How to read from file Java?

How to Read from a File in Java

Reading from a File in Java: A Comprehensive Guide

When working with files, Java provides several ways to read its contents. In this article, we’ll explore the various methods to read from a file in Java, including how to open, read, and close files.

Using java.io.FileInputStream

One of the most straightforward ways to read from a file in Java is by using the java.io.FileInputStream class. This class reads the contents of a file from a specified input stream and returns it as a byte array.

Example Code

import java.io.FileInputStream;

import java.io.IOException;



public class FileReadExample {

    public static void main(String[] args) {

        try (FileInputStream fileInputStream = new FileInputStream("example.txt")) {

            byte[] fileContent = fileInputStream.readAllBytes();

            System.out.println("File Content:");

            for (byte b : fileContent) {

                System.out.print(b + " ");

            }

        } catch (IOException e) {

            System.out.println("Error reading from file: " + e.getMessage());

        }

    }

}

Key Points:

• The FileInputStream class is used to read from a file.
• The readAllBytes() method reads the entire file into a byte array.
• The byte[] fileContent variable stores the file content.
• A try-with-resources statement is used to ensure the file input stream is closed properly, even if an exception occurs.

Using java.io.BufferedReader

Another way to read from a file in Java is by using the java.io.BufferedReader class. This class is more efficient than java.io.FileInputStream for reading large files.

Example Code

import java.io.BufferedReader;

import java.io.IOException;

import java.io.InputStreamReader;



public class FileReadExample {

    public static void main(String[] args) {

        try (BufferedReader reader = new BufferedReader(new InputStreamReader("example.txt"))) {

            String line;

            while ((line = reader.readLine())!= null) {

                System.out.println(line);

            }

        } catch (IOException e) {

            System.out.println("Error reading from file: " + e.getMessage());

        }

    }

}

Key Points:

• The BufferedReader class is used to read from a file line by line.
• The readLine() method reads the next line from the file and returns it as a string.
• The while loop continues until no more lines are available.
• A try-with-resources statement is used to ensure the file input stream is closed properly, even if an exception occurs.

Using java.io.FileReader

The java.io.FileReader class is a more advanced way to read from a file in Java, especially for large files. It is similar to java.io.BufferedReader, but it uses a single buffer to store all the characters in the file.

Example Code

import java.io.FileReader;

import java.io.IOException;



public class FileReadExample {

    public static void main(String[] args) {

        try (FileReader fileReader = new FileReader("example.txt")) {

            String line;

            while ((line = fileReader.readLine())!= null) {

                System.out.println(line);

            }

        } catch (IOException e) {

            System.out.println("Error reading from file: " + e.getMessage());

        }

    }

}

Key Points:

• The FileReader class is used to read from a file character by character.
• The readLine() method reads the next line from the file and returns it as a string.
• The while loop continues until no more lines are available.
• A try-with-resources statement is used to ensure the file input stream is closed properly, even if an exception occurs.

Conclusion

Reading from a file in Java is a common task that can be accomplished using various methods. The java.io.FileInputStream, java.io.BufferedReader, and java.io.FileReader classes are suitable for reading small to medium-sized files. However, for large files, the java.io.FileInputStream class or the java.io.BufferedReader class with a BufferedReader is recommended.

By choosing the right method for your specific use case, you can efficiently read from files in Java and improve the performance of your applications.

Additional Tips

• Always use a try-with-resources statement to ensure the file input stream is closed properly, even if an exception occurs.
• Use a BufferedReader or FileReader instead of FileInputStream for large files, as they are more efficient.
• Be mindful of file system permissions and access rights when reading from files.