独立思考能力，对于从事科学研究或其他任何工作，都是十分必要的。
jdk8开始已经含有base64编解码方法。这里是针对jdk7的实现，使用方法：Base64Decoder.decode(String str);
01 | package mybase64.decrypt; |
02 |
03 | import java.io.ByteArrayInputStream; |
04 | import java.io.ByteArrayOutputStream; |
05 | import java.io.FilterInputStream; |
06 | import java.io.IOException; |
07 | import java.io.InputStream; |
08 | import java.io.UnsupportedEncodingException; |
09 |
10 |
11 | class Base64Decoder extends FilterInputStream { |
12 |
13 | private static final char[] chars = { 'A', 'B', 'C', 'D', 'E', 'F', 'G', |
14 | 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', |
15 | 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', 'g', |
16 | 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', |
17 | 'u', 'v', 'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', |
18 | '7', '8', '9', '+', '/' }; |
19 |
20 | // A mapping between char values and six-bit integers |
21 | private static final int[] ints = new int[128]; |
22 | static { |
23 | for (int i = 0; i < 64; i++) { |
24 | ints[chars[i]] = i; |
25 | } |
26 | } |
27 |
28 | private int charCount; |
29 | private int carryOver; |
30 |
31 | /*** |
32 | * Constructs a new Base64 decoder that reads input from the given |
33 | * InputStream. |
34 | * |
35 | * @param in |
36 | * the input stream |
37 | */ |
38 | public Base64Decoder(InputStream in) { |
39 | super(in); |
40 | } |
41 |
42 | /*** |
43 | * Returns the next decoded character from the stream, or -1 if end of |
44 | * stream was reached. |
45 | * |
46 | * @return the decoded character, or -1 if the end of the input stream is |
47 | * reached |
48 | * @exception IOException |
49 | * if an I/O error occurs |
50 | */ |
51 | public int read() throws IOException { |
52 | // Read the next non-whitespace character |
53 | int x; |
54 | do { |
55 | x = in.read(); |
56 | if (x == -1) { |
57 | return -1; |
58 | } |
59 | } while (Character.isWhitespace((char) x)); |
60 | charCount++; |
61 |
62 | // The '=' sign is just padding |
63 | if (x == '=') { |
64 | return -1; // effective end of stream |
65 | } |
66 |
67 | // Convert from raw form to 6-bit form |
68 | x = ints[x]; |
69 |
70 | // Calculate which character we're decoding now |
71 | int mode = (charCount - 1) % 4; |
72 |
73 | // First char save all six bits, go for another |
74 | if (mode == 0) { |
75 | carryOver = x & 63; |
76 | return read(); |
77 | } |
78 | // Second char use previous six bits and first two new bits, |
79 | // save last four bits |
80 | else if (mode == 1) { |
81 | int decoded = ((carryOver << 2="">> 4)) & 255; |
82 | carryOver = x & 15; |
83 | return decoded; |
84 | } |
85 | // Third char use previous four bits and first four new bits, |
86 | // save last two bits |
87 | else if (mode == 2) { |
88 | int decoded = ((carryOver << 4="">> 2)) & 255; |
89 | carryOver = x & 3; |
90 | return decoded; |
91 | } |
92 | // Fourth char use previous two bits and all six new bits |
93 | else if (mode == 3) { |
94 | int decoded = ((carryOver << 6=""> |
