Java InputStreamReader Tutorial with Examples

InputStreamReader
UTF-16 InputStreamReader
UTF-8 InputStreamReader

1. InputStreamReader

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InputStreamReader is a subclass of Reader, which is a bridge that allows you to convert a byte stream into a character stream. In other words, it allows you to convert an InputStream into a Reader.

Tip: To convert an "InputStream" into a "Reader", you just need to concatenate these two words to form the word "InputStreamReader" and you will get the solution of problem.

InputStreamReader constructors

InputStreamReader(InputStream in)    

InputStreamReader(InputStream in, String charsetName)    

InputStreamReader(InputStream in, Charset cs)    

InputStreamReader(InputStream in, CharsetDecoder dec)

2. UTF-16 InputStreamReader

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UTF-16 is a fairly common encoding for Chinese or Japanese text. In this example, we will analyze how InputStreamReader reads UTF-16 texts.

First, take a look at the below Japanese text file, which is encoded in UTF-16.

https://s3.o7planning.com/txt/utf16-file-with-bom.txt

utf16-file-with-bom.txt

JP日本-八洲

Full code of example:

InputStreamReader_UTF16_Ex1.java

package org.o7planning.inputstreamreader.ex;

import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.MalformedURLException;
import java.net.URL;

public class InputStreamReader_UTF16_Ex1 {

    // A file in UTF-16.
    private static final String fileURL = "https://s3.o7planning.com/txt/utf16-file-with-bom.txt";
    
    public static void main(String[] args) throws MalformedURLException, IOException {
        System.out.println(" --- Characters in Character Stream (InputStreamReader) ---");
        readAs_UTF16_Character_Stream();

        System.out.println();
        System.out.println(" --- Bytes in UTF-16 file ---");
        readAs_Binary_Stream();
    }

    private static void readAs_UTF16_Character_Stream() throws MalformedURLException, IOException {

        InputStream is = new URL(fileURL).openStream();
        InputStreamReader isr = new InputStreamReader(is, "UTF-16");

        int charCode;
        while ((charCode = isr.read()) != -1) { // Read each character.
            System.out.println((char) charCode + "  " + charCode);
        }
        isr.close();
    }

    private static void readAs_Binary_Stream() throws MalformedURLException, IOException {

        InputStream is = new URL(fileURL).openStream();

        int byteValue;
        while ((byteValue = is.read()) != -1) { // Read each byte.
            System.out.println((char) byteValue + "  " + byteValue);
        }
        is.close();
    }
}

Output:

--- Characters in Character Stream (InputStreamReader) ---
J  74
P  80
日  26085
本  26412
-  45
八  20843
洲  27954

 --- Bytes in UTF-16 file ---
þ  254
ÿ  255
  0
J  74
  0
P  80
e  101
å  229
g  103
,  44
  0
-  45
Q  81
k  107
m  109
2  50

Create an InputStreamReader object with UTF-16 encoding and wrap an InputStream object:

String url = "https://s3.o7planning.com/txt/utf16-file-with-bom.txt";

InputStream is = new URL(url).openStream();
InputStreamReader isr = new InputStreamReader(is, "UTF-16");

Image below shows bytes in UTF-16 file. The first two bytes (254,255) are used to mark that it the beginning of a UTF-16 text.

InputStreamReader UTF-16 reads the first 2 bytes to determine encoding of the text, and knows that it is working with a UTF-16 text. It joins 2 consecutive bytes to form one character...

3. UTF-8 InputStreamReader

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UTF-8 is the world's most popular encoding, which can encode all writing in the world including Chinese characters and Japanese characters. Now we will analyze how InputStreamReader reads UTF-8 texts.

First, take a look at the below Japanese text file, which is encoded in UTF-8:

https://s3.o7planning.com/txt/utf8-file-without-bom.txt

utf8-file-without-bom.txt

JP日本-八洲

Full code of example:

InputStreamReader_UTF8_Ex1.java

package org.o7planning.inputstreamreader.ex;

import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.MalformedURLException;
import java.net.URL;

public class InputStreamReader_UTF8_Ex1 {

    // A file with UTF-8 encoding (And without BOM (Byte Order Mark)).
    private static final String fileURL = "https://s3.o7planning.com/txt/utf8-file-without-bom.txt";
    
    public static void main(String[] args) throws MalformedURLException, IOException {
        System.out.println(" --- Characters in Character Stream (InputStreamReader) ---");
        readAs_UTF8_Character_Stream();

        System.out.println();
        System.out.println(" --- Bytes in UTF-8 file ---");
        readAs_Binary_Stream();
    }

    private static void readAs_UTF8_Character_Stream() throws MalformedURLException, IOException {
        
        InputStream is = new URL(fileURL).openStream();
        InputStreamReader isr = new InputStreamReader(is, "UTF-8");

        int charCode;
        while ((charCode = isr.read()) != -1) { // Read each character.
            System.out.println((char) charCode + "  " + charCode);
        }
        isr.close();
    }

    private static void readAs_Binary_Stream() throws MalformedURLException, IOException {

        InputStream is = new URL(fileURL).openStream();

        int byteValue;
        while ((byteValue = is.read()) != -1) { // Read each byte.
            System.out.println((char) byteValue + "  " + byteValue);
        }
        is.close();
    }
}

Output:

--- Characters in Character Stream (InputStreamReader) ---
J  74
P  80
日  26085
本  26412
-  45
八  20843
洲  27954

 --- Bytes in UTF-8 file ---
J  74
P  80
æ  230
  151
¥  165
æ  230
  156
¬  172
-  45
å  229
  133
«  171
æ  230
´  180
²  178

Create an InputStreamReader object with UTF-8 encoding and wrap an InputStream object:

String url = "https://s3.o7planning.com/txt/utf8-file-without-bom.txt";

InputStream is = new URL(url).openStream();
InputStreamReader isr = new InputStreamReader(is, "UTF-8");

Image below shows bytes in UFT-8 file:

UTF-8 encoding is much more complicated than UTF-16. It takes 1, 2, 3 or 4 bytes to store a character. This depends on the character's code.

Number of bytes	From		To		Byte 1	Byte 2	Byte 3	Byte 4
1	U+0000	0	U+007F	127	0xxxxxxx
2	U+0080	128	U+07FF	2047	110xxxxx	10xxxxxx
3	U+0800	2048	U+FFFF	65535	1110xxxx	10xxxxxx	10xxxxxx
4	U+10000	65536	U+10FFFF	1114111	11110xxx	10xxxxxx	10xxxxxx	10xxxxxx

Image below is an example showing how UTF-8 InputStreamReader turns 3 bytes of UTF-8 into a 2-bytes Java character:

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Java InputStreamReader Tutorial with Examples

1. InputStreamReader

2. UTF-16 InputStreamReader

3. UTF-8 InputStreamReader

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