Failed to instantiate java.util.List using constructor NO_CONSTRUCTOR with arguments ]

Question

i am getting

Failed to instantiate java.util.List using constructor NO_CONSTRUCTOR with arguments ] with root cause
org.springframework.beans.BeanInstantiationException: Failed to instantiate [java.util.List]: Specified class is an interface

this exception while updating the mongodb nested document.

the problem is the same as it is dicscuseed it this link

http://forum.spring.io/forum/spring-projects/data/nosql/724397-mapping-exception-with-mongodb-aggregation-framework

but still no clue how to solve it. anyone gone thorugh this??

I've got no experience with mongodb but the mapper tried to instanciate a List which won't work because it is an interface. A workaround would be to convince your mapper to instead instantiate an ArrayList when List is needed. — Jeremy Grand
– Jeremy Grand, Commented Aug 3, 2017 at 13:49
Edit : actually, the issue in the thread you showed was that the query returned an Object instead of a single-element List, thus making the mapper fail to recognize an array. Is your issue the same ? — Jeremy Grand
– Jeremy Grand, Commented Aug 3, 2017 at 13:52
Its little vague without the code. Consider adding complete code including sample documents which when run will throw the exception — s7vr
– s7vr, Commented Aug 3, 2017 at 14:04

Daniel S. · Accepted Answer · 2017-09-04 02:34:42Z

8

I just had the same problem and solved it thanks to: Mongo db java unwind operation in aggregate query throwing exception

When in the aggregation the unwind happened, the results are flattened so in my case I had a class like:

MyClass {
   String _id;
   List<SomeObject> objectList;
}

The exception occurs because of the flattening, the results on my list object instead of coming up in an array, now are just a single object because of the $unwind.

What I did to fix this was to create the same class without the list:

MyClassAggregationResult {
  String _id;
  SomeObject objectList;
}

This way the results are mapped correctly.

Hope this works for you as well.

answered Sep 4, 2017 at 2:34

Daniel S.

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Ak S · Accepted Answer · 2018-03-01 11:14:17Z

1

change to as below it should work

String _id;

SomeObject objectList;

edited Mar 1, 2018 at 11:14

answered Mar 1, 2018 at 10:50

Ak S

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1 Comment

Light Yagami Over a year ago

How can this work? we need a list of SomeObject, right? Aren't you changing the definition?

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