关于Java下奇怪的Base64详解

package jiangbo.java.lang;

import java.io.IOException;
import java.nio.charset.Charset;

import javax.xml.bind.DatatypeConverter;

import sun.misc.BASE64Decoder;
import sun.misc.BASE64Encoder;

public class Base64Demo {

  public static void main(String[] args) throws IOException {

    String name = "jiangbo";
    Charset utf8 = Charset.forName("UTF-8");

    BASE64Encoder base64Encoder = new sun.misc.BASE64Encoder();

    String BASE64EncoderString = base64Encoder.encode(name.getBytes(utf8));
    System.out.println(BASE64EncoderString);

    BASE64Decoder base64Decoder = new sun.misc.BASE64Decoder();
    byte[] decodeBuffer = base64Decoder.decodeBuffer(BASE64EncoderString);
    System.out.println(new String(decodeBuffer, utf8));

    String base64String = DatatypeConverter.printBase64Binary(name.getBytes(utf8));
    System.out.println(base64String);

    byte[] base64Binary = DatatypeConverter.parseBase64Binary(base64String);
    System.out.println(new String(base64Binary, utf8));
  }
}

public void decodeBuffer(InputStream var1, OutputStream var2) throws IOException {
  int var4 = 0;
  PushbackInputStream var5 = new PushbackInputStream(var1);
  this.decodeBufferPrefix(var5, var2);

  while(true) {
    try {
      int var6 = this.decodeLinePrefix(var5, var2);

      int var3;
      for(var3 = 0; var3 + this.bytesPerAtom() < var6; var3 += this.bytesPerAtom()) {
        this.decodeAtom(var5, var2, this.bytesPerAtom());
        var4 += this.bytesPerAtom();
      }

      if (var3 + this.bytesPerAtom() == var6) {
        this.decodeAtom(var5, var2, this.bytesPerAtom());
        var4 += this.bytesPerAtom();
      } else {
        this.decodeAtom(var5, var2, var6 - var3);
        var4 += var6 - var3;
      }

      this.decodeLineSuffix(var5, var2);
    } catch (CEStreamExhausted var8) {
      this.decodeBufferSuffix(var5, var2);
      return;
    }
  }
}

public void decodeBuffer(InputStream var1, OutputStream var2) throws IOException {
  int var4 = 0;
  PushbackInputStream var5 = new PushbackInputStream(var1);
  this.decodeBufferPrefix(var5, var2);

  while(true) {
    try {
      int var6 = this.decodeLinePrefix(var5, var2);
  
protected int decodeLinePrefix(PushbackInputStream var1, OutputStream var2) throws IOException {
    return this.bytesPerLine();
  }
  
  protected int bytesPerLine() {
    return 72;
  }

      int var3;
      for(var3 = 0; var3 + this.bytesPerAtom() < var6; var3 += this.bytesPerAtom()) {
        this.decodeAtom(var5, var2, this.bytesPerAtom());
        var4 += this.bytesPerAtom();
      }
      
protected int bytesPerAtom() {
  return 4;
}

protected void decodeAtom(PushbackInputStream var1, OutputStream var2, int var3) throws IOException {
  byte var5 = -1;
  byte var6 = -1;
  byte var7 = -1;
  byte var8 = -1;
  if (var3 < 2) {
    throw new CEFormatException("BASE64Decoder: Not enough bytes for an atom.");
  } else {
    int var4;
    do {
      var4 = var1.read();
      if (var4 == -1) {
        throw new CEStreamExhausted();
      }
    } while(var4 == 10 || var4 == 13);

    this.decode_buffer[0] = (byte)var4;
    var4 = this.readFully(var1, this.decode_buffer, 1, var3 - 1);

if (var4 == -1) {
  throw new CEStreamExhausted();

private int decode0(byte[] src, int sp, int sl, byte[] dst) {
  int[] base64 = isURL ? fromBase64URL : fromBase64;
  int dp = 0;
  int bits = 0;
  int shiftto = 18;    // pos of first byte of 4-byte atom
  while (sp < sl) {
    int b = src[sp++] & 0xff;
    if ((b = base64[b]) < 0) {
      if (b == -2) {     // padding byte '='
        // =   shiftto==18 unnecessary padding
        // x=  shiftto==12 a dangling single x
        // x   to be handled together with non-padding case
        // xx=  shiftto==6&&sp==sl missing last =
        // xx=y shiftto==6 last is not =
        if (shiftto == 6 && (sp == sl || src[sp++] != '=') ||
          shiftto == 18) {
          throw new IllegalArgumentException(
            "Input byte array has wrong 4-byte ending unit");
        }
        break;
      }
      if (isMIME)  // skip if for rfc2045
        continue;
      else
        throw new IllegalArgumentException(
          "Illegal base64 character " +
          Integer.toString(src[sp - 1], 16));
    }

public static byte[] decode(byte[] src) {
  return src.length == 0 ? src : Base64.getDecoder().decode(src);
}
public static Decoder getDecoder() {
   return Decoder.RFC4648;
}
  static final Decoder RFC4648     = new Decoder(false, false);
  static final Decoder RFC4648_URLSAFE = new Decoder(true, false);
  static final Decoder RFC2045     = new Decoder(false, true);