base64decoder.java

数字图书馆的互操作接口

// Base64Decoder.java
// $Id: Base64Decoder.java,v 1.1 1999/07/17 01:53:29 melnik Exp $
// (c) COPYRIGHT MIT and INRIA, 1996.
// Please first read the full copyright statement in file COPYRIGHT.html

package org.w3c.tools.codec ;

import java.io.* ;

/**
 * Decode a BASE64 encoded input stream to some output stream.
 * This class implements BASE64 decoding, as specified in the
 * <a href="http://ds.internic.net/rfc/rfc1521.txt">MIME specification</a>.
 * @see w3c.tools.code.Base64Encoder
 */

public class Base64Decoder {
    private static final int BUFFER_SIZE = 1024 ;

    InputStream in       = null ;
    OutputStream out     = null ;
    boolean      stringp = false ;

    private void printHex (int x) {
	int h = (x&0xf0) >> 4 ;
	int l = (x&0x0f) ;
	System.out.print
	    ((new Character((char)((h>9) ? 'A'+h-10 : '0'+h))).toString()
	     +(new Character((char)((l>9) ? 'A'+l-10 : '0'+l))).toString());
    }

    private void printHex (byte buf[], int off, int len) {
	while (off < len) {
	    printHex (buf[off++]) ;
	    System.out.print (" ") ;
	}
	System.out.println ("") ;
    }

    private void printHex (String s) {
	byte bytes[] = s.getBytes () ;
	printHex (bytes, 0, bytes.length) ;
    }


    private final int get1 (byte buf[], int off) {
	return ((buf[off] & 0x3f) << 2) | ((buf[off+1] & 0x30) >>> 4) ;
    }

    private final int get2 (byte buf[], int off) {
	return ((buf[off+1] & 0x0f) << 4) | ((buf[off+2] &0x3c) >>> 2) ;
    }

    private final int get3 (byte buf[], int off) {
	return ((buf[off+2] & 0x03) << 6) | (buf[off+3] & 0x3f) ;
    }

    private final int check (int ch) {
	if ((ch >= 'A') && (ch <= 'Z')) {
	    return ch - 'A' ;
	} else if ((ch >= 'a') && (ch <= 'z')) {
	    return ch - 'a' + 26 ;
	} else if ((ch >= '0') && (ch <= '9')) {
	    return ch - '0' + 52 ;
	} else {
	    switch (ch) {
	      case '=':
		  return 65 ;
	      case '+':
		  return 62 ;
	      case '/':
		  return 63 ;
	      default:
		  return -1 ;
	    }
	}
    }

    /**
     * Do the actual decoding.
     * Process the input stream by decoding it and emiting the resulting bytes
     * into the output stream.
     * @exception IOException If the input or output stream accesses failed.
     * @exception Base64FormatException If the input stream is not compliant
     *    with the BASE64 specification.
     */

    public void process ()
	throws IOException, Base64FormatException
    {
	byte buffer[] = new byte[BUFFER_SIZE] ;
	byte chunk[]  = new byte[4] ;
	int  got      = -1 ;
	int  ready    = 0 ;

    fill:
	while ((got = in.read(buffer)) > 0) {
	    int skiped = 0 ;
	    while ( skiped < got ) {
		// Check for un-understood characters:
		while ( ready < 4 ) {
		    if ( skiped >= got )
			continue fill ;
		    int ch = check (buffer[skiped++]) ;
		    if ( ch >= 0 )
			chunk[ready++] = (byte) ch ;
		}
		if ( chunk[2] == 65 ) {
		    out.write(get1(chunk, 0));
		    return ;
		} else if ( chunk[3] == 65 ) {
		    out.write(get1(chunk, 0)) ;
		    out.write(get2(chunk, 0)) ;
		    return ;
		} else {
		    out.write(get1(chunk, 0)) ;
		    out.write(get2(chunk, 0)) ;
		    out.write(get3(chunk, 0)) ;
		}
		ready = 0 ;
	    }
	}
	if ( ready != 0 )
	    throw new Base64FormatException ("Invalid length.") ;
	out.flush() ;
    }

    /**
     * Do the decoding, and return a String.
     * This methods should be called when the decoder is used in
     * <em>String</em> mode. It decodes the input string to an output string
     * that is returned.
     * @exception RuntimeException If the object wasn't constructed to
     *    decode a String.
     * @exception Base64FormatException If the input string is not compliant
     *     with the BASE64 specification.
     */

    public String processString ()
	throws Base64FormatException
    {
	if ( ! stringp )
	    throw new RuntimeException (this.getClass().getName()
					+ "[processString]"
					+ "invalid call (not a String)");
	try {
	    process() ;
	} catch (IOException e) {
	}
	return ((ByteArrayOutputStream) out).toString() ;
    }

    /**
     * Create a decoder to decode a String.
     * @param input The string to be decoded.
     */

    public Base64Decoder (String input) {
	byte bytes[] = input.getBytes () ;
	this.stringp = true ;
	this.in      = new ByteArrayInputStream(bytes) ;
	this.out     = new ByteArrayOutputStream () ;
    }

    /**
     * Create a decoder to decode a stream.
     * @param in The input stream (to be decoded).
     * @param out The output stream, to write decoded data to.
     */

    public Base64Decoder (InputStream in, OutputStream out) {
	this.in = in ;
	this.out = out ;
	this.stringp = false ;
    }

    /**
     * Test the decoder.
     * Run it with one argument: the string to be decoded, it will print out
     * the decoded value.
     */

    public static void main (String args[]) {
	if (  true ) {
	    try {
		Base64Decoder b = new Base64Decoder ("YWpmYXM7N2xka2UsamFzOzdsZGssamFzO2Rsa2pzYTtkZmxranNhZGY7bGssanNhZGY7bGthc2pk\n\r" +
"Zjtsa2FqczthbGtzamQ7YTdzbGtqOzdzYWxrZGVqZjs3c2Fsa2RlamY7czdhZGtqd3Bsa2pvaWV1\n\r" +
"b2VpcnVqYWtsZGVqZmxhc2RrZWpmbGFzZGZqb2FzaWRqZmFzZG9pamFzZGZvYXNraWhkamZhc29p\n\r" +
"ZGZqd2Vqam56MTIzMjQ1ajgzMmQyMzI0MmRzMjNlMjM0c2RkYTNxZmRhc2QyM2RmMzQyZWV3ZjIz\n\r" +
"cjQ1Zg==") ;
		System.out.println ("["+b.processString()+"]") ;
	    } catch (Base64FormatException e) {
		System.out.println ("Invalid Base64 format !") ;
		System.exit (1) ;
	    }
	} else if ((args.length == 2) && (args[0].equals("-f"))) {
	    try {
		FileInputStream in = new FileInputStream(args[1]) ;
		Base64Decoder b = new Base64Decoder (in, System.out);
		b.process();
	    } catch (Exception ex) {
		System.out.println("error: " + ex.getMessage());
		System.exit(1) ;
	    }
	} else {
	    System.out.println("Base64Decoder [strong] [-f file]");
	}
	System.exit (0) ;
    }
}