Java Lambda 用于在两个 for 循环内中断

Question

我正在尝试将 Java 8 中的迭代代码块转换为函数式。函数式方法无法在共享的集合中找到匹配的消息。

List<Optional<Message>> allMessages = new ArrayList<>();

Set<Status> allStatuses = getAllStatuses();

//Iterative : Working
Set<StatusMessage> set = new HashSet<>(STATUS_MESSAGE.values());
for (StatusMessage statusMessage : set) {
    for (Status status : statusMessage.getStatusAndInfo().keySet()) {
        Optional<Message> message = MessageBuilder.createMessage(allStatuses, status, this::createMessage);
        if (message.isPresent()) {
            allMessages.add(message);
            break;
        }
    }
}

//Functional : Not working  - Never adds anything to the 
//map even when matching status is present
STATUS_MESSAGE.values().stream()
        .distinct()
        .map(statusMessage -> statusMessage.getStatusAndInfo().keySet())
        .flatMap(Collection::stream)
        .map(key -> MessageBuilder.createMessage(allStatuses, key, this::createMessage))
        .anyMatch(allMessages::add);

该MessageBuilder.createMessage如下所示：

Optional<Status> matchingStatus = statuses.stream()
                .filter(matchingStatus::equals)
                .findFirst();
System.out.println("Found : " + matchingStatus.toString());
return matchingStatus.flatMap(creator);

此外，出于调试目的，如何查看流的每个步骤中发生的情况？intellij 中调试器中的堆栈未在流中显示任何内容。

Answer 1

这应该这样做：

STATUS_MESSAGE.values().stream()
        .distinct()
        .forEach(statusMessage ->
            statusMessage.getStatusAndInfo().keySet().stream()
                    .map(status -> MessageBuilder.createMessage(allStatuses, status, this::createMessage))
                    .filter(Optional::isPresent)
                    .findFirst()
                    .ifPresent(allMessages::add)
        );

更新

要使用toList而不是添加到列表来构建结果列表：

List<Optional<Message>> allMessages = STATUS_MESSAGE.values().stream()
        .distinct()
        .flatMap(statusMessage ->
            statusMessage.getStatusAndInfo().keySet().stream()
                    .map(status -> MessageBuilder.createMessage(allStatuses, status, this::createMessage))
                    .filter(Optional::isPresent)
                    .limit(1)
        )
        .collect(Collectors.toList());