我有一个Base64编码的图像。Java中最好的解码方法是什么?希望只使用Sun Java 6中包含的库。
当前回答
Java .util的Java 8实现。Base64不依赖于其他Java 8特定的类。
我不确定这是否适用于Java 6项目，但可以复制并粘贴Base64.java文件到Java 7项目中，并编译它，除了导入Java .util. arrays和Java .util. objects之外，无需任何修改。
注意，Base64.java文件是由GNU GPL2覆盖的
其他回答
Java .util的Java 8实现。Base64不依赖于其他Java 8特定的类。
我不确定这是否适用于Java 6项目，但可以复制并粘贴Base64.java文件到Java 7项目中，并编译它，除了导入Java .util. arrays和Java .util. objects之外，无需任何修改。
注意，Base64.java文件是由GNU GPL2覆盖的
我的解决方法是最快最简单的。
public class MyBase64 {
private final static char[] ALPHABET = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/".toCharArray();
private static int[] toInt = new int[128];
static {
for(int i=0; i< ALPHABET.length; i++){
toInt[ALPHABET[i]]= i;
}
}
/**
* Translates the specified byte array into Base64 string.
*
* @param buf the byte array (not null)
* @return the translated Base64 string (not null)
*/
public static String encode(byte[] buf){
int size = buf.length;
char[] ar = new char[((size + 2) / 3) * 4];
int a = 0;
int i=0;
while(i < size){
byte b0 = buf[i++];
byte b1 = (i < size) ? buf[i++] : 0;
byte b2 = (i < size) ? buf[i++] : 0;
int mask = 0x3F;
ar[a++] = ALPHABET[(b0 >> 2) & mask];
ar[a++] = ALPHABET[((b0 << 4) | ((b1 & 0xFF) >> 4)) & mask];
ar[a++] = ALPHABET[((b1 << 2) | ((b2 & 0xFF) >> 6)) & mask];
ar[a++] = ALPHABET[b2 & mask];
}
switch(size % 3){
case 1: ar[--a] = '=';
case 2: ar[--a] = '=';
}
return new String(ar);
}
/**
* Translates the specified Base64 string into a byte array.
*
* @param s the Base64 string (not null)
* @return the byte array (not null)
*/
public static byte[] decode(String s){
int delta = s.endsWith( "==" ) ? 2 : s.endsWith( "=" ) ? 1 : 0;
byte[] buffer = new byte[s.length()*3/4 - delta];
int mask = 0xFF;
int index = 0;
for(int i=0; i< s.length(); i+=4){
int c0 = toInt[s.charAt( i )];
int c1 = toInt[s.charAt( i + 1)];
buffer[index++]= (byte)(((c0 << 2) | (c1 >> 4)) & mask);
if(index >= buffer.length){
return buffer;
}
int c2 = toInt[s.charAt( i + 2)];
buffer[index++]= (byte)(((c1 << 4) | (c2 >> 2)) & mask);
if(index >= buffer.length){
return buffer;
}
int c3 = toInt[s.charAt( i + 3 )];
buffer[index++]= (byte)(((c2 << 6) | c3) & mask);
}
return buffer;
}
}
我用的是android.util。Base64在没有任何依赖的情况下工作得很好:
用法:
byte[] decodedKey = Base64.decode(encodedPublicKey, Base64.DEFAULT);
包com.test;
import java.io.UnsupportedEncodingException;
/**
* Utilities for encoding and decoding the Base64 representation of
* binary data. See RFCs <a
* href="http://www.ietf.org/rfc/rfc2045.txt">2045</a> and <a
* href="http://www.ietf.org/rfc/rfc3548.txt">3548</a>.
*/
public class Base64 {
public static final int DEFAULT = 0;
public static final int NO_PADDING = 1;
public static final int NO_WRAP = 2;
public static final int CRLF = 4;
public static final int URL_SAFE = 8;
public static final int NO_CLOSE = 16;
// --------------------------------------------------------
// shared code
// --------------------------------------------------------
/* package */ static abstract class Coder {
public byte[] output;
public int op;
public abstract boolean process(byte[] input, int offset, int len, boolean finish);
public abstract int maxOutputSize(int len);
}
// --------------------------------------------------------
// decoding
// --------------------------------------------------------
public static byte[] decode(String str, int flags) {
return decode(str.getBytes(), flags);
}
public static byte[] decode(byte[] input, int flags) {
return decode(input, 0, input.length, flags);
}
public static byte[] decode(byte[] input, int offset, int len, int flags) {
// Allocate space for the most data the input could represent.
