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
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
其他回答
你可以简单地试试这个。
byte[] data = Base64.getDecoder().decode(base64fileContent);
Base64. getdecode()返回一个可以解码的Base64解码器。然后你需要再次使用.decode(<your base64>)解码。
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
从Java 8开始,就有了官方支持的用于Base64编码和解码的API。 随着时间的推移,这可能会成为默认的选择。
该API包括java.util类。Base64及其嵌套类。它支持三种不同的风格:基本的、URL安全的和MIME。
使用“基本”编码的示例代码:
import java.util.Base64;
byte[] bytes = "Hello, World!".getBytes("UTF-8");
String encoded = Base64.getEncoder().encodeToString(bytes);
byte[] decoded = Base64.getDecoder().decode(encoded);
String decodedStr = new String(decoded, StandardCharsets.UTF_8);
java.util的文档。Base64还包括一些配置编码器和解码器的方法,以及使用不同的类作为输入和输出(字节数组,字符串,ByteBuffers, java。io流)。
在用Java 7编译但可能运行在更高Java版本的代码中,检测Java .util的存在似乎很有用。Base64类,并使用在这里的其他问题中提到的给定JVM的最佳方法。
我使用了下面的代码:
private static final Method JAVA_UTIL_BASE64_GETENCODER;
static {
Method getEncoderMethod;
try {
final Class<?> base64Class = Class.forName("java.util.Base64");
getEncoderMethod = base64Class.getMethod("getEncoder");
} catch (ClassNotFoundException | NoSuchMethodException e) {
getEncoderMethod = null;
}
JAVA_UTIL_BASE64_GETENCODER = getEncoderMethod;
}
static String base64EncodeToString(String s) {
final byte[] bytes = s.getBytes(StandardCharsets.ISO_8859_1);
if (JAVA_UTIL_BASE64_GETENCODER == null) {
// Java 7 and older // TODO: remove this branch after switching to Java 8
return DatatypeConverter.printBase64Binary(bytes);
} else {
// Java 8 and newer
try {
final Object encoder = JAVA_UTIL_BASE64_GETENCODER.invoke(null);
final Class<?> encoderClass = encoder.getClass();
final Method encodeMethod = encoderClass.getMethod("encode", byte[].class);
final byte[] encodedBytes = (byte[]) encodeMethod.invoke(encoder, bytes);
return new String(encodedBytes);
} catch (NoSuchMethodException | IllegalAccessException | InvocationTargetException e) {
throw new IllegalStateException(e);
}
}
}
这是我自己的实现,如果它对某人有用的话:
public class Base64Coder {
// The line separator string of the operating system.
private static final String systemLineSeparator = System.getProperty("line.separator");
// Mapping table from 6-bit nibbles to Base64 characters.
private static final char[] map1 = new char[64];
static {
int i=0;
for (char c='A'; c<='Z'; c++) map1[i++] = c;
for (char c='a'; c<='z'; c++) map1[i++] = c;
for (char c='0'; c<='9'; c++) map1[i++] = c;
map1[i++] = '+'; map1[i++] = '/'; }
// Mapping table from Base64 characters to 6-bit nibbles.
private static final byte[] map2 = new byte[128];
static {
for (int i=0; i<map2.length; i++) map2[i] = -1;
for (int i=0; i<64; i++) map2[map1[i]] = (byte)i; }
/**
* Encodes a string into Base64 format.
* No blanks or line breaks are inserted.
* @param s A String to be encoded.
* @return A String containing the Base64 encoded data.
*/
public static String encodeString (String s) {
return new String(encode(s.getBytes())); }
/**
* Encodes a byte array into Base 64 format and breaks the output into lines of 76 characters.
* This method is compatible with <code>sun.misc.BASE64Encoder.encodeBuffer(byte[])</code>.
* @param in An array containing the data bytes to be encoded.
* @return A String containing the Base64 encoded data, broken into lines.
*/
public static String encodeLines (byte[] in) {
return encodeLines(in, 0, in.length, 76, systemLineSeparator); }
/**
* Encodes a byte array into Base 64 format and breaks the output into lines.
* @param in An array containing the data bytes to be encoded.
* @param iOff Offset of the first byte in <code>in</code> to be processed.
* @param iLen Number of bytes to be processed in <code>in</code>, starting at <code>iOff</code>.
* @param lineLen Line length for the output data. Should be a multiple of 4.
* @param lineSeparator The line separator to be used to separate the output lines.
* @return A String containing the Base64 encoded data, broken into lines.
*/
public static String encodeLines (byte[] in, int iOff, int iLen, int lineLen, String lineSeparator) {
int blockLen = (lineLen*3) / 4;
if (blockLen <= 0) throw new IllegalArgumentException();
int lines = (iLen+blockLen-1) / blockLen;
int bufLen = ((iLen+2)/3)*4 + lines*lineSeparator.length();
StringBuilder buf = new StringBuilder(bufLen);
int ip = 0;
while (ip < iLen) {
int l = Math.min(iLen-ip, blockLen);
buf.append (encode(in, iOff+ip, l));
buf.append (lineSeparator);
ip += l; }
return buf.toString(); }
/**
* Encodes a byte array into Base64 format.
* No blanks or line breaks are inserted in the output.
* @param in An array containing the data bytes to be encoded.
* @return A character array containing the Base64 encoded data.
*/
public static char[] encode (byte[] in) {
return encode(in, 0, in.length); }
/**
* Encodes a byte array into Base64 format.
