MyBatis系统学习篇 - 分页插件

MyBatis是一个非常流行的Java持久层框架，它简化了数据库操作的代码。分页是数据库查询中常见的需求，MyBatis本身并不直接支持分页功能，但可以通过插件来实现，从而帮助我们在查询数据库的时候更加方便快捷

引入依赖

<dependency><groupId>com.github.pagehelper</groupId><artifactId>pagehelper</artifactId><version>5.2.0</version>
</dependency>

在MyBatis-config.xml文件中配置分页插件

MyBatis核心配置文件中，标签的顺序：重点强调顺序，我被坑过

properties
settings
typeAliases
typeHandlers
objectFactory
objectWrapperFactory
reflectorFactory
plugins
environments
databaseIdProvider
mappers

<plugins><!--设置分页插件--><plugin interceptor="com.github.pagehelper.PageInterceptor"></plugin>
</plugins>

仅MyBatis的测试

引入相关依赖

        <dependency><groupId>org.mybatis</groupId><artifactId>mybatis</artifactId><version>3.5.7</version></dependency><dependency><groupId>junit</groupId><artifactId>junit</artifactId><version>4.12</version><scope>test</scope></dependency><dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId><version>8.0.28</version></dependency><dependency><groupId>log4j</groupId><artifactId>log4j</artifactId><version>1.2.17</version></dependency><!--  Mybatis 分页插件 --><dependency><groupId>com.github.pagehelper</groupId><artifactId>pagehelper</artifactId><version>5.2.0</version></dependency>

Mybatis-config.xml完整文件

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configurationPUBLIC "-//mybatis.org//DTD Config 3.0//EN""http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration><!--MyBatis核心配置文件中，标签的顺序：properties?,settings?,typeAliases?,typeHandlers?,objectFactory?,objectWrapperFactory?,reflectorFactory?,plugins?,environments?,databaseIdProvider?,mappers?--><!--引入properties文件--><properties resource="jdbc.properties" /><!--设置类型别名--><typeAliases><!--typeAlias：设置某个类型的别名属性：type：设置需要设置别名的类型alias：设置某个类型的别名，若不设置该属性，那么该类型拥有默认的别名，即类名且不区分大小写--><!--<typeAlias type="com.atguigu.mybatis.pojo.User"></typeAlias>--><!--以包为单位，将包下所有的类型设置默认的类型别名，即类名且不区分大小写--><package name="com.miaow.mybatis.bean"/></typeAliases><!--    该死的Mybatis 分页插件还有顺序  导入配置还要按照顺序进行--><plugins><plugin interceptor="com.github.pagehelper.PageInterceptor"></plugin></plugins><!--environments：配置多个连接数据库的环境属性：default：设置默认使用的环境的id--><environments default="development"><!--environment：配置某个具体的环境属性：id：表示连接数据库的环境的唯一标识，不能重复--><environment id="development"><!--transactionManager：设置事务管理方式属性：type="JDBC|MANAGED"JDBC：表示当前环境中，执行SQL时，使用的是JDBC中原生的事务管理方式，事务的提交或回滚需要手动处理MANAGED：被管理，例如Spring--><transactionManager type="JDBC"/><!--dataSource：配置数据源属性：type：设置数据源的类型type="POOLED|UNPOOLED|JNDI"POOLED：表示使用数据库连接池缓存数据库连接UNPOOLED：表示不使用数据库连接池JNDI：表示使用上下文中的数据源--><dataSource type="POOLED"><!--设置连接数据库的驱动--><property name="driver" value="${jdbc.driver}"/><!--设置连接数据库的连接地址--><property name="url" value="${jdbc.url}"/><!--设置连接数据库的用户名--><property name="username" value="${jdbc.username}"/><!--设置连接数据库的密码--><property name="password" value="${jdbc.password}"/></dataSource></environment><!-- 配置多个数据源 --><environment id="test"><transactionManager type="JDBC"/><dataSource type="POOLED"><property name="driver" value="com.mysql.cj.jdbc.Driver"/><property name="url" value="jdbc:mysql://localhost:3306/test?serverTimezone=UTC"/><property name="username" value="root"/><property name="password" value="123456"/></dataSource></environment></environments><!--引入映射文件--><mappers><!--xml引入配置文件  --><!--<mapper resource="mappers/UserMapper.xml"/>--><!--以包为单位引入映射文件要求：1、mapper接口所在的包要和映射文件所在的包一致2、mapper接口要和映射文件的名字一致--><package name="com.miaow.mybatis.mapper"/></mappers>
</configuration>

