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Extensions to JSR-173 StAX API.
There is a newer version: 2.1.0
/*
 * Copyright (c) 2011, 2018 Oracle and/or its affiliates. All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Distribution License v. 1.0, which is available at
 * http://www.eclipse.org/org/documents/edl-v10.php.
 *
 * SPDX-License-Identifier: BSD-3-Clause
 */

package org.jvnet.staxex;

import java.io.*;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.xml.stream.XMLStreamException;
import javax.xml.stream.XMLStreamWriter;

// for testing method
//import com.sun.xml.stream.writers.XMLStreamWriterImpl;

/**
 * This class implements a BASE64 Encoder. It is implemented as
 * a FilterOutputStream, so one can just wrap this class around
 * any output stream and write bytes into this filter. The Encoding
 * is done as the bytes are written out.
 *
 * @author John Mani
 * @author Bill Shannon
 * @author Martin Grebac
 */

public class Base64EncoderStream extends FilterOutputStream {
    private byte[] buffer; 	// cache of bytes that are yet to be encoded
    private int bufsize = 0;	// size of the cache

    private XMLStreamWriter outWriter;

    public Base64EncoderStream(OutputStream out) {
        super(out);
	buffer = new byte[3];
    }

    /**
     * Create a BASE64 encoder that encodes the specified input stream
     */
    public Base64EncoderStream(XMLStreamWriter outWriter, OutputStream out) {
        super(out);
	buffer = new byte[3];
        this.outWriter = outWriter;
    }

    /**
     * Encodes len bytes from the specified
     * byte array starting at offset off to
     * this output stream.
     *
     * @param      b     the data.
     * @param      off   the start offset in the data.
     * @param      len   the number of bytes to write.
     * @exception  IOException  if an I/O error occurs.
     */
    @Override
    public void write(byte[] b, int off, int len) throws IOException {
	for (int i = 0; i < len; i++)
	    write(b[off + i]);
    }

    /**
     * Encodes b.length bytes to this output stream.
     * @param      b   the data to be written.
     * @exception  IOException  if an I/O error occurs.
     */
    @Override
    public void write(byte[] b) throws IOException {
	write(b, 0, b.length);
    }

    /**
     * Encodes the specified byte to this output stream.
     * @param      c   the byte.
     * @exception  IOException  if an I/O error occurs.
     */
    @Override
    public void write(int c) throws IOException {
	buffer[bufsize++] = (byte)c;
	if (bufsize == 3) { // Encoding unit = 3 bytes
	    encode();
	    bufsize = 0;
	}
    }

    /**
     * Flushes this output stream and forces any buffered output bytes
     * to be encoded out to the stream.
     * @exception  IOException  if an I/O error occurs.
     */
    @Override
    public void flush() throws IOException {
	if (bufsize > 0) { // If there's unencoded characters in the buffer ..
	    encode();      // .. encode them
	    bufsize = 0;
	}
	out.flush();
        try {
            outWriter.flush();
        } catch (XMLStreamException ex) {
            Logger.getLogger(Base64EncoderStream.class.getName()).log(Level.SEVERE, null, ex);
            throw new IOException(ex);
        }
    }

    /**
     * Forces any buffered output bytes to be encoded out to the stream
     * and closes this output stream
     */
    @Override
    public void close() throws IOException {
	flush();
	out.close();
    }

    /** This array maps the characters to their 6 bit values */
    private final static char pem_array[] = {
	'A','B','C','D','E','F','G','H', // 0
	'I','J','K','L','M','N','O','P', // 1
	'Q','R','S','T','U','V','W','X', // 2
	'Y','Z','a','b','c','d','e','f', // 3
	'g','h','i','j','k','l','m','n', // 4
	'o','p','q','r','s','t','u','v', // 5
	'w','x','y','z','0','1','2','3', // 6
	'4','5','6','7','8','9','+','/'  // 7
    };

    private void encode() throws IOException {
	byte a, b, c;
        char[] buf = new char[4];
	if (bufsize == 1) {
	    a = buffer[0];
	    b = 0;
	    c = 0;
	    buf[0] = pem_array[(a >>> 2) & 0x3F];
	    buf[1] = pem_array[((a << 4) & 0x30) + ((b >>> 4) & 0xf)];
	    buf[2] = '='; // pad character
	    buf[3] = '='; // pad character
	} else if (bufsize == 2) {
	    a = buffer[0];
	    b = buffer[1];
	    c = 0;
	    buf[0] = pem_array[(a >>> 2) & 0x3F];
	    buf[1] = pem_array[((a << 4) & 0x30) + ((b >>> 4) & 0xf)];
	    buf[2] = pem_array[((b << 2) & 0x3c) + ((c >>> 6) & 0x3)];
	    buf[3] = '='; // pad character
	} else {
	    a = buffer[0];
	    b = buffer[1];
	    c = buffer[2];
	    buf[0] = pem_array[(a >>> 2) & 0x3F];
	    buf[1] = pem_array[((a << 4) & 0x30) + ((b >>> 4) & 0xf)];
	    buf[2] = pem_array[((b << 2) & 0x3c) + ((c >>> 6) & 0x3)];
	    buf[3] = pem_array[c & 0x3F];
        }
        try {
            outWriter.writeCharacters(buf, 0, 4);
        } catch (XMLStreamException ex) {
            Logger.getLogger(Base64EncoderStream.class.getName()).log(Level.SEVERE, null, ex);
            throw new IOException(ex);
        }
    }

//    public static void main(String argv[]) throws Exception {
//	FileInputStream infile = new FileInputStream(new File(argv[0]));
//        StringWriter sw = new StringWriter();
//        XMLStreamWriterImpl wi = new XMLStreamWriterImpl(sw, null);
//        ByteArrayOutputStream baos = new ByteArrayOutputStream();
//	Base64EncoderStream encoder = new Base64EncoderStream(wi, baos);
//	int c;
//
//	while ((c = infile.read()) != -1)
//	    encoder.write(c);
//	encoder.close();
//        
//        System.out.println("SW: " + sw.toString());
//        System.out.println("BAOS: " + baos.toString());
//
//    }
}