索引<Stream>数据Java

Question

需要在Java中索引流数据方面提供一些帮助。上下文是，我们需要手动为嵌入到其他文档中的文档设置索引(tldr；该方法中的输出需要为Stream )

return Stream.concat(firstStream, secondStream) <- these need to be indexed
      .sorted(// sorted using Comparator)
      .forEach? .map? // the class has index field with getter and setter so I think need to do `setIndex(i)` but wasnt sure where to get 'i'

任何建议都将不胜感激！

Answer 1

如果您可以从列表中自己构建流，则使用索引的IntStream而不是对象的Stream。

IntStream.range(0, firstList.size()).forEach(i -> firstList.get(i).setIndex(i));
int offsetForSecondList = firstList.size();
IntStream.range(0, secondList.size())
        .forEach(i -> secondList.get(i).setIndex(offsetForSecondList + i));

我没有尝试编译代码，所以请原谅任何错误。

否则，您的AtomicReference方法也会奏效。

Answer 2

假设您有一个类MyObject：

class MyObject{
    int index;
    String name;
    //getters,setters,cons, toString...
}

如下所示可能是一个起点：

public static Stream<MyObject> fooBar(){
    //just for example, inorder to get the streams to be concatnated
    List<MyObject> first = List.of(new MyObject("foo"),new MyObject("foo"),new MyObject("foo"));
    List<MyObject> second = List.of(new MyObject("bar"),new MyObject("bar"),new MyObject("bar"));

    AtomicInteger ai = new AtomicInteger(0);

    return Stream.concat(first.stream(), second.stream())
            .peek(myo -> myo.setIndex(ai.getAndIncrement()));
}