转自 ：https://www.jianshu.com/p/e6d9afd562b2

业务场景

• 公司APP需要将主模块拆分成多个APP给代理商运营
• 不同代理商代理的APP产生的数据需根据对应公司进行区分
• 公司总数据库需同步管理所有代理商运营的数据

设计思想

• 设计在最小修改原则保证产品业务无大变动只对表进行新增COMPAN_ID字段进行区分
• 综合以上需求场景产生的思路决定采用低耦合、高复用进行架构设计
• 通过MyBatis拦截器Sql进行处理，采用类自定义注解+反射的形式

代码实现

创建自定义注解 HmwCompanyAnnotation

@Target({ElementType.METHOD,ElementType.PARAMETER})
@Retention(RetentionPolicy.RUNTIME)
public @interface HmwCompanyAnnotation {

    /**
     * 公司ID(暂未启用)
     * @return
     */
    String CompanyId() default "";

    /**
     * 别名（针对复杂查询备用处理属性）
     * @return
     */
    String Alias() default "";

}

MyBatis的Mapper的实现示例
接口方法上添加 自定义注解@HmwCompanyAnnotation()

@Mapper
public interface SmsCodeDao  {

    /**
     * 新增
     *
     * @param smsCode
     * @return
     */
    @Options(useGeneratedKeys = true, keyProperty = "smsCodeId" , keyColumn = "SMS_CODE_ID")
    @Insert("insert into hmw_sms_code(SMS_TYPE, ... 省略字段..., COMPANY_ID) " +
            " values(#{smsType},...省略字段... ,#{companyId})")
    int save(SmsCode smsCode);


    /**
     * 查询用户每天发送的验证码数量
     *
     * @param sendTel 手机号
     * @return
     */
    @HmwCompanyAnnotation()
    @Select("  select " +
            "     count(0) as count_num " +
            "  from hmw_sms_code" +
            "  where " +
            "       SEND_TEL = #{sendTel} " +
            "   and TO_DAYS(NOW()) = TO_DAYS(SEND_TIME)  ")
    Long findTelTodayCount(String sendTel );


    /**
     * 根据短信类型查询是否已使用获取已过期
     *
     * @param sendTel 手机号
     * @param sendCode 验证码
     * @param smsType 短信类型
     * @param nowTime 当前服务器时间(请用服务器New出来的时间 不要用NOW())
     * @return
     */
    @HmwCompanyAnnotation()
    @Select(" select   " +
            "  count(0) as count_num   " +
            " from   " +
            "  hmw_sms_code  " +
            " where   " +
            "      SEND_TEL = #{sendTel,jdbcType=VARCHAR}   " +
            "  and SEND_CODE = #{sendCode,jdbcType=VARCHAR}  " +
            "  and SMS_STATE = 'N'  " +
            "  and SMS_TYPE  = #{smsType,jdbcType=VARCHAR}  " +
            "  and SEND_TIME >= DATE_SUB(#{sendTime},INTERVAL 5  MINUTE) ")
    Long findSmsCodeByTel(String sendTel , String sendCode , String smsType , Date nowTime);



}

MyBatis 拦截器具体实现

import com.hmw.annotation.HmwCompanyAnnotation;
import com.hmw.base.Const;
import com.hmw.utils.common.ReflectHelper;
import org.apache.ibatis.executor.statement.RoutingStatementHandler;
import org.apache.ibatis.executor.statement.StatementHandler;
import org.apache.ibatis.mapping.BoundSql;
import org.apache.ibatis.mapping.MappedStatement;
import org.apache.ibatis.plugin.*;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;
import java.lang.reflect.Method;
import java.sql.Connection;
import java.util.Properties;

/**
 * 功能：Mybatis 拦截器
 * 说明：拦截SQL执行前的语句 根据自定义注解对方法进行公司查询
 *
 * 开发：Bruce.Liu Create by 2018-03-12 20:15
 */

@Component
@Intercepts(
    {
        @Signature(
                type = StatementHandler.class,
                method = "prepare",
                args = {
                        Connection.class ,
                        Integer.class
                }
        )
    }
)
public class CompanySqlInterceptor implements Interceptor {

    @Value("${base.config.companyId}")
    private String COMPANY_ID;

    @Override
    public Object intercept(Invocation invocation) throws Throwable {
        try{
            if(invocation.getTarget() instanceof RoutingStatementHandler){
                RoutingStatementHandler statementHandler = (RoutingStatementHandler)invocation.getTarget();
                StatementHandler delegate = (StatementHandler) ReflectHelper.getFieldValue(statementHandler, "delegate");
                BoundSql boundSql = delegate.getBoundSql();
                MappedStatement mappedStatement = (MappedStatement) ReflectHelper.getFieldValue(delegate, "mappedStatement");
                Class<?> classType = Class.forName(mappedStatement.getId().substring(0,mappedStatement.getId().lastIndexOf(".")));
                String mName  = mappedStatement.getId().substring(mappedStatement.getId().lastIndexOf(".") + 1 ,mappedStatement.getId().length());
                for(Method method : classType.getDeclaredMethods()){
                    if(method.isAnnotationPresent(HmwCompanyAnnotation.class) && mName.equals(method.getName()) )
                    {
                        HmwCompanyAnnotation companyAnnotation =  method.getAnnotation(HmwCompanyAnnotation.class);
                        String sql = boundSql.getSql();
                        if( mappedStatement.getSqlCommandType().toString().equals(Const.SELECT) ||
                               mappedStatement.getSqlCommandType().toString().equals(Const.UPDATE) ||
                                 mappedStatement.getSqlCommandType().toString().equals(Const.DELETE )){
                            if(companyAnnotation.Alias().equals("")){
                                sql = sql + " and COMPANY_ID = '"+ COMPANY_ID +"' ";
                            } else {
                                sql = sql + " and "+ companyAnnotation.Alias()+".COMPANY_ID = '" + COMPANY_ID +"' ";
                            }
                        } else if( mappedStatement.getSqlCommandType().toString().equals(Const.INSERT)){
                          // System.err.println("Insert 实现已移到Service层处理了");
                        }
                        //System.err.println("执行后SQL:"+sql);
                        ReflectHelper.setFieldValue(boundSql, "sql", sql);
                        break;
                    }
                }

            }
        } catch (Exception e){
            e.printStackTrace();
        }
        return invocation.proceed();
    }

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

    @Override
    public void setProperties(Properties properties) {

    }

}

• 利用MyBatis拦截器@Signature对底层StatementHandler.class的 prepare方法进行拦截处理
• 在执行JDBC的SQL脚本之前对sql进行统一拼接处理
• 自定义注解标示出需要进行拦截处理的方法，通过反射机制获取方法以及SqlCommonType 然后作出相应的逻辑处理

作者：52HzBoo
链接：https://www.jianshu.com/p/e6d9afd562b2