1 package com.jf.utils;
2
3 import java.util.HashMap;
4 import java.util.Map;
5
6
7 public class Base64Utils {
8
9 private static final Map<Integer, Character> base64CharMap = new HashMap<Integer, Character>();
10 private static final String base64CharString = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
11
12 static {
13 for (int i = 0; i < base64CharString.length(); i++) {
14 char c = base64CharString.charAt(i);
15 base64CharMap.put(new Integer(i), new Character(c));
16 }
17 }
18
19 public static String encode(String origin) {
20 if (origin == null) {
21 return null;
22 }
23 if (origin.length() == 0) {
24 return "";
25 }
26 int length = origin.length();
27 String binaryString = "";
28 for (int i = 0; i < length; i++) {
29 int ascii = origin.charAt(i);
30 String binaryCharString = Integer.toBinaryString(ascii);
31 while (binaryCharString.length() < 8) {
32 binaryCharString = "0" + binaryCharString;
33 }
34 binaryString += binaryCharString;
35 }
36 int beginIndex = 0;
37 int endIndex = beginIndex + 6;
38 String base64BinaryString = "";
39 String charString = "";
40 while ((base64BinaryString = binaryString.substring(beginIndex, endIndex)).length() > 0) {
41 // if length is less than 6, add "0".
42 while (base64BinaryString.length() < 6) {
43 base64BinaryString += "0";
44 }
45 int index = Integer.parseInt(base64BinaryString, 2);
46 char base64Char = base64CharMap.get(index);
47 charString = charString + base64Char;
48 beginIndex += 6;
49 endIndex += 6;
50 if (endIndex >= binaryString.length()) {
51 endIndex = binaryString.length();
52 }
53 if (endIndex < beginIndex) {
54 break;
55 }
56 }
57 if (length % 3 == 2) {
58 charString += "=";
59 }
60 if (length % 3 == 1) {
61 charString += "==";
62 }
63 return charString;
64 }
65
66 /**
67 * This method is used to decode from base64 string to a normal string.
68 *
69 * @param encodedString
70 * The string to be decoded.
71 * @return The string after decoded.
72 */
73 public static String decode(String encodedString) {
74 if (encodedString == null) {
75 return null;
76 }
77 if (encodedString.length() == 0) {
78 return "";
79 }
80 // get origin base64 String
81 String origin = encodedString.substring(0, encodedString.indexOf("="));
82 String equals = encodedString.substring(encodedString.indexOf("="));
83 String binaryString = "";
84 // convert base64 string to binary string
85 for (int i = 0; i < origin.length(); i++) {
86 char c = origin.charAt(i);
87 int ascii = base64CharString.indexOf(c);
88 String binaryCharString = Integer.toBinaryString(ascii);
89 while (binaryCharString.length() < 6) {
90 binaryCharString = "0" + binaryCharString;
91 }
92 binaryString += binaryCharString;
93 }
94 // the encoded string has 1 "=", means that the binary string has append
95 // 2 "0"
96 if (equals.length() == 1) {
97 binaryString = binaryString.substring(0, binaryString.length() - 2);
98 }
99 // the encoded string has 2 "=", means that the binary string has append
100 // 4 "0"
101 if (equals.length() == 2) {
102 binaryString = binaryString.substring(0, binaryString.length() - 4);
103 }
104 // convert to String
105 String charString = "";
106 String resultString = "";
107 int beginIndex = 0;
108 int endIndex = beginIndex + 8;
109 while ((charString = binaryString.substring(beginIndex, endIndex)).length() == 8) {
110 int ascii = Integer.parseInt(charString, 2);
111 resultString += (char) ascii;
112 beginIndex += 8;
113 endIndex += 8;
114 if (endIndex > binaryString.length()) {
115 break;
116 }
117 }
118 return resultString;
119 }
120
121 public static void main(String[] args) {
122 String originString = "Man is distinguished, not only by his reason, but by this singular passion from other animals, which is a lust of the mind, that by a perseverance of delight in the continued and indefatigable generation of knowledge, exceeds the short vehemence of any carnal pleasure.";
123 String base64String = "TWFxxxbxx"
125 + "dGhlIG1xxYSBwZXJzxxxY2xxx0aGUgY29udGlu"
126 + "dxxxxlIGdlbmVyYXRpb24gb2YxxxBleGNlZWRzIHRo"
127 + "xxx";
128 System.out.println("===============encode=================");
129 String result = encode(originString);
130 System.out.println(result);
131 System.out.println(result.equals(base64String));
132
133 System.out.println("===============decode=================");
134 String decodedString = decode(base64String);
135 System.out.println(decodedString);
136 System.out.println(originString.equals(decodedString));
137
138 System.out.println(decode(encode("abcdefg")));
139 }
140 }
