Handling null values while extracting using java from MongoDB

Question

Frequently, I extract the data from mongo database using java (because I have to do it across very large number of collection across many databases). In the process, I generally use

Eg:

time = ((myObject.containsField("time"))) ? (myObject.get("time").toString().isEmpty()) ? "Empty" : myObject.get("time").toString() : "NA";

to make sure if the string exists or it is empty. but how do we do a null check, I mean if time has a value null

Eg: time=null

How do we extract the value to script so that I can save it to the extract as some string which represents null value?

.get is resulting in to a NullPointerException. This is a run time check and I often extract more than 20 values for each record. What is the best way to do a null check?

your help is much appreciated. Thanks in advance!! :)

Do you want the resulting time to be a String "null" or null — Patrick J Abare II
– Patrick J Abare II, Commented May 27, 2015 at 12:13
I want it to be racta string "null". so that I can save it as a value of time for a record — vijay krishna
– vijay krishna, Commented May 27, 2015 at 12:15
Need to find out where the NPE is actually coming from then... if myObject isn't null, then the returned .get("time") object is.. thus .get() isn't throwing the NPE, but toString() is.. I'll modify the answer below. — Patrick J Abare II
– Patrick J Abare II, Commented May 27, 2015 at 12:45

Patrick J Abare II · Accepted Answer · 2015-05-27 12:51:20Z

1

If .get() is throwing the the null pointer exception you could simply add another ternary case around it, for .get() to throw an NPE myObject must be null. Thus, this should work

time = myObject != null ? ((myObject.containsField("time")))?
       (myObject.get("time").toString().isEmpty())?"Empty":myObject.get("time").toString():"NA" : "null";

To account for the above comments, .get doesn't appear to be what is throwing the NPE, .toString() must be. Alter the code thusly:

time = myObject.containsField("time") ? myObject.get("time") != null ?
       (myObject.get("time").toString().isEmpty())?"Empty":myObject.get("time").toString():"NA" : "null";

The extra ternary block, will now check if the resulting "time" key results in a null pointer.

edited May 27, 2015 at 12:51

answered May 27, 2015 at 12:10

Patrick J Abare II

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1 Comment

vijay krishna Over a year ago

Its not working myObject is a DBObject. comparing myObject seems to be a not logical one as myObject will be having more than one columns to extract. I tried extracting it in the way you suggested but it is still failing

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