java 流 : straightforward reduce

Question

我有一个 MetricGroup 流，其中:

public class MetricGroup {

    private int uploadedDocs;
    private long uploadedKbs;

    // getters and setters

}

我需要将所有指标汇总到一个指标中。我的意思是，我需要将所有 metric.uploadedDocs 添加到 sumMetric.uploadedDocs 并将 metric.uploadedKds 添加到 sumMetric.uploadedKbs.

我发现我需要某种reduce

Stream.of(new MetricGroup(1,100), new MetricGroup(1,200))
    .reduce(????);

有什么想法吗？

Answer 1

您可以使用 reduce 的重载:

T reduce(T identity,
     BinaryOperator<T> accumulator)

像这样:

.reduce(new MetricGroup(0, 0),
        (x, y) -> new MetricGroup(
                      x.getUploadedDocs() + y.getUploadedDocs()
                      x.getUploadedKbs() + y.getUploadedKbs()
                  )
        )

你也可以使用collect方法:

private static MetricGroup combine(MetricGroup x, MetricGroup y) {
    x.setUploadedDocs(x.getUploadedDocs() + y.getUploadedDocs());
    x.setUploadedKbs(x.getUploadedKbs() + y.getUploadedKbs());
    return x;
}

// ....

.collect(() -> new MetricGroup(0, 0),
    YourClass::combine,
    YourClass::combine
)