Java groupingBy : sum multiple fields

Question

这个问题是对帖子的扩展:Java 8 groupingby with returning multiple field .

同样的问题，如何返回一个Customer的列表？例如，它应该返回:

Customer("A",4500,6500)
Customer("B",3000,3500)
Customer("C",4000,4500)

Answer 1

使用以下代码:

Map<String, Customer> retObj =
    listCust.stream()
        .collect(Collectors.groupingBy(Customer::getName,
                    Collector.of(
                        Customer::new,
                        (c1, c2) -> {
                            c1.setName(c2.getName());
                            c1.setTotal(c1.getTotal() + c2.getTotal());
                            c1.setBalance(c1.getBalance() + c2.getBalance());
                        },
                        (c3, c4) -> {
                            c3.setTotal(c3.getTotal() + c4.getTotal());
                            c3.setBalance(c3.getBalance() + c4.getBalance());
                            return c3;
                        })));

System.out.println(retObj);
System.out.println(retObj.values());       //If you want only the list of all Customers

输出:

{
 A=Customer [name=A, total=4500.0, balance=6500.0], 
 B=Customer [name=B, total=3000.0, balance=3500.0], 
 C=Customer [name=C, total=4000.0, balance=4500.0]
}