Java - 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]