unicodereader.java

java 词法分析器,用于一般的C,C++,VB,PS/SQL 语句的翻译

package fri.util.io;

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);
  }

}