// (It could contain less if it contains whitespace, etc.)
Decoder decoder = new Decoder(flags, new byte[len*3/4]);
if (!decoder.process(input, offset, len, true)) {
throw new IllegalArgumentException("bad base-64");
}
// Maybe we got lucky and allocated exactly enough output space.
if (decoder.op == decoder.output.length) {
return decoder.output;
}
// Need to shorten the array, so allocate a new one of the
// right size and copy.
byte[] temp = new byte[decoder.op];
System.arraycopy(decoder.output, 0, temp, 0, decoder.op);
return temp;
}
static class Decoder extends Coder {
private static final int DECODE[] = {
-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, -1, -1, 63,
52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -2, -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,
-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, -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, -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,
};
/**
* Decode lookup table for the "web safe" variant (RFC 3548
* sec. 4) where - and _ replace + and /.
*/
private static final int DECODE_WEBSAFE[] = {
-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, -1, -1, 62, -1, -1,
52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -2, -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, 63,
-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,
-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, -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, -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,
};
/** Non-data values in the DECODE arrays. */
private static final int SKIP = -1;
private static final int EQUALS = -2;
private int state; // state number (0 to 6)
private int value;
final private int[] alphabet;
public Decoder(int flags, byte[] output) {
this.output = output;
alphabet = ((flags & URL_SAFE) == 0) ? DECODE : DECODE_WEBSAFE;
state = 0;
value = 0;
}
public int maxOutputSize(int len) {
return len * 3/4 + 10;
}
/**
* Decode another block of input data.
*
* @return true if the state machine is still healthy. false if
* bad base-64 data has been detected in the input stream.
*/
public boolean process(byte[] input, int offset, int len, boolean finish) {
if (this.state == 6) return false;
int p = offset;
len += offset;
int state = this.state;
int value = this.value;
int op = 0;
final byte[] output = this.output;
final int[] alphabet = this.alphabet;
while (p < len) {
if (state == 0) {
while (p+4 <= len &&
(value = ((alphabet[input[p] & 0xff] << 18) |
(alphabet[input[p+1] & 0xff] << 12) |
(alphabet[input[p+2] & 0xff] << 6) |
(alphabet[input[p+3] & 0xff]))) >= 0) {
output[op+2] = (byte) value;
output[op+1] = (byte) (value >> 8);
output[op] = (byte) (value >> 16);
op += 3;
p += 4;
}
if (p >= len) break;
}
int d = alphabet[input[p++] & 0xff];
switch (state) {
case 0:
if (d >= 0) {
value = d;
++state;
} else if (d != SKIP) {
this.state = 6;
return false;
}
break;
case 1:
if (d >= 0) {
value = (value << 6) | d;
++state;
} else if (d != SKIP) {
this.state = 6;
return false;
}
break;
case 2:
if (d >= 0) {
value = (value << 6) | d;
++state;
} else if (d == EQUALS) {
// Emit the last (partial) output tuple;
// expect exactly one more padding character.
output[op++] = (byte) (value >> 4);
state = 4;
} else if (d != SKIP) {
this.state = 6;
return false;
}
break;
case 3:
if (d >= 0) {
// Emit the output triple and return to state 0.
value = (value << 6) | d;
output[op+2] = (byte) value;
output[op+1] = (byte) (value >> 8);
output[op] = (byte) (value >> 16);
op += 3;
state = 0;
} else if (d == EQUALS) {
// Emit the last (partial) output tuple;
// expect no further data or padding characters.
output[op+1] = (byte) (value >> 2);
output[op] = (byte) (value >> 10);
op += 2;
state = 5;
} else if (d != SKIP) {
this.state = 6;
return false;
}
break;
case 4:
if (d == EQUALS) {
++state;
} else if (d != SKIP) {
this.state = 6;
return false;
}
break;
case 5:
if (d != SKIP) {
this.state = 6;
return false;
}
break;
}
}
if (!finish) {
// We're out of input, but a future call could provide
// more.
