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  • Base 64

    import java.io.*;
    
    /**
     * Routines for converting between Strings of base64-encoded data and arrays of
     * binary data.
     * 
     * @author Brian Wellington
     */
    
    public class base64 {
    
    	private static final String Base64 = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=";
    
    	private base64() {
    	}
    
    	/**
    	 * Convert binary data to a base64-encoded String
    	 * 
    	 * @param b
    	 *            An array containing binary data
    	 * @return A String containing the encoded data
    	 */
    	public static String toString(byte[] b) {
    		ByteArrayOutputStream os = new ByteArrayOutputStream();
    
    		for (int i = 0; i < (b.length + 2) / 3; i++) {
    			short[] s = new short[3];
    			short[] t = new short[4];
    			for (int j = 0; j < 3; j++) {
    				if ((i * 3 + j) < b.length)
    					s[j] = (short) (b[i * 3 + j] & 0xFF);
    				else
    					s[j] = -1;
    			}
    
    			t[0] = (short) (s[0] >> 2);
    			if (s[1] == -1)
    				t[1] = (short) (((s[0] & 0x3) << 4));
    			else
    				t[1] = (short) (((s[0] & 0x3) << 4) + (s[1] >> 4));
    			if (s[1] == -1)
    				t[2] = t[3] = 64;
    			else if (s[2] == -1) {
    				t[2] = (short) (((s[1] & 0xF) << 2));
    				t[3] = 64;
    			} else {
    				t[2] = (short) (((s[1] & 0xF) << 2) + (s[2] >> 6));
    				t[3] = (short) (s[2] & 0x3F);
    			}
    			for (int j = 0; j < 4; j++)
    				os.write(Base64.charAt(t[j]));
    		}
    		return new String(os.toByteArray());
    	}
    
    	/**
    	 * Formats data into a nicely formatted base64 encoded String
    	 * 
    	 * @param b
    	 *            An array containing binary data
    	 * @param lineLength
    	 *            The number of characters per line
    	 * @param prefix
    	 *            A string prefixing the characters on each line
    	 * @param addClose
    	 *            Whether to add a close parenthesis or not
    	 * @return A String representing the formatted output
    	 */
    	public static String formatString(byte[] b, int lineLength, String prefix,
    			boolean addClose) {
    		String s = toString(b);
    		StringBuffer sb = new StringBuffer();
    		for (int i = 0; i < s.length(); i += lineLength) {
    			sb.append(prefix);
    			if (i + lineLength >= s.length()) {
    				sb.append(s.substring(i));
    				if (addClose)
    					sb.append(" )");
    			} else {
    				sb.append(s.substring(i, i + lineLength));
    				sb.append("\n");
    			}
    		}
    		return sb.toString();
    	}
    
    	/**
    	 * Convert a base64-encoded String to binary data
    	 * 
    	 * @param str
    	 *            A String containing the encoded data
    	 * @return An array containing the binary data, or null if the string is
    	 *         invalid
    	 */
    	public static byte[] fromString(String str) {
    		ByteArrayOutputStream bs = new ByteArrayOutputStream();
    		byte[] raw = str.getBytes();
    		for (int i = 0; i < raw.length; i++) {
    			if (!Character.isWhitespace((char) raw[i]))
    				bs.write(raw[i]);
    		}
    		byte[] in = bs.toByteArray();
    		if (in.length % 4 != 0) {
    			return null;
    		}
    
    		bs.reset();
    		DataOutputStream ds = new DataOutputStream(bs);
    
    		for (int i = 0; i < (in.length + 3) / 4; i++) {
    			short[] s = new short[4];
    			short[] t = new short[3];
    
    			for (int j = 0; j < 4; j++)
    				s[j] = (short) Base64.indexOf(in[i * 4 + j]);
    
    			t[0] = (short) ((s[0] << 2) + (s[1] >> 4));
    			if (s[2] == 64) {
    				t[1] = t[2] = (short) (-1);
    				if ((s[1] & 0xF) != 0)
    					return null;
    			} else if (s[3] == 64) {
    				t[1] = (short) (((s[1] << 4) + (s[2] >> 2)) & 0xFF);
    				t[2] = (short) (-1);
    				if ((s[2] & 0x3) != 0)
    					return null;
    			} else {
    				t[1] = (short) (((s[1] << 4) + (s[2] >> 2)) & 0xFF);
    				t[2] = (short) (((s[2] << 6) + s[3]) & 0xFF);
    			}
    
    			try {
    				for (int j = 0; j < 3; j++)
    					if (t[j] >= 0)
    						ds.writeByte(t[j]);
    			} catch (IOException e) {
    			}
    		}
    		return bs.toByteArray();
    	}
    
    }
    
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  • 原文地址:https://www.cnblogs.com/luxiaofeng54/p/2080014.html
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