Java Read File

In Java, a file can be read in many different ways. In this tutorial, we will learn some good ways to read a file in Java.

Table of Contents

1. Read file with BufferedReader
2. Read file with java.nio.file.Files
3. Read file with Apache Commons IOUtils
4. Read file with Guava

1. Read file with BufferedReader

A most simple, commonly used and efficient method used for long time with BufferedReader. It reads text from a character-input stream, buffering characters so as to provide for the efficient reading of characters, arrays, and lines.

Example 1: Read a file line by line using BufferedReader

public void readFile(String fileName) 
{
	try (BufferedReader br = new BufferedReader(new FileReader("C:\\testing.txt")))
	{
		String sCurrentLine;
		while ((sCurrentLine = br.readLine()) != null) 
		{
			System.out.println(sCurrentLine);
		}
	} 
	//Stream is closed automatically
	catch (IOException e) 
	{
		e.printStackTrace();
	} 	
}

2. Read a file with Java NIO Files

The Files class is part of Java NIO API, and make the code easy to read. This class consists exclusively of static methods that operate on files, directories, or other types of files.

Example 2: Read a file line by line with Java NIO

public void readFileWithNIO (String fileName) 
{
	Path path = Paths.get( fileName );
	
    try ( Stream<String> lines = Files.lines(path) )
    {
        lines.forEach(s -> System.out.println(s));
    } 
    catch (IOException ex) {
    	ex.printStackTrace();
    }
}

Please notice the use of lines.forEachOrdered(). If you will use lines.forEach() then you may not get the lines in correct sequence due to asynchronous nature of API.

3. Read a file with FileUtils

Apache Commons IO library does an excellent job by providing short and easy to use methods for almost all of IO related jobs in Java. The FileUtils class is a utility class for general file reading and manipulations.

Example 2: Read a file with Apache Commons IO

public void readFileWithApacheCommons (String fileName) 
{
    try 
    {
    	File file = new File( fileName );
    	List lines = FileUtils.readLines(file, "UTF-8");
    	for (String line : lines) {
			System.out.println( line );
		}
    } 
    catch (IOException ex) {
    	ex.printStackTrace();
    }
}

4. Read file with Guava

Guava has similar approach as Apache Commons IO. Only the class name is different – Use Files in place of FileUtils.

public void readFileWithGuava (String fileName) 
{
    try 
    {
    	File file = new File( fileName );
    	List lines = Files.readLines(file, "UTF-8");
    	for (String line : lines) {
			System.out.println( line );
		}
    } 
    catch (IOException ex) {
    	ex.printStackTrace();
    }
}

Let me know if you think any other way of reading a file in Java more efficiently.

Happy Learning !!