This section provides a tutorial example on how to encode characters with a given encoding using different encoding methods provided by JDK: Charset.encode(), CharsetEncoder.encode(), String.getBytes(), OutputStreamWriter.write().
There are 4 methods provided by JDK to encode characters:
Charset.encode()
CharsetEncoder.encode()
String.getBytes()
OutputStreamWriter.write()
Here is a program that demonstrate how to encode characters
using each of the above 4 methods:
/**
* EncodingSampler.java
* Copyright (c) 2002 by Dr. Herong Yang
*/
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, each of the encode method in the program should
return the exactly the same byte sequence.
getEncoding() is used on OuputStreamWriter class to get the name of the default
encoding.
There is now way to know the name of the default encoding on String class.
There is no default instance of Charset and Encoder.
In encodeByEncoder(), 0x00 is used as the output when the given character
can not be encoded by the encoder.
See sections below for testing results of different commonly used character encodings.
