File	Doc	Category	Size	Date	Package
Base64.java	API Doc	Java SE 5 API	10034	Fri Aug 26 14:57:28 BST 2005	java.util.prefs

Base64

• java.lang.Object

Fields Summary
private static final char[]	intToBase64 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.
private static final char[]	intToAltBase64 This array is a lookup table that translates 6-bit positive integer index values into their "Alternate Base64 Alphabet" equivalents. This is NOT the real Base64 Alphabet as per in Table 1 of RFC 2045. This alternate alphabet does not use the capital letters. It is designed for use in environments where "case folding" occurs.
private static final byte[]	base64ToInt 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.
private static final byte[]	altBase64ToInt This array is the analogue of base64ToInt, but for the nonstandard variant that avoids the use of uppercase alphabetic characters.

Constructors Summary

Methods Summary
static byte[]	altBase64ToByteArray(java.lang.String s) Translates the specified "aternate representation" Base64 string into a byte array. throw IllegalArgumentException or ArrayOutOfBoundsException if s is not a valid alternate representation Base64 string. return base64ToByteArray(s, true);
static byte[]	base64ToByteArray(java.lang.String s) Translates the specified Base64 string (as per Preferences.get(byte[])) into a byte array. throw IllegalArgumentException if s is not a valid Base64 string. return base64ToByteArray(s, false);
private static byte[]	base64ToByteArray(java.lang.String s, boolean alternate) byte[] alphaToInt = (alternate ? altBase64ToInt : base64ToInt); int sLen = s.length(); int numGroups = sLen/4; if (4*numGroups != sLen) throw new IllegalArgumentException( "String length must be a multiple of four."); int missingBytesInLastGroup = 0; int numFullGroups = numGroups; if (sLen != 0) { if (s.charAt(sLen-1) == '=") { missingBytesInLastGroup++; numFullGroups--; } if (s.charAt(sLen-2) == '=") missingBytesInLastGroup++; } byte[] result = new byte[3*numGroups - missingBytesInLastGroup]; // Translate all full groups from base64 to byte array elements int inCursor = 0, outCursor = 0; for (int i=0; i<numFullGroups; i++) { int ch0 = base64toInt(s.charAt(inCursor++), alphaToInt); int ch1 = base64toInt(s.charAt(inCursor++), alphaToInt); int ch2 = base64toInt(s.charAt(inCursor++), alphaToInt); int ch3 = base64toInt(s.charAt(inCursor++), alphaToInt); result[outCursor++] = (byte) ((ch0 << 2) | (ch1 >> 4)); result[outCursor++] = (byte) ((ch1 << 4) | (ch2 >> 2)); result[outCursor++] = (byte) ((ch2 << 6) | ch3); } // Translate partial group, if present if (missingBytesInLastGroup != 0) { int ch0 = base64toInt(s.charAt(inCursor++), alphaToInt); int ch1 = base64toInt(s.charAt(inCursor++), alphaToInt); result[outCursor++] = (byte) ((ch0 << 2) | (ch1 >> 4)); if (missingBytesInLastGroup == 1) { int ch2 = base64toInt(s.charAt(inCursor++), alphaToInt); result[outCursor++] = (byte) ((ch1 << 4) | (ch2 >> 2)); } } // assert inCursor == s.length()-missingBytesInLastGroup; // assert outCursor == result.length; return result;
private static int	base64toInt(char c, byte[] alphaToInt) Translates the specified character, which is assumed to be in the "Base 64 Alphabet" into its equivalent 6-bit positive integer. throw IllegalArgumentException or ArrayOutOfBoundsException if c is not in the Base64 Alphabet. int result = alphaToInt[c]; if (result < 0) throw new IllegalArgumentException("Illegal character " + c); return result;
static java.lang.String	byteArrayToAltBase64(byte[] a) Translates the specified byte array into an "aternate representation" Base64 string. This non-standard variant uses an alphabet that does not contain the uppercase alphabetic characters, which makes it suitable for use in situations where case-folding occurs. return byteArrayToBase64(a, true);
static java.lang.String	byteArrayToBase64(byte[] a) Translates the specified byte array into a Base64 string as per Preferences.put(byte[]). return byteArrayToBase64(a, false);
private static java.lang.String	byteArrayToBase64(byte[] a, boolean alternate) int aLen = a.length; int numFullGroups = aLen/3; int numBytesInPartialGroup = aLen - 3*numFullGroups; int resultLen = 4*((aLen + 2)/3); StringBuffer result = new StringBuffer(resultLen); char[] intToAlpha = (alternate ? intToAltBase64 : intToBase64); // Translate all full groups from byte array elements to Base64 int inCursor = 0; for (int i=0; i<numFullGroups; i++) { int byte0 = a[inCursor++] & 0xff; int byte1 = a[inCursor++] & 0xff; int byte2 = a[inCursor++] & 0xff; result.append(intToAlpha[byte0 >> 2]); result.append(intToAlpha[(byte0 << 4)&0x3f | (byte1 >> 4)]); result.append(intToAlpha[(byte1 << 2)&0x3f | (byte2 >> 6)]); result.append(intToAlpha[byte2 & 0x3f]); } // Translate partial group if present if (numBytesInPartialGroup != 0) { int byte0 = a[inCursor++] & 0xff; result.append(intToAlpha[byte0 >> 2]); if (numBytesInPartialGroup == 1) { result.append(intToAlpha[(byte0 << 4) & 0x3f]); result.append("=="); } else { // assert numBytesInPartialGroup == 2; int byte1 = a[inCursor++] & 0xff; result.append(intToAlpha[(byte0 << 4)&0x3f | (byte1 >> 4)]); result.append(intToAlpha[(byte1 << 2)&0x3f]); result.append('="); } } // assert inCursor == a.length; // assert result.length() == resultLen; return result.toString();
public static void	main(java.lang.String[] args) int numRuns = Integer.parseInt(args[0]); int numBytes = Integer.parseInt(args[1]); java.util.Random rnd = new java.util.Random(); for (int i=0; i<numRuns; i++) { for (int j=0; j<numBytes; j++) { byte[] arr = new byte[j]; for (int k=0; k<j; k++) arr[k] = (byte)rnd.nextInt(); String s = byteArrayToBase64(arr); byte [] b = base64ToByteArray(s); if (!java.util.Arrays.equals(arr, b)) System.out.println("Dismal failure!"); s = byteArrayToAltBase64(arr); b = altBase64ToByteArray(s); if (!java.util.Arrays.equals(arr, b)) System.out.println("Alternate dismal failure!"); } }