Mybatis(七) - Mybatis手写分页插件

Mybatis手写分页插件

本篇文章是通过看视频学习总结的内容, 如有错误的地方请谅解,并联系博主及时修改,谢谢您的阅读.

官网的解释

官网地址：mybatis 官网
源码地址：github 插件源码

前言： 在官网中描述，Mybatis只支持拦截四大对象Executor、ParameterHandler、ResultSetHandler、StatementHandler 且每个对象被拦截的方法是有限的，具体参照官网，在本篇博客中主要讲解对 Executor 对象的 query 方法进行拦截，在官网中提供了一个小 dome，本篇博客则是根据小 dome 写一个 类似 github 上很火的 PageHelper 插件

一、准备工作

• 1 引入依赖

<dependency>
    <groupId>org.mybatis</groupId>
    <artifactId>mybatis</artifactId>
    <version>3.5.4</version>
</dependency>

<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <!--<version>5.1.21</version>-->
    <version>8.0.15</version>
</dependency>

• 2 创建数据库和表

CREATE TABLE `t_user` (
  `id` varchar(10) NOT NULL COMMENT '主键',
  `user_name` varchar(10) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL COMMENT '用户名称',
  `password` varchar(32) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL COMMENT '密码',
  `address` varchar(48) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL COMMENT '居住地址',
  `phone` varchar(11) CHARACTER SET utf8 COLLATE utf8_general_ci DEFAULT NULL COMMENT '用户电话',
  PRIMARY KEY (`id`) USING BTREE
) ENGINE=InnoDB DEFAULT CHARSET=utf8 ROW_FORMAT=DYNAMIC;

• 3 创建mybatis-config.xml配置文件

<?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>

    <properties resource="db.properties"></properties>
    <settings>
        <!-- 打印查询语句 -->
        <setting name="logImpl" value="STDOUT_LOGGING" />
        <!-- 控制全局缓存（二级缓存），默认 true-->
        <setting name="cacheEnabled" value="false"/>
        <!-- 延迟加载的全局开关。当开启时，所有关联对象都会延迟加载。默认 false  -->
        <setting name="lazyLoadingEnabled" value="false"/>
        <!-- 当开启时，任何方法的调用都会加载该对象的所有属性。默认 false，可通过select标签的 fetchType来覆盖-->
        <setting name="aggressiveLazyLoading" value="false"/>
        <setting name="localCacheScope" value="SESSION"/>
    </settings>

    <typeAliases>
        <typeAlias alias="user" type="com.example.mybatis.domain.User" />
    </typeAliases>

    <environments default="development">
        <environment id="development">
            <transactionManager type="JDBC"/><!-- 单独使用时配置成MANAGED没有事务 -->
            <dataSource type="POOLED">
                <property name="driver" value="${jdbc.driver}"/>
                <property name="url" value="${jdbc.url}"/>
                <property name="username" value="${jdbc.username}"/>
                <property name="password" value="${jdbc.password}"/>
            </dataSource>
        </environment>
    </environments>

    <mappers>
        <mapper resource="UserMapper.xml"/>
    </mappers>

</configuration>

• 4 db.properties

## mysql 8.x 版本
jdbc.driver=com.mysql.cj.jdbc.Driver
jdbc.url=jdbc:mysql://localhost:3306/mybatis?useUnicode=true&characterEncoding=utf-8&rewriteBatchedStatements=true&serverTimezone=GMT%2B8
jdbc.username=root
jdbc.password=root

• 5 创建 User 对象

@Setter
@Getter
@ToString
public class User implements Serializable {

    private String id;
    private String username;
    private String password;
    private String address;
    private String phone;
}

• 6 UserMapper.java

public interface UserMapper {
    /**
     * 获取分页
     * @param phone 电话
     * @return
     */
    User selectUserById(String id);
}

• 7 UserMapper.xml

<?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="com.example.mybatis.mapper.UserMapper">
    <select id="getUserPage" resultType="user">
        SELECT id, user_name, password, address, phone FROM t_user where id= #{id}
    </select>
</mapper>

二、手写插件

• 1 根据官网描述，插件必须要继承 Interceptor 接口，并且类上需要添加注释 @Interceptors 注解
• 2 mybatis-config.xml 中加入插件标签，启用插件

package com.example.mybatis.plugin.intercepter;

import com.example.mybatis.plugin.util.Page;
import com.example.mybatis.plugin.util.PageUtil;
import lombok.extern.slf4j.Slf4j;
import org.apache.ibatis.builder.StaticSqlSource;
import org.apache.ibatis.executor.Executor;
import org.apache.ibatis.mapping.BoundSql;
import org.apache.ibatis.mapping.MappedStatement;
import org.apache.ibatis.mapping.SqlSource;
import org.apache.ibatis.plugin.*;
import org.apache.ibatis.session.ResultHandler;
import org.apache.ibatis.session.RowBounds;

import java.lang.reflect.Field;
import java.util.Properties;

/**
 * <p>
 * 自定义分页插件拦截器
 * </p>
 *
 * @author zyred
 * @createTime 2020/9/15 14:05
 **/
@Slf4j
@Intercepts(
        {
                @Signature(
                        // 拦截executor类, 拦截的方法 query
                        type = Executor.class, method = "query",
                        // Invocation 对象中 args参数类型
                        args = {MappedStatement.class, Object.class, RowBounds.class, ResultHandler.class}
                )
        }
)
public class PageInterceptor implements Interceptor {

