mybatis报错Mapped Statements collection does not contain value for com.inter.IOperation.getAllItems

在程序调用IOperation接口中的getAllItems方法时，出现了以下错误：

Exception in thread "main" org.apache.ibatis.binding.BindingException:Invalid bound statement (not found): com.inter.IOperation.getAllItems
at org.apache.ibatis.binding.MapperMethod$SqlCommand.<init>(MapperMethod.java:178)
at org.apache.ibatis.binding.MapperMethod.<init>(MapperMethod.java:38)
at org.apache.ibatis.binding.MapperProxy.cachedMapperMethod(MapperProxy.java:49)
at org.apache.ibatis.binding.MapperProxy.invoke(MapperProxy.java:42)
at com.sun.proxy.$Proxy0.getAllItems(Unknown Source)
at analysis.ReviewsMining.processProcessedReviews(ReviewsMining.java:88)
at analysis.ReviewsMining.main(ReviewsMining.java:152)
Caused by: java.lang.IllegalArgumentException: Mapped Statements collection does not contain value for com.inter.IOperation.getAllItems
at org.apache.ibatis.session.Configuration$StrictMap.get(Configuration.java:768)
at org.apache.ibatis.session.Configuration.getMappedStatement(Configuration.java:603)
at org.apache.ibatis.session.Configuration.getMappedStatement(Configuration.java:596)
at org.apache.ibatis.binding.MapperMethod$SqlCommand.<init>(MapperMethod.java:176)

出现这种错误有几种原因：

1、命名空间没写对，如果使用mapper，则<mapper namespace="com.inter.IOperation">（IOperation是个接口，里面含有方法getAllItems）

2、getAllItems方法在item.xml中没有，然后执行getAllItems方法会报错

3、getAllItems方法的返回值是List<Item>，而select元素没有正确配置ResultMap，或者只配置了ResultType

4、在与数据库连接相关的配置文件Configuration.xml中，在<mappers>中漏了<mapper resource="com/items/Item.xml"/>（这也是我这次错误的原因）