前面說了一題 MyBatis 有哪些分頁的方式?其原理是什麼?,後面還有一題 MyBatis 插件的運行原理是什麼?java
爲了方便調試,梳理出步驟與原理,先整一個 MyBatis-PageHelper 的使用 Demo。mysql
一、Maven 依賴,mysql 驅動 + MyBatis + pagehelpergit
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<parent>
<groupId>constxiong</groupId>
<artifactId>demo</artifactId>
<version>0.0.1-SNAPSHOT</version>
</parent>
<artifactId>mybatis-pageHelper</artifactId>
<dependencies>
<!-- MySQL 8.0.21 驅動 -->
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>8.0.21</version>
</dependency>
<!-- MyBatis -->
<dependency>
<groupId>org.mybatis</groupId>
<artifactId>mybatis</artifactId>
<version>3.5.5</version>
</dependency>
<dependency>
<groupId>com.github.pagehelper</groupId>
<artifactId>pagehelper</artifactId>
<version>5.2.0</version>
</dependency>
</dependencies>
<build>
</build>
</project>
二、MyBatis 配置文件 mybatis-config.xmlgithub
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<plugins>
<plugin interceptor="com.github.pagehelper.PageInterceptor">
<property name="helperDialect" value="mysql"/>
</plugin>
</plugins>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<property name="driver" value="com.mysql.cj.jdbc.Driver"/>
<property name="url" value="jdbc:mysql://172.31.32.184:3306/constxiong?serverTimezone=UTC&useSSL=false&useUnicode=true&characterEncoding=UTF-8"/>
<property name="username" value="root"/>
<property name="password" value="constxiong@123"/>
</dataSource>
</environment>
</environments>
<mappers>
<mapper resource="constxiong/mapper/UserMapper.xml"/>
</mappers>
</configuration>
三、寫 SQL 的 mapper xmlsql
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="constxiong.mapper.UserMapper">
<select id="selectUsers" resultType="constxiong.po.User">
select * from user
</select>
<insert id="insertUser" parameterType="constxiong.po.User">
insert into user values(#{id}, #{name})
</insert>
<delete id="deleteUsers">
delete from user
</delete>
</mapper>
四、Mapper 接口類數據庫
package constxiong.mapper;
import constxiong.po.User;
import java.util.List;
/**
* UserMapper 接口,映射對數據庫的操做
*/
public interface UserMapper {
List<User> selectUsers();
int insertUser(User user);
int deleteUsers();
}
五、User PO 模型apache
package constxiong.po;
/**
* 用戶表模型
*/
public class User {
private Integer id;
private String name;
private String mc;
public User(Integer id, String name) {
this.id = id;
this.name = name;
}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getMc() {
return mc;
}
public void setMc(String mc) {
this.mc = mc;
}
@Override
public String toString() {
return "User{" +
"id=" + id +
", name='" + name + '\'' +
", mc='" + mc + '\'' +
'}';
}
}
六、測試代碼
安全
package constxiong;
import com.github.pagehelper.ISelect;
import com.github.pagehelper.Page;
import com.github.pagehelper.PageHelper;
import constxiong.mapper.UserMapper;
import constxiong.po.User;
import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.RowBounds;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import java.io.IOException;
import java.io.InputStream;
import java.util.List;
/**
* 測試 Mybatis 分頁插件
*/
public class Test {
public static void main(String[] args) throws IOException {
testXmlConfigAndPager();
}
/**
* 測試 xml 配置方式分頁
*/
private static void testXmlConfigAndPager() throws IOException {
