base64.java

b64.java b64编码 这还不够长 这还不够长 这还不够长 这还不够长 这还不够长

import java.io.*;

public class Base64 {
	// 加密
	static public char[] encode(byte[] data) {
		char[] out = new char[((data.length + 2) / 3) * 4];

		for (int i = 0, index = 0; i < data.length; i += 3, index += 4) {
			boolean quad = false;
			boolean trip = false;

			int val = (0xFF & (int) data[i]);
			val <<= 8;
			if ((i + 1) < data.length) {
				val |= (0xFF & (int) data[i + 1]);
				trip = true;
			}
			val <<= 8;
			if ((i + 2) < data.length) {
				val |= (0xFF & (int) data[i + 2]);
				quad = true;
			}
			out[index + 3] = alphabet[(quad ? (val & 0x3F) : 64)];
			val >>= 6;
			out[index + 2] = alphabet[(trip ? (val & 0x3F) : 64)];
			val >>= 6;
			out[index + 1] = alphabet[val & 0x3F];
			val >>= 6;
			out[index + 0] = alphabet[val & 0x3F];
		}
		return out;
	}

	// 解密
	static public byte[] decode(char[] data) {

		int tempLen = data.length;
		for (int ix = 0; ix < data.length; ix++) {
			if ((data[ix] > 255) || codes[data[ix]] < 0)
				--tempLen;
		}

		int len = (tempLen / 4) * 3;
		if ((tempLen % 4) == 3)
			len += 2;
		if ((tempLen % 4) == 2)
			len += 1;

		byte[] out = new byte[len];

		int shift = 0;
		int accum = 0;
		int index = 0;

		for (int ix = 0; ix < data.length; ix++) {
			int value = (data[ix] > 255) ? -1 : codes[data[ix]];

			if (value >= 0) // skip over non-code
			{
				accum <<= 6; // bits shift up by 6 each time thru
				shift += 6; // loop, with new bits being put in
				accum |= value; // at the bottom.
				if (shift >= 8) // whenever there are 8 or more shifted in,
				{
					shift -= 8; // write them out (from the top, leaving any
					out[index++] = // excess at the bottom for next iteration.
					(byte) ((accum >> shift) & 0xff);
				}
			}

		}

		if (index != out.length) {
			throw new Error("Miscalculated data length (wrote " + index	+ " instead of " + out.length + ")");
		}

		return out;
	}

	static private char[] alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=".toCharArray();

	static private byte[] codes = new byte[256];
	static {
		for (int i = 0; i < 256; i++)
			codes[i] = -1;
		for (int i = 'A'; i <= 'Z'; i++)
			codes[i] = (byte) (i - 'A');
		for (int i = 'a'; i <= 'z'; i++)
			codes[i] = (byte) (26 + i - 'a');
		for (int i = '0'; i <= '9'; i++)
			codes[i] = (byte) (52 + i - '0');
		codes['+'] = 62;
		codes['/'] = 63;
	}

	// 解密:java Base64 -decode 文件名
	// 解密:java Base64 -d 文件名
	// 加密:java Base64 文件名
	//
	public static void main(String[] args) {
		boolean decode = false;

		if (args.length == 0) {
			System.out.println("usage:  java Base64 [-d[ecode]] filename");
			System.exit(0);
		}
		for (int i = 0; i < args.length; i++) {
			if ("-decode".equalsIgnoreCase(args[i]))
				decode = true;
			else if ("-d".equalsIgnoreCase(args[i]))
				decode = true;
		}

		String filename = args[args.length - 1];
		File file = new File(filename);
		if (!file.exists()) {
			System.out.println("Error:  file '" + filename + "' doesn't exist!");
			System.exit(0);
		}

		if (decode) {
			char[] encoded = readChars(file);
			byte[] decoded = decode(encoded);
			writeBytes(file, decoded);
		} else {
			byte[] decoded = readBytes(file);
			char[] encoded = encode(decoded);
			writeChars(file, encoded);
		}
	}
}