net.clementlevallois.utils.UnicodeBOMInputStream Maven / Gradle / Ivy
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package net.clementlevallois.utils;
/* ____________________________________________________________________________
*
* File: UnicodeBOMInputStream.java
* Author: Gregory Pakosz.
* Date: 02 - November - 2005
* ____________________________________________________________________________
*/
import java.io.IOException;
import java.io.InputStream;
import java.io.PushbackInputStream;
/**
* The UnicodeBOMInputStream class wraps any
* InputStream and detects the presence of any Unicode BOM (Byte
* Order Mark) at its beginning, as defined by
* RFC 3629 - UTF-8, a
* transformation format of ISO 10646
*
*
* The
* Unicode FAQ
* defines 5 types of BOMs:
*
* 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
*
*
* Use the {@link #getBOM()} method to know whether a BOM has been detected or
* not.
*
*
* Use the {@link #skipBOM()} method to remove the detected BOM from the wrapped
* InputStream object.
*
* see https://stackoverflow.com/questions/1835430/byte-order-mark-screws-up-file-reading-in-java/1835529#1835529
*/
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 String representation of this BOM
* value.
*/
public final String toString() {
return description;
}
/**
* Returns the bytes corresponding to this BOM value.
* @return
*/
public final 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 UnicodeBOMInputStream that wraps the
* specified InputStream.
*
* @param inputStream an InputStream.
*
* @throws NullPointerException when inputStream is
* null.
* @throws IOException on reading from the specified
* InputStream 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 BOM that was detected in the wrapped
* InputStream object.
*
* @return a BOM value.
*/
public final BOM getBOM() {
// BOM type is immutable.
return bom;
}
/**
* Skips the BOM that was found in the wrapped
* InputStream object.
*
* @return this UnicodeBOMInputStream.
*
* @throws IOException when trying to skip the BOM from the wrapped
* InputStream object.
*/
public final synchronized UnicodeBOMInputStream skipBOM() throws IOException {
if (!skipped) {
in.skip(bom.bytes.length);
skipped = true;
}
return this;
}
/**
* {@inheritDoc}
*/
public int read() throws IOException {
return in.read();
}
/**
* {@inheritDoc}
*/
public int read(final byte b[]) throws IOException,
NullPointerException {
return in.read(b, 0, b.length);
}
/**
* {@inheritDoc}
*/
public int read(final byte b[],
final int off,
final int len) throws IOException,
NullPointerException {
return in.read(b, off, len);
}
/**
* {@inheritDoc}
*/
public long skip(final long n) throws IOException {
return in.skip(n);
}
/**
* {@inheritDoc}
*/
public int available() throws IOException {
return in.available();
}
/**
* {@inheritDoc}
*/
public void close() throws IOException {
in.close();
}
/**
* {@inheritDoc}
*/
public synchronized void mark(final int readlimit) {
in.mark(readlimit);
}
/**
* {@inheritDoc}
*/
public synchronized void reset() throws IOException {
in.reset();
}
/**
* {@inheritDoc}
*/
public boolean markSupported() {
return in.markSupported();
}
private final PushbackInputStream in;
private final BOM bom;
private boolean skipped = false;
} // UnicodeBOMInputStream