Java Read File to String

Learn to read file to string in Java. Given examples use Files.readAllBytes(), Files.lines() (to read line by line) and FileReader & BufferedReader to read text file to String.

1. Files.readString() – Java 11

With the new method readString() introduced in Java 11, it takes only a single line to read a file’s content in to String.

Example 1: Read a file to String in Java 11

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;

public class WriteToFile 
{
	public static void main(String[] args) throws IOException 
	{
		Path fileName = Path.of("demo.txt");
	    String content  = "hello world !!";
	    Files.writeString(fileName, content);
	    
	    String actual = Files.readString(fileName);
	    System.out.println(actual);
	}
}

2. Files.lines() – Java 8

lines() method read all lines from a file to stream and populates lazily as the stream is consumed. Bytes from the file are decoded into characters using the specified charset.

Example 2: Reading a file line by line in Java 8

import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.stream.Stream;

public class ReadFileToString 
{
	public static void main(String[] args) 
	{
		String filePath = "c:/temp/data.txt";

		System.out.println( readLineByLineJava8( filePath ) );
	}


	//Read file content into the string with - Files.lines(Path path, Charset cs)

	private static String readLineByLineJava8(String filePath) 
	{
		StringBuilder contentBuilder = new StringBuilder();

		try (Stream<String> stream = Files.lines( Paths.get(filePath), StandardCharsets.UTF_8)) 
		{
			stream.forEach(s -> contentBuilder.append(s).append("\n"));
		}
		catch (IOException e) 
		{
			e.printStackTrace();
		}

		return contentBuilder.toString();
	}
}

Output:

Welcome to howtodoinjava.com blog. 
Learn to grow.

3. Files.readAllBytes() – Read the entire File to String – Java 7

readAllBytes() method reads all the bytes from a file. The method ensures that the file is closed when all bytes have been read or an I/O error, or other runtime exception, is thrown.

After reading all bytes, we pass those bytes to String class constructor to create a string.

Example 3: Java program to read entire file to String

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Paths;

public class ReadFileToString 
{
	public static void main(String[] args) 
	{
		String filePath = "c:/temp/data.txt";

		System.out.println( readAllBytesJava7( filePath ) );
	}

	//Read file content into string with - Files.readAllBytes(Path path)

	private static String readAllBytesJava7(String filePath) 
	{
		String content = "";

		try 
		{
			content = new String ( Files.readAllBytes( Paths.get(filePath) ) );
		} 
		catch (IOException e) 
		{
			e.printStackTrace();
		}

		return content;
	}
}

Output:

Welcome to howtodoinjava.com blog. 
Learn to grow.

4. BufferedReader – Java 6 and below

If you are still not using Java 7 or later, then use BufferedReader class. It’s readLine() method reads the file one line at a time and return the content.

Example 4: Java program to read a file line by line

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

public class ReadFileToString 
{
	public static void main(String[] args) 
	{
		String filePath = "c:/temp/data.txt";

		System.out.println( usingBufferedReader( filePath ) );
	}

	//Read file content into the string with - using BufferedReader and FileReader
	//You can use this if you are still not using Java 8

	private static String usingBufferedReader(String filePath) 
	{
		StringBuilder contentBuilder = new StringBuilder();
		try (BufferedReader br = new BufferedReader(new FileReader(filePath))) 
		{

			String sCurrentLine;
			while ((sCurrentLine = br.readLine()) != null) 
			{
				contentBuilder.append(sCurrentLine).append("\n");
			}
		} 
		catch (IOException e) 
		{
			e.printStackTrace();
		}
		return contentBuilder.toString();
	}
}

Output:

Welcome to howtodoinjava.com blog. 
Learn to grow.

Use any of the above-given methods for reading a file into a string using Java.

Happy Learning !!