在工作中，我们常常需要在不改变源码的条件下对sql进行一些修改。

  在这过程中用到的技术原理就是mybatis的拦截器（对于mybatis的内置对象笔者也还知之甚少，但这个不耽误咱使用mybatis的拦截器）。

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使用步骤1：

    自定义自己的拦截器类并实现mybatis的Interceptor：

package com.interceptors.mybatis;

import lombok.extern.slf4j.Slf4j;

import org.apache.commons.lang3.StringUtils;

import org.apache.ibatis.executor.statement.StatementHandler;

import org.apache.ibatis.mapping.BoundSql;

import org.apache.ibatis.mapping.MappedStatement;

import org.apache.ibatis.mapping.SqlCommandType;

import org.apache.ibatis.mapping.SqlSource;

import org.apache.ibatis.plugin.*;

import org.apache.ibatis.reflection.DefaultReflectorFactory;

import org.apache.ibatis.reflection.MetaObject;

import org.apache.ibatis.reflection.SystemMetaObject;

import org.apache.ibatis.reflection.factory.DefaultObjectFactory;

import org.apache.ibatis.reflection.wrapper.DefaultObjectWrapperFactory;

import org.apache.ibatis.session.ResultHandler;

import org.apache.ibatis.session.RowBounds;

import org.springframework.stereotype.Component;

import java.lang.reflect.Field;

import java.lang.reflect.Method;

import java.sql.Connection;

import java.util.Properties;

@Component

@Intercepts({

@Signature(

type = StatementHandler.class, method ="prepare", args = {Connection.class, Integer.class})

})

@Slf4j

public class MybatisSqlInterceptorimplements Interceptor {

@Override

    public Object intercept(Invocation invocation)throws Throwable {

StatementHandler statementHandler = (StatementHandler) invocation.getTarget();

MetaObject metaObject = MetaObject.forObject(statementHandler, SystemMetaObject.DEFAULT_OBJECT_FACTORY, SystemMetaObject.DEFAULT_OBJECT_WRAPPER_FACTORY,new DefaultReflectorFactory());

//先拦截到RoutingStatementHandler，里面有个StatementHandler类型的delegate变量，其实现类是BaseStatementHandler，然后就到BaseStatementHandler的成员变量mappedStatement

        MappedStatement mappedStatement = (MappedStatement) metaObject.getValue("delegate.mappedStatement");

//id为执行的mapper方法的全路径名

        String id = mappedStatement.getId();

//sql语句类型 select、delete、insert、update

        String sqlCommandType = mappedStatement.getSqlCommandType().toString();

BoundSql boundSql = statementHandler.getBoundSql();

//获取到原始sql语句

        String sql = boundSql.getSql();

String mSql = sql;

//TODO 修改位置

        //注解逻辑判断  添加注解了才拦截

        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(InterceptAnnotation.class) && mName.equals(method.getName())) {

InterceptAnnotation interceptorAnnotation = method.getAnnotation(InterceptAnnotation.class);

if (interceptorAnnotation.flag()) {

//重新设置mapper接口的参数或者对sql进行改造

                    boundSql.setAdditionalParameter("","");

}

}

}

//通过反射修改sql语句

        Field field = boundSql.getClass().getDeclaredField("sql");

field.setAccessible(true);

field.set(boundSql, mSql);

return invocation.proceed();

}

@Override

    public Object plugin(Object target) {

if (targetinstanceof StatementHandler) {

return Plugin.wrap(target,this);

}else {

return target;

}

}

@Override

    public void setProperties(Properties properties) {

}

}

步骤2：

    自定义注解（将该注解加到需要拦截的repository的接口上）

package com.interceptors.mybatis;

import java.lang.annotation.ElementType;

import java.lang.annotation.Retention;

import java.lang.annotation.RetentionPolicy;

import java.lang.annotation.Target;

@Target({ElementType.METHOD, ElementType.PARAMETER})

@Retention(RetentionPolicy.RUNTIME)

public @interface InterceptAnnotation {

boolean flag()default true;

}

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（对于mybatis拦截器的使用还需要了解mybatis更多的内置方法，本篇文章也只是mybatis拦截器的一点皮毛）