How to feed CharsetDecoder (nio Buffer problems)

Question

Hi there,
I have no idea how to feed bytes into a CharsetDecoder in presence of multibyte sequences. I am trying something along the following lines.
If a multibyte char is being fed (I tried c3 +a4 = �), the first call to decode returns UNDERFLOW with bout.hasRemaining() == false as expected, but the 2nd call yields MALFORMED[1], no matter what rewind/flip method I throw in at // *1*
I probably "misgrok" something here with Buffers. Can someone point out what?
  ByteBuffer bin = ByteBuffer.allocate(3);
  CharBuffer bout = CharBuffer.allocate(1);
  Charset cs = Charset.forName("UTF-8");
  CharsetDecoder dec = cs.newDecoder();
  public void addChar( int ch ) throws Exception {
    bin.put((byte)ch);
    bin.flip();
    CoderResult res = dec.decode(bin,bout,false);
    bout.flip();
    if( bout.hasRemaining() ) {
      emit( bout.get() );
      bin.clear();
      bout.clear();
    } else {
      bout.flip();
      //bin.flip(); // *1*
  }

Answer 1

But the result character is already in the output buffer?! Applying my program code to ISO-8859-1, all character yield underflows and the data is successfully being converted.
Here is a complete test program:
import java.io.*;
import java.nio.*;
import java.nio.charset.*;
public class DecoderTest {
  public static void main( String[] args ) throws Exception {
    dec = Charset.forName(args[1]).newDecoder();
    new DecoderTest().run(args[0]);
  ByteBuffer bin = ByteBuffer.allocate(3);
  CharBuffer bout = CharBuffer.allocate(1);
  static CharsetDecoder dec;
  public void run( String filename ) throws Exception {
    FileInputStream in = new FileInputStream(filename);
    int ch;
    while( (ch=in.read())>=0 ) {
      addChar(ch);
  public void addChar( int ch ) throws Exception {
    System.out.print( "byte "+(0xff & ch) + " => " );
    bin.put((byte)ch);
    bin.flip();
    CoderResult res = dec.decode(bin,bout,false);
    System.out.print( res + " => " );
    if( res.isError() ) {
      bin.clear();
      bout.clear();
    } else {
      bout.flip();
      if( bout.hasRemaining() ) {
        System.err.print( "char " + ((int)bout.get()) );
        bin.clear();
        bout.clear();
      } else {
        bout.flip();
       // what to do with bin here???
    System.err.println();
}Passing in iso latin code lopoks like this:
byte 98 => UNDERFLOW => char 98
byte 228 => UNDERFLOW => char 228
byte 104 => UNDERFLOW => char 104
byte 32 => UNDERFLOW => char 32
byte 98 => UNDERFLOW => char 98
byte 228 => UNDERFLOW => char 228
byte 104 => UNDERFLOW => char 104
byte 10 => UNDERFLOW => char 10Utf-code looks like this:
byte 98 => UNDERFLOW => char 98
byte 195 => UNDERFLOW =>
byte 164 => MALFORMED[1] =>
byte 104 => UNDERFLOW => char 104
byte 32 => UNDERFLOW => char 32
byte 98 => UNDERFLOW => char 98
byte 195 => UNDERFLOW =>
byte 164 => MALFORMED[1] =>
byte 104 => UNDERFLOW => char 104
byte 10 => UNDERFLOW => char 10Message was edited by:
HolgerK