Parsing JSONObject but running into NullPointer exception

Question

I am parsing a JSONObject which I extract from a Mongo DB. The number values map to java.lang.number objects according to the documentation, However, I get an error when I try to make the following declarations, specifically in the first System.out.println(value.floatVlaue()).

    //For data
    int counter = 0;
    float score = 0;
    Number value = 0;

    while(cur.hasNext()){
        JSONObject jsonObj = (JSONObject) JSONValue.parse(cur.next().toString());
        metricsIterator = ((JSONObject)((JSONObject)((JSONObject)((JSONObject)jsonObj.get("level_1")).get("level_2")).get("level_3")).get("metrics")).keySet().iterator();

        while(metricsIterator.hasNext()){
            System.out.println(metricsIterator.next().toString());
            value = (Number) jsonObj.get(metricsIterator.next());

            System.out.println(value.floatValue());

            System.out.println(value.toString());

            someLogic(value.doubleValue(), ((Number)jsonObj.get("long")).intValue(), start, end, days);
        }
    }

I think the problem line definitely comes from the value = (Number) jsonObj.get(metrics Iterator.next())

the Json im parsing looks like this

    { "_id" : "9223370663181869423_cnn_1" , 
    "long" : 1373672925000 , 
    "level_1" : 
            { "level_2" : 
                { "level_3level" : 
                    { "metrics" : 
                          {"key1" : 0.003333333333333334 , 
                          "key2" : 0.005833333333333334 , 
                          "key3" : 0.005833333333333334 , 
                          "key4" : 0.009166666666666667 , 
                          "key5" : 0.1391666666666667 , 
                          "key6" : 0.1241666666666667 , 
                          "key7" : 0.01666666666666667
                           }
                     }
                 }
            }
    }

Thanks so much for any help at all!

Harshal Pandya · Accepted Answer · 2013-07-28 07:22:08Z

1

Iterators can only be traversed once. This means that once you do metricsIterator.next() in System.out.println(metricsIterator.next().toString());, you end up using up that value and when you call .next() again in value = (Number) jsonObj.get(metricsIterator.next()); you get the value after the one that you are expecting, in other words you skip a value. As a result when you hit the last value, the next value is null which results in the null pointer. Try removing the sysout before assignment to value, it should solve the nullpointer.

answered Jul 28, 2013 at 7:22

Harshal Pandya

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Udy · Accepted Answer · 2013-07-28 07:23:32Z

0

you are doing twice the metricsIterator.next()

first: System.out.println(metricsIterator.next().toString()); second: value = (Number) jsonObj.get(metricsIterator.next());

then you get to the end without checking if hasNext()

answered Jul 28, 2013 at 7:23

Udy

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