In this example we will show how to open and read a file in Java. There are many ways to do this, but we will show two of them. For this example, we will read the contents of a text file named “test_file.txt”.
1. Read a file using BufferedReader
This is the most commonly-used method in order to read a file in Java. BufferedReader reads text from a character-input stream, buffering the characters for the more efficient reading of characters, arrays, and lines.
Create a java class named ReadFileBufferedReader.java with the following code:
ReadFileBufferedReader.java
01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 | package com.javacodegeeks.javaio.readfile;import java.io.BufferedReader;import java.io.FileReader;import java.io.IOException;public class ReadFileBufferedReader { private static String filepath = "/home/konstantina/test_file.txt"; public static void main(String[] args) { BufferedReader br; String curline; try { br = new BufferedReader(new FileReader(filepath)); while ((curline = br.readLine()) != null) { System.out.println(curline); } br.close(); } catch (IOException e) { e.printStackTrace(); } }} |
In this case, we used the class FileReader along with BufferedReader. FileReader needs the file’s name and path so as to open the file. The BufferedReader class provides a method named readLine() so as to read each line of the file. There is a while loop which is executed till readLine() reaches the end of the file.
If we run the above code, we will see the contents of the file “test_file.txt”.
- Output:
This is a test file.
Read file example
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examples.javacodegeeks.com
2. Read a file using FileInputStream
This is another way of reading a file. FileInputStream reads streams of raw bytes from a file. So, we need to convert those bytes to characters in order to display the contents of the file to the screen.
Create a java class named ReadFileInputStream.java with the following code:
ReadFileInputStream.java
01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 | package com.javacodegeeks.javaio.readfile;import java.io.File;import java.io.FileInputStream;import java.io.IOException;public class ReadFileInputStream { private static String filepath = "/home/konstantina/test_file.txt"; public static void main(String[] args) { try { File file = new File(filepath); FileInputStream in = new FileInputStream(file); System.out.println("Total bytes to read from file : " + in.available()); int i; StringBuffer buf = new StringBuffer(""); while ((i = in.read()) != -1) { // convert byte to char and append to StringBuffer buf.append((char) i); } in.close(); System.out.println("File contents :"); System.out.println(buf); } catch (IOException e) { e.printStackTrace(); } }} |
If we run the above code, we will have the following results:
- Output:
Total bytes to read from file : 78
File contents :
This is a test file.
Read file example
provided by
examples.javacodegeeks.com
3. Download the source code
You can download the source code of this example from here: ReadFileExample.zip
