Invalid Characters in Encoding with JAVA

Imagine you’ve got some text you’ve been told is ASCII and you’ve
told java that it’s ASCII using:

Reader reader = new InputStreamReader(inputstream, "ASCII");

Imagine your surprise when it happily reads in non-ascii values, say
UTF-8 or ISO8859-1, and converts them to a random character.

import java.io.*;

public class Example1 {

   public static void main(String[] args) {
      try{
         FileInputStream is = new FileInputStream(args[0]);
         BufferedReader reader
            = new BufferedReader(new InputStreamReader(is, args[1]));
         String line;
         while ((line = reader.readLine()) != null) {
            System.out.println(line);
         }
      } catch (Exception e) {
         System.out.println(e);
      }
   }
}

beebo david% java Example1 utf8file.txt ascii
I��t��rn��ti��n��liz��ti��n
beebo david% java Example1 utf8file.txt utf8
Iñtërnâtiônàlizætiøn

So, I hear
you ask, how do you get Java to be strict about the conversion. Well, answer
is to lookup a Charset object, ask it for a CharsetDecoder object and
then set the onMalformedInput option to
CodingErrorAction.REPORT. The resulting code is:

import java.io.*;
import java.nio.charset.*;

public class Example2 {

   public static void main(String[] args) {
      try{
         FileInputStream is = new FileInputStream(args[0]);
         Charset charset = Charset.forName(args[1]);
         CharsetDecoder csd = charset.newDecoder();
         csd.onMalformedInput(CodingErrorAction.REPORT);
         BufferedReader reader
            = new BufferedReader(new InputStreamReader(is, csd));
         String line;
         while ((line = reader.readLine()) != null) {
            System.out.println(line);
         }
      } catch (Exception e) {
         System.out.println(e);
      }
   }
}

This time when we run it,we get:

beebo david% java Example2 utf8file.txt ascii
java.nio.charset.MalformedInputException: Input length = 1
beebo david% java Example2 utf8file.txt utf8
Iñtërnâtiônàlizætiøn

On a slightly related note, if anyone knows how to get Java to decode
UTF32, VISCII, TCVN-5712, KOI8-U or KOI8-T, I would love to know.

Update: (2007-01-26) Java 6 has support for UTF32
and KOI8-U.