Java 8相当于Streams的getLineNumber（） [英] Java 8 equivalent to getLineNumber() for Streams

问题描述

Java 8中的Streams是否等效于getLineNumber（）？

Is there an equivalent to getLineNumber() for Streams in Java 8?

我想在文本文件中搜索一个单词并将行号作为整数返回。
这是我的搜索方法：

I want to search for a word in a textfile and return the line number as Integer. This is my search Method:

result = Files.lines(Paths.get(fileName))
            .filter(w -> w.contains(word))
            .collect(Collectors.<String> toList());

推荐答案

我认为没有，因为流是不是为了提供对元素的访问，而不是像集合一样。

I don't think there is, because streams are not designed to provide an access to their elements, not like collections.

一种解决方法是读取列表中的文件，然后使用 IntStream 生成相应的索引，然后您可以从中应用过滤器：

One workaround would be to read the file in the list, then use an IntStream to generate the corresponding indices, from which you can then apply your filter:

List<String> list =  Files.readAllLines(Paths.get("file"));

//readAllLines current implementation returns a RandomAccessList so 
//using get will not have a big performance impact.
//The pipeline can be safely run in parallel
List<Integer> lineNumbers = 
     IntStream.range(0, list.size())
              .filter(i -> list.get(i).contains(word))
              .mapToObj(i -> i + 1)
              .collect(toList());

因为冒风险将整个文件的内容加载到列表中可能会保留，所以有点矫枉过正之后只有几个元素。如果它不满足你，你可以写好for循环，它的代码不多。

It's a bit overkill as you take the risk to load the entire file's content into a list to maybe keep only a few elements after. If it doesn't satisfy you, you can write the good for loop, it's not much code.

也许你可能对这个问题感兴趣使用带有lambda的JDK8压缩流（java.util.stream.Streams.zip ）。例如，使用 proton-pack 库：

Maybe you can be interested in this question Zipping streams using JDK8 with lambda (java.util.stream.Streams.zip). For example, using the proton-pack library:

List<Long> lineNumbers = 
    StreamUtils.zipWithIndex(Files.lines(Paths.get("file")))
               .filter(in -> in.getValue().contains(word))
               .map(in -> in.getIndex() + 1)
               .collect(toList());

或者您可以从a创建 LineNumberReader BufferedReader ，然后调用 lines（）并将每一行映射到文件中的行号。请注意，如果管道并行运行，此方法将失败，因此我不推荐它。

Or you can create a LineNumberReader from a BufferedReader, then call lines() and map each line to its line number in the file. Note that this approach will fail if the pipeline is run in parallel, so I don't recommend it.

LineNumberReader numberRdr = new LineNumberReader(Files.newBufferedReader(Paths.get("file")));

List<Integer> linesNumbers = numberRdr.lines()
                                      .filter(w -> w.contains(word))
                                      .map(w -> numberRdr.getLineNumber())
                                      .collect(toList());

这篇关于Java 8相当于Streams的getLineNumber（）的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！