src/com/sun/xml/internal/stream/writers/UTF8OutputStreamWriter.java

/*
 * Copyright (c) 2006, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package com.sun.xml.internal.stream.writers;

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

import com.sun.org.apache.xerces.internal.util.XMLChar;

/**
 * <p>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.</p>
 *
 * <p>It is more efficient than using a <code>java.io.OutputStreamWriter</code>
 * because it does not need to be wrapped in a
 * <code>java.io.BufferedWriter</code>. Creating multiple instances
 * of <code>java.io.BufferedWriter</code> has been shown to be very
 * expensive in JAX-WS.</p>
 *
 * @author Santiago.PericasGeertsen@sun.com
 */
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();
    }

}