字符编码 Base64Coder

Base64Coder是一个常用的编码类，经常会用于各种网络数据传输时用来加密和解密用，用来确保数据的唯一性及用于Base64编码用在HTTP环境下传递较长的标识信息。因此这个编码是相当有用的，下面将和大家分享一下这个功能类：

核心代码：

public class Base64Coder {

    // The line separator string of the operating system.
    private static final String systemLineSeparator = System.getProperty("line.separator");

    // Mapping table from 6-bit nibbles to Base64 characters.
    private static char[] map1 = new char[64];
    static {
    int i = 0;
    for (char c = 'A'; c <= 'Z'; c++)
        map1[i++] = c;
    for (char c = 'a'; c <= 'z'; c++)
        map1[i++] = c;
    for (char c = '0'; c <= '9'; c++)
        map1[i++] = c;
    map1[i++] = '+';
    map1[i++] = '/';
    }

    // Mapping table from Base64 characters to 6-bit nibbles.
    private static byte[] map2 = new byte[128];
    static {
    for (int i = 0; i < map2.length; i++)
        map2[i] = -1;
    for (int i = 0; i < 64; i++)
        map2[map1[i]] = (byte) i;
    }

    /**
     * Encodes a string into Base64 format. No blanks or line breaks are
     * inserted.
     * 
     * @param s
     *            A String to be encoded.
     * @return A String containing the Base64 encoded data.
     */
    public static String encodeString(String s) {
    return new String(encode(s.getBytes()));
    }

    /**
     * Encodes a byte array into Base 64 format and breaks the output into lines
     * of 76 characters. This method is compatible with
     * <code>sun.misc.BASE64Encoder.encodeBuffer(byte[])</code>.
     * 
     * @param in
     *            An array containing the data bytes to be encoded.
     * @return A String containing the Base64 encoded data, broken into lines.
     */
    public static String encodeLines(byte[] in) {
    return encodeLines(in, 0, in.length, 76, systemLineSeparator);
    }

    /**
     * Encodes a byte array into Base 64 format and breaks the output into
     * lines.
     * 
     * @param in
     *            An array containing the data bytes to be encoded.
     * @param iOff
     *            Offset of the first byte in <code>in</code> to be processed.
     * @param iLen
     *            Number of bytes to be processed in <code>in</code>, starting
     *            at <code>iOff</code>.
     * @param lineLen
     *            Line length for the output data. Should be a multiple of 4.
     * @param lineSeparator
     *            The line separator to be used to separate the output lines.
     * @return A String containing the Base64 encoded data, broken into lines.
     */
    public static String encodeLines(byte[] in, int iOff, int iLen, int lineLen, String lineSeparator) {
    int blockLen = (lineLen * 3) / 4;
    if (blockLen <= 0)
        throw new IllegalArgumentException();
    int lines = (iLen + blockLen - 1) / blockLen;
    int bufLen = ((iLen + 2) / 3) * 4 + lines * lineSeparator.length();
    StringBuilder buf = new StringBuilder(bufLen);
    int ip = 0;
    while (ip < iLen) {
        int l = Math.min(iLen - ip, blockLen);
        buf.append(encode(in, iOff + ip, l));
        buf.append(lineSeparator);
        ip += l;
    }
    return buf.toString();
    }

    /**
     * Encodes a byte array into Base64 format. No blanks or line breaks are
     * inserted in the output.
     * 
     * @param in
     *            An array containing the data bytes to be encoded.
     * @return A character array containing the Base64 encoded data.
     */
    public static char[] encode(byte[] in) {
    return encode(in, 0, in.length);
    }

    /**
     * Encodes a byte array into Base64 format. No blanks or line breaks are
     * inserted in the output.
     * 
     * @param in
     *            An array containing the data bytes to be encoded.
     * @param iLen
     *            Number of bytes to process in <code>in</code>.
     * @return A character array containing the Base64 encoded data.
     */
    public static char[] encode(byte[] in, int iLen) {
    return encode(in, 0, iLen);
    }

    /**
     * Encodes a byte array into Base64 format. No blanks or line breaks are
     * inserted in the output.
     * 
     * @param in
     *            An array containing the data bytes to be encoded.
     * @param iOff
     *            Offset of the first byte in <code>in</code> to be processed.
     * @param iLen
     *            Number of bytes to process in <code>in</code>, starting at
     *            <code>iOff</code>.
     * @return A character array containing the Base64 encoded data.
     */
    public static char[] encode(byte[] in, int iOff, int iLen) {
    int oDataLen = (iLen * 4 + 2) / 3; // output length without padding
    int oLen = ((iLen + 2) / 3) * 4; // output length including padding
    char[] out = new char[oLen];
    int ip = iOff;
    int iEnd = iOff + iLen;
    int op = 0;
    while (ip < iEnd) {
        int i0 = in[ip++] & 0xff;
        int i1 = ip < iEnd ? in[ip++] & 0xff : 0;
        int i2 = ip < iEnd ? in[ip++] & 0xff : 0;
        int o0 = i0 >>> 2;
        int o1 = ((i0 & 3) << 4) | (i1 >>> 4);
        int o2 = ((i1 & 0xf) << 2) | (i2 >>> 6);
        int o3 = i2 & 0x3F;
        out[op++] = map1[o0];
        out[op++] = map1[o1];
        out[op] = op < oDataLen ? map1[o2] : '=';
        op++;
        out[op] = op < oDataLen ? map1[o3] : '=';
        op++;
    }
    return out;
    }