String resource = "mybatis-config.xml";//xml配置文件路徑
InputStream inputStream = Resources.getResourceAsStream(resource);//讀取配置
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);//構建 SqlSessionFactory
SqlSession sqlSession = sqlSessionFactory.openSession(true);//經過 SqlSessionfactory 獲取 SqlSession
UserMapper userMapper = sqlSession.getMapper(UserMapper.class);//經過 SqlSession 獲取 Mapper 接口
//刪除 user
userMapper.deleteUsers();
//插入 user
for (int i = 1; i <= 35; i++) {
userMapper.insertUser(new User(i, "ConstXiong" + i));
}
//查詢全部 user
List<User> users = userMapper.selectUsers();
System.out.println(users);
//未打開 mybatis-config.xml 中 plugins 標籤使用內存分頁;打開標籤使用插件的物理分頁
int pageNo = 2;
int pageSize = 10;
users = sqlSession.selectList("constxiong.mapper.UserMapper.selectUsers", null, new RowBounds((pageNo - 1) * pageSize, pageSize));
System.out.println(users);
//使用靜態方法 startPage
PageHelper.startPage(pageNo, pageSize);
users = userMapper.selectUsers();
System.out.println(users);
//使用靜態方法 offsetPage
PageHelper.offsetPage(pageNo, pageSize);
users = userMapper.selectUsers();
System.out.println(users);
//匿名類
Page<User> page = PageHelper.startPage(pageNo, pageSize).doSelectPage(new ISelect() {
@Override
public void doSelect() {
userMapper.selectUsers();
}
});
System.out.println(page);
// lambda
page = PageHelper.startPage(pageNo, pageSize).doSelectPage(() -> {
userMapper.selectUsers();
});
System.out.println(page);
//僅合計
long count = PageHelper.count(new ISelect() {
@Override
public void doSelect() {
userMapper.selectUsers();
}
});
System.out.println(count);
//lambda
count = PageHelper.count(() -> {
userMapper.selectUsers();
});
System.out.println(count);
//關閉 SqlSession
sqlSession.close();
}
}
七、運行結果session
[User{id=1, name='ConstXiong1', mc='null'}, User{id=2, name='ConstXiong2', mc='null'}, User{id=3, name='ConstXiong3', mc='null'}, User{id=4, name='ConstXiong4', mc='null'}, User{id=5, name='ConstXiong5', mc='null'}, User{id=6, name='ConstXiong6', mc='null'}, User{id=7, name='ConstXiong7', mc='null'}, User{id=8, name='ConstXiong8', mc='null'}, User{id=9, name='ConstXiong9', mc='null'}, User{id=10, name='ConstXiong10', mc='null'}, User{id=11, name='ConstXiong11', mc='null'}, User{id=12, name='ConstXiong12', mc='null'}, User{id=13, name='ConstXiong13', mc='null'}, User{id=14, name='ConstXiong14', mc='null'}, User{id=15, name='ConstXiong15', mc='null'}, User{id=16, name='ConstXiong16', mc='null'}, User{id=17, name='ConstXiong17', mc='null'}, User{id=18, name='ConstXiong18', mc='null'}, User{id=19, name='ConstXiong19', mc='null'}, User{id=20, name='ConstXiong20', mc='null'}, User{id=21, name='ConstXiong21', mc='null'}, User{id=22, name='ConstXiong22', mc='null'}, User{id=23, name='ConstXiong23', mc='null'}, User{id=24, name='ConstXiong24', mc='null'}, User{id=25, name='ConstXiong25', mc='null'}, User{id=26, name='ConstXiong26', mc='null'}, User{id=27, name='ConstXiong27', mc='null'}, User{id=28, name='ConstXiong28', mc='null'}, User{id=29, name='ConstXiong29', mc='null'}, User{id=30, name='ConstXiong30', mc='null'}, User{id=31, name='ConstXiong31', mc='null'}, User{id=32, name='ConstXiong32', mc='null'}, User{id=33, name='ConstXiong33', mc='null'}, User{id=34, name='ConstXiong34', mc='null'}, User{id=35, name='ConstXiong35', mc='null'}]
