How to read data from all files in a directory using Java?

The class named File of the java.io package represents a file or directory (pathnames) in the system. This class provides various methods to perform various operations on files/directories.
To get the list of all the existing files in a directory this class provides five different methods to get the details of all files in a particular folder −
String[] list()
File[] listFiles()
String[] list(FilenameFilter filter)
File[] listFiles(FilenameFilter filter)
File[] listFiles(FileFilter filter)
This method returns an array holding the objects (abstract paths) of all the files (and directories) in the path represented by the current (File) object.
The following Java program prints the name, path and, size of all the files in the path D:\\ExampleDirectory.
 Live Demo
import java.io.File;
import java.io.IOException;
public class ListOfFiles {
   public static void main(String args[]) throws IOException {
      //Creating a File object for directory
      File directoryPath = new File("D:\\ExampleDirectory");
      //List of all files and directories
      File filesList[] = directoryPath.listFiles();
      System.out.println("List of files and directories in the specified directory:");
      for(File file : filesList) {
         System.out.println("File name: "+file.getName());
         System.out.println("File path: "+file.getAbsolutePath());
         System.out.println("Size :"+file.getTotalSpace());
         System.out.println(" ");
      }
   }
}
List of files and directories in the specified directory:
File name: SampleDirectory1
File path: D:\ExampleDirectory\SampleDirectory1
Size :262538260480
File name: SampleDirectory2
File path: D:\ExampleDirectory\SampleDirectory2
Size :262538260480
File name: SampleFile1.txt
File path: D:\ExampleDirectory\SampleFile1.txt
Size :262538260480
File name: SampleFile2.txt
File path: D:\ExampleDirectory\SampleFile2.txt
Size :262538260480
File name: SapmleFile3.txt
File path: D:\ExampleDirectory\SapmleFile3.txt
Size :262538260480
To read the contents of all files in a particular directory, get the File objects of all files in it as an array, using the above-mentioned method and then, read contents of each file object in the array using the Scanner class and its methods.
 Live Demo
import java.io.File;
import java.io.IOException;
import java.util.Scanner;
public class ListOfFiles {
   public static void main(String args[]) throws IOException {
      //Creating a File object for directory
      File directoryPath = new File("D:\\Demo");
      //List of all files and directories
      File filesList[] = directoryPath.listFiles();
      System.out.println("List of files and directories in the specified directory:");
      Scanner sc = null;
      for(File file : filesList) {
         System.out.println("File name: "+file.getName());
         System.out.println("File path: "+file.getAbsolutePath());
         System.out.println("Size :"+file.getTotalSpace());
         //Instantiating the Scanner class
         sc= new Scanner(file);
         String input;
         StringBuffer sb = new StringBuffer();
         while (sc.hasNextLine()) {
            input = sc.nextLine();
            sb.append(input+" ");
         }
         System.out.println("Contents of the file: "+sb.toString());
         System.out.println(" ");
      }
   }
}
List of files and directories in the specified directory:
File name: samplefile1.txt
File path: D:\Demo\samplefile1.txt
Size :262538260480
Contents of the file: Contents of the sample file 1
File name: samplefile2.txt
File path: D:\Demo\samplefile2.txt
Size :262538260480
Contents of the file: Contents of the sample file 2
File name: samplefile3.txt
File path: D:\Demo\samplefile3.txt
Size :262538260480
Contents of the file: Contents of the sample file 3
File name: samplefile4.txt
File path: D:\Demo\samplefile4.txt
Size :262538260480
Contents of the file: Contents of the sample file 4
File name: samplefile5.txt
File path: D:\Demo\samplefile5.txt
Size :262538260480
Contents of the file: Contents of the sample file 5