|
/*
* Copyright (c) 2004 David Flanagan. All rights reserved.
* This code is from the book Java Examples in a Nutshell, 3nd Edition.
* It is provided AS-IS, WITHOUT ANY WARRANTY either expressed or implied.
* You may study, use, and modify it for any non-commercial purpose,
* including teaching and use in open-source projects.
* You may distribute it non-commercially as long as you retain this notice.
* For a commercial use license, or to purchase the book,
* please visit http://www.davidflanagan.com/javaexamples3.
*/
//package je3.nio;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.io.Writer;
import java.nio.ByteBuffer;
import java.nio.CharBuffer;
import java.nio.channels.FileChannel;
import java.nio.channels.ReadableByteChannel;
import java.nio.charset.Charset;
import java.nio.charset.CharsetDecoder;
import java.nio.charset.CodingErrorAction;
public class ChannelToWriter {
/**
* Read bytes from the specified channel, decode them using the specified
* Charset, and write the resulting characters to the specified writer
*/
public static void copy(ReadableByteChannel channel, Writer writer, Charset charset)
throws IOException {
// Get and configure the CharsetDecoder we'll use
CharsetDecoder decoder = charset.newDecoder();
decoder.onMalformedInput(CodingErrorAction.IGNORE);
decoder.onUnmappableCharacter(CodingErrorAction.IGNORE);
// Get the buffers we'll use, and the backing array for the CharBuffer.
ByteBuffer bytes = ByteBuffer.allocateDirect(2 * 1024);
CharBuffer chars = CharBuffer.allocate(2 * 1024);
char[] array = chars.array();
while (channel.read(bytes) != -1) { // Read from channel until EOF
bytes.flip(); // Switch to drain mode for decoding
// Decode the byte buffer into the char buffer.
// Pass false to indicate that we're not done.
decoder.decode(bytes, chars, false);
// Put the char buffer into drain mode, and write its contents
// to the Writer, reading them from the backing array.
chars.flip();
writer.write(array, chars.position(), chars.remaining());
// Discard all bytes we decoded, and put the byte buffer back into
// fill mode. Since all characters were output, clear that buffer.
bytes.compact(); // Discard decoded bytes
chars.clear(); // Clear the character buffer
}
// At this point there may still be some bytes in the buffer to decode
// So put the buffer into drain mode call decode() a final time, and
// finish with a flush().
bytes.flip();
decoder.decode(bytes, chars, true); // True means final call
decoder.flush(chars); // Flush any buffered chars
// Write these final chars (if any) to the writer.
chars.flip();
writer.write(array, chars.position(), chars.remaining());
writer.flush();
}
// A test method: copy a UTF-8 file to standard out
public static void main(String[] args) throws IOException {
FileChannel c = new FileInputStream(args[0]).getChannel();
OutputStreamWriter w = new OutputStreamWriter(System.out);
Charset utf8 = Charset.forName("UTF-8");
ChannelToWriter.copy(c, w, utf8);
c.close();
w.close();
}
}
|