this.state = state;
this.value = value;
this.op = op;
return true;
}
switch (state) {
case 0:
break;
case 1:
this.state = 6;
return false;
case 2:
output[op++] = (byte) (value >> 4);
break;
case 3:
output[op++] = (byte) (value >> 10);
output[op++] = (byte) (value >> 2);
break;
case 4:
this.state = 6;
return false;
case 5:
break;
}
this.state = state;
this.op = op;
return true;
}
}
// --------------------------------------------------------
// encoding
// --------------------------------------------------------
public static String encodeToString(byte[] input, int flags) {
try {
return new String(encode(input, flags), "US-ASCII");
} catch (UnsupportedEncodingException e) {
// US-ASCII is guaranteed to be available.
throw new AssertionError(e);
}
}
public static String encodeToString(byte[] input, int offset, int len, int flags) {
try {
return new String(encode(input, offset, len, flags), "US-ASCII");
} catch (UnsupportedEncodingException e) {
// US-ASCII is guaranteed to be available.
throw new AssertionError(e);
}
}
public static byte[] encode(byte[] input, int flags) {
return encode(input, 0, input.length, flags);
}
public static byte[] encode(byte[] input, int offset, int len, int flags) {
Encoder encoder = new Encoder(flags, null);
// Compute the exact length of the array we will produce.
int output_len = len / 3 * 4;
// Account for the tail of the data and the padding bytes, if any.
if (encoder.do_padding) {
if (len % 3 > 0) {
output_len += 4;
}
} else {
switch (len % 3) {
case 0: break;
case 1: output_len += 2; break;
case 2: output_len += 3; break;
}
}
// Account for the newlines, if any.
if (encoder.do_newline && len > 0) {
output_len += (((len-1) / (3 * Encoder.LINE_GROUPS)) + 1) *
(encoder.do_cr ? 2 : 1);
}
encoder.output = new byte[output_len];
encoder.process(input, offset, len, true);
assert encoder.op == output_len;
return encoder.output;
}
/* package */ static class Encoder extends Coder {
/**
* Emit a new line every this many output tuples. Corresponds to
* a 76-character line length (the maximum allowable according to
* <a href="http://www.ietf.org/rfc/rfc2045.txt">RFC 2045</a>).
*/
public static final int LINE_GROUPS = 19;
/**
* Lookup table for turning Base64 alphabet positions (6 bits)
* into output bytes.
*/
private static final byte ENCODE[] = {
'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', '+', '/',
};
/**
* Lookup table for turning Base64 alphabet positions (6 bits)
* into output bytes.
*/
private static final byte ENCODE_WEBSAFE[] = {
'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', '-', '_',
};
final private byte[] tail;
/* package */ int tailLen;
private int count;
final public boolean do_padding;
final public boolean do_newline;
final public boolean do_cr;
final private byte[] alphabet;
public Encoder(int flags, byte[] output) {
this.output = output;
do_padding = (flags & NO_PADDING) == 0;
do_newline = (flags & NO_WRAP) == 0;
do_cr = (flags & CRLF) != 0;
alphabet = ((flags & URL_SAFE) == 0) ? ENCODE : ENCODE_WEBSAFE;
tail = new byte[2];
tailLen = 0;
count = do_newline ? LINE_GROUPS : -1;
}
/**
* @return an overestimate for the number of bytes {@code
* len} bytes could encode to.
*/
public int maxOutputSize(int len) {
return len * 8/5 + 10;
}
public boolean process(byte[] input, int offset, int len, boolean finish) {
// Using local variables makes the encoder about 9% faster.
final byte[] alphabet = this.alphabet;
final byte[] output = this.output;
int op = 0;
int count = this.count;
int p = offset;
len += offset;
int v = -1;
// First we need to concatenate the tail of the previous call
// with any input bytes available now and see if we can empty
// the tail.
switch (tailLen) {
case 0:
// There was no tail.
break;
case 1:
if (p+2 <= len) {
// A 1-byte tail with at least 2 bytes of
// input available now.
v = ((tail[0] & 0xff) << 16) |
((input[p++] & 0xff) << 8) |
(input[p++] & 0xff);
tailLen = 0;
};
break;
case 2:
if (p+1 <= len) {
// A 2-byte tail with at least 1 byte of input.
