删除目录中除最后 3 个修改过的文件之外的所有文件

Question

I have a directory of backups saved on the phone, but I can't work out the logic to remove all but the last three.

As it stands I have:

public static void checkLocalBackup(){

            String path = Global.backupSingleLocalLocation;
            Log.d("Files", "Path: " + path);
            File f = new File(path);        
            File file[] = f.listFiles();
            for (int i=0; i < file.length; i++)
            {
                Log.d("Files", "FileName:" + file[i].lastModified());
                //sudo code 
                if(isNotInLastThreeFiles){
                    deleteFile(file[i]);
                }
            }
        }

This loops through and lists all the last modified files, but I cant work out how to select the oldest files and leave the newest 3?

Any guidance will be really appreciated.

Answer 1

Store all of the File objects in a List<File> and sort them using a custom Comparator so that they are ordered by "lastModified".

Finally, select the last three items from the list (or the first three, depending upon your sort order).

Answer 2

You can sort your files array by modified date:

File[] files = folder.listFiles();

Arrays.sort(files, new Comparator<File>(){
    public int compare(File f1, File f2) {
        return Long.valueOf(f1.lastModified()).compareTo(f2.lastModified());
    }
});

Answer 3

This post shows how to list files by modified date; once you do that, you can easily find the last three:

Best way to list files in Java, sorted by Date Modified?

Answer 4

使用 Comparator，您可以轻松实现在所需目录中获取最后三个修改文件的要求。

Answer 5

       // delete all except 10 latest files
        deleteAllExcept(10);      

  private static void deleteAllExcept(int i) {
        ArrayList<File> files = new ArrayList<>();

        for(File file : new File(path_to_folder).listFiles()) {
            files.add(file);
            System.out.println(file.getName());      
        }       
        
        files.stream()
        .filter((File p) -> p.getName().contains("."))
        .sorted(getReverseLastModifiedComparator())
        .skip(i)
        .forEach(x -> ((File) x).delete());
    }
    
    private static Comparator<File> getReverseLastModifiedComparator() {
        return (File o1, File o2) -> {
            if (o1.lastModified() < o2.lastModified()) {
                return 1;
            }
            if (o1.lastModified() > o2.lastModified()) {
                return -1;
            }
            return 0;
        };
    }