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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