Outdated: EncodingSampler.java - BMP Character Encoding

Unicode Tutorials - Herong's Tutorial Examples

∟Outdated: EncodingSampler.java - BMP Character Encoding

This section provides a tutorial example on how to use 4 different methods provided in Java to encode characters with a given encoding for BMP (Basic Multilingual Plane) characters only.

Java offers 4 methods to encode characters:

CharsetEncoder.encode()
Charset.encode()
String.getBytes()
OutputStreamWriter.write()

Here is a program that demonstrate how to encode BMP (Basic Multilingual Plane) characters with each of above 4 methods:

/**
 * EncodingSampler.java
 - Copyright (c) 2009, HerongYang.com, All Rights Reserved.
 */
import java.io.*;
import java.nio.*;
import java.nio.charset.*;
class EncodingSampler {
   static String dfltCharset = null;
   static char[] chars={0x0000, 0x003F, 0x0040, 0x007F, 0x0080, 0x00BF,
                        0x00C0, 0x00FF, 0x0100, 0x3FFF, 0x4000, 0x7FFF,
                        0x8000, 0xBFFF, 0xC000, 0xEFFF, 0xF000, 0xFFFF};
   static char hexDigit[] = {'0', '1', '2', '3', '4', '5', '6', '7',
                             '8', '9', 'A', 'B', 'C', 'D', 'E', 'F'};
   public static void main(String[] arg) {
      String charset = null;
      if (arg.length>0) charset = arg[0];
      OutputStreamWriter o = new OutputStreamWriter(
         new ByteArrayOutputStream());
      dfltCharset = o.getEncoding();
      if (charset==null) System.out.println("Default ("+dfltCharset
         +") encoding:");
      else System.out.println(charset+" encoding:");
      System.out.println("Char, String, Writer, Charset, Encoder");
      for (int i=0; i<chars.length; i++) {
         char c = chars[i];
         byte[] b1 = encodeByString(c,charset);
         byte[] b2 = encodeByWriter(c,charset);
         byte[] b3 = encodeByCharset(c,charset);
         byte[] b4 = encodeByEncoder(c,charset);
         System.out.print(charToHex(c)+",");
         printBytes(b1);
         System.out.print(",");
         printBytes(b2);
         System.out.print(",");
         printBytes(b3);
         System.out.print(",");
         printBytes(b4);
         System.out.println("");
      }
   }
   public static byte[] encodeByCharset(char c, String cs) {
      Charset cso = null;
      byte[] b = null;
      try {     
         if (cs==null) cso = Charset.forName(dfltCharset);
         else cso = Charset.forName(cs);
         ByteBuffer bb = cso.encode(String.valueOf(c));
         b = copyBytes(bb.array(),bb.limit());
      } catch (IllegalCharsetNameException e) {
         System.out.println(e.toString());
      }        
      return b;
   }
   public static byte[] encodeByEncoder(char c, String cs) {
      Charset cso = null;
      byte[] b = null;
      try {     
         if (cs==null) cso = Charset.forName(dfltCharset);
         else cso = Charset.forName(cs);
         CharsetEncoder e =  cso.newEncoder();
         e.reset();
         ByteBuffer bb = e.encode(CharBuffer.wrap(new char[] {c}));
         b = copyBytes(bb.array(),bb.limit());
      } catch (IllegalCharsetNameException e) {
         System.out.println(e.toString());
      } catch (CharacterCodingException e) {
         //System.out.println(e.toString());
         b = new byte[] {(byte)0x00};
      }        
      return b;
   }
   public static byte[] encodeByString(char c, String cs) {
      String s = String.valueOf(c);
      byte[] b = null;
      if (cs==null) {
         b = s.getBytes();
      } else {
         try {
            b = s.getBytes(cs);
         } catch (UnsupportedEncodingException e) {
            System.out.println(e.toString());
         }
      }
      return b;
   }
   public static byte[] encodeByWriter(char c, String cs) {
      byte[] b = null;
      ByteArrayOutputStream bs = new ByteArrayOutputStream();
      OutputStreamWriter o = null;
      if (cs==null) {
         o = new OutputStreamWriter(bs);
      } else {
         try {
            o = new OutputStreamWriter(bs, cs);
         } catch (UnsupportedEncodingException e) {
            System.out.println(e.toString());
         }
      }
      String s = String.valueOf(c);
      try {
         o.write(s);
         o.flush();
         b = bs.toByteArray();
         o.close();
      } catch (IOException e) {
         System.out.println(e.toString());
      }
      return b;
   }
   public static byte[] copyBytes(byte[] a, int l) {
      byte[] b = new byte[l];
      for (int i=0; i<Math.min(l,a.length); i++) b[i] = a[i];
      return b;
   }
   public static void printBytes(byte[] b) {
      for (int j=0; j<b.length; j++)
         System.out.print(" "+byteToHex(b[j]));
   }
   public static String byteToHex(byte b) {
      char[] a = { hexDigit[(b >> 4) & 0x0f], hexDigit[b & 0x0f] };
      return new String(a);
   }
   public static String charToHex(char c) {
      byte hi = (byte) (c >>> 8);
      byte lo = (byte) (c & 0xff);
      return byteToHex(hi) + byteToHex(lo);
   }
}

Note that:

If the same encoding is used, all 4 methods: encodeByString(), encodeByWriter(), encodeByCharset() and encodeByEncoder(), should return the exactly the same byte sequence.
getEncoding() is used on OuputStreamWriter class to get the name of the default encoding.
There is no way to know the name of the default encoding on String class.
There is no default instance of Charset and Encoder.

This tutorial example program only works for BMP characters. The newer version of this program presented earlier in this book can support both BMP and supplementary characters in range of 0x0000 - 0x10FFFF.