* No blanks or line breaks are inserted in the output.
* @param in An array containing the data bytes to be encoded.
* @param iLen Number of bytes to process in <code>in</code>.
* @return A character array containing the Base64 encoded data.
*/
public static char[] encode (byte[] in, int iLen) {
return encode(in, 0, iLen); }
/**
* Encodes a byte array into Base64 format.
* No blanks or line breaks are inserted in the output.
* @param in An array containing the data bytes to be encoded.
* @param iOff Offset of the first byte in <code>in</code> to be processed.
* @param iLen Number of bytes to process in <code>in</code>, starting at <code>iOff</code>.
* @return A character array containing the Base64 encoded data.
*/
public static char[] encode (byte[] in, int iOff, int iLen) {
int oDataLen = (iLen*4+2)/3; // output length without padding
int oLen = ((iLen+2)/3)*4; // output length including padding
char[] out = new char[oLen];
int ip = iOff;
int iEnd = iOff + iLen;
int op = 0;
while (ip < iEnd) {
int i0 = in[ip++] & 0xff;
int i1 = ip < iEnd ? in[ip++] & 0xff : 0;
int i2 = ip < iEnd ? in[ip++] & 0xff : 0;
int o0 = i0 >>> 2;
int o1 = ((i0 & 3) << 4) | (i1 >>> 4);
int o2 = ((i1 & 0xf) << 2) | (i2 >>> 6);
int o3 = i2 & 0x3F;
out[op++] = map1[o0];
out[op++] = map1[o1];
out[op] = op < oDataLen ? map1[o2] : '='; op++;
out[op] = op < oDataLen ? map1[o3] : '='; op++; }
return out; }
/**
* Decodes a string from Base64 format.
* No blanks or line breaks are allowed within the Base64 encoded input data.
* @param s A Base64 String to be decoded.
* @return A String containing the decoded data.
* @throws IllegalArgumentException If the input is not valid Base64 encoded data.
*/
public static String decodeString (String s) {
return new String(decode(s)); }
/**
* Decodes a byte array from Base64 format and ignores line separators, tabs and blanks.
* CR, LF, Tab and Space characters are ignored in the input data.
* This method is compatible with <code>sun.misc.BASE64Decoder.decodeBuffer(String)</code>.
* @param s A Base64 String to be decoded.
* @return An array containing the decoded data bytes.
* @throws IllegalArgumentException If the input is not valid Base64 encoded data.
*/
public static byte[] decodeLines (String s) {
char[] buf = new char[s.length()];
int p = 0;
for (int ip = 0; ip < s.length(); ip++) {
char c = s.charAt(ip);
if (c != ' ' && c != '\r' && c != '\n' && c != '\t')
buf[p++] = c; }
return decode(buf, 0, p); }
/**
* Decodes a byte array from Base64 format.
* No blanks or line breaks are allowed within the Base64 encoded input data.
* @param s A Base64 String to be decoded.
* @return An array containing the decoded data bytes.
* @throws IllegalArgumentException If the input is not valid Base64 encoded data.
*/
public static byte[] decode (String s) {
return decode(s.toCharArray()); }
/**
* Decodes a byte array from Base64 format.
* No blanks or line breaks are allowed within the Base64 encoded input data.
* @param in A character array containing the Base64 encoded data.
* @return An array containing the decoded data bytes.
* @throws IllegalArgumentException If the input is not valid Base64 encoded data.
*/
public static byte[] decode (char[] in) {
return decode(in, 0, in.length); }
/**
* Decodes a byte array from Base64 format.
* No blanks or line breaks are allowed within the Base64 encoded input data.
* @param in A character array containing the Base64 encoded data.
* @param iOff Offset of the first character in <code>in</code> to be processed.
* @param iLen Number of characters to process in <code>in</code>, starting at <code>iOff</code>.
* @return An array containing the decoded data bytes.
* @throws IllegalArgumentException If the input is not valid Base64 encoded data.
*/
public static byte[] decode (char[] in, int iOff, int iLen) {
if (iLen%4 != 0) throw new IllegalArgumentException ("Length of Base64 encoded input string is not a multiple of 4.");
while (iLen > 0 && in[iOff+iLen-1] == '=') iLen--;
int oLen = (iLen*3) / 4;
byte[] out = new byte[oLen];
int ip = iOff;
int iEnd = iOff + iLen;
int op = 0;
while (ip < iEnd) {
int i0 = in[ip++];
int i1 = in[ip++];
int i2 = ip < iEnd ? in[ip++] : 'A';
int i3 = ip < iEnd ? in[ip++] : 'A';
if (i0 > 127 || i1 > 127 || i2 > 127 || i3 > 127)
throw new IllegalArgumentException ("Illegal character in Base64 encoded data.");
int b0 = map2[i0];
int b1 = map2[i1];
int b2 = map2[i2];
int b3 = map2[i3];
if (b0 < 0 || b1 < 0 || b2 < 0 || b3 < 0)
throw new IllegalArgumentException ("Illegal character in Base64 encoded data.");
int o0 = ( b0 <<2) | (b1>>>4);
int o1 = ((b1 & 0xf)<<4) | (b2>>>2);
int o2 = ((b2 & 3)<<6) | b3;
out[op++] = (byte)o0;
if (op<oLen) out[op++] = (byte)o1;
if (op<oLen) out[op++] = (byte)o2; }
return out; }
// Dummy constructor.
private Base64Coder() {}
}
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