Page{count=false, pageNum=2, pageSize=10, startRow=10, endRow=20, total=-1, pages=1, reasonable=false, pageSizeZero=false}[User{id=11, name='ConstXiong11', mc='null'}, User{id=12, name='ConstXiong12', mc='null'}, User{id=13, name='ConstXiong13', mc='null'}, User{id=14, name='ConstXiong14', mc='null'}, User{id=15, name='ConstXiong15', mc='null'}, User{id=16, name='ConstXiong16', mc='null'}, User{id=17, name='ConstXiong17', mc='null'}, User{id=18, name='ConstXiong18', mc='null'}, User{id=19, name='ConstXiong19', mc='null'}, User{id=20, name='ConstXiong20', mc='null'}]
Page{count=true, pageNum=2, pageSize=10, startRow=10, endRow=20, total=35, pages=4, reasonable=false, pageSizeZero=false}[User{id=11, name='ConstXiong11', mc='null'}, User{id=12, name='ConstXiong12', mc='null'}, User{id=13, name='ConstXiong13', mc='null'}, User{id=14, name='ConstXiong14', mc='null'}, User{id=15, name='ConstXiong15', mc='null'}, User{id=16, name='ConstXiong16', mc='null'}, User{id=17, name='ConstXiong17', mc='null'}, User{id=18, name='ConstXiong18', mc='null'}, User{id=19, name='ConstXiong19', mc='null'}, User{id=20, name='ConstXiong20', mc='null'}]
Page{count=true, pageNum=2, pageSize=10, startRow=2, endRow=12, total=35, pages=4, reasonable=false, pageSizeZero=false}[User{id=3, name='ConstXiong3', mc='null'}, User{id=4, name='ConstXiong4', mc='null'}, User{id=5, name='ConstXiong5', mc='null'}, User{id=6, name='ConstXiong6', mc='null'}, User{id=7, name='ConstXiong7', mc='null'}, User{id=8, name='ConstXiong8', mc='null'}, User{id=9, name='ConstXiong9', mc='null'}, User{id=10, name='ConstXiong10', mc='null'}, User{id=11, name='ConstXiong11', mc='null'}, User{id=12, name='ConstXiong12', mc='null'}]
Page{count=true, pageNum=2, pageSize=10, startRow=10, endRow=20, total=35, pages=4, reasonable=false, pageSizeZero=false}[User{id=11, name='ConstXiong11', mc='null'}, User{id=12, name='ConstXiong12', mc='null'}, User{id=13, name='ConstXiong13', mc='null'}, User{id=14, name='ConstXiong14', mc='null'}, User{id=15, name='ConstXiong15', mc='null'}, User{id=16, name='ConstXiong16', mc='null'}, User{id=17, name='ConstXiong17', mc='null'}, User{id=18, name='ConstXiong18', mc='null'}, User{id=19, name='ConstXiong19', mc='null'}, User{id=20, name='ConstXiong20', mc='null'}]
Page{count=true, pageNum=2, pageSize=10, startRow=10, endRow=20, total=35, pages=4, reasonable=false, pageSizeZero=false}[User{id=11, name='ConstXiong11', mc='null'}, User{id=12, name='ConstXiong12', mc='null'}, User{id=13, name='ConstXiong13', mc='null'}, User{id=14, name='ConstXiong14', mc='null'}, User{id=15, name='ConstXiong15', mc='null'}, User{id=16, name='ConstXiong16', mc='null'}, User{id=17, name='ConstXiong17', mc='null'}, User{id=18, name='ConstXiong18', mc='null'}, User{id=19, name='ConstXiong19', mc='null'}, User{id=20, name='ConstXiong20', mc='null'}]
35
35
八、結論mybatis
啓用分頁插件的方式:
查詢使用 RowBounds 參數
使用靜態方法 PageHelper.startPage
使用靜態方法 PageHelper.offsetPage
PageHelper.startPage、PageHelper.offsetPage 返回的 Page 對象調用 doSelectPage 方法傳入 ISelect 的實現類或 Lambda
官方文檔給出說明,只要是正常使用以上方法都是線程安全的。
被分頁插件處理過的查詢結果,返回的是 com.github.pagehelper.Page 類的對象。
PageHelper.count 方法支持僅獲取統計結果。