目錄前言首先創(chuàng)建一個Maven項目數(shù)據(jù)庫中創(chuàng)建一張表設(shè)置Mybatis配置文件編寫pojo實(shí)體類和mapper接口和mapper映射文件創(chuàng)建測試類總結(jié)前言

Mybatis算是對數(shù)據(jù)庫操作的利器了。但是在處理分頁的時候，Mybatis并沒有什么特別的方法，一般需要自己去寫limit子句實(shí)現(xiàn)，成本較高。好在有國內(nèi)開發(fā)者寫了一個PageHelper插件，可以幫助我們快速實(shí)現(xiàn)分頁查詢。

官網(wǎng)地址

首先創(chuàng)建一個Maven項目

導(dǎo)入相關(guān)依賴：

<!-- 依賴列表--> <dependencies><!--mysql驅(qū)動--><dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> <version>8.0.25</version></dependency><!--單元測試--><dependency> <groupId>junit</groupId> <artifactId>junit</artifactId> <version>4.13</version> <scope>test</scope></dependency><!--pageHelper依賴--><dependency> <groupId>com.github.pagehelper</groupId> <artifactId>pagehelper</artifactId> <version>5.2.1</version></dependency><!--mybatis依賴--><dependency> <groupId>org.mybatis</groupId> <artifactId>mybatis</artifactId> <version>3.5.7</version></dependency><!--log4j日志依賴--><dependency> <groupId>log4j</groupId> <artifactId>log4j</artifactId> <version>1.2.17</version></dependency> </dependencies>

記住導(dǎo)入PageHelper依賴：

<dependency><groupId>com.github.pagehelper</groupId><artifactId>pagehelper</artifactId><version>5.2.1</version></dependency>數(shù)據(jù)庫中創(chuàng)建一張表

設(shè)置Mybatis配置文件

在resources目錄下,創(chuàng)建一個sqlMapConfig.xml文件,用于做一些全局的mybatis基本的配置,例如數(shù)據(jù)庫連接信息,事務(wù),mapper映射文件路徑,日志實(shí)現(xiàn),類的別名,也包含了分頁插件的基本配置。

<configuration><!--使用外部屬性配置文件 resource:指定類路徑下的某個屬性配置文件--><properties resource='db.properties' /><settings><!--日志的實(shí)現(xiàn)是LOG4J--><setting name='logImpl' value='LOG4J' /></settings> <!--聲明別名--><typeAliases><package name='com.ren.domain' /></typeAliases> <!--mybatis的插件配置--><plugins><!-- com.github.pagehelper為PageHelper類所在包名 --><plugin interceptor='com.github.pagehelper.PageInterceptor'><!-- 表示使用mysql的分頁方法 --><property name='helperDialect' value='mysql' /><!-- 表示當(dāng)頁碼長度為0 的時候,就不進(jìn)行分頁查詢 --><property name='pageSizeZero' value='true'/></plugin></plugins><!-- 配置連接數(shù)據(jù)庫四要素 --><environments default='dev'><environment id='dev'><transactionManager type='JDBC' /><dataSource type='POOLED'><property name='driver' value='${driverClassName}' /><property name='url' value='${url}' /><property name='username' value='${username}' /><property name='password' value='${password}' /></dataSource></environment></environments> <mappers><mapper resource='com/ren/mapper/StudentMapper.xml' /></mappers></configuration>編寫pojo實(shí)體類和mapper接口和mapper映射文件

Student實(shí)體類

package pojo;public class Student { private Integer id; private String name; private String email; private Integer age; public Student() { } public Student(Integer id, String name, String email, Integer age) {this.id = id;this.name = name;this.email = email;this.age = age; } 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 getEmail() {return email; } public void setEmail(String email) {this.email = email; } public Integer getAge() {return age; } public void setAge(Integer age) {this.age = age; } @Override public String toString() {return 'Student{' +'id=' + id +', name=’' + name + ’’’ +', email=’' + email + ’’’ +', age=' + age +’}’; }}

mapper接口

package mapper;import pojo.Student;import java.util.List;public interface StudentMapper { //查詢所有學(xué)生 List<Student> selectAll();}

Mapper映射文件

<?xml version='1.0' encoding='UTF-8' ?><!DOCTYPE mapperPUBLIC '-//mybatis.org//DTD Mapper 3.0//EN''http://mybatis.org/dtd/mybatis-3-mapper.dtd'><mapper namespace='mapper.StudentMapper'> <select resultType='pojo.Student'>select * from student order by id </select></mapper>

在sqlMapConfig文件中指定Mapper文件位置

<!-- mapper映射文件位置--><mappers><package name='mapper'/></mappers>

編寫MyBatisUtils

package utils;import org.apache.ibatis.io.Resources;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;/** * 工具類：創(chuàng)建SqlSession對象 */public class MyBatisUtil { private static SqlSessionFactory factory = null; static {String config='sqlMapConfig.xml';try { InputStream inputStream =Resources.getResourceAsStream(config); factory = new SqlSessionFactoryBuilder().build(inputStream);} catch (IOException e) { e.printStackTrace();} } //創(chuàng)建方法，獲取SqlSession對象 public static SqlSession getSqlSession(){SqlSession session = null;if( factory != null ){ session =factory.openSession();// openSession(true);}return session; }}創(chuàng)建測試類

import com.github.pagehelper.PageHelper;import mapper.StudentMapper;import org.apache.ibatis.session.SqlSession;import org.junit.Test;import pojo.Student;import utils.MyBatisUtil;import java.util.List;public class pageHelper_Test { @Test public void PageHelperTest(){//獲取sqlSessionSqlSession sqlSession = MyBatisUtil.getSqlSession();//獲取mapper代理StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);//調(diào)用PageHelperPageHelper.startPage(2,2);//查詢所有學(xué)生List<Student> studentList = mapper.selectAll();//遍歷結(jié)果List集合studentList.forEach(student -> System.out.println(student));//關(guān)閉sqlSession對象sqlSession.close(); }}

查看結(jié)果

可以看到sql語句,在mapper文件中并沒有寫limit,pageHelper已經(jīng)幫我們加上了limit關(guān)鍵字完成了查詢.OK了

總結(jié)

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