Monday, July 23, 2012

How to read file line by line in Java - BufferedReader Scanner Example Tutorial

Line by Line reading in Java using BufferedReader and Scanner
There are multiple ways to read file line by line in Java. Most simple example of reading file line by line is using BufferedReader which provides method readLine() for reading file. Apart from generics, enum and varargs Java 1.5  has also introduced several new class in Java API one of the  utility class is Scanner, which can also be used to read any file line by line in Java. Though BufferedReader is available in Java from JDK 1.1,  java.util.Scanner provides more utility methods compared to BufferedReader. Scanner has method like hasNextLine() and nextLine() to facilitate line by line reading of file's contents. nextLine() returns String similar to  readLine() but scanner has more utility methods like nextInt(), nextLong() which can be used to directly read numbers from file instead of converting String to Integer or other Number classes. By the way Scanner is rather new approach for reading file and BufferedReader is the standard one. This is my 6th tutorial on Java IO,  In last couple of post we have seen creating file and directory in Java, parsing XML files using DOM and how to read properties file in Java. In this post we will focus on reading file line by line in Java using both BufferedReader and Scanner.

Reading file line by line in Java - BufferedReader Example

Java file read line by line example BufferedReader ScannerIn this example we are using BufferedReader for reading file content line by line. BufferedReader needs an InputStream which is a FileInputStream in this case and readLine() returns value of line or null if end of Stream has reached. line is terminated with line terminator e.g. \n or \r

import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 * BufferedReader and Scanner can be used to read line by line from any File or
 * console in Java.
 * This Java program demonstrate line by line reading using BufferedReader in Java
 *
 * @author Javin Paul
 */

public class BufferedReaderExample {  

    public static void main(String args[]) {
     
        //reading file line by line in Java using BufferedReader      
        FileInputStream fis = null;
        BufferedReader reader = null;
     
        try {
            fis = new FileInputStream("C:/sample.txt");
            reader = new BufferedReader(new InputStreamReader(fis));
         
            System.out.println("Reading File line by line using BufferedReader");
         
            String line = reader.readLine();
            while(line != null){
                System.out.println(line);
                line = reader.readLine();
            }          
         
        } catch (FileNotFoundException ex) {
            Logger.getLogger(BufferedReaderExample.class.getName()).log(Level.SEVERE, null, ex);
        } catch (IOException ex) {
            Logger.getLogger(BufferedReaderExample.class.getName()).log(Level.SEVERE, null, ex);
         
        } finally {
            try {
                reader.close();
                fis.close();
            } catch (IOException ex) {
                Logger.getLogger(BufferedReaderExample.class.getName()).log(Level.SEVERE, null, ex);
            }
        }
  }

Output:
Reading File line by line using BufferedReader
first line in file
second line
third line
fourth line
fifth line
last line in file


while using FileInputStream or any IO Reader don't forget to close the stream in finally block so that file descriptor associated with this operation get released. If not closed properly Java program may leak file descriptors which is a limited resource and in worst case program will not be able to open any new file. If you are Java 7 then you can use Automatic resource management or ARM blocks to let those resource automatically get closed by Java.


Reading file line by line in Java - Scanner Example

Scanner is new addition in Java 1.5 along-with several other changes like auto-boxing and has been a preferred choice for reading inputs from console. Since Scanner is able to read from InputStream , it can also be used to read from text File and it provide many utility methods to read line by line contents using nextLine() or nextInt() etc.

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.util.Scanner;

/**
 * @author Javin Paul
 * Java program to read file line by line using Scanner. Scanner is a rather new
 * utility class in Java and introduced in JDK 1.5 and preferred way to read input
 * from console.
 */

public class ScannerExample {
 

    public static void main(String args[]) throws FileNotFoundException  {
     
       //Scanner Example - read file line by line in Java using Scanner
        FileInputStream fis = new FileInputStream("C:/sample.txt");
        Scanner scanner = new Scanner(fis);
     
        //reading file line by line using Scanner in Java
        System.out.println("Reading file line by line in Java using Scanner");
     
        while(scanner.hasNextLine()){
            System.out.println(scanner.nextLine());
        }
     
        scanner.close();
    }  
     
}

Output:
Reading file line by line in Java using Scanner
first line in file
second line
third line
fourth line
fifth line
last line in file


That's all on How to read file line by line in Java. We have seen two simple examples of line by line reading using BufferedReader and Scanner. If you look code with Scanner looks more clean and give wide variety of data conversion method it supports, it just an handy choice for reading file line by line in Java.

Other Java IO tutorials from Javarevisited blog

1 comment :

Javin @Linkded List vs ArrayList said...

Thanks Sanaulla for JDK 7 way of reading all lines from File, I know there are lot of useful File API changes in Java7 which is worth looking, thanks for bringing this up.

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