我有一个 ItemDTO 对象,其中一些字段包含来自 BigQuery 数据库的数据,其中很少来自 DB2 数据库。我想使用流检索数据并合并到 DTO 对象,但它不符合预期。
BigQuery 表包含的数据如下:
DB2表数据:
预期结果:合并所有字段:
我使用流来执行合并:
public static class ItemDTO {
String itemNumber;
String itemName;
int postcode;
String location;
String price;
//getter & setters
}
List<ItemDTO> bigQueryResults = //resultset from BigQueryDB
/*Retrieved bigquery results: [{
"itemNumber":"101"
"Name":"chair"
"Postcode":"4513"
"Location":null
"Price":null
},
{
"itemNumber":"102"
"Name":"Table"
"Postcode":"2341"
"Location":null
"Price":null
}]*/
List<ItemDTO> db2Results = //resultset from DB2
/*Retrieved db2 results: [{
"itemNumber":"102"
"Name":null
"Postcode":null
"Location":"New York"
"Price":"120"
},
{
"itemNumber":"101"
"Name":null
"Postcode":null
"Location":"Amsterdam"
"Price":"250"
}]*/
// retrieving a list of combined results from both db2 and BQ with key as itemNumber
List<ItemDTO> resultList = db2List.stream()
.filter(a -> bqList.stream().anyMatch(item -> item.getItem_nbr().equals(a.getItem_nbr())))
.collect(Collectors.toList());
/* Expected Output: [{
"itemNumber":"101"
"Name":"chair"
"Postcode":"4513"
"Location":"Amsterdam"
"Price":"250"
},
{
"itemNumber":"102"
"Name":"Table"
"Postcode":"2341"
"Location":"New York"
"Price":"120"
}]*/
/* ResultList output: [{
"itemNumber":"101"
"Name":"chair"
"Postcode":"4513"
"Location":null
"Price":null
},
{
"itemNumber":"102"
"Name":"Table"
"Postcode":"2341"
"Location":null
"Price":null
}]*/
但是当我使用它时,我得到的行仅包含 BigQuery 字段的映射值。 DB2 中存在的字段填充为空。 请让我知道是否有其他方法来处理这种映射。任何建议将不胜感激。
这将合并具有相同 ItemNumber 的所有部分数据库提取。
bigq
创建一个地图collectingAndThen
,对映射进行后处理,流式传输 dbq
dbq
商品设置。类定义
class ItemDTO {
String itemNumber;
String itemName;
int postcode;
String location;
String price;
public ItemDTO(String itemNumber, String itemName, int postcode,
String location, String price) {
this.itemNumber = itemNumber;
this.itemName = itemName;
this.postcode = postcode;
this.location = location;
this.price = price;
}
public String getItemNumber() {
return itemNumber;
}
public void setItemNumber(String itemNumber) {
this.itemNumber = itemNumber;
}
public String getItemName() {
return itemName;
}
public void setItemName(String itemName) {
this.itemName = itemName;
}
public int getPostcode() {
return postcode;
}
public void setPostcode(int postcode) {
this.postcode = postcode;
}
public String getLocation() {
return location;
}
public void setLocation(String location) {
this.location = location;
}
public String getPrice() {
return price;
}
public void setPrice(String price) {
this.price = price;
}
@Override
public String toString() {
return itemNumber + ", " + itemName + ", " + postcode + ", " + location
+ ", " + price;
}
}
过程
List<ItemDTO> bigQueryResults = List.of(
new ItemDTO("101", "chair", 4513, null, null),
new ItemDTO("102", "Table", 2341, null, null),
new ItemDTO("103", "Television", 5607, null, null),
new ItemDTO("104", "Microwave", 2378, null, null),
new ItemDTO("105", "Sofa", 1278, null, null));
List<ItemDTO> dbQueryResults = List.of(
new ItemDTO("102", null, 0, "New York", "120"),
new ItemDTO("106", null, 0, "Budapest", "300"),
new ItemDTO("101", null, 0, "Amsterdam", "250)"));
// retrieving the db2 results for itemNumbers from bigQueryResults
List<ItemDTO> mergedResult = bigQueryResults.stream()
.collect(Collectors.collectingAndThen(
Collectors.groupingBy(ItemDTO::getItemNumber),
mp -> dbQueryResults.stream().<ItemDTO>mapMulti((item, consumer) -> {
List<ItemDTO> sameNumberList = mp.get(item.getItemNumber());
if (sameNumberList != null) { // item number may not be
// in map
for (ItemDTO i : sameNumberList) {
i.setLocation(item.getLocation());
i.setPrice(item.getPrice());
consumer.accept(i); // put updated item on stream
}
}
}))).toList();
mergedResult.forEach(System.out::println);
为提供的数据打印以下内容
102, Table, 2341, New York, 120
101, chair, 4513, Amsterdam, 250)
推荐您查看mapMulti、CollectingAndThen、Collectors.groupingBy
更新了 Java-8 的答案。
ItemDTO
添加到合并结果列表中。Map<String, List<ItemDTO>> mapByItemNumber = bigQueryResults.stream()
.collect(Collectors.groupingBy(ItemDTO::getItemNumber));
List<ItemDTO> mergedResults = new ArrayList<>();
for (ItemDTO item : dbQueryResults) {
if (mapByItemNumber.containsKey(item.getItemNumber())) {
for (ItemDTO i : mapByItemNumber.get(item.getItemNumber())) {
i.setLocation(item.getLocation());
i.setPrice(item.getPrice());
mergedResults.add(i);
}
}
}
mergedResults.forEach(System.out::println);