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Wednesday, July 28, 2021

Difference between FileInputStream and FileReader in Java | InputStream vs Reader Example

Before going to explain specific difference between FileInputStream and FileReader in Java, I would like to state fundamental difference between an InputStream and a Reader in Java, and when to use InputStream and when to go for Reader. Actually, Both InputStream and Reader are abstractions to read data from source, which can be either file or socket, but main difference between them is, InputStream is used to read binary data, while Reader is used to read text data, precisely Unicode characters. So what is difference between binary and text data? well everything you read is essentially bytes, but to convert a byte to text, you need a character encoding scheme. Reader classes uses character encoding to decode bytes and return characters to caller.

Reader can either use default character encoding of platform on which your Java program is running or accept a Charset object or name of character encoding in String format e.g. "UTF-8". Despite being one of the simplest concept, lots of Java developers make mistakes of not specifying character encoding, while reading text files or text data from socket.

Remember, if you don't specify correct encoding, or your program is not using character encoding already present in protocol e.g. encoding specified in "Content-Type" for HTML files and encoding presents in header of XML files, you may not read all data correctly. Some characters which are not present in default encoding, may come up as ? or little square.

Once you know this fundamental difference between stream and reader, understanding difference between FileInputStream and FileReader is quite easy. Both allows you to read data from File, but FileInputStream is used to read binary data, while FileReader is used to read character data.

FileReader vs FileInputStream Java

Since FileReader extends InputStreamReader, it uses character encoding provided to this class, or else default character encoding of platform. Remember, InputStreamReader caches the character encoding and setting character encoding after creating object will not have any affect. Let's see an example of How to use FileInputStream and FileReader in Java. You can provide either a File object or a String, containing location of file to start reading character data from File. 

Difference between FileInputStream and FileReader in Java

This is similar to FileInputStream, which also provides similar constructors for reading from file source. Though its advised to use BufferedReader to read data from file.

import java.awt.Color;

 * Java Program to read data from file as stream of bytes and stream of 
 * characters.
 * It also highlight key difference between FileInputStream and FileReader that
 * FileReader is meant for reading streams of characters. 
 * For reading streams of raw bytes, consider using a FileInputStream.
 * @author Javin Paul
public class HowToReadFileInJava {
    public static void main(String args[]) {

        // Example 1 - Reading File's content using FileInputStream
        try (FileInputStream fis = new FileInputStream("data.txt")) {
            int data =;
            while (data != -1) {
                data =;
        } catch (IOException e) {
            System.out.println("Failed to read binary data from File");

        // Example 2 - Reading File data using FileReader in Java
        try (FileReader reader = new FileReader("data.txt")) {
            int character =;
            while (character != -1) {
                System.out.print((char) character);
                character =;
        } catch (IOException io) {
            System.out.println("Failed to read character data from File");

AWS-Amazon Web Service
GS-Goldman Sachs

Our first example is reading data from file byte by byte, so its bound to be very slow. read() method from FileInputStream is a blocking method, which reads a byte of data or blocks if no input is yet available. It either returns next byte of data, or -1 if the end of the file is reached. This means we read one byte in each iteration of loop and prints it as Hexadecimal String. By the way, there is options to convert InputStream into byte array as well. 

On the other hand, in example 2 are reading data character by character. read() method from InputStreamReader, which is inherited by FileReader reads a single character and returns the character read, or -1 if the end of the stream has been reached. This is why you see exactly same text as written in file output from our example 2.

That's all on difference between FileInputStream and FileReader in Java. Bottom line is use FileReader or BufferedReader to read stream of characters or text data from File and always specify character encoding. Use FileInputStream to read raw streams of bytes from file or socket in Java.


Pravin Jain said...

It is always good to use InputStreamReader rather than using the FileReader.

Dieter Adriaenssens said...

Thanks for writing all these posts on Java, they are very useful.

You mention specifying charset when using FileReader. Maybe you could add this to your coding example as well.

pratik singhal said...

If FileReader reads character by character, then why does the read function return a integer instead of a character ?

Arun said...

if I cast the FileInputStream data, to char I get the same result as FileReader, i.e. o/p will be in a readable format.

while(data != -1){
data =;

Can you please explain this.

Anonymous said...

nice explanation..Thanks

Rajkumar said...

What does happen when Reader reads binary file and write the same into another file using Writer? After all bytes should be read and write right? But if we use Reader/Writer on binary file, binary file is not working at all. What happens when Reader reads binary file?

Smartphones : Latest & New Smartphones List 2020 said...

The code you provided does indeed show how you can read binary data from a `FileInputStream` and cast it to a `char` to display it as text. However, there are still some key differences between using `FileReader` and casting `FileInputStream` to `char`:

1. **Character Encoding Handling:** When you use a `FileReader`, it automatically handles character encoding, making it suitable for text files in various character sets. If the file uses a specific encoding (e.g., UTF-8, UTF-16, etc.), FileReader ensures the correct conversion. In contrast, casting `FileInputStream` to `char` doesn't handle character encoding. If your file uses a different encoding, you may get incorrect results.

2. **Efficiency:** FileReader is optimized for reading character data and is more efficient for text files than `FileInputStream` since it performs character decoding. Casting `FileInputStream` to `char` may involve additional steps and might be less efficient.

3. **Readability:** Using `FileReader` is more straightforward and readable when your intention is to read text data. It's clear that you're dealing with character data. Casting `FileInputStream` to `char` can make your code less readable and harder to understand for someone else.

In summary, while you can cast `FileInputStream` data to `char` and get text output, it's recommended to use `FileReader` for reading character data from text files. It ensures proper character encoding handling, is more efficient, and results in cleaner and more readable code.

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