实体类User

package com.miaow.mybatis.bean;import java.util.List;/*** @author HWZ* @date 2024年05月07日 22:58* @description**/
public class User {private int id;private String name;private  String username;private String sex;private Book book;private Integer uid;private String bookName;private String cool;private List<Book> books;public List<Book> getBooks() {return books;}public void setBooks(List<Book> books) {this.books = books;}//    @Override
//    public String toString() {
//        return "User{" +
//                "id=" + id +
//                ", name='" + name + '\'' +
//                ", username='" + username + '\'' +
//                ", sex='" + sex + '\'' +
//                ", book=" + book +
//                '}';
//    }@Overridepublic String toString() {return "User{" +"id=" + id +", name='" + name + '\'' +", username='" + username + '\'' +", sex='" + sex + '\'' +", book=" + book +", uid=" + uid +", bookName='" + bookName + '\'' +", cool='" + cool + '\'' +", books=" + books +'}';}public Integer getUid() {return uid;}public void setUid(Integer uid) {this.uid = uid;}public String getBookName() {return bookName;}public void setBookName(String bookName) {this.bookName = bookName;}public String getCool() {return cool;}public void setCool(String cool) {this.cool = cool;}public Book getBook() {return book;}public void setBook(Book book) {this.book = book;}public int getId() {return id;}public void setId(int id) {this.id = id;}public String getName() {return name;}public void setName(String name) {this.name = name;}public String getUsername() {return username;}public void setUsername(String username) {this.username = username;}public String getSex() {return sex;}public void setSex(String sex) {this.sex = sex;}public User(int id, String name, String username, String sex) {this.id = id;this.name = name;this.username = username;this.sex = sex;}public User() {}
}

Mapper接口

@Mapper
public interface UserMapper {/*** 查询用户对象*/User selectUser(@Param("user") User user);/*** 插入用户数据*/int insertUser(User user);/*** 更新数据*/int updateUser(@Param("user") User user);/*** 删除用户数据*/int deleteUser(int id);/*** 批量删除用户数据*/int  deleteUserBatch(@Param("ids") String ids);/*** 查询所有用户数据*/List<User> selectAll();/*** 查询单条数据，并转化为Map对象数据*/Map<String,Object> getUserToMap(@Param("id") int id);/*** 查询多条数据斌并转化为Map对象数据*/List<Map<String,Object>> get100UserToMap();/*** 查询多条数据并转换为Map对象的数据的第二种方式*/@MapKey("id")Map<Integer,User> get100UserToMap2();/*** 模糊查询*/List<User> selectUserLike(@Param("user") User user);/*** 动态设置表名查询数据*/List<User> selectUserByTableName(@Param("tableName") String tableName);User getUserById(int id);/*** 分步查询，先不考虑*/// User getUserById1(int id);/***  多对一 association*/User getUserBookById(int id);/*** 一对多 collection*/List<User> getDeptByUid(int id);/*** 动态插入*/int insertUserDynamic(@Param("users") List<User> users);/*** 根据传入的条件动态查询*/List<User> selectUserByCondition(@Param("user") User user);/*** trim用于去掉或添加标签中的内容*/List<User> selectUserByConditionTrim(@Param("user") User user);/*** choose、when、 otherwise相当于if...else if..else*/List<User> selectUserByConditionChoose(@Param("user") User user);/***  Mybatis的foreach标签用于循环集合，并生成SQL语句的in子句。*  实现批量删除*/int deleteMoreByArray(@Param("ids") int [] ids);
}

