Java OutputStreamWriter Tutorial with Examples

OutputStreamWriter
UTF-16 OutputStreamWriter
UTF-8 OutputStreamWriter

1. OutputStreamWriter

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OutputStreamWriter is a subclass of Writer, it is a bridge that allows you to convert a byte stream into a character stream, or in other words it allows you to convert an OutputStream into a Writer.

Tip: To convert an "OutputStream" into a "Writer" you just need to concatenate these two words to form "OutputStreamWriter" and you will get the solution.

OutputStreamWriter constructors

OutputStreamWriter(OutputStream out)     

OutputStreamWriter(OutputStream out, String charsetName)     
 
OutputStreamWriter(OutputStream out, Charset cs)     

OutputStreamWriter(OutputStream out, CharsetEncoder enc)

Besides those methods inherited from the superclass, OutputStreamWriter has a few other methods of its own.

Method	Description
String getEncoding()	Returns the name of the character encoding being used by OutputStreamWriter.

2. UTF-16 OutputStreamWriter

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UTF-16 is a quite common encoding for Chinese or Japanese text. In this example we will analyze how to write a file using UTF-16 encoding.

And here is the content to write to the file:

JP日本-八洲

In this example we use UTF-16 OutputStreamWriter to write characters to a file, then use FileInputStream to read each byte of that file.

OutputStreamWriter_UTF16_Ex1.java

package org.o7planning.outputstreamwriter.ex;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.nio.charset.StandardCharsets;

public class OutputStreamWriter_UTF16_Ex1 {

    private static final String filePath = "/Volumes/Data/test/utf16-file-out.txt";
    
    public static void main(String[] args) throws IOException {
        System.out.println(" --- Write UTF-16 File --- ");
        write_UTF16_Character_Stream();
        
        System.out.println(" --- Read File as Binary Stream --- ");
        readAs_Binary_Stream();
    }

    private static void write_UTF16_Character_Stream() throws IOException   {
        File outFile = new File(filePath);
        outFile.getParentFile().mkdirs(); // Create parent folder.

        // Create OutputStream to write a file.
        OutputStream os = new FileOutputStream(outFile);

        // Create a OutputStreamWriter  
        OutputStreamWriter osw = new OutputStreamWriter(os, StandardCharsets.UTF_16);

        String s = "JP日本-八洲";
        osw.write(s);
        osw.close();
    }

    private static void readAs_Binary_Stream() throws IOException {
        InputStream is = new FileInputStream(filePath);

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

Output:

--- Write UTF-16 File ---
 --- Read File as Binary Stream ---
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

In Java, char data type is 2 bytes in size, and UTF-16 is used to encode the String type. The image below shows the characters on OutputStreamWriter:

We see from the analysis of the bytes on the newly created file: the first 2 bytes(254, 255) are used to mark that this is an UTF-16 encoded text. They are also known as BOM (Byte Order Mark), the next bytes are the same as the bytes on the OutputStreamWriter.

3. UTF-8 OutputStreamWriter

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UTF-8 is the world's most popular encoding. It can encode all writings in the world including Chinese characters and Japanese characters. Starting from Java5, UTF-8 is the default encoding for reading and writing files.

UTF-8 files created by Java have no BOM (Byte Order Mark) (The first bytes of the file to mark that this is an UTF-8 file).

OutputStreamWriter_UTF8_Ex1.java

package org.o7planning.outputstreamwriter.ex;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.nio.charset.StandardCharsets;

public class OutputStreamWriter_UTF8_Ex1 {

    private static final String filePath = "/Volumes/Data/test/utf8-file-out.txt";
    
    public static void main(String[] args) throws IOException {
        System.out.println(" --- Write UTF-8 File --- ");
        write_UTF8_Character_Stream();
        
        System.out.println(" --- Read File as Binary Stream --- ");
        readAs_Binary_Stream();
    }

    private static void write_UTF8_Character_Stream() throws IOException   {
        File outFile = new File(filePath);
        outFile.getParentFile().mkdirs(); // Create parent folder.

        // Create OutputStream to write a file.
        OutputStream os = new FileOutputStream(outFile);

        // Create a OutputStreamWriter  
        OutputStreamWriter osw = new OutputStreamWriter(os, StandardCharsets.UTF_8);

        String s = "JP日本-八洲";
        osw.write(s);
        osw.close();
    }

    private static void readAs_Binary_Stream() throws IOException {
        InputStream is = new FileInputStream(filePath);

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

Output:

--- Write UTF-8 File ---
 --- Read File as Binary Stream ---
J  74
P  80
æ  230
  151
¥  165
æ  230
  156
¬  172
-  45
å  229
  133
«  171
æ  230
´  180
²  178

In Java, char data type is 2 bytes in size, and UTF-16 is used to encode the String type. The image below shows the characters on OutputStreamWriter:

UTF-8 is encoded much more complex than UTF-16, it uses 1, 2, 3 or 4 bytes to store a character. Detailed analysis of the bytes on the newly created UTF-8 file clearly shows that.

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

For example, character "日" has code of 26085, in the range [2048,65535], UTF-8 needs 3 bytes to store it.

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Java OutputStreamWriter Tutorial with Examples

1. OutputStreamWriter

2. UTF-16 OutputStreamWriter

3. UTF-8 OutputStreamWriter

Java IO Tutorials

Java IO Tutorials

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