Java tutorial
/* * Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright ownership. * The ASF licenses this file to You under the Apache License, Version 2.0 * (the "License"); you may not use this file except in compliance with * the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.apache.commons.io.output; import java.io.File; import java.io.FileNotFoundException; import java.io.FileOutputStream; import java.io.IOException; import java.io.OutputStream; import java.io.OutputStreamWriter; import java.io.StringWriter; import java.io.Writer; import java.util.regex.Matcher; import java.util.regex.Pattern; import org.apache.commons.io.input.XmlStreamReader; /** * Character stream that handles all the necessary Voodo to figure out the * charset encoding of the XML document written to the stream. * * @author Herve Boutemy * @version $Id: XmlStreamWriter.java 1004737 2010-10-05 17:56:04Z niallp $ * @see XmlStreamReader * @since Commons IO 2.0 */ public class XmlStreamWriter extends Writer { private static final int BUFFER_SIZE = 4096; private final OutputStream out; private final String defaultEncoding; private StringWriter xmlPrologWriter = new StringWriter(BUFFER_SIZE); private Writer writer; private String encoding; /** * Construct an new XML stream writer for the specified output stream * with a default encoding of UTF-8. * * @param out The output stream */ public XmlStreamWriter(OutputStream out) { this(out, null); } /** * Construct an new XML stream writer for the specified output stream * with the specified default encoding. * * @param out The output stream * @param defaultEncoding The default encoding if not encoding could be detected */ public XmlStreamWriter(OutputStream out, String defaultEncoding) { this.out = out; this.defaultEncoding = (defaultEncoding != null ? defaultEncoding : "UTF-8"); } /** * Construct an new XML stream writer for the specified file * with a default encoding of UTF-8. * * @param file The file to write to * @throws FileNotFoundException if there is an error creating or * opening the file */ public XmlStreamWriter(File file) throws FileNotFoundException { this(file, null); } /** * Construct an new XML stream writer for the specified file * with the specified default encoding. * * @param file The file to write to * @param defaultEncoding The default encoding if not encoding could be detected * @throws FileNotFoundException if there is an error creating or * opening the file */ public XmlStreamWriter(File file, String defaultEncoding) throws FileNotFoundException { this(new FileOutputStream(file), defaultEncoding); } /** * Return the detected encoding. * * @return the detected encoding */ public String getEncoding() { return encoding; } /** * Return the default encoding. * * @return the default encoding */ public String getDefaultEncoding() { return defaultEncoding; } /** * Close the underlying writer. * * @throws IOException if an error occurs closing the underlying writer */ @Override public void close() throws IOException { if (writer == null) { encoding = defaultEncoding; writer = new OutputStreamWriter(out, encoding); writer.write(xmlPrologWriter.toString()); } writer.close(); } /** * Flush the underlying writer. * * @throws IOException if an error occurs flushing the underlying writer */ @Override public void flush() throws IOException { if (writer != null) { writer.flush(); } } /** * Detect the encoding. * * @param cbuf the buffer to write the characters from * @param off The start offset * @param len The number of characters to write * @throws IOException if an error occurs detecting the encoding */ private void detectEncoding(char[] cbuf, int off, int len) throws IOException { int size = len; StringBuffer xmlProlog = xmlPrologWriter.getBuffer(); if (xmlProlog.length() + len > BUFFER_SIZE) { size = BUFFER_SIZE - xmlProlog.length(); } xmlPrologWriter.write(cbuf, off, size); // try to determine encoding if (xmlProlog.length() >= 5) { if (xmlProlog.substring(0, 5).equals("<?xml")) { // try to extract encoding from XML prolog int xmlPrologEnd = xmlProlog.indexOf("?>"); if (xmlPrologEnd > 0) { // ok, full XML prolog written: let's extract encoding Matcher m = ENCODING_PATTERN.matcher(xmlProlog.substring(0, xmlPrologEnd)); if (m.find()) { encoding = m.group(1).toUpperCase(); encoding = encoding.substring(1, encoding.length() - 1); } else { // no encoding found in XML prolog: using default // encoding encoding = defaultEncoding; } } else { if (xmlProlog.length() >= BUFFER_SIZE) { // no encoding found in first characters: using default // encoding encoding = defaultEncoding; } } } else { // no XML prolog: using default encoding encoding = defaultEncoding; } if (encoding != null) { // encoding has been chosen: let's do it xmlPrologWriter = null; writer = new OutputStreamWriter(out, encoding); writer.write(xmlProlog.toString()); if (len > size) { writer.write(cbuf, off + size, len - size); } } } } /** * Write the characters to the underlying writer, detecing encoding. * * @param cbuf the buffer to write the characters from * @param off The start offset * @param len The number of characters to write * @throws IOException if an error occurs detecting the encoding */ @Override public void write(char[] cbuf, int off, int len) throws IOException { if (xmlPrologWriter != null) { detectEncoding(cbuf, off, len); } else { writer.write(cbuf, off, len); } } static final Pattern ENCODING_PATTERN = XmlStreamReader.ENCODING_PATTERN; }