Mapper接口的xml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="com.miaow.mybatis.mapper.UserMapper"><!--    启用二级缓存 --><cache/><!--resultMap：设置自定义映射属性：id：表示自定义映射的唯一标识type：查询的数据要映射的实体类的类型子标签：id：设置主键的映射关系result：设置普通字段的映射关系association：设置多对一的映射关系collection：设置一对多的映射关系属性：property：设置映射关系中实体类中的属性名column：设置映射关系中表中的字段名--><resultMap id="userMap" type="User"><!--        实际山和我们数据库字段别名差不多--><id property="id" column="id"></id><result property="name" column="name"></result><result property="username" column="username"></result><result property="sex" column="sex"></result><association property="book" javaType="Book"><id property="uid" column="uid"></id><result property="book" column="bookName"></result><result property="cool" column="cool"></result></association></resultMap><sql id="baseColum">id,name,username,sex</sql><resultMap id="deptMap" type="User"><id property="id" column="id"></id><result property="name" column="name"></result><result property="username" column="username"></result><result property="sex" column="sex"></result><collection property="books" ofType="Book"><result property="uid" column="uid"></result><result property="book" column="bookName"></result><result property="cool" column="cool"></result></collection></resultMap><select id="getDeptByUid" resultMap="deptMap">select a.*, b.uid as uid, b.book as bookName, b.cool as coolfrom user aleft join book b on a.id = b.uidwhere a.id = #{id}</select><!--    <resultMap id="userBookMap" type="User">--><!--        &lt;!&ndash;        实际山和我们数据库字段别名差不多&ndash;&gt;--><!--        <id property="id" column="id"></id>--><!--        <result property="name" column="name"></result>--><!--        <result property="username" column="username"></result>--><!--        <result property="sex" column="sex"></result>--><!--        <association property="book" select="com.miaow.mybatis.mapper.BookMapper.getBooksByUserUId" column="uid"/>--><!--&lt;!&ndash;        分步查询 ，再三考虑觉得还是跳过这种方式， &ndash;&gt;--><!--    </resultMap>--><!--    根据resultMap获取相关数据--><select id="getUserById" resultMap="userMap" parameterType="int" useCache="true">select <include refid="baseColum"></include>from userwhere id = #{id};</select><!--    <select id="getUserById1" resultMap="userBookMap" parameterType="int">--><!--        select * from user where id = #{id};--><!--    </select>--><!--    管理其他表多对一查询 --><select id="getUserBookById" resultMap="userMap" parameterType="int">select a.*, b.uid as uid, b.book as bookName, b.cool as coolfrom user aleft join book b on a.id = b.uidwhere a.id = #{id}</select><!--    插入单条数据* useGeneratedKeys：设置使用自增的主键* keyProperty：因为增删改有统一的返回值是受影响的行数，因此只能将获取的自增的主键放在传输的参数user对象的某个属性中--><insert id="insertUser" parameterType="com.miaow.mybatis.bean.User" useGeneratedKeys="true" keyProperty="id">insert into uservalues (#{id}, #{username}, #{name}, #{sex})</insert><!--    更新数据 --><update id="updateUser" parameterType="com.miaow.mybatis.bean.User">update userset name = #{user.name}where id = #{user.id}</update><!--    删除单条数据--><delete id="deleteUser" parameterType="int">deletefrom userwhere id = #{id}</delete><!--    批量删除数据--><delete id="deleteUserBatch" parameterType="java.lang.String">deletefrom userwhere id in (${ids})</delete><!--    foreach 批量删除数据-->
<!--    <delete id="deleteMoreByArray">-->
<!--        delete  from user where-->
<!--            <foreach collection="ids" item="id" separator="or">-->
<!--                id = #{id}-->
<!--            </foreach>-->
<!--    </delete>--><!--    批量删除方式2 --><delete id="deleteMoreByArray">delete  from user where id in<foreach collection="ids" item="id" separator="," open="(" close=")">#{id}</foreach></delete><!--   根据ID查询相关数据--><select id="selectUser" resultType="com.miaow.mybatis.bean.User">select *from userwhere id = #{user.id}</select><!--    查询数据库所有数据--><select id="selectAll" resultType="com.miaow.mybatis.bean.User">select *from user</select><select id="getUserToMap" resultType="java.util.Map" parameterType="int">select *from userwhere id = #{id};</select><select id="get100UserToMap" resultType="java.util.Map">select *from userlimit 100;</select><select id="get100UserToMap2" resultType="java.util.Map">select *from userlimit 100;</select><select id="selectUserLike" resultType="com.miaow.mybatis.bean.User"parameterType="com.miaow.mybatis.bean.User">select *from userwhere username like "%" #{user.username} "%"</select><!--    动态设置表名查询数据 --><select id="selectUserByTableName" resultType="com.miaow.mybatis.bean.User"parameterType="java.lang.String">select *from ${tableName}limit 100</select><!--    实现动态插入--><insert id="insertUserDynamic">insert into user values<foreach collection="users" item="user" separator=",">(#{user.id},#{user.username}, #{user.name},#{user.sex})</foreach></insert><!--根据条件动态查询--><select id="selectUserByCondition" resultType="com.miaow.mybatis.bean.User">select * from user<where><if test="user.id != null">id = #{user.id}</if><if test="user.userName != '' and user.userName != null">and username = #{user.username}</if><if test="user.name != '' and user.name != null">and name = #{user.name}</if><if test="user.sex != '' and user.sex != null">and sex = #{user.sex}</if></where></select><!--    trimprefix：在trim标签中的内容的前面添加某些内容prefixOverrides：在trim标签中的内容的前面去掉某些内容suffix：在trim标签中的内容的后面添加某些内容suffixOverrides：在trim标签中的内容的后面去掉某些内容--><select id="selectUserByConditionTrim" resultType="com.miaow.mybatis.bean.User">select * from user<trim prefix="where" suffixOverrides="and"><if test="user.id != null">id = #{user.id}</if><if test="user.userName != '' and user.userName != null">and username = #{user.username}</if><if test="user.name != '' and user.name != null">and name = #{user.name}</if><if test="user.sex != '' and user.sex != null">and sex = #{user.sex}</if></trim></select><!--    choose、when、 otherwise相当于if...else if..else--><select id="selectUserByConditionChoose" resultType="com.miaow.mybatis.bean.User">select * from user<where><choose><when test="user.id != null">id = #{user.id}</when><when test="user.userName != '' and user.userName != null">and username = #{user.username}</when><when test="user.name != '' and user.name != null">and name = #{user.name}</when><when test="user.sex != '' and user.sex != null">and sex = #{user.sex}</when></choose></where></select>
</mapper>

