起因

使用Mybatis动态SQL进行遍历条件的时候报了下面这个错误：

Caused by: java.lang.Illegal@R_777_2358@eException: TyPE handler was null on parameter mapping for PRoperty '__frch_ITem_0'. It was either not specified and/or could not be found for the javaType (com.test.Report) : jdbcType (null) combination.     at org.apache.ibatis.mapping.ParameterMapping$Builder.validate (ParameterMapping.java:117)     at org.apache.ibatis.mapping.ParameterMapping$Builder.build (ParameterMapping.java:104)     at org.apache.ibatis.builder.SqlSourceBuilder$ParameterMappingTokenHandler.buildParameterMapping (SqlSourceBuilder.java:123)     at org.apache.ibatis.builder.SqlSourceBuilder$ParameterMappingTokenHandler.handleToken (SqlSourceBuilder.java:67)     at org.apache.ibatis.parsing.GenericTokenParser.parse (GenericTokenParser.java:69)     at org.apache.ibatis.builder.SqlSourceBuilder.parse (SqlSourceBuilder.java:45)     at org.apache.ibatis.scripting.XMltags.DynamicSqlSource.getBoundSql (DynamicSqlSource.java:44)     at org.apache.ibatis.mapping.Mappedstatement.getBoundSql (MappedStatement.java:292)     at org.apache.ibatis.executor.CachingExecutor.query (CachingExecutor.java:81)     at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList (DefaultSqlSession.java:148)     at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList (DefaultSqlSession.java:141)     at sun.reflect.NativeMethodAccessorImpl.invoke0 (Native Method)     at sun.reflect.NativeMethodAccessorImpl.invoke (NativeMethodAccessorImpl.java:62)     at sun.reflect.DelegatingMethodAccessorImpl.invoke (DelegatingMethodAccessorImpl.java:43)     at java.lang.reflect.Method.invoke (Method.java:498)     at org.mybatis.spring.SqlSessionTemplate$SqlSessionInterceptor.invoke (SqlSessionTemplate.java:434)     at com.sun.Proxy.$Proxy57.selectList (Unknown Source)     at org.mybatis.spring.SqlSessionTemplate.selectList (SqlSessionTemplate.java:231)

<select id="getById" parameterType="map" resultType="Report">         select * from test         where orderid in         <foreach collection="idlist" item="item" index="index" open="(" separator="," close=")">             #{item}         </foreach>              </select>

怎么找都没找到原因，最后发现这个sql之所以报错并不是这个sql写错了，而是传入的参数报错了，我认为参数是这个样子的：

{   "name":"张三",   "idlsit":{1,2,3} } 

最后发现，参数是这个样子的的：

{   "name":"张三",   "idlsit":{Report对象,Report对象,Report对象} }

看到这里可能会觉得怎么可能出现这种问题，编译都不会通过，但是通过特殊的情况确实产生了，我的代码如下：

        List<String> idList = reportDao.getIdList(start, end);          if (null != idList &amp;& idList.size() >= 1) {             result = orderReportDao.getById(idList, start);         }

sql:

    <select id="getIdList" parameterType="map" resultType="Report">//这个返回值类型错了         select id from test_id     </select>      <select id="getById" parameterType="map" resultType="Report">         select * from test         where orderid in         <foreach collection="idlist" item="item" index="index" open="(" separator="," close=")">             #{item}         </foreach>              </select>

实际上在执行过程中getIdList的返回类型错了，但是没有报错误，返回值List < String > idList实际上是List < Report > idList，这竟然没有报错，可能反射有关。