Exception handling in java stream reduce lambda

I am trying to handle exceptions inside the reduce(item,aggregator) function for a stream in java.
This is what my original code looks like:

List<ReportRow> totalList = newList.stream()
                .collect(Collectors.groupingBy(a -> a.getEngagementCode()))
                .entrySet().stream()
                .map(engagement -> engagement.getValue().stream()
                        .reduce((item, aggregator) -> 
                                new ReportRow(item.getEnvironment(), item.getApplicationName(), item.getEngagementCode(), item.getTotalHits() + aggregator.getTotalHits(), item.getServiceLine(), Float.toString(Float.parseFloat(item.getTotalCost().replace(",", "")) + Float.parseFloat(aggregator.getTotalCost().replace(",", ""))), item.getPrimaryOwnerEmail(), item.getDeploymentId()))
                        .get())
                .collect(Collectors.toList());

and this is roughly what I expect it to look like (doesn't work though).

List<ReportRow> totalList = newList.stream()
                .collect(Collectors.groupingBy(a -> a.getEngagementCode()))
                .entrySet().stream()
                .map(engagement -> engagement.getValue().stream()
                        .reduce((item, aggregator) -> {
                            try {
                                new ReportRow(item.getEnvironment(), item.getApplicationName(), item.getEngagementCode(), item.getTotalHits() + aggregator.getTotalHits(), item.getServiceLine(), Float.toString(Float.parseFloat(item.getTotalCost().replace(",", "")) + Float.parseFloat(aggregator.getTotalCost().replace(",", ""))), item.getPrimaryOwnerEmail(), item.getDeploymentId()))
                            } catch (Exception e) {
                                throw new ImproperDataException("No Deployment Id present in row: "+ item.toString());
                            }
                        }
                        .get())
                .collect(Collectors.toList());

The exception happens when I am trying to call the ReportRow() constructor.
What would be the way to handle this exception while still making using of collect, stream and map as in the original method ?

If an unchecked exception occurs it will terminate the stream processing. This is useful in case of unexpected problems that you cannot recover from. To do this, the ImproperDataException should extend RuntimeException. For readability reasons I would move the try-catch and throw logic inside a method.

For checked exceptions you should decide what needs to happen. Either continue the process (by skipping the item or using a default value) or terminate by wrapping it in an unchecked exception. You cannot propagate checked exceptions from a stream expression.

Here is a simplified and slightly contrived example. When the ArithmeticException occurs, the costPerHit calculation is skipped in the report.

static class Value {
int hits;
int cost;
Value(int hits, int cost) {
this.hits = hits;
this.cost = cost;
}
}
static class Report {
int values;
int hits;
int cost;
double costPerHit;
Report accumulate(Value value) {
values++;
hits += value.hits;
cost += value.cost;
updateCostPerHit();
return this;
}
Report combine(Report report) {
values += report.values;
hits += report.hits;
cost += report.cost;
updateCostPerHit();
return this;
}
private void updateCostPerHit() {
try {
costPerHit = cost / hits;
} catch (ArithmeticException e) {
e.printStackTrace();
}
}
@Override
public String toString() {
return String.format("Report{values=%d, hits=%d, cost=%d, costPerHit=%.2f}", values, hits, cost, costPerHit);
}
}
public static void main(String[] args) {
List<Value> values = List.of(
new Value(0, 3), // causes ArithmeticException
new Value(5, 1),
new Value(1, 2),
new Value(3, 8)
);
Report output = values.stream().reduce(new Report(), Report::accumulate, Report::combine);
System.out.println(output);
}

Output:

java.lang.ArithmeticException: / by zero
at ErrorHandling$Report.updateCostPerHit(ErrorHandling.java:42)
at ErrorHandling$Report.accumulate(ErrorHandling.java:28)
at java.base/java.util.stream.ReduceOps$1ReducingSink.accept(ReduceOps.java:80)
at java.base/java.util.AbstractList$RandomAccessSpliterator.forEachRemaining(AbstractList.java:720)
at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:484)
at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:474)
at java.base/java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:913)
at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
at java.base/java.util.stream.ReferencePipeline.reduce(ReferencePipeline.java:563)
at interview.streams.ErrorHandling.main(ErrorHandling.java:63)
Report{values=4, hits=9, cost=14, costPerHit=1.00}

Actually since I am using a single ReportRow as a mutable container of sorts, it's probably better to use collect instead of reduce:

Report output = values.stream().collect(Report::new, Report::accumulate, Report::combine);

I think this might also be better for your actual code