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 paddingint oLen = ((iLen + 2) / 3) * 4; // output length including paddingchar[] 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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