base64 代码

向右看齐 2022-03-12 07:11 152阅读 0赞

package com.demo.base64;
    
    public class Base64 {
    	
    	private static char[] Base64Code = { 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P',
    			'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k',
    			'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5',
    			'6', '7', '8', '9', '+', '/' };
    
    	private static byte[] Base64Decode = { -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    			-1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, 63,
    			-1, 63, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, 0, -1, -1, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10,
    			11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1, -1, 26, 27, 28, 29, 30, 31,
    			32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, -1, -1, -1, -1, -1 };
    
    	public static String encode(byte[] b) {
    		int code = 0;
    		if (b == null)
    			return null;
    		StringBuffer sb = new StringBuffer((b.length - 1) / 3 << 6);
    		for (int i = 0; i < b.length; i++) {
    			code |= b[i] << 16 - i % 3 * 8 & 255 << 16 - i % 3 * 8;
    			if ((i % 3 != 2) && (i != b.length - 1))
    				continue;
    			sb.append(Base64Code[((code & 0xFC0000) >>> 18)]);
    			sb.append(Base64Code[((code & 0x3F000) >>> 12)]);
    			sb.append(Base64Code[((code & 0xFC0) >>> 6)]);
    			sb.append(Base64Code[(code & 0x3F)]);
    			code = 0;
    		}
    
    		if (b.length % 3 > 0)
    			sb.setCharAt(sb.length() - 1, '=');
    		if (b.length % 3 == 1)
    			sb.setCharAt(sb.length() - 2, '=');
    		return sb.toString();
    	}
    
    	public static byte[] decode(String code) {
    		if (code == null)
    			return null;
    		int len = code.length();
    		if (len % 4 != 0)
    			throw new IllegalArgumentException("Base64 string length must be 4*n");
    		if (code.length() == 0)
    			return new byte[0];
    		int pad = 0;
    		if (code.charAt(len - 1) == '=')
    			pad++;
    		if (code.charAt(len - 2) == '=')
    			pad++;
    		int retLen = len / 4 * 3 - pad;
    		byte[] ret = new byte[retLen];
    		for (int i = 0; i < len; i += 4) {
    			int j = i / 4 * 3;
    			char ch1 = code.charAt(i);
    			char ch2 = code.charAt(i + 1);
    			char ch3 = code.charAt(i + 2);
    			char ch4 = code.charAt(i + 3);
    			int tmp = Base64Decode[ch1] << 18 | Base64Decode[ch2] << 12 | Base64Decode[ch3] << 6 | Base64Decode[ch4];
    			ret[j] = (byte) ((tmp & 0xFF0000) >> 16);
    			if (i < len - 4) {
    				ret[(j + 1)] = (byte) ((tmp & 0xFF00) >> 8);
    				ret[(j + 2)] = (byte) (tmp & 0xFF);
    			} else {
    				if (j + 1 < retLen)
    					ret[(j + 1)] = (byte) ((tmp & 0xFF00) >> 8);
    				if (j + 2 < retLen)
    					ret[(j + 2)] = (byte) (tmp & 0xFF);
    			}
    		}
    		return ret;
    	}
    	
    	public static void main(String[] args) {
    		String str = "1234567890abcdefg";
    		String res = encode(str.getBytes());
    		System.out.println(res);
    		
    		byte[] a = decode(res);
    		System.out.println(new String(a));
    	}
    
    }