    /**
     * 真正拦截执行的方法
     *
     * @param invocation
     * @return
     * @throws Throwable
     */
    @Override
    public Object intercept(Invocation invocation) throws Throwable {
        log.info("page plugin running ...");
        Object[] args = invocation.getArgs();

        MappedStatement ms = (MappedStatement) args[0];

        BoundSql boundSql = ms.getBoundSql(args[1]);

        Page page = PageUtil.getPage();

        // 无需分页
        if (page == null) {
            return invocation.proceed();
        }

        // 需要分页，则修改sql逻辑
        String sql = boundSql.getSql();
        log.info("before sql ： {}", sql);
        String limit = String.format(" limit %s, %s", page.getOffset(), page.getLimit());
        sql += limit;
        log.info("after sql ： {}", sql);

        // 利用反射，重新把SqlSource对象写入到MappedStatment对象中
        SqlSource sqlSource = new StaticSqlSource(ms.getConfiguration(), sql, boundSql.getParameterMappings());
        Field field = MappedStatement.class.getDeclaredField("sqlSource");
        field.setAccessible(true);
        field.set(ms, sqlSource);

        // 执行被拦截的方法
        Object result = invocation.proceed();
        PageUtil.remove();
        return result;
    }

    @Override
    public Object plugin(Object target) {
        return Plugin.wrap(target, this);
    }

    @Override
    public void setProperties(Properties properties) {

    }
}

• 3 分页工具类

/**
 * <p>
 *      分页工具
 * </p>
 *
 * @author zyred
 * @createTime 2020/9/15 15:21
 **/
public class PageUtil {

    private static final ThreadLocal<Page> local_page = new ThreadLocal<>();

    public static void setPage(int offset, int limit){
        Page page = new Page();
        page.setOffset(offset);
        page.setLimit(limit);
        local_page.set(page);
    }

    public static void remove(){
        local_page.remove();
    }
    
    public static Page getPage(){
        return local_page.get();
    }
}

• 4 Page对象

package com.example.mybatis.plugin.util;

import lombok.Getter;
import lombok.Setter;

/**
 * <p>
 *
 * </p>
 *
 * @author zyred
 * @createTime 2020/9/15 15:56
 **/
@Setter
@Getter
public class Page {

    private int offset = 0;

    private int limit = 10;
    
}

• 5 mybatis-config.xml 中加上插件的配置

<!-- 配置插件 -->
<plugins>
    <plugin interceptor="com.example.mybatis.plugin.intercepter.PageInterceptor">
        <property name="gupao" value="betterme" />
    </plugin>
    <plugin interceptor="com.example.mybatis.plugin.intercepter.LevelOfTableInterceptor">
        <property name="gupao" value="betterme" />
    </plugin>
    <!--<plugin interceptor="com.gupaoedu.interceptor.MyPageInterceptor">
    </plugin>-->
</plugins>

• 6 Juint 测试

package com.example.mybatis;

import com.example.mybatis.domain.Fee;
import com.example.mybatis.domain.User;
import com.example.mybatis.mapper.FeeMapper;
import com.example.mybatis.mapper.UserMapper;
import com.example.mybatis.plugin.util.PageUtil;
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 org.junit.Before;
import org.junit.Test;

import java.io.IOException;
import java.io.InputStream;
import java.text.ParseException;
import java.util.Date;
import java.util.List;

public class MyBatisTest {

    private SqlSessionFactory sqlSessionFactory;

    @Before
    public void prepare() throws IOException {
        String resource = "mybatis-config.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
    }

    @Test
    public void customPagePlugin() {
        // 自定义的插件
        PageUtil.setPage(0, 4);
        SqlSession session = this.sqlSessionFactory.openSession();
        UserMapper mapper = session.getMapper(UserMapper.class);
        List<User> page = mapper.getUserPage("10086");
        System.out.println(page.size());
        page.stream().forEach(System.out::println);
    }
}

• 7 不使用插件执行

==>  Preparing: SELECT id, username, password, address, phone FROM t_user where phone = ? 
==> Parameters: 10086(String)
<==    Columns: id, username, password, address, phone
<==        Row: 1, ZYRED1, 123456, 北京, 10086
<==        Row: 2, ZYRED3, 123456, 上海, 10086
<==        Row: 3, ZYRED3, 123456, 广州, 10086
<==        Row: 4, ZYRED4, 123456, 深圳, 10086
<==        Row: 5, ZYRED5, 123456, 杭州, 10086
<==      Total: 5
5

• 8 使用插件执行

==>  Preparing: SELECT id, username, password, address, phone FROM t_user where phone = ? limit 0, 4 
==> Parameters: 10086(String)
<==    Columns: id, username, password, address, phone
<==        Row: 1, ZYRED1, 123456, 北京, 10086
<==        Row: 2, ZYRED3, 123456, 上海, 10086
<==        Row: 3, ZYRED3, 123456, 广州, 10086
<==        Row: 4, ZYRED4, 123456, 深圳, 10086
<==      Total: 4
4

• 9 不足，没有再次获取数据库中总条数

总结

mybatis 的插件开发其实并不难，只要掌握了应该拦截哪个方法，使用自己的逻辑去处理对应的逻辑就可以。

本文地址：https://blog.csdn.net/qq_38800175/article/details/108714189