Unicode reader : Code Unicode « Development Class « Java

1. Java
2. Development Class
3. Code Unicode

Unicode reader

     


// revised from runcc 0.7

import java.io.*;

/**
 * Reads away UNICODE Byte Order Mark on construction. See
 * http://www.unicode.org/unicode/faq/utf_bom.html
 * 
 * <pre>
 *  00 00 FE FF    = UTF-32, big-endian
 *  FF FE 00 00    = UTF-32, little-endian
 *  FE FF          = UTF-16, big-endian
 *  FF FE          = UTF-16, little-endian
 *  EF BB BF       = UTF-8
 * </pre>
 */
public class UnicodeReader extends Reader
{
  private static final int BOM_MAX_SIZE = 4;

  private InputStreamReader delegate;

  public UnicodeReader(InputStream in) throws IOException {
    init(in, null);
  }

  public UnicodeReader(InputStream in, String defaultEnc) throws IOException {
    init(in, defaultEnc);
  }

  /** Returns the encoding that was read from byte order mark if there was one. */
  public String getEncoding() {
    return delegate.getEncoding();
  }

  /**
   * Read-ahead four bytes and check for BOM marks. Extra bytes are unread back
   * to the stream, only BOM bytes are skipped.
   */
  private void init(InputStream in, String defaultEnc) throws IOException {
    String encoding;
    byte bom[] = new byte[BOM_MAX_SIZE];
    int n, unread;
    PushbackInputStream internalIn = new PushbackInputStream(in, BOM_MAX_SIZE);
    n = internalIn.read(bom, 0, bom.length);

    if ((bom[0] == (byte) 0xEF) && (bom[1] == (byte) 0xBB) && (bom[2] == (byte) 0xBF)) {
      encoding = "UTF-8";
      unread = n - 3;
    }
    else
    if ((bom[0] == (byte) 0xFE) && (bom[1] == (byte) 0xFF)) {
      encoding = "UTF-16BE";
      unread = n - 2;
    }
    else
    if ((bom[0] == (byte) 0xFF) && (bom[1] == (byte) 0xFE)) {
      encoding = "UTF-16LE";
      unread = n - 2;
    }
    else
    if ((bom[0] == (byte) 0x00) && (bom[1] == (byte) 0x00) && (bom[2] == (byte) 0xFE) && (bom[3] == (byte) 0xFF)) {
      encoding = "UTF-32BE";
      unread = n - 4;
    }
    else
    if ((bom[0] == (byte) 0xFF) && (bom[1] == (byte) 0xFE) && (bom[2] == (byte) 0x00) && (bom[3] == (byte) 0x00)) {
      encoding = "UTF-32LE";
      unread = n - 4;
    }
    else {
      // Unicode BOM mark not found, unread all bytes
      encoding = defaultEnc;
      unread = n;
    }

    if (unread > 0)
      internalIn.unread(bom, (n - unread), unread);
    else
    if (unread < -1)
      internalIn.unread(bom, 0, 0);

    // Use BOM or default encoding
    if (encoding == null) {
      delegate = new InputStreamReader(internalIn);
    }
    else {
      delegate = new InputStreamReader(internalIn, encoding);
    }
  }

  /** Overridden to use delegate reader. */
  public void close() throws IOException {
    delegate.close();
  }

  /** Overridden to use delegate reader. */
  public int read(char[] cbuf, int off, int len) throws IOException {
    return delegate.read(cbuf, off, len);
  }

}

   
    
    
    
    
  

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