UnicodeReader.java

/* ==================================================================
 * UnicodeReader.java - Oct 2, 2011 9:55:32 PM
 * 
 * Copyright 2011 SolarNetwork.net Dev Team
 * 
 * This program is free software; you can redistribute it and/or 
 * modify it under the terms of the GNU General Public License as 
 * published by the Free Software Foundation; either version 2 of 
 * the License, or (at your option) any later version.
 * 
 * This program is distributed in the hope that it will be useful, 
 * but WITHOUT ANY WARRANTY; without even the implied warranty of 
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 
 * General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License 
 * along with this program; if not, write to the Free Software 
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 
 * 02111-1307 USA
 * ==================================================================
 */

package net.solarnetwork.support;

import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.PushbackInputStream;
import java.io.Reader;

/**
 * Reader that can detect a Unicode BOM.
 * 
 * Adapted from Google Data API.
 * 
 * @author matt
 * @version 1.0
 * @since 1.35
 */
public class UnicodeReader extends Reader {

	private static final int BOM_SIZE = 4;
	private final InputStreamReader reader;

	/**
	 * Construct UnicodeReader.
	 * 
	 * @param in
	 *        Input stream.
	 * @param defaultEncoding
	 *        Default encoding to be used if BOM is not found, or
	 *        <code>null</code> to use system default encoding.
	 * @throws IOException
	 *         If an I/O error occurs.
	 */
	public UnicodeReader(InputStream in, String defaultEncoding) throws IOException {
		byte bom[] = new byte[BOM_SIZE];
		String encoding;
		int unread;
		PushbackInputStream pushbackStream = new PushbackInputStream(in, BOM_SIZE);
		int n = pushbackStream.read(bom, 0, bom.length);

		// Read ahead four bytes and check for BOM marks.
		if ( (bom[0] == (byte) 0xEF) && (bom[1] == (byte) 0xBB) && (bom[2] == (byte) 0xBF) ) {
			encoding = "UTF-8";
			unread = n - 3;
		} else if ( (bom[0] == (byte) 0xFE) && (bom[1] == (byte) 0xFF) ) {
			encoding = "UTF-16BE";
			unread = n - 2;
		} else if ( (bom[0] == (byte) 0xFF) && (bom[1] == (byte) 0xFE) ) {
			encoding = "UTF-16LE";
			unread = n - 2;
		} else if ( (bom[0] == (byte) 0x00) && (bom[1] == (byte) 0x00) && (bom[2] == (byte) 0xFE)
				&& (bom[3] == (byte) 0xFF) ) {
			encoding = "UTF-32BE";
			unread = n - 4;
		} else if ( (bom[0] == (byte) 0xFF) && (bom[1] == (byte) 0xFE) && (bom[2] == (byte) 0x00)
				&& (bom[3] == (byte) 0x00) ) {
			encoding = "UTF-32LE";
			unread = n - 4;
		} else {
			encoding = defaultEncoding;
			unread = n;
		}

		// Unread bytes if necessary and skip BOM marks.
		if ( unread > 0 ) {
			pushbackStream.unread(bom, (n - unread), unread);
		} else if ( unread < -1 ) {
			pushbackStream.unread(bom, 0, 0);
		}

		// Use given encoding.
		if ( encoding == null ) {
			reader = new InputStreamReader(pushbackStream);
		} else {
			reader = new InputStreamReader(pushbackStream, encoding);
		}
	}

	public String getEncoding() {
		return reader.getEncoding();
	}

	@Override
	public int read(char[] cbuf, int off, int len) throws IOException {
		return reader.read(cbuf, off, len);
	}

	@Override
	public void close() throws IOException {
		reader.close();
	}

}