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Sun Java Streaming XML Parser (SJSXP) is the implementation of JSR 173.
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/*
 * $Id: UTF8OutputStreamWriter.java,v 1.4 2007-07-19 22:33:14 ofung Exp $
 */

/*
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER.
 * 
 * Copyright 1997-2007 Sun Microsystems, Inc. All rights reserved.
 * 
 * The contents of this file are subject to the terms of either the GNU
 * General Public License Version 2 only ("GPL") or the Common Development
 * and Distribution License("CDDL") (collectively, the "License").  You
 * may not use this file except in compliance with the License. You can obtain
 * a copy of the License at https://glassfish.dev.java.net/public/CDDL+GPL.html
 * or glassfish/bootstrap/legal/LICENSE.txt.  See the License for the specific
 * language governing permissions and limitations under the License.
 * 
 * When distributing the software, include this License Header Notice in each
 * file and include the License file at glassfish/bootstrap/legal/LICENSE.txt.
 * Sun designates this particular file as subject to the "Classpath" exception
 * as provided by Sun in the GPL Version 2 section of the License file that
 * accompanied this code.  If applicable, add the following below the License
 * Header, with the fields enclosed by brackets [] replaced by your own
 * identifying information: "Portions Copyrighted [year]
 * [name of copyright owner]"
 * 
 * Contributor(s):
 * 
 * If you wish your version of this file to be governed by only the CDDL or
 * only the GPL Version 2, indicate your decision by adding "[Contributor]
 * elects to include this software in this distribution under the [CDDL or GPL
 * Version 2] license."  If you don't indicate a single choice of license, a
 * recipient has the option to distribute your version of this file under
 * either the CDDL, the GPL Version 2 or to extend the choice of license to
 * its licensees as provided above.  However, if you add GPL Version 2 code
 * and therefore, elected the GPL Version 2 license, then the option applies
 * only if the new code is made subject to such option by the copyright
 * holder.
 */

package com.sun.xml.stream.writers;

import java.io.Writer;
import java.io.OutputStream;
import java.io.IOException;

import com.sun.xml.stream.xerces.util.XMLChar;

/**
 * This class is used to write a stream of chars as a stream of
 * bytes using the UTF8 encoding. It assumes that the underlying
 * output stream is buffered or does not need additional buffering.
 *
 * It is more efficient than using a java.io.OutputStreamWriter
 * because it does not need to be wrapped in a 
 * java.io.BufferedWriter. Creating multiple instances 
 * of java.io.BufferedWriter has been shown to be very 
 * expensive in JAX-WS.
 *
 * @author [email protected]
 */
public final class UTF8OutputStreamWriter extends Writer {
    
    /**
     * Undelying output stream. This class assumes that this
     * output stream does not need buffering.
     */
    OutputStream out;
    
    /**
     * Java represents chars that are not in the Basic Multilingual
     * Plane (BMP) in UTF-16. This int stores the first code unit 
     * for a code point encoded in two UTF-16 code units.
     */
    int lastUTF16CodePoint = 0;
    
    public UTF8OutputStreamWriter(OutputStream out) {
        this.out = out;
    }
    
    public String getEncoding() {
        return "UTF-8";
    }
    
    public void write(int c) throws IOException {
        // Check in we are encoding at high and low surrogates
        if (lastUTF16CodePoint != 0) {
            final int uc = 
                (((lastUTF16CodePoint & 0x3ff) << 10) | (c & 0x3ff)) + 0x10000;
            
            if (uc < 0 || uc >= 0x200000) {
                throw new IOException("Atttempting to write invalid Unicode code point '" + uc + "'");
            }

            out.write(0xF0 | (uc >> 18));
            out.write(0x80 | ((uc >> 12) & 0x3F));
            out.write(0x80 | ((uc >> 6) & 0x3F));
            out.write(0x80 | (uc & 0x3F));
            
            lastUTF16CodePoint = 0;
            return;
        }
        
        // Otherwise, encode char as defined in UTF-8
        if (c < 0x80) {
            // 1 byte, 7 bits
            out.write((int) c);
        } 
        else if (c < 0x800) {
            // 2 bytes, 11 bits
            out.write(0xC0 | (c >> 6));    // first 5
            out.write(0x80 | (c & 0x3F));  // second 6
        } 
        else if (c <= '\uFFFF') { 
            if (!XMLChar.isHighSurrogate(c) && !XMLChar.isLowSurrogate(c)) {
                // 3 bytes, 16 bits
                out.write(0xE0 | (c >> 12));   // first 4
                out.write(0x80 | ((c >> 6) & 0x3F));  // second 6
                out.write(0x80 | (c & 0x3F));  // third 6
            } 
            else {
                lastUTF16CodePoint = c;
            }
        }
    }

    public void write(char cbuf[]) throws IOException {
        for (int i = 0; i < cbuf.length; i++) {
            write(cbuf[i]);
        }
    }

    public void write(char cbuf[], int off, int len) throws IOException {
        for (int i = 0; i < len; i++) {
            write(cbuf[off + i]);
        }
    }

    public void write(String str) throws IOException {
        final int len = str.length();
        for (int i = 0; i < len; i++) {
            write(str.charAt(i));
        }
    }

    public void write(String str, int off, int len) throws IOException {
        for (int i = 0; i < len; i++) {
            write(str.charAt(off + i));
        }
    }

    public void flush() throws IOException {
        out.flush();
    }

    public void close() throws IOException {
        if (lastUTF16CodePoint != 0) {
            throw new IllegalStateException("Attempting to close a UTF8OutputStreamWriter" 
                + " while awaiting for a UTF-16 code unit");
        }
        out.close();
    }
    
}