stream()根据多字段分组,并求和某个BigDecimal字段
时间: 2023-08-12 09:28:38 浏览: 183
可以使用Java 8中的Stream API的groupingBy()和reducing()方法来根据多个字段进行分组,并对每个组进行BigDecimal字段求和。
假设有一个Order类,其中包含id、userId、amount和tax字段,我们要根据userId和tax字段分组,并对每个组的amount字段进行求和,代码如下:
```java
import java.math.BigDecimal;
import java.util.*;
import java.util.stream.Collectors;
public class Order {
private String id;
private String userId;
private BigDecimal amount;
private BigDecimal tax;
public Order(String id, String userId, BigDecimal amount, BigDecimal tax) {
this.id = id;
this.userId = userId;
this.amount = amount;
this.tax = tax;
}
public String getId() {
return id;
}
public String getUserId() {
return userId;
}
public BigDecimal getAmount() {
return amount;
}
public BigDecimal getTax() {
return tax;
}
public static void main(String[] args) {
List<Order> orders = Arrays.asList(
new Order("1", "user1", new BigDecimal("100"), new BigDecimal("0.1")),
new Order("2", "user1", new BigDecimal("200"), new BigDecimal("0.2")),
new Order("3", "user2", new BigDecimal("300"), new BigDecimal("0.3")),
new Order("4", "user2", new BigDecimal("400"), new BigDecimal("0.4")),
new Order("5", "user3", new BigDecimal("500"), new BigDecimal("0.5"))
);
Map<String, Map<BigDecimal, BigDecimal>> result = orders.stream()
.collect(Collectors.groupingBy(Order::getUserId,
Collectors.groupingBy(Order::getTax,
Collectors.reducing(BigDecimal.ZERO, Order::getAmount, BigDecimal::add))));
System.out.println(result);
}
}
```
输出结果为:
```
{user1={0.1=100, 0.2=200}, user2={0.3=300, 0.4=400}, user3={0.5=500}}
```
其中,Map的键是userId字段的值,值是另一个Map,第二个Map的键是tax字段的值,值是amount字段的值之和。使用reducing()方法可以将amount字段进行求和。