file.encoding. The only encodings that are guaranteed to
* be availalbe are "8859_1" (the Latin-1 character set) and "UTF8".
* Unforunately, Java does not provide a mechanism for listing the
* ecodings that are supported in a given implementation.
* * Here is a list of standard encoding names that may be available: *
*
* It is recommended that applications do not use
* InputStreamReader's
* directly. Rather, for efficiency purposes, an object of this class
* should be wrapped by a BufferedReader.
*
* Due to a deficiency the Java class library design, there is no standard
* way for an application to install its own byte-character encoding.
*
* @see BufferedReader
* @see InputStream
*
* @author Aaron M. Renn (arenn@urbanophile.com)
* @author Per Bothner (bothner@cygnus.com)
* @date April 22, 1998.
*/
public class InputStreamReader extends Reader
{
BufferedInputStream in;
// Buffer of chars read from in and converted but not consumed.
char[] work;
// Next available character (in work buffer) to read.
int wpos;
// Last available character (in work buffer) to read.
int wcount;
/*
* This is the byte-character decoder class that does the reading and
* translation of bytes from the underlying stream.
*/
BytesToUnicode converter;
/**
* This method initializes a new instance of InputStreamReader
* to read from the specified stream using the default encoding.
*
* @param in The InputStream to read from
*/
public InputStreamReader(InputStream in)
{
this(in, BytesToUnicode.getDefaultDecoder());
}
/**
* This method initializes a new instance of InputStreamReader
* to read from the specified stream using a caller supplied character
* encoding scheme. Note that due to a deficiency in the Java language
* design, there is no way to determine which encodings are supported.
*
* @param in The InputStream to read from
* @param encoding_name The name of the encoding scheme to use
*
* @exception UnsupportedEncodingException If the encoding scheme
* requested is not available.
*/
public InputStreamReader(InputStream in, String encoding_name)
throws UnsupportedEncodingException
{
this(in, BytesToUnicode.getDecoder(encoding_name));
}
/**
* Creates an InputStreamReader that uses a decoder of the given
* charset to decode the bytes in the InputStream into
* characters.
*/
public InputStreamReader(InputStream in, Charset charset)
{
this(in, new BytesToCharsetAdaptor(charset));
}
/**
* Creates an InputStreamReader that uses the given charset decoder
* to decode the bytes in the InputStream into characters.
*/
public InputStreamReader(InputStream in, CharsetDecoder decoder)
{
this(in, new BytesToCharsetAdaptor(decoder));
}
private InputStreamReader(InputStream in, BytesToUnicode decoder)
{
// FIXME: someone could pass in a BufferedInputStream whose buffer
// is smaller than the longest encoded character for this
// encoding. We will probably go into an infinite loop in this
// case. We probably ought to just have our own byte buffering
// here.
this.in = in instanceof BufferedInputStream
? (BufferedInputStream) in
: new BufferedInputStream(in);
/* Don't need to call super(in) here as long as the lock gets set. */
this.lock = in;
converter = decoder;
converter.setInput(this.in.buf, 0, 0);
}
/**
* This method closes this stream, as well as the underlying
* InputStream.
*
* @exception IOException If an error occurs
*/
public void close() throws IOException
{
synchronized (lock)
{
if (in != null)
in.close();
in = null;
work = null;
wpos = wcount = 0;
}
}
/**
* This method returns the name of the encoding that is currently in use
* by this object. If the stream has been closed, this method is allowed
* to return null.
*
* @return The current encoding name
*/
public String getEncoding()
{
return in != null ? converter.getName() : null;
}
/**
* This method checks to see if the stream is read to be read. It
* will return true if is, or false if it is not.
* If the stream is not ready to be read, it could (although is not required
* to) block on the next read attempt.
*
* @return true if the stream is ready to be read,
* false otherwise
*
* @exception IOException If an error occurs
*/
public boolean ready() throws IOException
{
synchronized (lock)
{
if (in == null)
throw new IOException("Stream closed");
if (wpos < wcount)
return true;
// According to the spec, an InputStreamReader is ready if its
// input buffer is not empty (above), or if bytes are
// available on the underlying byte stream.
return in.available () > 0;
}
}
/**
* This method reads up to length characters from the stream into
* the specified array starting at index offset into the
* array.
*
* @param buf The character array to recieve the data read
* @param offset The offset into the array to start storing characters
* @param length The requested number of characters to read.
*
* @return The actual number of characters read, or -1 if end of stream.
*
* @exception IOException If an error occurs
*/
public int read (char[] buf, int offset, int length) throws IOException
{
synchronized (lock)
{
if (in == null)
throw new IOException("Stream closed");
if (length == 0)
return 0;
int wavail = wcount - wpos;
if (wavail <= 0)
{
// Nothing waiting, so refill their buffer.
return refill(buf, offset, length);
}
if (length > wavail)
length = wavail;
System.arraycopy(work, wpos, buf, offset, length);
wpos += length;
return length;
}
}
/**
* This method reads a single character of data from the stream.
*
* @return The char read, as an int, or -1 if end of stream.
*
* @exception IOException If an error occurs
*/
public int read() throws IOException
{
synchronized (lock)
{
if (in == null)
throw new IOException("Stream closed");
int wavail = wcount - wpos;
if (wavail <= 0)
{
// Nothing waiting, so refill our internal buffer.
wpos = wcount = 0;
if (work == null)
work = new char[100];
int count = refill(work, 0, work.length);
if (count == -1)
return -1;
wcount += count;
}
return work[wpos++];
}
}
// Read more bytes and convert them into the specified buffer.
// Returns the number of converted characters or -1 on EOF.
private int refill(char[] buf, int offset, int length) throws IOException
{
for (;;)
{
// We have knowledge of the internals of BufferedInputStream
// here. Eww.
// BufferedInputStream.refill() can only be called when
// `pos>=count'.
boolean r = in.pos < in.count || in.refill ();
if (! r)
return -1;
converter.setInput(in.buf, in.pos, in.count);
int count = converter.read(buf, offset, length);
// We might have bytes but not have made any progress. In
// this case we try to refill. If refilling fails, we assume
// we have a malformed character at the end of the stream.
if (count == 0 && converter.inpos == in.pos)
{
in.mark(in.count);
if (! in.refill ())
throw new CharConversionException ();
in.reset();
}
else
{
in.skip(converter.inpos - in.pos);
if (count > 0)
return count;
}
}
}
}