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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.IllegalStateException: 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 && 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。
