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）。
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;
}
（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）
