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A set of utilities and tools to speed up and ease programming in Java.
There is a newer version: 0.5
/*
 * (c) 2005 David B. Bracewell
 *
 * 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 com.davidbracewell.io;

import com.google.common.base.Charsets;

import java.io.*;
import java.nio.charset.Charset;

/**
 * A reader that understands Unicode Byte Order Marks and can also guess the character set if a BOM is not present
 * and a character set has not been specified.
 *
 * @author David B. Bracewell
 */
public class CharsetDetectingReader extends Reader {

  private final static int BUFFER_SIZE = 8000;

  private final InputStream inStream;
  private Reader backing = null;
  private final Charset defaultCharset;
  private Charset charset = null;


  /**
   * Instantiates a new Espresso reader.
   *
   * @param inStream the in stream
   */
  public CharsetDetectingReader(InputStream inStream) {
    this(inStream, null);
  }

  /**
   * Instantiates a new Espresso reader.
   *
   * @param inStream the in stream
   * @param defaultCharset the default charset
   */
  public CharsetDetectingReader(InputStream inStream, Charset defaultCharset) {
    this.inStream = inStream;
    this.defaultCharset = defaultCharset;
    this.charset = null;
  }


  private void determineCharset() throws IOException {
    PushbackInputStream pbIStream = new PushbackInputStream(inStream, BUFFER_SIZE);

    byte[] buffer = new byte[BUFFER_SIZE];
    int read = pbIStream.read(buffer, 0, buffer.length);
    if (read == -1) {
      return;
    }

    int bomOffset = 0;

    for (CommonBOM bom : CommonBOM.values()) {
      if (bom.matches(buffer)) {
        charset = bom.getCharset();
        bomOffset = bom.length();
        break;
      }
    }

    if (charset == null && defaultCharset == null) {
      charset = CharsetDetector.detect(buffer, 0, read);
      if (charset == null) {
        charset = Charsets.UTF_8;
      }
    } else if (charset == null) {
      charset = defaultCharset;
    }

    pbIStream.unread(buffer, bomOffset, read - bomOffset);

    backing = new InputStreamReader(pbIStream, charset);
  }


  @Override
  public int read(char[] cbuf, int off, int len) throws IOException {
    if (backing == null) {
      determineCharset();
    }
    if (backing == null) {
      return -1;
    }
    return backing.read(cbuf, off, len);
  }

  @Override
  public void close() throws IOException {
    if (backing != null) {
      backing.close();
    }
  }

  /**
   * Gets charset.
   *
   * @return the charset
   */
  public Charset getCharset() {
    return charset;
  }

}//END OF CharsetDetectingReader