How to know the number of files in a folder using Java?

You can use the FileFilter interface for this:

File f = new File("/home/user/pasta");

File[] files = f.listFiles(new FileFilter() {
    @Override
    public boolean accept(File pathname) {
        return pathname.isFile();
    }
});

System.out.println(files.length);

The accept method of inteface FileFilter is called for each file in the folder in question. In the case on screen a test is done if the item is a file ( isFile() ), if it returns true and the file enters the vector that will be returned.

In Java 8 you could lay claim to Lambda:

File file = new File("/home/user/pasta");

Arrays.stream(file.listFiles())
        .filter(f -> f.isFile())
        .forEach(f -> System.out.println(f.getAbsolutePath()));

Where is running System.out.println(f.getAbsolutePath()) you could call the routine that does the parser of the file.

To tell the files do this:

long quantidade = Arrays.stream(file.listFiles())
        .filter(f -> f.isFile())
        .count();

Create an instance of the File class containing the path to which you want to get the total number of files.

File pasta = new File("/caminho/do/diretorio");

Now just create an array with the files using the method listFiles() After iterating over this array counting the number of files, without further ado it would look like this:

int contador = 0;
File pasta = new File("/caminho/do/diretorio");
File[] lista = pasta.listFiles();

for (File file : lista) {
    if (file.isFile()) {
        contador ++;
    }
}

This way you do not count directory folders, if you want to find out the total number of files counting folders, just do lista.length

Att.