java如何链接不同类的两个对象？

Question

我想为库构建一个RESTAPI（端点是客户和发票）。其中一个功能是添加发票（使用客户id提交请求）。首先，我必须检查传递的客户id（通过URL中的PUT）是否存在，这意味着要检查customerMap并查看讨论中的id。问题在于customerMap是clientService类（而不是invoiceService类）中的HashMap（使用该映射而不是数据库）。如何获取地图中存储的数据？在此，守则的相关部分：

客户

public class client {

private static final AtomicLong counter = new AtomicLong();

private final long id;

public client() {
    this.id = counter.getAndIncrement();
}

public long getId() {
    return id;
}
}

客户服务

public class clientService {
public Map<Long, client> clientMap = new HashMap<>();

public client put(client g) {
    clientMap.put(g.getId(), g);
    return g;
}

public Collection<client> getAll() {
    return clientMap.values();
}
}

发票

invoice  {

private static final AtomicLong counter = new AtomicLong();

private final long id;
private client client;

public invoice() {
    this.id = counter.getAndIncrement();
}

public long getId() {
    return id;
}
}

发票服务

public class invoiceService {
private Map<Long, invoice> invoiceMap = new HashMap<>();

public Rechnung createinvoice(invoice g, long id) {

    if(<!--client exists-->)
    invoicegMap.put(g.getId(), g);
    return g;
}}

Answer 1

首先，向ClientService添加一个方法，以按id查找客户端：

public Client getClientById(Long clientId) {
   return clientMap.get(clientId);
}

然后将ClientService注入到发票服务中

public class invoiceService {
private Map<Long, invoice> invoiceMap = new HashMap<>();
private ClientService clientService; // provide a getter or a constructor argument for the service

public Rechnung createinvoice(invoice g, long id) {

    if(clientService.getClientById(id) != null) {
      invoicegMap.put(g.getId(), g);
}
    return g;
}}

Answer 2

为什么不将clientmap设为静态，并直接从客户端服务类访问它呢