    /**
     * Decodes a string from Base64 format. No blanks or line breaks are allowed
     * within the Base64 encoded input data.
     * 
     * @param s
     *            A Base64 String to be decoded.
     * @return A String containing the decoded data.
     * @throws IllegalArgumentException
     *             If the input is not valid Base64 encoded data.
     */
    public static String decodeString(String s) {
    return new String(decode(s));
    }

    /**
     * Decodes a byte array from Base64 format and ignores line separators, tabs
     * and blanks. CR, LF, Tab and Space characters are ignored in the input
     * data. This method is compatible with
     * <code>sun.misc.BASE64Decoder.decodeBuffer(String)</code>.
     * 
     * @param s
     *            A Base64 String to be decoded.
     * @return An array containing the decoded data bytes.
     * @throws IllegalArgumentException
     *             If the input is not valid Base64 encoded data.
     */
    public static byte[] decodeLines(String s) {
    char[] buf = new char[s.length()];
    int p = 0;
    for (int ip = 0; ip < s.length(); ip++) {
        char c = s.charAt(ip);
        if (c != ' ' && c != '\r' && c != '\n' && c != '\t')
        buf[p++] = c;
    }
    return decode(buf, 0, p);
    }

    /**
     * Decodes a byte array from Base64 format. No blanks or line breaks are
     * allowed within the Base64 encoded input data.
     * 
     * @param s
     *            A Base64 String to be decoded.
     * @return An array containing the decoded data bytes.
     * @throws IllegalArgumentException
     *             If the input is not valid Base64 encoded data.
     */
    public static byte[] decode(String s) {
    return decode(s.toCharArray());
    }

    /**
     * Decodes a byte array from Base64 format. No blanks or line breaks are
     * allowed within the Base64 encoded input data.
     * 
     * @param in
     *            A character array containing the Base64 encoded data.
     * @return An array containing the decoded data bytes.
     * @throws IllegalArgumentException
     *             If the input is not valid Base64 encoded data.
     */
    public static byte[] decode(char[] in) {
    return decode(in, 0, in.length);
    }

    /**
     * Decodes a byte array from Base64 format. No blanks or line breaks are
     * allowed within the Base64 encoded input data.
     * 
     * @param in
     *            A character array containing the Base64 encoded data.
     * @param iOff
     *            Offset of the first character in <code>in</code> to be
     *            processed.
     * @param iLen
     *            Number of characters to process in <code>in</code>, starting
     *            at <code>iOff</code>.
     * @return An array containing the decoded data bytes.
     * @throws IllegalArgumentException
     *             If the input is not valid Base64 encoded data.
     */
    public static byte[] decode(char[] in, int iOff, int iLen) {
    if (iLen % 4 != 0)
        throw new IllegalArgumentException("Length of Base64 encoded input string is not a multiple of 4.");
    while (iLen > 0 && in[iOff + iLen - 1] == '=')
        iLen--;
    int oLen = (iLen * 3) / 4;
    byte[] out = new byte[oLen];
    int ip = iOff;
    int iEnd = iOff + iLen;
    int op = 0;
    while (ip < iEnd) {
        int i0 = in[ip++];
        int i1 = in[ip++];
        int i2 = ip < iEnd ? in[ip++] : 'A';
        int i3 = ip < iEnd ? in[ip++] : 'A';
        if (i0 > 127 || i1 > 127 || i2 > 127 || i3 > 127)
        throw new IllegalArgumentException("Illegal character in Base64 encoded data.");
        int b0 = map2[i0];
        int b1 = map2[i1];
        int b2 = map2[i2];
        int b3 = map2[i3];
        if (b0 < 0 || b1 < 0 || b2 < 0 || b3 < 0)
        throw new IllegalArgumentException("Illegal character in Base64 encoded data.");
        int o0 = (b0 << 2) | (b1 >>> 4);
        int o1 = ((b1 & 0xf) << 4) | (b2 >>> 2);
        int o2 = ((b2 & 3) << 6) | b3;
        out[op++] = (byte) o0;
        if (op < oLen)
        out[op++] = (byte) o1;
        if (op < oLen)
        out[op++] = (byte) o2;
    }
    return out;
    }

    // Dummy constructor.
    private Base64Coder() {
    }

} // end class Base64Coder

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