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Recently started using the lambda in Java.

Map<Category, Double> lMap = rptData.stream().collect(Collectors.groupingBy(Expense::getCategory,
            Collectors.summingDouble(j -> j.getFltAmt().doubleValue())));

The above code returns map, which returns out put of rest service as JSON.

{"Category(intCatId=10013, strCatName=Home Maint)":4134.99,"Category(intCatId=10019, strCatName=Lease Breakage)":2600.0,"Category(intCatId=10011, strCatName=Utility Bill)":2067.76,"Category(intCatId=10010, strCatName=Fuel)":1018.77,"Category(intCatId=10012, strCatName=Entertainment)":192.4,"Category(intCatId=6, strCatName=Shopping)":1528.25,"Category(intCatId=4, strCatName=Medicine)":128.55,"Category(intCatId=10021, strCatName=Interest)":24.61,"Category(intCatId=3, strCatName=Phone)":539.09,"Category(intCatId=10020, strCatName=Movers)":1350.0,"Category(intCatId=5, strCatName=Grocery)":3519.83,"Category(intCatId=8, strCatName=School)":311.0,"Category(intCatId=10009, strCatName=Insurance)":1117.75,"Category(intCatId=7, strCatName=Eating Out)":614.22,"Category(intCatId=1, strCatName=Vehicle)":2843.58,"Category(intCatId=10018, strCatName=Courier)":22.65,"Category(intCatId=2, strCatName=Rent)":16506.95,"TotCount":13.0,"Category(intCatId=10017, strCatName=Travel)":800.42,"Category(intCatId=10015, strCatName=Donation)":326.0}

In the above JSON I have whole Category as key in map, instead I am looking for just the intCatId. So the output will be like

{"10013":4134.99,"10019":...}

Is there any way?

Example:

Domain

Expense{ Double fltAmt Date dtDate (formula "month(dtDate) - year(dtDate)") String monthYear (joinedby intCatId) Category category ... }

Category{ int intCatId String CatName ... }

I want to get average of (sum of all expense amounts by category and monthYear) by monthYear.

In above example, rptData is List with sum(fltAmt), monthYear and Category.

Shamseer
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2 Answers2

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Edited as per Shamseer comments

You almost did it.

All you need is change the Map<Category, Double> to Map<Integer, Double> and then, in the grouping function, substitute Expense::getCategory for another lambda e -> e.getCategory().getIntCatId() (there is a getter for intCatId, right?)

This will produce the following output:

{10013:4134.99,10019:...}

Manuel Vera Silvestre
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  • It shows an error that category in Expense should should be static. It is impacting Expense class dependent in other classes, cannot be made as static. – Shamseer Jan 18 '17 at 01:31
  • then @Shamseer, simply hava a lambda do the work for you and substitute the classifier function for this one: e -> e.getCategory().getIntCatId(). Not so compact but gets the job done. Remember that if expense and / or category are nullable you should perform a null check (I have omitted this in my answer, but can be easily done wiht a filter). I have edited my response accorddingly. – Manuel Vera Silvestre Jan 18 '17 at 06:50
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    even though the STS does not show the suggestions, when I pasted the code, it worked...!!!. – Shamseer Jan 22 '17 at 00:01
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As your map contains key as Category object, the same is present in your output JSON as the serializer you are using is converting the Category object to JSON ......

What you could do is write a custom serializer for category object which would return category id as its corresponding JSON value..... Will need more details about the serializer you are using to further show how you can create a custom serializer.

Or the other way would be to change the type of map and use CategoryId(String type) as the key....

Kaushik Patel
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  • How can I change groupingBy to categoryID? something like this-Collectors.groupingBy(Expense::getCategory.getIntCatId ? But this is showing error, is there similar way? – Shamseer Jan 15 '17 at 13:40