一?点睛
MyBatis Plus 自带分页插件，只要简单的配置即可实现分页功能。
分页查询的开发流程见下图。
二?实战
1?数据库中的数据
mysql> select * from user;
+---------------------+--------------+------+--------------------+---------------------+---------------------+---------+
| id | NAME | age | email | create_time | update_time | version |
+---------------------+--------------+------+--------------------+---------------------+---------------------+---------+
| 0 | auto | 20 | 1243@qq.com | NULL | NULL | NULL |
| 1 | Jone | 18 | test1@baomidou.com | NULL | NULL | NULL |
| 2 | Jack | 20 | test2@baomidou.com | NULL | NULL | NULL |
| 3 | Tom | 28 | test3@baomidou.com | NULL | NULL | NULL |
| 4 | Sandy | 21 | test4@baomidou.com | NULL | NULL | NULL |
| 5 | Billie | 24 | test5@baomidou.com | NULL | NULL | NULL |
| 1443158688033337346 | lucymaryupup | 20 | 1243@qq.com | NULL | 2021-09-30 08:51:12 | NULL |
| 1443378040145903617 | ASSIGN_ID | 20 | 1243@qq.com | 2021-09-30 08:51:56 | 2021-09-30 08:51:56 | NULL |
| 1444192337759502338 | zhangsan | 20 | 1243@qq.com | 2021-10-02 14:47:40 | 2021-10-02 14:55:10 | 2 |
+---------------------+--------------+------+--------------------+---------------------+---------------------+---------+
9 rows in set (0.00 sec)?2?配置分页插件
@Configuration
@MapperScan("com.cakin.demomptest.mapper")
public class MpConfig {
/**
* 乐观锁插件
*/
@Bean
public OptimisticLockerInterceptor optimisticLockerInterceptor() {
return new OptimisticLockerInterceptor();
}
/**
* 分页插件
*/
@Bean
public PaginationInterceptor paginationInterceptor() {
return new PaginationInterceptor();
}
}3?测试 selectPage 分页
// 分页查询
@Test
public void testSelectPage() {
Page<User> page = new Page(1, 3);
Page<User> userPage = userMapper.selectPage(page, null);
// 返回对象得到分页所有数据
long pages = userPage.getPages(); // 总页数
long current = userPage.getCurrent(); // 当前页
List<User> records = userPage.getRecords(); // 查询数据集合
long total = userPage.getTotal(); // 总记录数
boolean hasNext = userPage.hasNext(); // 下一页
boolean hasPrevious = userPage.hasPrevious(); // 上一页
System.out.println(pages);
System.out.println(current);
System.out.println(records);
System.out.println(total);
System.out.println(hasNext);
System.out.println(hasPrevious);
}4?查询结果
Creating a new SqlSession
SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@7f829c76] was not registered for synchronization because synchronization is not active
2021-10-02 15:55:10.203 INFO 1756 --- [ main] com.zaxxer.hikari.HikariDataSource : HikariPool-1 - Starting...
2021-10-02 15:55:12.209 INFO 1756 --- [ main] com.zaxxer.hikari.HikariDataSource : HikariPool-1 - Start completed.
JDBC Connection [HikariProxyConnection@668929853 wrapping com.mysql.cj.jdbc.ConnectionImpl@c35af2a] will not be managed by Spring
JsqlParserCountOptimize sql=SELECT id,name,age,email,create_time,update_time,version FROM user
==> Preparing: SELECT COUNT(1) FROM user
==> Parameters:
<== Columns: COUNT(1)
<== Row: 9
==> Preparing: SELECT id,name,age,email,create_time,update_time,version FROM user LIMIT ?,?
==> Parameters: 0(Long), 3(Long)
<== Columns: id, name, age, email, create_time, update_time, version
<== Row: 0, auto, 20, 1243@qq.com, null, null, null
<== Row: 1, Jone, 18, test1@baomidou.com, null, null, null
<== Row: 2, Jack, 20, test2@baomidou.com, null, null, null
<== Total: 3
Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@7f829c76]
3
1
[User(id=0, name=auto, age=20, email=1243@qq.com, createTime=null, updateTime=null, version=null), User(id=1, name=Jone, age=18, email=test1@baomidou.com, createTime=null, updateTime=null, version=null), User(id=2, name=Jack, age=20, email=test2@baomidou.com, createTime=null, updateTime=null, version=null)]
9
true
false5?测试 selectMapsPage 分页
当指定了特定的查询列时，希望分页结果列表只返回被查询的列，而不是很多 null 值
// 分页查询
@Test
public void testSelectMapsPage() {
// Page 不需要泛型
Page<Map<String, Object>> page = new Page<>(1, 5);
Page<Map<String, Object>> pageParam = userMapper.selectMapsPage(page, null);
List<Map<String, Object>> records = pageParam.getRecords();
records.forEach(System.out::println);
System.out.println(pageParam.getCurrent());
System.out.println(pageParam.getPages());
System.out.println(pageParam.getSize());
System.out.println(pageParam.getTotal());
System.out.println(pageParam.hasNext());
System.out.println(pageParam.hasPrevious());
}测试 selectMapsPage 分页：结果集是 Map
Creating a new SqlSession
SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@6ae7deac] was not registered for synchronization because synchronization is not active
2021-10-02 15:59:14.475 INFO 20468 --- [ main] com.zaxxer.hikari.HikariDataSource : HikariPool-1 - Starting...
2021-10-02 15:59:16.276 INFO 20468 --- [ main] com.zaxxer.hikari.HikariDataSource : HikariPool-1 - Start completed.
JDBC Connection [HikariProxyConnection@1018742990 wrapping com.mysql.cj.jdbc.ConnectionImpl@1fde0371] will not be managed by Spring
JsqlParserCountOptimize sql=SELECT id,name,age,email,create_time,update_time,version FROM user
==> Preparing: SELECT COUNT(1) FROM user
==> Parameters:
<== Columns: COUNT(1)
<== Row: 9
==> Preparing: SELECT id,name,age,email,create_time,update_time,version FROM user LIMIT ?,?
==> Parameters: 0(Long), 5(Long)
<== Columns: id, name, age, email, create_time, update_time, version
<== Row: 0, auto, 20, 1243@qq.com, null, null, null
<== Row: 1, Jone, 18, test1@baomidou.com, null, null, null
<== Row: 2, Jack, 20, test2@baomidou.com, null, null, null
<== Row: 3, Tom, 28, test3@baomidou.com, null, null, null
<== Row: 4, Sandy, 21, test4@baomidou.com, null, null, null
<== Total: 5
Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@6ae7deac]
{name=auto, id=0, age=20, email=1243@qq.com}
{name=Jone, id=1, age=18, email=test1@baomidou.com}
{name=Jack, id=2, age=20, email=test2@baomidou.com}
{name=Tom, id=3, age=28, email=test3@baomidou.com}
{name=Sandy, id=4, age=21, email=test4@baomidou.com}
1
2
5
9
true
false