解码base64字符串Java 5

Question

Is there a straight forward way to decode a base64 string using ONLY THE JAVA 1.5 LIBRARIES?

I have to use Java 1.5 due to cross platform compatibility issues between Windows and Mac OS X (only Mac 10.5 supports Java 1.6, everything lower than 10.5 has Java 1.5 as default).

The object "sun.misc.Base64Decoder" exists in Java 6, but not in Java 5.

Answer 1

No, it's not possible based on just using JDK 5.0.

You'll need to roll your own implementation (it isn't that hard) or preferably use one of the open source implementations. There are lots including Commons Codec which provides Base64 http://commons.apache.org/codec/api-release/org/apache/commons/codec/binary/Base64.html

JavaMail also provides Base64 encoding/decoding via MimeUtility which also does quoted printable encoding etc...

http://java.sun.com/products/javamail/javadocs/javax/mail/internet/MimeUtility.html

Answer 2

Apache Commons Codec

FYI, you should be using this even in Java 6. Don't use classes in sun.*

Answer 3

Just use http://iharder.sourceforge.net/current/java/base64/ . It is in the public domain. So you can just drop the code into your project without worrying about license issues or including other jars. The class you are looking for is not in JDK 1.5.

Answer 4

Here's my version - it should be completely standalone:

public class Base64
{

// *****************************************************************************
// INSTANCE PROPERTIES
// *****************************************************************************

private String                          lineSeparator;
private int                             lineLength;

// *****************************************************************************
// INSTANCE CONSTRUCTION/INITIALIZATON/FINALIZATION, OPEN/CLOSE
// *****************************************************************************

public Base64() {
    lineSeparator=System.getProperty("line.separator");
    lineLength=0;
    }

// *****************************************************************************
// INSTANCE METHODS
// *****************************************************************************

public String encode(byte[] bin) {
    return encode(bin,0,bin.length);
    }
/**
 * Encode an array of bytes as Base64.
 * It will be broken into lines if the line length is not 0.  If broken into lines,
 * the last line is not terminated with a line separator.
 *
 * param ba         The byte array to encode.
 */
public String encode(byte[] bin, int str, int len) {
    int                                 ol;                                     // output length
    StringBuffer                        sb;                                     // string buffer for output(must be local for recursion to work).
    int                                 lp;                                     // line position(must be local for recursion to work).
    int                                 el;                                     // even multiple of 3 length
    int                                 ll;                                     // leftover length

    // CREATE OUTPUT BUFFER
    ol=(((len+2)/3)*4);
    if(lineLength!=0) {
        int lines=(((ol+lineLength-1)/lineLength)-1);
        if(lines>0) { ol+=(lines*lineSeparator.length()); }
        }
    sb=new StringBuffer(ol);
    lp=0;

    // EVEN MULTIPLES OF 3
    el=(len/3)*3;
    ll=(len-el);
    for(int xa=0; xa<el; xa+=3) {
        int cv;
        int c0,c1,c2,c3;

        if(lineLength!=0) {
            lp+=4;
            if(lp>lineLength) { sb.append(lineSeparator); lp=4; }
            }

        // get next three bytes in unsigned form lined up, in big-endian order
        cv =(bin[xa+str+0]&0xFF); cv<<=8;
        cv|=(bin[xa+str+1]&0xFF); cv<<=8;
        cv|=(bin[xa+str+2]&0xFF);

        // break those 24 bits into a 4 groups of 6 bits, working LSB to MSB.
        c3=cv&0x3F; cv >>>=6;
        c2=cv&0x3F; cv >>>=6;
        c1=cv&0x3F; cv >>>=6;
        c0=cv&0x3F;

        // Translate into the equivalent alpha character emitting them in big-endian order.
        sb.append(ENCODE[c0]);
        sb.append(ENCODE[c1]);
        sb.append(ENCODE[c2]);
        sb.append(ENCODE[c3]);
        }

    // LEFTOVERS
    if(lineLength!=0 && ll>0) {
        lp+=4;
        if(lp>lineLength) { sb.append(lineSeparator); lp=4; }
        }
    if(ll==1) {
        sb.append(encode(new byte[] { bin[el+str], 0, 0 }).substring(0,2)).append("==");            // Use recursion so escaping logic is not repeated, replacing last 2 chars with "==".
        }
    else if(ll==2) {
        sb.append(encode(new byte[] { bin[el+str], bin[el+str+1], 0 }).substring(0,3)).append("="); // Use recursion so escaping logic is not repeated, replacing last char and  "=".
        }
    if(ol!=sb.length()) { throw new RuntimeException("Error in Base64 encoding method: Calculated output length of "+ol+" did not match actual length of "+sb.length()); }
    return sb.toString();
    }

