Base64Encoder源码

import java.io.*;

/*******************************************************************************
 * A class to encode Base64 streams and strings. See RFC 1521 section 5.2 for
 * details of the Base64 algorithm.
 * <p>
 * This class can be used for encoding strings: <blockquote>
 * 
 * <pre>
 * String unencoded = &quot;webmaster:try2gueSS&quot;;
 * String encoded = Base64Encoder.encode(unencoded);
 * </pre>
 * 
 * </blockquote> or for encoding streams: <blockquote>
 * 
 * <pre>
 * OutputStream out = new Base64Encoder(System.out);
 * </pre>
 * 
 * </blockquote>
 * 
 * @author <b>Jason Hunter</b>, Copyright &#169; 2000
 * @version 1.2, 2002/11/01, added encode(byte[]) method to better handle binary
 *          data (thanks to Sean Graham)
 * @version 1.1, 2000/11/17, fixed bug with sign bit for char values
 * @version 1.0, 2000/06/11
 */
public class Base64Encoder extends FilterOutputStream {

	private static final char[] chars = { 'A', 'B', 'C', 'D', 'E', 'F', 'G',
			'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T',
			'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', 'g',
			'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't',
			'u', 'v', 'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6',
			'7', '8', '9', '+', '/' };

	private int charCount;
	private int carryOver;

	/***************************************************************************
	 * Constructs a new Base64 encoder that writes output to the given
	 * OutputStream.
	 * 
	 * @param out
	 *            the output stream
	 */
	public Base64Encoder(OutputStream out) {
		super(out);
	}

	/***************************************************************************
	 * Writes the given byte to the output stream in an encoded form.
	 * 
	 * @exception IOException
	 *                if an I/O error occurs
	 */
	public void write(int b) throws IOException {
		// Take 24-bits from three octets, translate into four encoded chars
		// Break lines at 76 chars
		// If necessary, pad with 0 bits on the right at the end
		// Use = signs as padding at the end to ensure encodedLength % 4 == 0

		// Remove the sign bit,
		// thanks to Christian Schweingruber <[e-mail]>
		if (b < 0) {
			b += 256;
		}

		// First byte use first six bits, save last two bits
		if (charCount % 3 == 0) {
			int lookup = b >> 2;
			carryOver = b & 3; // last two bits
			out.write(chars[lookup]);
		}
		// Second byte use previous two bits and first four new bits,
		// save last four bits
		else if (charCount % 3 == 1) {
			int lookup = ((carryOver << 4) + (b >> 4)) & 63;
			carryOver = b & 15; // last four bits
			out.write(chars[lookup]);
		}
		// Third byte use previous four bits and first two new bits,
		// then use last six new bits
		else if (charCount % 3 == 2) {
			int lookup = ((carryOver << 2) + (b >> 6)) & 63;
			out.write(chars[lookup]);
			lookup = b & 63; // last six bits
			out.write(chars[lookup]);
			carryOver = 0;
		}
		charCount++;

		// Add newline every 76 output chars (that's 57 input chars)
		if (charCount % 57 == 0) {
			out.write('\n');
		}
	}

	/***************************************************************************
	 * Writes the given byte array to the output stream in an encoded form.
	 * 
	 * @param buf
	 *            the data to be written
	 * @param off
	 *            the start offset of the data
	 * @param len
	 *            the length of the data
	 * @exception IOException
	 *                if an I/O error occurs
	 */
	public void write(byte[] buf, int off, int len) throws IOException {
		// This could of course be optimized
		for (int i = 0; i < len; i++) {
			write(buf[off + i]);
		}
	}

	/***************************************************************************
	 * Closes the stream, this MUST be called to ensure proper padding is
	 * written to the end of the output stream.
	 * 
	 * @exception IOException
	 *                if an I/O error occurs
	 */
	public void close() throws IOException {
		// Handle leftover bytes
		if (charCount % 3 == 1) { // one leftover
			int lookup = (carryOver << 4) & 63;
			out.write(chars[lookup]);
			out.write('=');
			out.write('=');
		} else if (charCount % 3 == 2) { // two leftovers
			int lookup = (carryOver << 2) & 63;
			out.write(chars[lookup]);
			out.write('=');
		}
		super.close();
	}

	/***************************************************************************
	 * Returns the encoded form of the given unencoded string. The encoder uses
	 * the ISO-8859-1 (Latin-1) encoding to convert the string to bytes. For
	 * greater control over the encoding, encode the string to bytes yourself
	 * and use encode(byte[]).
	 * 
	 * @param unencoded
	 *            the string to encode
	 * @return the encoded form of the unencoded string
	 */
	public static String encode(String unencoded) {
		byte[] bytes = null;
		try {
			bytes = unencoded.getBytes("8859_1");
		} catch (UnsupportedEncodingException ignored) {
		}
		return encode(bytes);
	}

	/***************************************************************************
	 * Returns the encoded form of the given unencoded string.
	 * 
	 * @param bytes
	 *            the bytes to encode
	 * @return the encoded form of the unencoded string
	 */
	public static String encode(byte[] bytes) {
		ByteArrayOutputStream out = new ByteArrayOutputStream((int) (bytes.length * 1.37));
		Base64Encoder encodedOut = new Base64Encoder(out);

		try {
			encodedOut.write(bytes);
			encodedOut.close();

			return out.toString("8859_1");
		} catch (IOException ignored) {
			return null;
		}
	}

	public static void main(String[] args) throws Exception {
		if (args.length != 1) {
			System.err.println("Usage: java com.oreilly.servlet.Base64Encoder fileToEncode");
			return;
		}

		Base64Encoder encoder = null;
		BufferedInputStream in = null;
		try {
			encoder = new Base64Encoder(System.out);
			in = new BufferedInputStream(new FileInputStream(args[0]));

			byte[] buf = new byte[4 * 1024]; // 4K buffer
			int bytesRead;
			while ((bytesRead = in.read(buf)) != -1) {
				encoder.write(buf, 0, bytesRead);
			}
		} finally {
			if (in != null)
				in.close();
			if (encoder != null)
				encoder.close();
		}
	}
}

 

评论

2 楼 guoranaccp 2016-04-06  

太帅了

1 楼 lyfi 2012-08-02