Read Multiple Files In Java

Question

I want to read multiple files into Java at once. File names are like:

• nnnnn_UM2012.txt
• ghkjdf_UM2045.txt
• erey_UM2189.txt
• ....

There are over 1,000 files and I do not want to write all files names in Java one by one, using code similar to the following one:

String fileNames = {"nnnnn_UM2012.txt","ghkjdf_UM2045.txt","erey_UM2189.txt", …}

Maybe the filenames should be read in reverse order. How can I do that?

Answer 1

To get all files in a folder (sub-folders are included in the list of files):

    // get all files in the folder
    final File folder = new File(".");
    final List<File> fileList = Arrays.asList(folder.listFiles());

To get all files in a folder, excluding sub-folders:

    // get all files in the folder excluding sub-folders
    final File folder = new File(".");
    final List<File> fileList = Arrays.asList(folder.listFiles(new FileFilter() {
        public boolean accept(File pathname) {
            return pathname.isFile();
        }
    }));

To sort the list of files into reverse case-sensitive order:

    // sort the files into reverse order
    Collections.sort(fileList, new Comparator<File>() {
        public int compare(File o1, File o2) {
            return o2.getName().compareTo(o1.getName());
        }
    });

To sort the list of files into reverse case-insensitive order:

    // sort the files into reverse order ignoring case
    Collections.sort(fileList, new Comparator<File>() {
        public int compare(File o1, File o2) {
            return o2.getName().compareToIgnoreCase(o1.getName());
        }
    });

Answer 2

您可以使用listFiles方法获取文件夹中的所有文件。

Answer 3

File rep = new File("path to rep");
File[] list = rep.listFiles();
ArrayList<String> filenames = new ArrayList<String>();
for ( int i = 0; i < list.length; i++) {
    filenames.add(list[i].getName());
} 

I guess it can be a solution to your problem.

Answer 4

You can follow the below approach if all the files are in a single directory. Get a reference to the directory by providing its fully qualified path and then use the list() function get all the file names into a String array inside the directory.

After this step you can sort the files according to the way you want (For eg by its name,length,etc..).