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Java OutputStreamWriter Tutorial

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1- OutputStreamWriter

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.
  • TODO Link!
  • TODO Link!
  • TODO Link!
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

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

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
œ  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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