Java8写一个共通方法，将两个类型不同的stream输入按多个字段进行匹配，并返回匹配成功的两个输出数据。已知stream输入已按匹配字段排好序，为了提高效率，使用了迭代器和循环来避免嵌套循环。要求当StreamA中匹配成功的两条key相等时，只返回最后一条数据

可以使用以下方法来实现：

public static <T, U, K extends Comparable<? super K>> Optional<Pair<T, U>> matchStreamsByMultipleKeys(Stream<T> streamA, Stream<U> streamB, Function<T, K[]> keyExtractorA, Function<U, K[]> keyExtractorB) {
    Iterator<T> iterA = streamA.iterator();
    Iterator<U> iterB = streamB.iterator();
    T currentA = null;
    U currentB = null;
    K[] keysA = null;
    K[] keysB = null;
    while (iterA.hasNext() && iterB.hasNext()) {
        if (currentA == null) {
            currentA = iterA.next();
            keysA = keyExtractorA.apply(currentA);
        }
        if (currentB == null) {
            currentB = iterB.next();
            keysB = keyExtractorB.apply(currentB);
        }
        int compare = compareKeys(keysA, keysB);
        if (compare == 0) {
            // Match found
            Optional<Pair<T, U>> result = Optional.of(new Pair<>(currentA, currentB));
            // Skip to the last match in streamA
            while (iterA.hasNext()) {
                T nextA = iterA.next();
                K[] nextKeysA = keyExtractorA.apply(nextA);
                if (compareKeys(nextKeysA, keysB) == 0) {
                    currentA = nextA;
                    keysA = nextKeysA;
                    result = Optional.empty();
                } else {
                    currentA = nextA;
                    keysA = nextKeysA;
                    break;
                }
            }
            // Skip to the next match in streamB
            while (iterB.hasNext()) {
                U nextB = iterB.next();
                K[] nextKeysB = keyExtractorB.apply(nextB);
                if (compareKeys(keysA, nextKeysB) == 0) {
                    currentB = nextB;
                    keysB = nextKeysB;
                    result = Optional.empty();
                } else {
                    currentB = nextB;
                    keysB = nextKeysB;
                    break;
                }
            }
            return result;
        } else if (compare < 0) {
            currentA = null;
            keysA = null;
        } else {
            currentB = null;
            keysB = null;
        }
    }
    return Optional.empty();
}

private static <K extends Comparable<? super K>> int compareKeys(K[] keysA, K[] keysB) {
    for (int i = 0; i < Math.min(keysA.length, keysB.length); i++) {
        int compare = keysA[i].compareTo(keysB[i]);
        if (compare != 0) {
            return compare;
        }
    }
    return Integer.compare(keysA.length, keysB.length);
}

这个方法使用了两个迭代器来遍历两个输入流，同时使用两个函数来提取每个元素的匹配键。在迭代器循环中，我们比较当前A和B的键，如果它们匹配，则返回匹配对。否则，我们将当前指针移到下一个不匹配的元素，直到下一个匹配的元素出现。如果在StreamA中有多个匹配的元素，则我们只返回最后一个匹配的元素，因为它们是按照匹配字段排序的。

注意，为了提高效率，我们使用了一个简单的循环来比较匹配键，而不是使用Java 8的Stream API。这是因为Stream API需要创建中间流对象，这可能会影响性能。