java 8 sum field from list of object with common
我有这个对象列表
List<DetailDto> details;
@Value
public class DetailDto implements Serializable {
String category1;
Integer category2;
Integer price;
transient Integer totalPrice;
}
有了这份清单
[
{
"category1": "ABC",
"category2": 30,
"price": 195,
"totalPrice": null
},
{
"category1": "ABC",
"category2": 30,
"price": 195,
"totalPrice": null
},
{
"category1": "ABC",
"category2": 30,
"price": 195,
"totalPrice": null
},
{
"category1": "ABC",
"category2": 30,
"price": 390,
"totalPrice": null
},
{
"category1": "ABC",
"category2": 30,
"price": 390,
"totalPrice": null
},
{
"category1": "DEF",
"category2": 30,
"price": 455,
"totalPrice": null
},
{
"category1": "DEF",
"category2": 30,
"price": 455,
"totalPrice": null
},
{
"category1": "DEF",
"category2": 30,
"price": 455,
"totalPrice": null
},
{
"category1": "DEF",
"category2": 30,
"price": 455,
"totalPrice": null
},
{
"category1": "GHI",
"category2": 1,
"price": 18000,
"totalPrice": null
}
]
我想通过将字段List<DetailDto>总结为条件为的字段来制作另一个对象：pricetotalPrice
字符串category1很常见
整数category2很常见
整数price很常见
在这一点上我有这个
List<List<DetailDto>> summarizedList = detail().stream()
.collect(Collectors.groupingBy(DetailDto::category1,
Collectors.groupingBy(DetailDto::category2,
Collectors.groupingBy(DetailDto::price))))
.values()
.stream()
.flatMap(c1 -> c1.values().stream())
.flatMap(c2 -> c2.values().stream())
.collect(Collectors.toList());
返回我List<List<DetailDto>>
而且我不知道如何使它正确，在我尝试这个之后
summarizedList.stream().map(dto -> dto.stream().reduce((x,y) -> new DetailDto(x.productCode(), x.productQt(), x.orderPrice(), Integer.sum(x.orderPrice(), y.orderPrice()).orElse(null).collect(Collectors.toList());
你们能帮帮我吗？
尚方宝剑之说1回答
-
白猪掌柜的
这是一种可能性：使用复合键一次分组：.collect(Collectors.groupingBy(DetailDto::key, Collectors.summarizingInt(DetailDto::getPrice)))请参阅KeyDetailDto.java 中的定义（并注意其 eclipse 生成hashCode的equals方法）：import java.io.Serializable;@SuppressWarnings("serial")public class DetailDto implements Serializable { String category1; Integer category2; Integer price; transient Integer totalPrice; public DetailDto() { } public DetailDto(String category1, Integer category2, Integer price, Integer totalPrice) { super(); this.category1 = category1; this.category2 = category2; this.price = price; this.totalPrice = totalPrice; } public String getCategory1() { return category1; } public void setCategory1(String category1) { this.category1 = category1; } public Integer getCategory2() { return category2; } public void setCategory2(Integer category2) { this.category2 = category2; } public Integer getPrice() { return price; } public void setPrice(Integer price) { this.price = price; } public Integer getTotalPrice() { return totalPrice; } public void setTotalPrice(Integer totalPrice) { this.totalPrice = totalPrice; } Key key() { return new Key(category1, category2, price); }}class Key { String category1; Integer category2; Integer price; public Key(String category1, Integer category2, Integer price) { super(); this.category1 = category1; this.category2 = category2; this.price = price; } public String getCategory1() { return category1; } public Integer getCategory2() { return category2; } public Integer getPrice() { return price; } @Override public int hashCode() { final int prime = 31; int result = 1; result = prime * result + ((category1 == null) ? 0 : category1.hashCode()); result = prime * result + ((category2 == null) ? 0 : category2.hashCode()); result = prime * result + ((price == null) ? 0 : price.hashCode()); return result; } @Override public boolean equals(Object obj) { if (this == obj) return true; if (obj == null) return false; if (getClass() != obj.getClass()) return false; Key other = (Key) obj; if (category1 == null) { if (other.category1 != null) return false; } else if (!category1.equals(other.category1)) return false; if (category2 == null) { if (other.category2 != null) return false; } else if (!category2.equals(other.category2)) return false; if (price == null) { if (other.price != null) return false; } else if (!price.equals(other.price)) return false; return true; }}Main.javaimport java.io.IOException;import java.util.IntSummaryStatistics;import java.util.Map;import java.util.stream.Collectors;import java.util.stream.Stream;import com.fasterxml.jackson.core.JsonProcessingException;import com.fasterxml.jackson.databind.ObjectMapper;import com.fasterxml.jackson.databind.ObjectWriter;public class Main { public static void main(String[] args) throws IOException { DetailDto[] values = new ObjectMapper().readerFor(DetailDto[].class) .readValue(Main.class.getResourceAsStream("data.json"));// for (DetailDto dto : values) {// display(dto);// } Map<Key, IntSummaryStatistics> res = Stream.of(values) .collect(Collectors.groupingBy(DetailDto::key, Collectors.summarizingInt(DetailDto::getPrice))); Stream<DetailDto> agg = res.entrySet().stream().map(e -> new DetailDto(e.getKey().category1, e.getKey().category2, e.getKey().price, (int) e.getValue().getSum())); agg.forEach(Main::display); } protected static void display(DetailDto dto) { final ObjectWriter json = new ObjectMapper().writerFor(DetailDto.class).withDefaultPrettyPrinter(); try { System.out.println(json.writeValueAsString(dto)); } catch (JsonProcessingException e) { throw new RuntimeException(e); } }}！
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