public byte[] decode(String b64) {
    return decode(b64,0,b64.length());
    }

/**
 * Decode a Base64 string to an array of bytes.
 * The string must have a length evenly divisible by 4 (not counting line separators and other
 * ignorable characters, like whitespace).
 */
public byte[] decode(String b64, int str, int len) {
    byte[]                              ba;                                     // target byte array
    int                                 dc;                                     // decode cycle (within sequence of 4 input chars).
    int                                 rv;                                     // reconstituted value
    int                                 ol;                                     // output length
    int                                 pc;                                     // padding count

    ba=new byte[(len/4)*3];                                                     // create array to largest possible size.
    dc=0;
    rv=0;
    ol=0;
    pc=0;

    for(int xa=0; xa<len; xa++) {
        int ch=b64.charAt(xa+str);
        int value=(ch<=255 ? DECODE[ch] : IGNORE);
        if(value!=IGNORE) {
            if(value==PAD) {
                value=0;
                pc++;
                }
            switch(dc) {
                case 0: {
                    rv=value;
                    dc=1;
                    } break;

                case 1: {
                    rv<<=6;
                    rv|=value;
                    dc=2;
                    } break;

                case 2: {
                    rv<<=6;
                    rv|=value;
                    dc=3;
                    } break;

                case 3: {
                    rv<<=6;
                    rv|=value;

                    // Completed a cycle of 4 chars, so recombine the four 6-bit values in big-endian order
                    ba[ol+2]=(byte)rv;  rv>>>=8;
                    ba[ol+1]=(byte)rv;  rv>>>=8;
                    ba[ol]=(byte)rv;    ol+=3;
                    dc=0;
                    } break;
                }
            }
        }
    if(dc!=0) {
        throw new ArrayIndexOutOfBoundsException("Base64 data given as input was not an even multiple of 4 characters (should be padded with '=' characters).");
        }
    ol-=pc;
    if(ba.length!=ol) {
        byte[] b2=new byte[ol];
        System.arraycopy(ba, 0, b2, 0, ol);
        ba=b2;
        }
    return ba;
    }

/**
* Set maximum line length for encoded lines.
* Ignored by decode.
* @param len        Length of each line. 0 means no newlines inserted. Must be a multiple of 4.
*/
public void setLineLength(int len) {
  this.lineLength=(len/4)*4;
  }

/**
* Set the line separator sequence for encoded lines.
* Ignored by decode.
* Usually contains only a combination of chars \n and \r, but could be any chars except 'A'-'Z', 'a'-'z', '0'-'9', '+' and '/'.
* @param linsep     Line separator - may be "" but not null.
*/
public void setLineSeparator(String linsep) {
  this.lineSeparator=linsep;
  }

// *****************************************************************************
// STATIC PROPERTIES
// *****************************************************************************

static private final char[]             ENCODE=new char[64];                    // translation array for encoding
static private final int[]              DECODE=new int[256];                    // translation array for decoding
static private final int                IGNORE=-1;                              // flag for values to ignore when decoding
static private final int                PAD=-2;                                 // flag value for padding value when decoding

static private final Base64             BASE64=new Base64();                    // default converter

// *****************************************************************************
// STATIC INIT & MAIN
// *****************************************************************************

static {
    for(int xa=0; xa<=25; xa++) { ENCODE[xa]=(char)('A'+xa); }                  //  0..25 -> 'A'..'Z'
    for(int xa=0; xa<=25; xa++) { ENCODE[xa+26]=(char)('a'+xa); }               // 26..51 -> 'a'..'z'
    for(int xa=0; xa<= 9; xa++) { ENCODE[xa+52]=(char)('0'+xa); }               // 52..61 -> '0'..'9'
    ENCODE[62]='+';
    ENCODE[63]='/';

    for(int xa=0; xa<256; xa++) { DECODE[xa]=IGNORE;     }                      // set all chars to IGNORE, first
    for(int xa=0; xa< 64; xa++) { DECODE[ENCODE[xa]]=xa; }                      // set the Base 64 chars to their integer byte values
    DECODE['=']=PAD;
    }

// *****************************************************************************
// STATIC METHODS
// *****************************************************************************

static public String toString(byte[] dta) {
    return BASE64.encode(dta);
    }

static public String toString(byte[] dta, int str, int len) {
    return BASE64.encode(dta,str,len);
    }

static public byte[] toBytes(String b64) {
    return BASE64.decode(b64);
    }

static public byte[] toBytes(String b64, int str, int len) {
    return BASE64.decode(b64,str,len);
    }

} // END PUBLIC CLASS

Answer 5

此页面上还有各种实现： http ： //www.rgagnon.com/javadetails/java-0598.html