拦截器介绍

mybatis提供了@Intercepts注解允许开发者对mybatis的执行器Executor进行拦截。

Executor接口方法主要有update、query、commit、rollback等等。

主要思路为:

1. 进入拦截器方法中
2. 获取拦截器方法参数
3. 获取解析参数及MappedStatement
4. 从MappedStatement声明类中获取resultMap
5. 获取resultMappings并且进行自定义
6. 重新组装新的ResultMap
7. 利用反射将新的ResultMap设置进入MappedStatement中

拦截器代码

import org.apache.ibatis.cache.CacheKey;

import org.apache.ibatis.executor.Executor;

import org.apache.ibatis.mapping.BoundSql;

import org.apache.ibatis.mapping.MappedStatement;

import org.apache.ibatis.mapping.ResultMap;

import org.apache.ibatis.mapping.ResultMapping;

import org.apache.ibatis.plugin.Interceptor;

import org.apache.ibatis.plugin.Intercepts;

import org.apache.ibatis.plugin.Invocation;

import org.apache.ibatis.plugin.Plugin;

import org.apache.ibatis.session.ResultHandler;

import org.apache.ibatis.session.RowBounds;

import org.springframework.stereotype.Component;

import org.springframework.util.ReflectionUtils;

import java.lang.reflect.Field;

import java.util.*;

@Component

@Intercepts({@org.apache.ibatis.plugin.Signature(type = Executor.class, method = "query",

        args = {

                MappedStatement.class,

                Object.class,

                RowBounds.class,

                ResultHandler.class,

                CacheKey.class,

                BoundSql.class})})

public class MybatisInterceptorConfig implements Interceptor {

    /*重置ResultMapping*/

    private List<ResultMapping> resetResultMap(List<ResultMapping> resultMaps){

            //ResultMaps.add

        return resultMaps;

    }

    @Override

    public Object intercept(Invocation invocation) throws Throwable {

        resetResultMap(invocation);

        return invocation.proceed();

    }

    @Override

    public Object plugin(Object o) {

        return Plugin.wrap(o, this);

    }

    @Override

    public void setProperties(Properties properties) {

    }

    private void resetResultMap(Invocation invocation) {

        final Object[] args = invocation.getArgs();

        MappedStatement mappedStatement = (MappedStatement) args[5];

        ResultMap resultMap = mappedStatement.getResultMaps().iterator().next();

        if (resultMap != null) {

            List<ResultMapping> resultMappings = resultMap.getResultMappings();

            if (resultMappings != null && !(resultMappings instanceof AdjustedList)) {

                List<ResultMapping> newResultMappings = this.resetResultMap(new AdjustedList(resultMappings));

                ResultMap newResultMap = new ResultMap.Builder(mappedStatement.getConfiguration(), resultMap.getId(), resultMap.getType(), newResultMappings).build();

                Field field = ReflectionUtils.findField(MappedStatement.class, "resultMaps");

                ReflectionUtils.makeAccessible(field);

                ReflectionUtils.setField(field, mappedStatement, Collections.singletonList(newResultMap));

            }

        }

    }

    private class AdjustedList<E> extends ArrayList<E> {

        public AdjustedList(Collection<? extends E> c) {

            super(c);

        }

    }

}