mybatis异常： invalid comparison: java.util.ArrayList and java.lang.String

开发中遇到一个奇怪的问题：

Caused by: org.apache.ibatis.exceptions.PersistenceException: 
### Error updating database.  Cause: java.lang.IllegalArgumentException: invalid comparison: java.util.ArrayList and java.lang.String
### Cause: java.lang.IllegalArgumentException: invalid comparison: java.util.ArrayList and java.lang.String
	at org.apache.ibatis.exceptions.ExceptionFactory.wrapException(ExceptionFactory.java:30)
	at org.apache.ibatis.session.defaults.DefaultSqlSession.update(DefaultSqlSession.java:172)
	at org.apache.ibatis.session.defaults.DefaultSqlSession.delete(DefaultSqlSession.java:185)
	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:386)
	... 132 common frames omitted
Caused by: java.lang.IllegalArgumentException: invalid comparison: java.util.ArrayList and java.lang.String
	at ognl.OgnlOps.compareWithConversion(OgnlOps.java:92)
	at ognl.OgnlOps.isEqual(OgnlOps.java:142)
	at ognl.OgnlOps.equal(OgnlOps.java:794)
	at ognl.ASTNotEq.getValueBody(ASTNotEq.java:53)
	at ognl.SimpleNode.evaluateGetValueBody(SimpleNode.java:212)
	at ognl.SimpleNode.getValue(SimpleNode.java:258)
	at ognl.ASTAnd.getValueBody(ASTAnd.java:61)
	at ognl.SimpleNode.evaluateGetValueBody(SimpleNode.java:212)
	at ognl.SimpleNode.getValue(SimpleNode.java:258)
	at ognl.Ognl.getValue(Ognl.java:494)
	at ognl.Ognl.getValue(Ognl.java:458)
	at org.apache.ibatis.scripting.xmltags.OgnlCache.getValue(OgnlCache.java:44)
	at org.apache.ibatis.scripting.xmltags.ExpressionEvaluator.evaluateBoolean(ExpressionEvaluator.java:32)
	at org.apache.ibatis.scripting.xmltags.IfSqlNode.apply(IfSqlNode.java:34)
	at org.apache.ibatis.scripting.xmltags.MixedSqlNode.apply(MixedSqlNode.java:33)
	at org.apache.ibatis.scripting.xmltags.DynamicSqlSource.getBoundSql(DynamicSqlSource.java:41)
	at org.apache.ibatis.mapping.MappedStatement.getBoundSql(MappedStatement.java:280)
	at org.apache.ibatis.executor.statement.BaseStatementHandler.<init>(BaseStatementHandler.java:64)
	at org.apache.ibatis.executor.statement.PreparedStatementHandler.<init>(PreparedStatementHandler.java:39)
	at org.apache.ibatis.executor.statement.RoutingStatementHandler.<init>(RoutingStatementHandler.java:45)
	at org.apache.ibatis.session.Configuration.newStatementHandler(Configuration.java:490)
	at org.apache.ibatis.executor.ReuseExecutor.doUpdate(ReuseExecutor.java:49)
	at org.apache.ibatis.executor.BaseExecutor.update(BaseExecutor.java:115)
	at org.apache.ibatis.executor.CachingExecutor.update(CachingExecutor.java:75)
	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.apache.ibatis.plugin.Plugin.invoke(Plugin.java:63)
	at com.sun.proxy.$Proxy136.update(Unknown Source)
	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.apache.ibatis.plugin.Plugin.invoke(Plugin.java:63)
	at com.sun.proxy.$Proxy136.update(Unknown Source)
	at org.apache.ibatis.session.defaults.DefaultSqlSession.update(DefaultSqlSession.java:170)
	... 138 common frames omitted

所用 mybatis版本：3.4.4。

以下是mapper中对应的sql：

<delete id="deleteById">
  	  delete from table1
  	      where DEF_DB_ID = #{defDbId} 
  	   <if test="refDbIds != null and refDbIds != '' ">
  	        and REF_DB_ID in 
	  	   <foreach collection="refDbIds" item="refDbId" open="(" close=")" separator=",">
	  	      #{refDbId}
	  	   </foreach>
  	   </if>
  	</delete>

感觉应该是类型不符合的问题，网上查找资料，发现问题应该出现在：

<if test="refDbIds != null and refDbIds != '' "> 

其中 refDbIds 参数的类型为ArrayList，调用时传入的refDbIds内容是空的，即refDbIds！=null 并且 refDbIds.length等于0，

因此在执行此sql时，类型为ArrayList的refDbIds与空字符串''进行比较就会出现异常。处理方法是去掉上面代码中的

refDbIds != '' 

即将：

<if test="refDbIds != null and refDbIds != '' ">
  	        and REF_DB_ID in 
	  	   <foreach collection="refDbIds" item="refDbId" open="(" close=")" separator=",">
	  	      #{refDbId}
	  	   </foreach>
  	   </if>

修改为：

<if test="refDbIds != null">
  	        and REF_DB_ID in 
	  	   <foreach collection="refDbIds" item="refDbId" open="(" close=")" separator=",">
	  	      #{refDbId}
	  	   </foreach>
  	   </if>