java8 stream lambda 一个例子

import java.io.File;
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public class Cleaner6 {

    public static void main(String[] args) throws IOException, InterruptedException {
        String filePath = args[0];

        File originalFodler = new File(filePath);
        String[] fileNames = originalFodler.list();

        List<String> keepList = Stream.of(fileNames)
                .collect(Collectors.groupingBy(t -> t.split("_")[0], 
                        Collectors.groupingBy(t -> t.split("_")[2])))
                .entrySet().stream().flatMap(p -> {
                    Map<String, List<String>> map = p.getValue();
                    String maxKey = Collections.max(map.keySet());
                    return map.get(maxKey).stream();
                }).collect(Collectors.toList());

        List<String> deleteList = new ArrayList<String>();
        Collections.addAll(deleteList, fileNames);
        deleteList.removeAll(keepList);
        
          
          deleteList.parallelStream().forEach(a->{          
            try {
                Files.delete(Paths.get(filePath + "\" + a));
            } catch (IOException e) {
                e.printStackTrace();
            }
        });
         

        System.out.println(fileNames.length);
        System.out.println(keepList.size());
        System.out.println(deleteList.size());
    }

}

两次group，一次flatmap，并行 foreach。

感悟：stream出现其实是颠覆循环