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      Reading File

      Java Tutorial

      This Java tutorial is tailored for newcomers, offering a journey from basic principles to complex Java programming techniques. Completing this tutorial equips you with a solid understanding of Java, preparing you for advanced learning. You'll emerge ready to tackle the challenges of becoming a top-tier software engineer, with the skills to innovate and excel in the vast world of software development.

      Reading File

      Reading a File in Java

      We can read a file in Java using multiple ways. Following are three most popular ways to create a file in Java
      • Using FileInputStream() constructor
      • Using FileReader.read() method
      • Using Files.readAllLines() method
      Let's take a look at each of the way to read file in Java.

      Reading File Using FileInputStream() Constructor

      FileInputStream is used for reading data from the files. Objects can be created using the keyword new and there are several types of constructors available.

      Syntax

      Following constructor takes a file name as a string to create an input stream object to read the file
      InputStream f = new FileInputStream("C:/java/hello.txt");

      Syntax

      Following constructor takes a file object to create an input stream object to read the file. First we create a file object using File() method as follows 
      File f = new File("C:/java/hello.txt");
      InputStream f = new FileInputStream(f);

      Example: Reading File Using FileInputStream() Constructor

      Following is the example to demonstrate FileInputStream to read a file from current directory 
      package com.tutorialspoint;
      
      import java.io.FileInputStream;
      import java.io.FileOutputStream;
      import java.io.IOException;
      import java.io.InputStream;
      import java.io.OutputStream;
      
      public class FileTest {
         public static void main(String args[]) {
            try {
               byte bWrite [] = {65, 66, 67, 68, 69};
               OutputStream os = new FileOutputStream("test.txt");
               for(int x = 0; x < bWrite.length ; x++) {
                  os.write( bWrite[x] );   // writes the bytes
               }
               os.close();
           
               InputStream is = new FileInputStream("test.txt");
               int size = is.available();
      
               for(int i = 0; i < size; i++) {
                  System.out.print((char)is.read() + "  ");
               }
               is.close();
            } catch (IOException e) {
               System.out.print("Exception");
            }	
         }
      }
      The above code would create file test.txt and would write given numbers in binary format. Same would be read using FileInputStream and the output is printed on the stdout screen.

      Output

      A  B  C  D  E

      Reading File Using FileReader.read() Method

      FileReader.read() method of FileReader class allows to read chars from a file as shown below

      Syntax

      // get an existing file
      File file = new File("d://test//testFile1.txt");
      
      // read content
      FileReader reader = new FileReader(file);
      
      int c;
      while ((c = reader.read()) != -1) {
         char ch = (char) c;
         System.out.print(ch);
      }

      Example: Reading File Using FileReader.read() Method

      Following is the example to demonstrate File to read a file in given directory using FileReader.read() method 
      package com.tutorialspoint;
      
      import java.io.File;
      import java.io.FileReader;
      import java.io.FileWriter;
      import java.io.IOException;
      
      public class FileTest {
         public static void main(String args[]) {
            try {
               File file = new File("d://test//testFile1.txt");
      
               //Create the file
               if (file.createNewFile()) {
                  System.out.println("File is created!");
               } else {
                  System.out.println("File already exists.");
               } 
      
               // Write Content
               FileWriter writer = new FileWriter(file);
               writer.write("Test data");
               writer.close();
      
      
               // read content
               FileReader reader = new FileReader(file);
      
               int c;
               while ((c = reader.read()) != -1) {
                  char ch = (char) c;
                  System.out.print(ch);
               }
            } catch (IOException e) {
               System.out.print("Exception");
            }	
         }
      }
      The above code would create file test.txt and would write given string in text format. Same would be the output on the stdout screen.

      Output

      File is created!
      Test data

      Reading File Using Files.readAllLines() Method

      Files.readAllLines() is a newer method to read all content of a file as a List of String as shown below

      Syntax

      List<String> content = Files.readAllLines(Paths.get("d://test/testFile3.txt"));

      Example: Reading File Using Files.readAllLines() Method

      Following is the example to demonstrate File to read a file from a given directory using readAllLines() method 
      package com.tutorialspoint;
      
      import java.io.IOException;
      import java.nio.charset.StandardCharsets;
      import java.nio.file.Files;
      import java.nio.file.Paths;
      import java.nio.file.StandardOpenOption;
      import java.util.Arrays;
      import java.util.List;
      
      public class FileTest {
         public static void main(String args[]) {
            try {
          	  String data = "Test data";
                Files.write(Paths.get("d://test/testFile3.txt"), data.getBytes());
                List<String> lines = Arrays.asList("1st line", "2nd line");
                Files.write(Paths.get(
                   "file6.txt"), lines, StandardCharsets.UTF_8, 
                   StandardOpenOption.CREATE, StandardOpenOption.APPEND);
                
                List<String> content = Files.readAllLines(Paths.get("d://test/testFile3.txt"));
      
                System.out.println(content);
                
                content = Files.readAllLines(Paths.get("file6.txt"));
      
                System.out.println(content);
            } catch (IOException e) {
               System.out.print("Exception");
            }	
         }
      }
      The above code would create file test.txt and would write given strings in text format. Same would be the output on the stdout screen.

      Output

      [Test data]
      [1st line, 2nd line]