Java 8 access previous value in Nested Lists

Question

I have following class

class Customer {
  List<String> itemCodes;
  String customerId;
}

Lets say I have List of customers and I need to search the customerId of a first customer in this list with a specific itemCode.

The way I do currently is as follows

    for (Customer cust : Customers) {
            if (cust.getItemCodes() != null && cust.getItemCodes().contains("SPECIFIC_CODE")) {
                return cust.getCustomerId();
            }
}

I wanted to convert above loop using Java8

The best I could get right now is

customers.stream().flatMap(cust -> cust.getItemCodes().stream()).filter(code -> code.equals("SPECIFIC_CODE")).findFirst();

But this returns me Optional with value as a item code itself. But I need the customerId of that person. Problem is, I am not sure how I can access previous value of lambda here?

So is there any way I can use java8 to replace above loop?

Eran · Accepted Answer · 2017-10-10 00:59:06Z

4

You don't need flatMap here. Just use filter to locate matching Customer and map to obtain the CustomerId of that Customer.

return customers.stream()
                .filter(c -> c.getItemCodes() != null && c.getItemCodes().contains("SPECIFIC_CODE"))
                .map(Customer::getCustomerId)
                .findFirst()
                .orElse(null); // default value in case no match is found

answered Oct 10, 2017 at 0:59

Eran

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1 Comment

mihir S Over a year ago

Thanks a lot! was close yet so far :)

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