目录

一.分页的原理

二.Mybatis实现

三.PageHelper

第⼀步：引⼊依赖

第⼆步：在mybatis-config.xml⽂件中配置插件

第三步：编写Java代码

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一.分页的原理

pageindex 页数 pagindex 页内数据

(pageindex-1)*pagesize,pagesize

SELECT * FROM table 
LIMIT(PageNo - 1)*PageSize, PageSize;

二.Mybatis实现

测试程序 就全查出来 然后分页

        int pageIndex = 1;pageIndex = (pageIndex - 1) * pageSize;List<Employee> employees = mapper.queryEmployeeByPage(pageIndex, pageSize);

  List<Employee> queryEmployeeByPage(@Param("pageindex") int pageindex, @Param("pagesize")int pageSize);

三.PageHelper

第⼀步：引⼊依赖

pom.xml

<!-- https://mvnrepository.com/artifact/com.github.pagehelper/pagehelper -->
<dependency><groupId>com.github.pagehelper</groupId><artifactId>pagehelper</artifactId><version>5.3.3</version>
</dependency>

第⼆步：在mybatis-config.xml⽂件中配置插件

typeAliases标签下⾯进⾏配置：

<plugins><plugin interceptor="com.github.pagehelper.PageInterceptor"></plugin></plugins>

第三步：编写Java代码

关键点：PageHelper.startPage(pageIndex,pageSize); //开启分页

  PageInfo<Car> pageInfo = new PageInfo<>(cars, 5); 获取分页信息

• 在查询语句之前开启分⻚功能。

• 在查询语句之后封装PageInfo对象。（PageInfo对象将来会存储到request域当中。在⻚⾯上展 示。）

 //开启分页int pageNum=2;int pageSize=4;PageHelper.startPage(pageNum,pageSize);// 执⾏查询语句List<Car> cars = mapper.queryCarList();cars.forEach(new Consumer<Car>() {@Overridepublic void accept(Car car) {System.out.println(car);}});// 获取分⻚信息对象PageInfo<Car> pageInfo = new PageInfo<>(cars, 5);System.out.println(pageInfo);

四关于sqlSession 线程代码

public class SqlSessionUtil {static   ThreadLocal<SqlSession> sqlSessionThreadLocal = new InheritableThreadLocal<>();static SqlSession sqlSession;static {SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();try {InputStream inputStream = Resources.getResourceAsStream("mybatis-config.xml");SqlSessionFactory build = sqlSessionFactoryBuilder.build(inputStream);sqlSession = build.openSession(false);sqlSessionThreadLocal.set(sqlSession);} catch (IOException e) {throw new RuntimeException(e);}}public static SqlSession getSqlSession() {return sqlSession;}public static void close(SqlSession sqlSession) {if (sqlSession != null) {sqlSession.close();}sqlSessionThreadLocal.remove();}