Class Base64

src/main/java/org/apache/commons/codec/binary/Base64.java:54–808

Provides Base64 encoding and decoding as defined by RFC 2045 . This class implements section 6.8. Base64 Content-Transfer-Encoding from RFC 2045 Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message

 * @since 1.0
 */
public class Base64 extends BaseNCodec {

    /**
     * BASE32 characters are 6 bits in length.
     * They are formed by taking a block of 3 octets to form a 24-bit string,
     * which is converted into 4 BASE64 characters.
     */
    private static final int BITS_PER_ENCODED_BYTE = 6;
    private static final int BYTES_PER_UNENCODED_BLOCK = 3;
    private static final int BYTES_PER_ENCODED_BLOCK = 4;

    /**
     * Chunk separator per RFC 2045 section 2.1.
     *
     * <p>
     * N.B. The next major release may break compatibility and make this field private.
     * </p>
     *
     * @see <a href="http://www.ietf.org/rfc/rfc2045.txt">RFC 2045 section 2.1</a>
     */
    static final byte[] CHUNK_SEPARATOR = {'\r', '\n'};

    /**
     * This array is a lookup table that translates 6-bit positive integer index values into their "Base64 Alphabet"
     * equivalents as specified in Table 1 of RFC 2045.
     *
     * Thanks to "commons" project in ws.apache.org for this code.
     * http://svn.apache.org/repos/asf/webservices/commons/trunk/modules/util/
     */
    private static final byte[] STANDARD_ENCODE_TABLE = {
            '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', '+', '/'
    };

    /**
     * This is a copy of the STANDARD_ENCODE_TABLE above, but with + and /
     * changed to - and _ to make the encoded Base64 results more URL-SAFE.
     * This table is only used when the Base64's mode is set to URL-SAFE.
     */
    private static final byte[] URL_SAFE_ENCODE_TABLE = {
            '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', '-', '_'
    };

    /**
     * This array is a lookup table that translates Unicode characters drawn from the "Base64 Alphabet" (as specified
     * in Table 1 of RFC 2045) into their 6-bit positive integer equivalents. Characters that are not in the Base64
     * alphabet but fall within the bounds of the array are translated to -1.
     *
     * Note: '+' and '-' both decode to 62. '/' and '_' both decode to 63. This means decoder seamlessly handles both
     * URL_SAFE and STANDARD base64. (The encoder, on the other hand, needs to know ahead of time what to emit).
     *