java - 如何在 Java 8 中的两个流之间进行搜索

Question

如果我有 2 个 Streams，就像下面所示的方法一样

public Stream<Transaction> getPendingTransaction(Stream<PendingTransaction> pendingTransactionStream,Stream<ProcessedTransaction> processedTransactionStream){ }

并且我想根据某些标准(如

if transaction.getId() is same for an Transaction object present in pendingTransactionStream and processedTransactionStreamthen that object is same and we can collect them in a list.

我试过这样做但是它给出了错误

processedTransactionStream
        .filter( (processedTransaction)->
        {
            pendingTransactionStream.anyMatch(s->s.getTransactionId().equals(processedTransaction.getTransactionId()) );
        } 
        ).collect(Collectors.toList());

Answer 1

嗯，您不能多次使用 pendingTransactionStream Stream。您可以将其转换为交易 ID 的 List(或者更好的是 Set)，以在 filter 方法中使用。

Set<String> pending = pendingTransactionStream.map(PendingTransaction::getTransactionId)
                                              .collect(Collectors.toSet());
List<ProcessedTransaction> processed = 
    processedTransactionStream.filter(pt -> pending.contains(pt.getTransactionId()))
                              .collect(Collectors.toList());