测试方法

 @Testpublic void test17() throws IOException {InputStream is = Resources.getResourceAsStream("D:\\myProgram\\IDEAProgram\\java-again\\SSM\\src\\main\\resources\\mybatis-config.xml");SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(is);SqlSession session = sqlSessionFactory.openSession(true);UserMapper userMapper = session.getMapper(UserMapper.class);//查询之前，设置分页条件//显示第1页10条数据Page<Object> page = PageHelper.startPage(1, 10);User user = new User();List<User> users = userMapper.selectAll();if (users == null || users.size() == 0) {System.out.println("你查询的表无数据");return;}for (User user1 : users) {System.out.println(user1);}//获取分页System.out.println("总条数：" + page.getTotal());System.out.println("总页数：" + page.getPages());System.out.println("当前页：" + page.getPageNum());System.out.println("每页显示条数：" + page.getPageSize());session.close();}

在这里插入图片描述

pageNum：当前页的页码
pageSize：每页显示的条数
size：当前页显示的真实条数
total：总记录数
pages：总页数
prePage：上一页的页码
nextPage：下一页的页码
isFirstPage/isLastPage：是否为第一页/最后一页
hasPreviousPage/hasNextPage：是否存在上一页/下一页
navigatePages：导航分页的页码数
navigatepageNums：导航分页的页码，[1,2,3,4,5]

Spring + MyBatis 相对完整的案例

引入依赖

首先，在pom.xml文件中引入MyBatis和分页插件的依赖。

<dependency><groupId>org.mybatis.spring</groupId><artifactId>mybatis-spring</artifactId><version>2.0.6</version>
</dependency>
<dependency><groupId>com.github.pagehelper</groupId><artifactId>pagehelper</artifactId><version>5.2.0</version>
</dependency>

配置MyBatis分页插件

在在Spring的配置文件中（如applicationContext.xml），配置分页插件。

<bean id="pageHelper" class="com.github.pagehelper.PageInterceptor"><property name="properties"><props><prop key="helperDialect">mysql</prop><prop key="reasonable">true</prop><prop key="supportMethodsArguments">true</prop><prop key="params">count=countSql</prop></props></property>
</bean>

配置MyBatis SqlSessionFactory

在Spring的配置文件中，配置MyBatis的SqlSessionFactory，并将分页插件添加到SqlSessionFactory中。

<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean"><property name="dataSource" ref="dataSource" /><property name="plugins"><array><ref bean="pageHelper" /></array></property><property name="mapperLocations" value="classpath*:mappers/*.xml" />
</bean>

配置数据源和事务管理

配置数据源和事务管理器。

<bean id="dataSource" class="com.zaxxer.hikari.HikariDataSource"><property name="driverClassName" value="com.mysql.cj.jdbc.Driver" /><property name="jdbcUrl" value="jdbc:mysql://localhost:3306/your_database" /><property name="username" value="your_username" /><property name="password" value="your_password" />
</bean><bean id="transactionManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager"><property name="dataSource" ref="dataSource" />
</bean><tx:annotation-driven transaction-manager="transactionManager" />

创建Mapper接口

定义Mapper接口，并编写查询方法。例如：

@Mapper
public interface UserMapper {@Select("SELECT * FROM users")List<User> selectAllUsers();
}

使用分页插件

在Service层或Controller层中使用PageHelper进行分页操作。

@Service
public class UserService {@Autowiredprivate UserMapper userMapper;public PageInfo<User> getUsers(int pageNum, int pageSize) {PageHelper.startPage(pageNum, pageSize);List<User> users = userMapper.selectAllUsers();return new PageInfo<>(users);}
}

调用分页方法

在Controller中调用分页方法，并返回分页结果。

@RestController
public class UserController {@Autowiredprivate UserService userService;@GetMapping("/users")public PageInfo<User> getUsers(@RequestParam(defaultValue = "1") int pageNum,@RequestParam(defaultValue = "10") int pageSize) {return userService.getUsers(pageNum, pageSize);}
}