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/*
* 09/23/2004
*
* UnicodeReader.java - A reader for Unicode input streams that is capable of
* discerning which particular encoding is being used via the BOM.
*
* This library is distributed under a modified BSD license. See the included
* LICENSE file for details.
*/
package org.fife.io;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.PushbackInputStream;
import java.io.Reader;
/**
* A reader capable of identifying Unicode streams by their BOMs. This class
* will recognize the following encodings:
*
* - UTF-8
*
- UTF-16LE
*
- UTF-16BE
*
- UTF-32LE
*
- UTF-32BE
*
* If the stream is not found to be any of the above, then a default encoding
* is used for reading. The user can specify this default encoding, or a system
* default will be used.
*
* For optimum performance, it is recommended that you wrap all instances of
* UnicodeReader with a java.io.BufferedReader.
*
* This class is mostly ripped off from the workaround in the description of
* Java Bug 4508058.
*
* @author Robert Futrell
* @version 0.9
*/
@SuppressWarnings({ "checkstyle:magicnumber" })
public class UnicodeReader extends Reader {
/**
* The input stream from which we're really reading.
*/
private InputStreamReader internalIn = null;
/**
* The encoding being used. We keep our own instead of using the string
* returned by java.io.InputStreamReader since that class
* does not return user-friendly names.
*/
private String encoding;
/**
* The size of a BOM.
*/
private static final int BOM_SIZE = 4;
/**
* This utility constructor is here because you will usually use a
* UnicodeReader on files.
* Creates a reader using the encoding specified by the BOM in the file;
* if there is no recognized BOM, then a system default encoding is used.
*
* @param file The file from which you want to read.
* @throws IOException If an error occurs when checking for/reading the
* BOM.
* @throws SecurityException If a security manager exists and its
* checkRead method denies read access to the file.
*/
public UnicodeReader(String file) throws IOException {
this(new File(file));
}
/**
* This utility constructor is here because you will usually use a
* UnicodeReader on files.
* Creates a reader using the encoding specified by the BOM in the file;
* if there is no recognized BOM, then a system default encoding is used.
*
* @param file The file from which you want to read.
* @throws IOException If an error occurs when checking for/reading the
* BOM.
* @throws SecurityException If a security manager exists and its
* checkRead method denies read access to the file.
*/
public UnicodeReader(File file) throws IOException {
this(new FileInputStream(file));
}
/**
* This utility constructor is here because you will usually use a
* UnicodeReader on files.
* Creates a reader using the encoding specified by the BOM in the file;
* if there is no recognized BOM, then a specified default encoding is
* used.
*
* @param file The file from which you want to read.
* @param defaultEncoding The encoding to use if no BOM is found. If
* this value is null, a system default is used.
* @throws IOException If an error occurs when checking for/reading the
* BOM.
* @throws SecurityException If a security manager exists and its
* checkRead method denies read access to the file.
*/
public UnicodeReader(File file, String defaultEncoding) throws IOException {
this(new FileInputStream(file), defaultEncoding);
}
/**
* Creates a reader using the encoding specified by the BOM in the file;
* if there is no recognized BOM, then a system default encoding is used.
*
* @param in The input stream from which to read.
* @throws IOException If an error occurs when checking for/reading the
* BOM.
*/
public UnicodeReader(InputStream in) throws IOException {
this(in, null);
}
/**
* Creates a reader using the encoding specified by the BOM in the file;
* if there is no recognized BOM, then defaultEncoding is
* used.
*
* @param in The input stream from which to read.
* @param defaultEncoding The encoding to use if no recognized BOM is
* found. If this value is null, a system default
* is used.
* @throws IOException If an error occurs when checking for/reading the
* BOM.
*/
public UnicodeReader(InputStream in, String defaultEncoding)
throws IOException {
init(in, defaultEncoding);
}
/**
* Closes this reader.
*/
@Override
public void close() throws IOException {
internalIn.close();
}
/**
* Returns the encoding being used to read this input stream (i.e., the
* encoding of the file). If a BOM was recognized, then the specific
* Unicode type is returned; otherwise, either the default encoding passed
* into the constructor or the system default is returned.
*
* @return The encoding of the stream.
*/
public String getEncoding() {
return encoding;
}
/**
* Read-ahead four bytes and check for BOM marks. Extra bytes are
* unread back to the stream, only BOM bytes are skipped.
*
* @param defaultEncoding The encoding to use if no BOM was recognized. If
* this value is null, then a system default is used.
* @throws IOException If an error occurs when trying to read a BOM.
*/
protected void init(InputStream in, String defaultEncoding)
throws IOException {
PushbackInputStream tempIn = new PushbackInputStream(in, BOM_SIZE);
byte[] bom = new byte[BOM_SIZE];
int n, unread;
n = tempIn.read(bom, 0, bom.length);
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 (n==BOM_SIZE && // Last 2 bytes are 0; could be an empty UTF-16
(bom[0]==(byte)0xFF) && (bom[1]==(byte)0xFE) &&
(bom[2]==(byte)0x00) && (bom[3]==(byte)0x00)) {
encoding = "UTF-32LE";
unread = n - 4;
}
else 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 {
// Unicode BOM mark not found, unread all bytes
encoding = defaultEncoding;
unread = n;
}
if (unread > 0) {
tempIn.unread(bom, (n - unread), unread);
}
else if (unread < -1) {
tempIn.unread(bom, 0, 0);
}
// Use given encoding
if (encoding == null) {
internalIn = new InputStreamReader(tempIn);
encoding = internalIn.getEncoding(); // Get the default.
}
else {
internalIn = new InputStreamReader(tempIn, encoding);
}
}
/**
* Read characters into a portion of an array. This method will block until
* some input is available, an I/O error occurs, or the end of the stream
* is reached.
*
* @param cbuf The buffer into which to read.
* @param off The offset at which to start storing characters.
* @param len The maximum number of characters to read.
*
* @return The number of characters read, or -1 if the end
* of the stream has been reached.
*/
@Override
public int read(char[] cbuf, int off, int len) throws IOException {
return internalIn.read(cbuf, off, len);
}
}