问题

长时间的读者/潜水者，第一次发帖。
可能是一个有点愚蠢的问题，我相信有一个简单的解决办法。

我有一个客户列表和一个供应商列表

客户：
```java
    private int ID;
    private String name;
    private Integer age;
    private LocalDateTime createdDate;
    private String supplerName;

供应商：

    private int ID;
    private String name;
    private Integer age;
    private int customerID;
    private LocalDateTime createdDate;

我正在获取一些虚拟信息：

List<Supplier> suppliersList = supplierRepository.findAll();
List<Customer> customersList = customerRepository.findAll();

这将返回类似于以下内容：

供应商列表:
==============================================================================================
  Supplier{ID=1, name='Supplier A', age=19, customerID=1, createdDate=2020-09-25T23:15:31.798}
, Supplier{ID=2, name='Supplier B', age=20, customerID=1, createdDate=2020-09-25T23:15:31.799}
, Supplier{ID=3, name='Supplier C', age=21, customerID=2, createdDate=2020-09-25T23:15:31.799}
, Supplier{ID=4, name='Supplier D', age=22, customerID=3, createdDate=2020-09-25T23:15:31.799}
==============================================================================================
客户列表:
  Customer{ID=1, name='Customer A', age=19, createdDate=2020-09-25T23:15:31.770}
, Customer{ID=2, name='Customer B', age=20, createdDate=2020-09-25T23:15:31.779}
, Customer{ID=3, name='Customer C', age=21, createdDate=2020-09-25T23:15:31.779}
, Customer{ID=4, name='Customer D', age=22, createdDate=2020-09-25T23:15:31.779}
==============================================================================================

基本上，我想要做的是，如果供应商中的customerID与客户中的ID匹配，我希望将客户的supplierName设置为供应商中的name值。

我已经有一个流，它找到了匹配项：

List<Customer> filteredList = customersList.stream()
                .filter(cust -> suppliersList.stream()
                        .anyMatch(supl -> String.valueOf(cust.getID())
                                .equals(String.valueOf(supl.getCustomerID())))
                ).collect(Collectors.toList());

这会为我找到3个匹配的ID生成以下输出：

  Customer{ID=1, name='Customer A', age=19, createdDate=2020-09-25T23:22:16.768}
, Customer{ID=2, name='Customer B', age=20, createdDate=2020-09-25T23:22:16.776}
, Customer{ID=3, name='Customer C', age=21, createdDate=2020-09-25T23:22:16.777}

长话短说，我想要实现的是，对于所有这些匹配项，我想要将客户的供应商名称设置为供应商中的name值。

在某个时候，我还想将另一个对象流加入（这样我们现在会有3个流），并将一个对象中的一个或多个值设置到另一个对象中。如果有人有解决办法的话，那就更好了

<details>
<summary>英文:</summary>

Long time reader/ lurker in the shadows, first time poster.
Might be a bit of a silly question and I am sure there is an easy solution.

What I have is a List of Customers and a List of Suppliers

Customers:
```java
    private int ID;
    private String name;
    private Integer age;
    private LocalDateTime createdDate;
    private String supplerName;

Suppliers

    private int ID;
    private String name;
    private Integer age;
    private int customerID;
    private LocalDateTime createdDate;

I am fetching some dummy info with:

List<Supplier> suppliersList = supplierRepository.findAll();
List<Customer> customersList = customerRepository.findAll();

Which is returning me something like this:

Suppliers List:
==============================================================================================
  Supplier{ID=1, name='Supplier A', age=19, customerID=1, createdDate=2020-09-25T23:15:31.798}
, Supplier{ID=2, name='Supplier B', age=20, customerID=1, createdDate=2020-09-25T23:15:31.799}
, Supplier{ID=3, name='Supplier C', age=21, customerID=2, createdDate=2020-09-25T23:15:31.799}
, Supplier{ID=4, name='Supplier D', age=22, customerID=3, createdDate=2020-09-25T23:15:31.799}
==============================================================================================
Customers List:
  Customer{ID=1, name='Customer A', age=19, createdDate=2020-09-25T23:15:31.770}
, Customer{ID=2, name='Customer B', age=20, createdDate=2020-09-25T23:15:31.779}
, Customer{ID=3, name='Customer C', age=21, createdDate=2020-09-25T23:15:31.779}
, Customer{ID=4, name='Customer D', age=22, createdDate=2020-09-25T23:15:31.779}
==============================================================================================

Basically what I want to do is if the customerID in Suppliers matches the ID in customer I want to set the supplierName in customers to the name value from Suppliers.

I already have a stream that is finding me the matches

List<Customer> filteredList = customersList.stream()
                .filter(cust -> suppliersList.stream()
                        .anyMatch(supl -> String.valueOf(cust.getID())
                                .equals(String.valueOf(supl.getCustomerID())))
                ).collect(Collectors.toList());

which gives me the following output for the 3 matched ID's

  Customer{ID=1, name='Customer A', age=19, createdDate=2020-09-25T23:22:16.768}
, Customer{ID=2, name='Customer B', age=20, createdDate=2020-09-25T23:22:16.776}
, Customer{ID=3, name='Customer C', age=21, createdDate=2020-09-25T23:22:16.777}

So long story short what I am trying to achieve is for all these matches I want to set the Customer supplierName to the name value in Supplier.

At some point I would also like to also join another stream of objects (so we would now have 3 streams) and set one or multiple values from one object to another. Bonus points if anyone has a solution for that

答案1

得分: 1

我认为这个任务最好不要使用纯流解决方案来完成。以下是分步骤的做法：

Map<Integer, List<Supplier>> suppliersByCustomerId = suppliersList.stream()
        .collect(Collectors.groupingBy(Supplier::getCustomerID));

这将供应商按customerID分组。然后，我们需要迭代客户，并检查是否有供应商为每个客户提供服务。如果有匹配项，我们将第一个供应商的名称设置给客户。

customers.forEach(c -> {
    List<Supplier> suppliers = suppliersByCustomerId.get(c.getID());
    if (suppliers != null && !suppliers.isEmpty()) {
        Supplier first = suppliers.get(0);
        String supplierName = first.getName();
        c.setSupplierName(supplierName);
    }
});

由于您没有指定如果每个客户有多个供应商要执行什么操作，所以我决定将第一个供应商的名称设置给客户。

Map<Integer, List<Supplier>> suppliersByCustomerId = suppliersList.stream()
        .collect(Collectors.groupingBy(Supplier::getCustomerID));

customers.forEach(c -> {
    List<Supplier> suppliers = suppliersByCustomerId.get(c.getID());
    if (suppliers != null && !suppliers.isEmpty()) {
        Supplier first = suppliers.get(0);
        String suppliername = first.getName();
        c.setSupplierName(supplierName);
    }
});