在嵌套集合中使用过滤器过滤对象？

Question

DeviceType.java

private String Id;
private List<DeviceTelemetry> telemetries = new ArrayList<>()
//Getter Setter

DeviceTelemetry.java (Enum Class)

private String name;
private String description;
//Getter Setter

I want to fetch all DeviceType Id , which have DeviceTelemetry name start with "System"(String).

I did something like this:-

List<DeviceType> filteredStartWithDeviceType =deviceTypes.stream().
             filter(f -> f.getTelemetries().stream()
             .anyMatch(g -> g.getName().startsWith("System"))).collect(Collectors.toList());

Can Anyone tell me how can I get DeviceType Id from this?

Answer 1

You just need to map the values from DeviceType to String

List<String> filteredStartWithDeviceType = deviceTypes.stream()
    .filter(f -> f.getTelemetries().stream()
             .anyMatch(g -> g.getName().startsWith("System")))
    .map(DeviceType::getId) // or .map(dt -> dt.getId()) if you prefer this syntax
    .collect(Collectors.toList());