Java 将对象列表分组以创建扩展对象列表
我从数据库中获得了这些样本记录,这是分组查询的结果:Java 将对象列表分组以创建扩展对象列表,java,lambda,java-8,java-stream,Java,Lambda,Java 8,Java Stream,我从数据库中获得了这些样本记录,这是分组查询的结果: [ { "name": "Troy", "acct": 1123, "type": " Savings", "total": 50 }, { "name": "Larry", "acct": 4233, "type": " Savings", "total": 200 }, { "name": "Troy", "acct": 1123, "type": " Curre
[
{
"name": "Troy",
"acct": 1123,
"type": " Savings",
"total": 50
},
{
"name": "Larry",
"acct": 4233,
"type": " Savings",
"total": 200
},
{
"name": "Troy",
"acct": 1123,
"type": " Current",
"total": 120
},
{
"name": "Larry",
"acct": 4233,
"type": " Current",
"total": 220
}
]
现在,我需要创建一个如下所示的报告:
[
{
"name": "Troy",
"acct": 1123,
"totalSavings": 50,
"totalCurrent": 120
},
{
"name": "Larry",
"acct": 4233,
"totalSavings": 200,
"totalCurrent": 220
}
]
我已经尝试使用一些lambda技术,如下面的一种,但我仍然没有接近我想要的解决方案
Map<String, List<DbTrans>> collect = transList.stream().collect(
Collectors.groupingBy(f -> f.getType()));
Map collect=transList.stream().collect(
Collectors.groupby(f->f.getType());
首先,响应Dto与请求Dto不同,我建议创建一个新的响应类LETS调用它:
public class DbTransResponse {
private String name;
private String acct;
private double totalSavings;
private double totalCurrent;
// getters and setters
}
那么结果可以是这样的:
List<DbTransResponse> result = transList.stream()
.collect(Collectors.groupingBy(DbTrans::getAcct))
.values().stream()
.map(trans -> new DbTransResponse(
trans.get(0).getName(),
trans.get(0).getAcct(),
trans.get(0).getTotal(),
trans.get(1).getTotal()
)).collect(Collectors.toList());
为此,您可以使用
collector::toMap
(通过单个collect
操作)
还有一个用于DbTransResponse
类的附加构造函数,不过您可以将此逻辑移动到方法中
DbTransResponse(DbTrans dbTrans) {
this.name = dbTrans.getName();
this.acct = dbTrans.getAcct();
this.totalSavings = "Savings".equals(dbTrans.getType()) ? dbTrans.getTotal() : 0;
this.totalCurrent = "Current".equals(dbTrans.getType()) ? dbTrans.getTotal() : 0;
}
可能是我在银行业工作:)但如果类型是交易类型,您的考虑是错误的,并且可能存在同一类型的多笔交易。但是奥兰托比应该回答这个问题。顺便说一句,按名称分组没有意义。帐户与个人唯一关联。因此,按accountnumber分组就足够了。除非我怀疑的不是帐户的所有者,而是交易发起人。@AlexandarPetrov我同意第二条评论,按帐户分组更好,关于第一条评论,如果OP想要用多个字段分组,那么执行
.collector(Collectors.groupingBy)并不容易(DbTrans::getName,Collectors.groupingBy(DbTrans::getAcct))).values().stream().flatMap(m->m.values().stream())
DbTransResponse{name='Larry', acct='4233', totalSavings=200.0, totalCurrent=220.0}
DbTransResponse{name='Troy', acct='1123', totalSavings=50.0, totalCurrent=120.0}
Map<Integer, DbTransResponse> collect = transList.stream()
.collect(Collectors.toMap(DbTrans::getAcct,
DbTransResponse::new,
DbTransResponse::merge));
Collection<DbTransResponse> result = collect.values();
static DbTransResponse merge(DbTransResponse r1, DbTransResponse r2) {
return new DbTransResponse(
r1.name, r1.acct,
r1.totalSavings + r2.totalSavings,
r1.totalCurrent + r2.totalCurrent
);
}
DbTransResponse(DbTrans dbTrans) {
this.name = dbTrans.getName();
this.acct = dbTrans.getAcct();
this.totalSavings = "Savings".equals(dbTrans.getType()) ? dbTrans.getTotal() : 0;
this.totalCurrent = "Current".equals(dbTrans.getType()) ? dbTrans.getTotal() : 0;