How to return an Optional from MyBatis query

Question

有什么方法可以让MyBatis返回Optional<MyClass>实例而不是简单的MyClass实例吗？

Answer 1

Mybatis pre 3.5.0

Create custom ObjectFactory like this:

class OptionalAwareObjectFactory extends DefaultObjectFactory {

  public Object create(Class type, List<Class> constructorArgTypes, List<Object> constructorArgs) {
     if (Optional.class.isAssignableFrom(type)) {
        return Optional.fromNullable(Iterables.getOnlyElement(constructorArgs));
     } else {
        return super.create(type, constructorArgTypes, constructorArgs);
     }
  }
}

And configure it to be used in mybatis.xml :

 <objectFactory type="my.company.project.OptionalAwareObjectFactory"/>

Mybatis 3.5.0+

Since 3.5.0 Optional is supported natively as fankai pointed out.

Answer 2

Mybatis supports Optional return type officially now since 3.5.0, refer to http://blog.mybatis.org/2019/01/mybatis-350-released.html

Not sure how Roman's answer worked ... it might work in earlier version of Mybatis, as the method signature suggests, but apparently doesn't work with latest versions.