Saturday, July 10, 2021

Reading File in Java Using BufferedReader

Java NIO and Java 8 provide many new ways to read a file in Java, like using Scanner to read file in Java or Reading File in Java 8 but reading a file in Java using BufferedReader still remains one of the most used way.

The advantage of using buffered I/O streams for reading/writing file in Java is that each request doesn't trigger disk access or network activity.

When buffered input stream is used to read a file in Java data is read from a memory area known as a buffer; the native input API is called only when the buffer is empty.

In case of buffered output stream data is written to a buffer, and the native output API is called only when the buffer is full.

Java Program to read a file using BufferedReader

In the program readLine() method of the BufferedReader class is used to read the file. This method reads data from file one line at a time. A line is considered to be terminated by any one of a line feed ('\n'), a carriage return ('\r'), or a carriage return followed immediately by a linefeed.

import java.io.BufferedReader;
import java.io.IOException;

public class FileRead {

 public static void main(String[] args) {
  BufferedReader br = null;
  try{
   String strLine;
   // Instance of FileReader wrapped in a BufferedReader
   br = new BufferedReader(new java.io.FileReader("F:\\abc.txt"));
   
   // Read lines from the file, returns null when end of stream 
   // is reached
   while((strLine = br.readLine()) != null){
    System.out.println("Line is - " + strLine);
   }
  }catch(IOException ioExp){
   System.out.println("Error while reading file " + ioExp.getMessage());
  }finally {
   try {
    // Close the stream
    if(br != null){
     br.close();
    }
   } catch (IOException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
   }
  }
 }
}

Output

Line is - This is a test file.
Line is - BuferedReader is used to read this file.

Using BufferedReader With try-with-resources

If you are using Java 7 or above you can use try-with-resources for automatic resource management while reading file using BufferedReader. In that case you don't have to explicitly close the resources using try-catch Block. Resources (in this case stream) will be closed automatically after the program is finished with it.

Resource will be declared with the try statement itself when using try-with-resources.

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

public class FileRead {

 public static void main(String[] args) {
  
  try(BufferedReader br  = new BufferedReader(new FileReader("F://abc.txt"))){
   String strLine;
   // Read lines from the file, returns null when end of stream 
   // is reached
   while((strLine = br.readLine()) != null){
    System.out.println("Line is - " + strLine);
   }
  }catch(IOException ioExp){
   System.out.println("Error while reading file " + ioExp.getMessage());
  }
 }
}

That's all for this topic Reading File in Java Using BufferedReader. If you have any doubt or any suggestions to make please drop a comment. Thanks!

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