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The Apache Commons IO library contains utility classes, stream implementations, file filters,
file comparators, endian transformation classes, and much more.
/*
* 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 org.apache.commons.io.input;
import static org.apache.commons.io.IOUtils.EOF;
import java.io.IOException;
import java.io.InputStream;
import java.util.Arrays;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
import org.apache.commons.io.ByteOrderMark;
/**
* This class is used to wrap a stream that includes an encoded {@link ByteOrderMark} as its first bytes.
*
* This class detects these bytes and, if required, can automatically skip them and return the subsequent byte as the
* first byte in the stream.
*
* The {@link ByteOrderMark} implementation has the following pre-defined BOMs:
*
* - UTF-8 - {@link ByteOrderMark#UTF_8}
* - UTF-16BE - {@link ByteOrderMark#UTF_16LE}
* - UTF-16LE - {@link ByteOrderMark#UTF_16BE}
* - UTF-32BE - {@link ByteOrderMark#UTF_32LE}
* - UTF-32LE - {@link ByteOrderMark#UTF_32BE}
*
*
*
* Example 1 - Detect and exclude a UTF-8 BOM
*
*
* BOMInputStream bomIn = new BOMInputStream(in);
* if (bomIn.hasBOM()) {
* // has a UTF-8 BOM
* }
*
*
* Example 2 - Detect a UTF-8 BOM (but don't exclude it)
*
*
* boolean include = true;
* BOMInputStream bomIn = new BOMInputStream(in, include);
* if (bomIn.hasBOM()) {
* // has a UTF-8 BOM
* }
*
*
* Example 3 - Detect Multiple BOMs
*
*
* BOMInputStream bomIn = new BOMInputStream(in,
* ByteOrderMark.UTF_16LE, ByteOrderMark.UTF_16BE,
* ByteOrderMark.UTF_32LE, ByteOrderMark.UTF_32BE
* );
* if (bomIn.hasBOM() == false) {
* // No BOM found
* } else if (bomIn.hasBOM(ByteOrderMark.UTF_16LE)) {
* // has a UTF-16LE BOM
* } else if (bomIn.hasBOM(ByteOrderMark.UTF_16BE)) {
* // has a UTF-16BE BOM
* } else if (bomIn.hasBOM(ByteOrderMark.UTF_32LE)) {
* // has a UTF-32LE BOM
* } else if (bomIn.hasBOM(ByteOrderMark.UTF_32BE)) {
* // has a UTF-32BE BOM
* }
*
*
* @see org.apache.commons.io.ByteOrderMark
* @see Wikipedia - Byte Order Mark
* @since 2.0
*/
public class BOMInputStream extends ProxyInputStream {
private final boolean include;
/**
* BOMs are sorted from longest to shortest.
*/
private final List boms;
private ByteOrderMark byteOrderMark;
private int[] firstBytes;
private int fbLength;
private int fbIndex;
private int markFbIndex;
private boolean markedAtStart;
/**
* Constructs a new BOM InputStream that excludes a {@link ByteOrderMark#UTF_8} BOM.
*
* @param delegate
* the InputStream to delegate to
*/
public BOMInputStream(final InputStream delegate) {
this(delegate, false, ByteOrderMark.UTF_8);
}
/**
* Constructs a new BOM InputStream that detects a a {@link ByteOrderMark#UTF_8} and optionally includes it.
*
* @param delegate
* the InputStream to delegate to
* @param include
* true to include the UTF-8 BOM or false to exclude it
*/
public BOMInputStream(final InputStream delegate, final boolean include) {
this(delegate, include, ByteOrderMark.UTF_8);
}
/**
* Constructs a new BOM InputStream that excludes the specified BOMs.
*
* @param delegate
* the InputStream to delegate to
* @param boms
* The BOMs to detect and exclude
*/
public BOMInputStream(final InputStream delegate, final ByteOrderMark... boms) {
this(delegate, false, boms);
}
/**
* Compares ByteOrderMark objects in descending length order.
*/
private static final Comparator ByteOrderMarkLengthComparator = new Comparator() {
@Override
public int compare(final ByteOrderMark bom1, final ByteOrderMark bom2) {
final int len1 = bom1.length();
final int len2 = bom2.length();
if (len1 > len2) {
return EOF;
}
if (len2 > len1) {
return 1;
}
return 0;
}
};
/**
* Constructs a new BOM InputStream that detects the specified BOMs and optionally includes them.
*
* @param delegate
* the InputStream to delegate to
* @param include
* true to include the specified BOMs or false to exclude them
* @param boms
* The BOMs to detect and optionally exclude
*/
public BOMInputStream(final InputStream delegate, final boolean include, final ByteOrderMark... boms) {
super(delegate);
if (boms == null || boms.length == 0) {
throw new IllegalArgumentException("No BOMs specified");
}
this.include = include;
final List list = Arrays.asList(boms);
// Sort the BOMs to match the longest BOM first because some BOMs have the same starting two bytes.
Collections.sort(list, ByteOrderMarkLengthComparator);
this.boms = list;
}
/**
* Indicates whether the stream contains one of the specified BOMs.
*
* @return true if the stream has one of the specified BOMs, otherwise false if it does not
* @throws IOException
* if an error reading the first bytes of the stream occurs
*/
public boolean hasBOM() throws IOException {
return getBOM() != null;
}
/**
* Indicates whether the stream contains the specified BOM.
