how to use java stream to group fields and create a summary

Question

public class Call {
    private String status;
    private String callName;
}

I have a list of calls and i have to create a summary, like this:

public class CallSummary {
    private String callName;
    private List<ItemSummary> items;
}
public class itemSummary {
    private String status;
    private Integer percentage;
}

My goal is show a percentage of calls with some status like :

INBOUND_CALL : {
FAILED = 30%
SUCCESS = 70%
}

how can i do it using java 8 stream and Collectors ?

Answer 1

The idea behind the grouping would be to nest is in such a way that you have a call name and then status based count lookup available. I would also suggest using an enumeration for the status

enum CallStatus {
    FAILED, SUCCESS
}

and adapting it in other classes as

class Call {
    private CallStatus status;
    private String callName;
}

Then you can implement a nested grouping and start off with an intermediate result such as:

List<Call> sampleCalls = List.of(new Call(CallStatus.SUCCESS,"naman"),new Call(CallStatus.FAILED,"naman"),
        new Call(CallStatus.SUCCESS,"diego"), new Call(CallStatus.FAILED,"diego"), new Call(CallStatus.SUCCESS,"diego"));

Map<String, Map<CallStatus, Long>> groupedMap = sampleCalls.stream()
        .collect(Collectors.groupingBy(Call::getCallName,
                Collectors.groupingBy(Call::getStatus, Collectors.counting())));

which would give you an output of

{diego={FAILED=1, SUCCESS=2}, naman={FAILED=1, SUCCESS=1}}

and you can further evaluate the percentages as well. (though representing them in Integer might lose precision depending on how you evaluate them further.)

---

To solve it further, you can keep another Map for the name-based count lookup as:

Map<String, Long> nameBasedCount = calls.stream()
        .collect(Collectors.groupingBy(Call::getCallName, Collectors.counting()));

and further, compute summaries of type CallSummary in a List as :

List<CallSummary> summaries = groupedMap.entrySet().stream()
        .map(entry -> new CallSummary(entry.getKey(), entry.getValue().entrySet()
                .stream()
                .map(en -> new ItemSummary(en.getKey(), percentage(en.getValue(),
                        nameBasedCount.get(entry.getKey()))))
                .collect(Collectors.toList()))
        ).collect(Collectors.toList());

where percentage count be implemented by you using the signature int percentage(long val, long total) aligned with the datatype chosen in ItemSummary as well.

Sample result:

[
CallSummary(callName=diego, items=[ItemSummary(status=FAILED, percentage=33), ItemSummary(status=SUCCESS, percentage=66)]), 
CallSummary(callName=naman, items=[ItemSummary(status=FAILED, percentage=50), ItemSummary(status=SUCCESS, percentage=50)])
]