package experiments.evaluation;
/* ____________________________________________________________________________
*
* File: UnicodeBOMInputStream.java
* Author: Gregory Pakosz.
* Date: 02 - November - 2005
* ____________________________________________________________________________
*/
import java.io.IOException;
import java.io.InputStream;
import java.io.PushbackInputStream;
/**
* The <code>UnicodeBOMInputStream</code> class wraps any
* <code>InputStream</code> and detects the presence of any Unicode BOM (Byte
* Order Mark) at its beginning, as defined by <a
* href="http://www.faqs.org/rfcs/rfc3629.html">RFC 3629 - UTF-8, a
* transformation format of ISO 10646</a>
*
* <p>
* The <a href="http://www.unicode.org/unicode/faq/utf_bom.html">Unicode FAQ</a>
* defines 5 types of BOMs:
* <ul>
* <li>
*
* <pre>
* 00 00 FE FF = UTF-32, big-endian
* </pre>
*
* </li>
* <li>
*
* <pre>
* FF FE 00 00 = UTF-32, little-endian
* </pre>
*
* </li>
* <li>
*
* <pre>
* FE FF = UTF-16, big-endian
* </pre>
*
* </li>
* <li>
*
* <pre>
* FF FE = UTF-16, little-endian
* </pre>
*
* </li>
* <li>
*
* <pre>
* EF BB BF = UTF-8
* </pre>
*
* </li>
* </ul>
* </p>
*
* <p>
* Use the {@link #getBOM()} method to know whether a BOM has been detected or
* not.
* </p>
* <p>
* Use the {@link #skipBOM()} method to remove the detected BOM from the wrapped
* <code>InputStream</code> object.
* </p>
*/
public class UnicodeBOMInputStream extends InputStream {
/**
* Type safe enumeration class that describes the different types of Unicode
* BOMs.
*/
public static final class BOM {
/**
* NONE.
*/
public static final BOM NONE = new BOM(new byte[] {}, "NONE");
/**
* UTF-8 BOM (EF BB BF).
*/
public static final BOM UTF_8 = new BOM(new byte[] { (byte) 0xEF,
(byte) 0xBB, (byte) 0xBF }, "UTF-8");
/**
* UTF-16, little-endian (FF FE).
*/
public static final BOM UTF_16_LE = new BOM(new byte[] { (byte) 0xFF,
(byte) 0xFE }, "UTF-16 little-endian");
/**
* UTF-16, big-endian (FE FF).
*/
public static final BOM UTF_16_BE = new BOM(new byte[] { (byte) 0xFE,
(byte) 0xFF }, "UTF-16 big-endian");
/**
* UTF-32, little-endian (FF FE 00 00).
*/
public static final BOM UTF_32_LE = new BOM(new byte[] { (byte) 0xFF,
(byte) 0xFE, (byte) 0x00, (byte) 0x00 }, "UTF-32 little-endian");
/**
* UTF-32, big-endian (00 00 FE FF).
*/
public static final BOM UTF_32_BE = new BOM(new byte[] { (byte) 0x00,
(byte) 0x00, (byte) 0xFE, (byte) 0xFF }, "UTF-32 big-endian");
/**
* Returns a <code>String</code> representation of this <code>BOM</code>
* value.
*/
@Override
public String toString() {
return description;
}
/**
* Returns the bytes corresponding to this <code>BOM</code> value.
*/
public byte[] getBytes() {
final int length = bytes.length;
final byte[] result = new byte[length];
// Make a defensive copy
System.arraycopy(bytes, 0, result, 0, length);
return result;
}
private BOM(final byte bom[], final String description) {
assert (bom != null) : "invalid BOM: null is not allowed";
assert (description != null) : "invalid description: null is not allowed";
assert (description.length() != 0) : "invalid description: empty string is not allowed";
this.bytes = bom;
this.description = description;
}
final byte bytes[];
private final String description;
} // BOM
/**
* Constructs a new <code>UnicodeBOMInputStream</code> that wraps the
* specified <code>InputStream</code>.
*
* @param inputStream
* an <code>InputStream</code>.
*
* @throws NullPointerException
* when <code>inputStream</code> is <code>null</code>.
* @throws IOException
* on reading from the specified <code>InputStream</code> when
* trying to detect the Unicode BOM.
*/
public UnicodeBOMInputStream(final InputStream inputStream)
throws NullPointerException, IOException
{
if (inputStream == null)
throw new NullPointerException(
"invalid input stream: null is not allowed");
in = new PushbackInputStream(inputStream, 4);
final byte bom[] = new byte[4];
final int read = in.read(bom);
switch (read) {
case 4:
if ((bom[0] == (byte) 0xFF) && (bom[1] == (byte) 0xFE)
&& (bom[2] == (byte) 0x00) && (bom[3] == (byte) 0x00)) {
this.bom = BOM.UTF_32_LE;
break;
} else if ((bom[0] == (byte) 0x00) && (bom[1] == (byte) 0x00)
&& (bom[2] == (byte) 0xFE) && (bom[3] == (byte) 0xFF)) {
this.bom = BOM.UTF_32_BE;
break;
}
case 3:
if ((bom[0] == (byte) 0xEF) && (bom[1] == (byte) 0xBB)
&& (bom[2] == (byte) 0xBF)) {
this.bom = BOM.UTF_8;
break;
}
case 2:
if ((bom[0] == (byte) 0xFF) && (bom[1] == (byte) 0xFE)) {
this.bom = BOM.UTF_16_LE;
break;
} else if ((bom[0] == (byte) 0xFE) && (bom[1] == (byte) 0xFF)) {
this.bom = BOM.UTF_16_BE;
break;
}
default:
this.bom = BOM.NONE;
break;
}
if (read > 0)
in.unread(bom, 0, read);
}
/**
* Returns the <code>BOM</code> that was detected in the wrapped
* <code>InputStream</code> object.
*
* @return a <code>BOM</code> value.
*/
public final BOM getBOM() {
// BOM type is immutable.
return bom;
}
/**
* Skips the <code>BOM</code> that was found in the wrapped
* <code>InputStream</code> object.
*
* @return this <code>UnicodeBOMInputStream</code>.
*
* @throws IOException
* when trying to skip the BOM from the wrapped
* <code>InputStream</code> object.
*/
public final synchronized UnicodeBOMInputStream skipBOM()
throws IOException {
if (!skipped) {
in.skip(bom.bytes.length);
skipped = true;
}
return this;
}
/**
* {@inheritDoc}
*/
@Override
public int read() throws IOException {
return in.read();
}
/**
* {@inheritDoc}
*/
@Override
public int read(final byte b[]) throws IOException, NullPointerException {
return in.read(b, 0, b.length);
}
/**
* {@inheritDoc}
*/
@Override
public int read(final byte b[], final int off, final int len)
throws IOException, NullPointerException {
return in.read(b, off, len);
}
/**
* {@inheritDoc}
*/
@Override
public long skip(final long n) throws IOException {
return in.skip(n);
}
/**
* {@inheritDoc}
*/
@Override
public int available() throws IOException {
return in.available();
}
/**
* {@inheritDoc}
*/
@Override
public void close() throws IOException {
in.close();
}
/**
* {@inheritDoc}
*/
@Override
public synchronized void mark(final int readlimit) {
in.mark(readlimit);
}
/**
* {@inheritDoc}
*/
@Override
public synchronized void reset() throws IOException {
in.reset();
}
/**
* {@inheritDoc}
*/
@Override
public boolean markSupported() {
return in.markSupported();
}
private final PushbackInputStream in;
private final BOM bom;
private boolean skipped = false;
} // UnicodeBOMInputStream