CODEWITHSUNDEEP
jacksonfasterxml
Shellong
Shellong

Reputation: 381

Jackson ObjectMapper.readValue throws NullPointerException, LRUMap.get(LRUMap.java:68)

I write a hive UDF which looks like below:

public class DemoUDF extends GenericUDF{
      private ObjectMapper mapper = new ObjectMapper();
      
      ... initialize() method...

      public Object evaluate(DeferredObject[] deferredObjects) throws HiveException{
           ... ...
           ActionVO vo = mapper.readValue(target_str, ActionVO.class);
           ... ...
      }
}

While I add this function into hive,and execute it with some query,there exists the exception below:

Caused by : java.lang.NullPointerException at com.fasterxml.jackson.databind.util.LRUMap.get(LRUMap.java:68) at com.fasterxml.jackson.databind.type.TypeFactory._fromClass(TypeFactory.java:1255) at com.fasterxml.jackson.databind.type.TypeFactory._fromAny(TypeFactory.java:1194) at com.fasterxml.jackson.databind.type.TypeFactory.constructType(TypeFactory.java:608)

while I change the ObjectMapper declaration to below,it works fine!

private static final ObjectMapper mapper = new ObjectMapper();

So why? What effect does it make?

Upvotes: 0

Views: 341

Answers (1)

Ashish
Ashish

Reputation: 5791

I think once you make a variable static then its class level thing and only one copy of that will be stored. The JVM allocates static variable during the class loading time. For non-static ones multiple copies will be created as per class instances and hence need more memory. Static variables are shared by all objects of a class and have a single instance, while non-static variables are unique to each object and have different values for different objects.

Upvotes: 0

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