v = ((tail[0] & 0xff) << 16) |
((tail[1] & 0xff) << 8) |
(input[p++] & 0xff);
tailLen = 0;
}
break;
}
if (v != -1) {
output[op++] = alphabet[(v >> 18) & 0x3f];
output[op++] = alphabet[(v >> 12) & 0x3f];
output[op++] = alphabet[(v >> 6) & 0x3f];
output[op++] = alphabet[v & 0x3f];
if (--count == 0) {
if (do_cr) output[op++] = '\r';
output[op++] = '\n';
count = LINE_GROUPS;
}
}
// At this point either there is no tail, or there are fewer
// than 3 bytes of input available.
// The main loop, turning 3 input bytes into 4 output bytes on
// each iteration.
while (p+3 <= len) {
v = ((input[p] & 0xff) << 16) |
((input[p+1] & 0xff) << 8) |
(input[p+2] & 0xff);
output[op] = alphabet[(v >> 18) & 0x3f];
output[op+1] = alphabet[(v >> 12) & 0x3f];
output[op+2] = alphabet[(v >> 6) & 0x3f];
output[op+3] = alphabet[v & 0x3f];
p += 3;
op += 4;
if (--count == 0) {
if (do_cr) output[op++] = '\r';
output[op++] = '\n';
count = LINE_GROUPS;
}
}
if (finish) {
if (p-tailLen == len-1) {
int t = 0;
v = ((tailLen > 0 ? tail[t++] : input[p++]) & 0xff) << 4;
tailLen -= t;
output[op++] = alphabet[(v >> 6) & 0x3f];
output[op++] = alphabet[v & 0x3f];
if (do_padding) {
output[op++] = '=';
output[op++] = '=';
}
if (do_newline) {
if (do_cr) output[op++] = '\r';
output[op++] = '\n';
}
} else if (p-tailLen == len-2) {
int t = 0;
v = (((tailLen > 1 ? tail[t++] : input[p++]) & 0xff) << 10) |
(((tailLen > 0 ? tail[t++] : input[p++]) & 0xff) << 2);
tailLen -= t;
output[op++] = alphabet[(v >> 12) & 0x3f];
output[op++] = alphabet[(v >> 6) & 0x3f];
output[op++] = alphabet[v & 0x3f];
if (do_padding) {
output[op++] = '=';
}
if (do_newline) {
if (do_cr) output[op++] = '\r';
output[op++] = '\n';
}
} else if (do_newline && op > 0 && count != LINE_GROUPS) {
if (do_cr) output[op++] = '\r';
output[op++] = '\n';
}
assert tailLen == 0;
assert p == len;
} else {
// Save the leftovers in tail to be consumed on the next
// call to encodeInternal.
if (p == len-1) {
tail[tailLen++] = input[p];
} else if (p == len-2) {
tail[tailLen++] = input[p];
tail[tailLen++] = input[p+1];
}
}
this.op = op;
this.count = count;
return true;
}
}
private Base64() { } // don't instantiate
}
番石榴现在内置了Base64解码。
使用BaseEncoding.base64 () .decode ()
至于处理输入使用中可能出现的空白
BaseEncoding.base64 () .decode (CharMatcher.WHITESPACE.removeFrom(…));
有关更多信息，请参阅此讨论
不需要使用commons——Sun在Java中附带了base64编码器。你可以这样导入它:
import sun.misc.BASE64Decoder;
然后像这样使用它:
BASE64Decoder decoder = new BASE64Decoder();
byte[] decodedBytes = decoder.decodeBuffer(encodedBytes);
其中encodedBytes是java.lang.String或java.io.InputStream。只是要当心太阳。*类不是Sun的“官方支持”。
编辑:谁能想到这将是我发表过的最具争议的答案呢?我知道太阳。*不支持或保证软件包继续存在，我确实了解Commons并一直在使用它。然而，发帖者要求一个“包含在Sun Java 6中”的类，这就是我试图回答的问题。总的来说，我同意Commons是最好的方式。
编辑2:正如amir75在下面指出的那样，Java 6+附带了JAXB，其中包含支持的编码/解码Base64的代码。请看下面Jeremy Ross的回答。
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