Mybatis手写分页插件
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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
