(Model model) throws Exception{
List<Category> categories=categoryMapper.findAll();
model.addAttribute("category",categories);
System.out.println();
return "listCategory";
}
}

3.listCategory.html

<!DOCTYPE html>
<html lang="en" xmlns:th="http://www.thymeleaf.org">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<title>Title</title>
</head>
<body>
<div class="showing">
<h2>SpringBoot+mybatis</h2> <table>
<thead>
<tr>
<th>id</th>
<th>name</th>
</tr>
</thead>
<tbody>
<tr th:each="c: ${category}">
<td align="center" th:text="${c.id}"></td>
<td align="center" th:text="${c.name}"></td>
</tr>
</tbody>
</table>
</div>
</body>
</html>

二、xml方式(有问题)

三、SpringBoot+Mybatis抽插数据库

1.使用第三方插件PageHelper进行分页查询

增加依赖：

<dependency>
<groupId>com.github.pagehelper</groupId>
<artifactId>pagehelper</artifactId>
<version>4.1.6</version>
</dependency>

2.配置PageHelper

PageHelperConfig.java

package com.example.springbootmybatisdemo.config; import com.github.pagehelper.PageHelper;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration; import java.util.Properties; @Configuration
public class PageHelperConfig {
@Bean
public PageHelper pageHelper(){
PageHelper pageHelper = new PageHelper();
Properties p = new Properties();
p.setProperty("offsetAsPageNum", "true");
p.setProperty("rowBoundsWithCount", "true");
p.setProperty("reasonable", "true");
pageHelper.setProperties(p);
return pageHelper;
}
}

注解@Configuration 表示PageHelperConfig 这个类是用来做配置的。
注解@Bean 表示启动PageHelper这个拦截器。

offsetAsPageNum:设置为true时，会将RowBounds第一个参数offset当成pageNum页码使用.

p.setProperty("offsetAsPageNum", "true");

rowBoundsWithCount:设置为true时，使用RowBounds分页会进行count查询.

p.setProperty("rowBoundsWithCount", "true");

reasonable：启用合理化时，如果pageNum<1会查询第一页，如果pageNum>pages会查询最后一页。比jpa中Pageable进行分页查询时更合理，不需要再去处理。

p.setProperty("reasonable", "true");

3.修改映射mapper

CategoryMapper.java

package com.example.springbootmybatisdemo.mapper; import com.example.springbootmybatisdemo.pojo.Category;
import org.apache.ibatis.annotations.*; import java.util.List; @Mapper
public interface CategoryMapper {
@Select("select * from category")
List<Category> findAll(); @Insert("insert into category(name) values (#{name})")
int save(Category category); @Delete(" delete from category where id= #{id} ")
void delete(int id); @Select("select * from category where id= #{id} ")
Category get(int id); @Update("update category set name=#{name} where id=#{id} ")
int update(Category category);
}

4.控制层

CategoryController.java

package com.example.springbootmybatisdemo.controller; import com.example.springbootmybatisdemo.mapper.CategoryMapper;
import com.example.springbootmybatisdemo.pojo.Category;
import com.github.pagehelper.PageHelper;
import com.github.pagehelper.PageInfo;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam; import java.util.List; @Controller
public class CategoryController {
@Autowired
private CategoryMapper categoryMapper; @RequestMapping("/listCategory")
public String listCategory(Model model) throws Exception{
List<Category> categories=categoryMapper.findAll();
model.addAttribute("category",categories);
System.out.println();
return "listCategory";
} @RequestMapping("/listCategories")
public String listCategories(Model model,
@RequestParam(value = "start",defaultValue = "0")int start,
@RequestParam(value = "size",defaultValue = "5") int size) throws Exception{
PageHelper.startPage(start,size,"id desc");
List<Category> categories=categoryMapper.findAll();
PageInfo<Category> pageInfo=new PageInfo<>(categories);
System.out.println(pageInfo.getPageNum());
model.addAttribute("pageInfo",pageInfo);
return "listCategories";
} @RequestMapping("/addCategory")
public String addCategory(Category category) throws Exception{
categoryMapper.save(category);
return "redirect:listCategories";
}
@RequestMapping("/deleteCategory")
public String deleteCategory(Category category)throws Exception{
categoryMapper.delete(category.getId());
return "redirect:listCategories";
}
@RequestMapping("/updateCategory")
public String updateCategory(Category category)throws Exception{
categoryMapper.update(category);
return "redirect:listCategories";
}
@RequestMapping("/editCategory")
public String editCategory(int id,Model model)throws Exception{
Category category=categoryMapper.get(id);
model.addAttribute("category",category);
return "editCategory";
} }

根据start,size进行分页，并且设置id 倒排序

PageHelper.startPage(start,size,"id desc");

因为PageHelper的作用，这里就会返回当前分页的集合了

List<Category> categories=categoryMapper.findAll();

根据返回的集合，创建PageInfo对象

PageInfo<Category> page = new PageInfo<>(categories);

5.视图层

listCategories.html

<!DOCTYPE html>
<html lang="en" xmlns:th="http://www.thymeleaf.org">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<title>Title</title>
</head>
<body>
<div class="showing">
<h2>SpringBoot+Mybatis</h2>
<div style="width:500px;margin:20px auto;text-align: center">
<table align="center" border="1" cellspacing="0">
<thead>
<tr>
<th>id</th>
<th>name</th>
<td>编辑</td>
<td>删除</td>
</tr>
</thead>
<tbody>
<tr th:each="c: ${pageInfo.list}">
<td align="center" th:text="${c.id}"></td>
<td align="center" th:text="${c.name}"></td>
<td align="center" ><a th:href="@{/editCategory(id=${c.id})}">编辑</a></td>
<td align="center" ><a th:href="@{/deleteCategory(id=${c.id})}">删除</a></td>
</tr>
</tbody>
</table>
<br />
<div>
<a th:href="@{/listCategories(start=1)}">[首页]</a>
<a th:href="@{/listCategories(start=${pageInfo.pageNum -1})}">[上一页]</a>
<a th:href="@{/listCategories(start=${pageInfo.pageNum +1})}">[下一页]</a>
<a th:href="@{/listCategories(start=${pageInfo.pages})}">[末页]</a>
</div>
<form action="/addCategory" method="post">
name:<input name="name"/><br/>
<button type="submit">提交</button>
</form>
</div>
</div>
</body>
</html>