*
* @param bom
* The BOM to check for
* @return true if the stream has the specified BOM, otherwise false if it does not
* @throws IllegalArgumentException
* if the BOM is not one the stream is configured to detect
* @throws IOException
* if an error reading the first bytes of the stream occurs
*/
public boolean hasBOM(final ByteOrderMark bom) throws IOException {
if (!boms.contains(bom)) {
throw new IllegalArgumentException("Stream not configure to detect " + bom);
}
getBOM();
return byteOrderMark != null && byteOrderMark.equals(bom);
}
/**
* Return the BOM (Byte Order Mark).
*
* @return The BOM or null if none
* @throws IOException
* if an error reading the first bytes of the stream occurs
*/
public ByteOrderMark getBOM() throws IOException {
if (firstBytes == null) {
fbLength = 0;
// BOMs are sorted from longest to shortest
final int maxBomSize = boms.get(0).length();
firstBytes = new int[maxBomSize];
// Read first maxBomSize bytes
for (int i = 0; i < firstBytes.length; i++) {
firstBytes[i] = in.read();
fbLength++;
if (firstBytes[i] < 0) {
break;
}
}
// match BOM in firstBytes
byteOrderMark = find();
if (byteOrderMark != null) {
if (!include) {
if (byteOrderMark.length() < firstBytes.length) {
fbIndex = byteOrderMark.length();
} else {
fbLength = 0;
}
}
}
}
return byteOrderMark;
}
/**
* Return the BOM charset Name - {@link ByteOrderMark#getCharsetName()}.
*
* @return The BOM charset Name or null if no BOM found
* @throws IOException
* if an error reading the first bytes of the stream occurs
*
*/
public String getBOMCharsetName() throws IOException {
getBOM();
return byteOrderMark == null ? null : byteOrderMark.getCharsetName();
}
/**
* This method reads and either preserves or skips the first bytes in the stream. It behaves like the single-byte
* read() method, either returning a valid byte or -1 to indicate that the initial bytes have been
* processed already.
*
* @return the byte read (excluding BOM) or -1 if the end of stream
* @throws IOException
* if an I/O error occurs
*/
private int readFirstBytes() throws IOException {
getBOM();
return fbIndex < fbLength ? firstBytes[fbIndex++] : EOF;
}
/**
* Find a BOM with the specified bytes.
*
* @return The matched BOM or null if none matched
*/
private ByteOrderMark find() {
for (final ByteOrderMark bom : boms) {
if (matches(bom)) {
return bom;
}
}
return null;
}
/**
* Check if the bytes match a BOM.
*
* @param bom
* The BOM
* @return true if the bytes match the bom, otherwise false
*/
private boolean matches(final ByteOrderMark bom) {
// if (bom.length() != fbLength) {
// return false;
// }
// firstBytes may be bigger than the BOM bytes
for (int i = 0; i < bom.length(); i++) {
if (bom.get(i) != firstBytes[i]) {
return false;
}
}
return true;
}
// ----------------------------------------------------------------------------
// Implementation of InputStream
// ----------------------------------------------------------------------------
/**
* Invokes the delegate's read() method, detecting and optionally skipping BOM.
*
* @return the byte read (excluding BOM) or -1 if the end of stream
* @throws IOException
* if an I/O error occurs
*/
@Override
public int read() throws IOException {
final int b = readFirstBytes();
return b >= 0 ? b : in.read();
}
/**
* Invokes the delegate's read(byte[], int, int) method, detecting and optionally skipping BOM.
*
* @param buf
* the buffer to read the bytes into
* @param off
* The start offset
* @param len
* The number of bytes to read (excluding BOM)
* @return the number of bytes read or -1 if the end of stream
* @throws IOException
* if an I/O error occurs
*/
@Override
public int read(final byte[] buf, int off, int len) throws IOException {
int firstCount = 0;
int b = 0;
while (len > 0 && b >= 0) {
b = readFirstBytes();
if (b >= 0) {
buf[off++] = (byte) (b & 0xFF);
len--;
firstCount++;
}
}
final int secondCount = in.read(buf, off, len);
return secondCount < 0 ? firstCount > 0 ? firstCount : EOF : firstCount + secondCount;
}
/**
* Invokes the delegate's read(byte[]) method, detecting and optionally skipping BOM.
*
* @param buf
* the buffer to read the bytes into
* @return the number of bytes read (excluding BOM) or -1 if the end of stream
* @throws IOException
* if an I/O error occurs
*/
@Override
public int read(final byte[] buf) throws IOException {
return read(buf, 0, buf.length);
}
/**
* Invokes the delegate's mark(int) method.
*
* @param readlimit
* read ahead limit
*/
@Override
public synchronized void mark(final int readlimit) {
markFbIndex = fbIndex;
markedAtStart = firstBytes == null;
in.mark(readlimit);
}
/**
* Invokes the delegate's reset() method.
*
* @throws IOException
* if an I/O error occurs
*/
@Override
public synchronized void reset() throws IOException {
fbIndex = markFbIndex;
if (markedAtStart) {
firstBytes = null;
}
in.reset();
}
/**
* Invokes the delegate's skip(long) method, detecting and optionally skipping BOM.
*
* @param n
* the number of bytes to skip
* @return the number of bytes to skipped or -1 if the end of stream
* @throws IOException
* if an I/O error occurs
*/
@Override
public long skip(final long n) throws IOException {
int skipped = 0;
while ((n > skipped) && (readFirstBytes() >= 0)) {
skipped++;
}
return in.skip(n - skipped) + skipped;
}
}
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