Generic Unicode text reader, which uses a BOM (Byte Order Mark) to identify the encoding to be used.
/* Copyright (c) 2008 Google Inc.
*
* Licensed 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 com.google.gdata.util.io.base;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.PushbackInputStream;
import java.io.Reader;
/**
* Generic Unicode text reader, which uses a BOM (Byte Order Mark) to identify
* the encoding to be used. This also has the side effect of removing the BOM
* from the input stream (when present).
*
* @see <a href="http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4508058">
* JDK Bug 4508058</a>
*
*
*/
public class UnicodeReader extends Reader {
private final InputStreamReader internalInputStreamReader;
private final String defaultEnc;
private static final int BOM_SIZE = 4;
/**
* @param in input stream
* @param defaultEnc default encoding (used only if BOM is not found) or
* <code>null</code> to use system default
* @throws IOException if an I/O error occurs
*/
public UnicodeReader(InputStream in, String defaultEnc) throws IOException {
this.defaultEnc = defaultEnc;
// Read ahead four bytes and check for BOM marks. Extra bytes are unread
// back to the stream; only BOM bytes are skipped.
String encoding;
byte bom[] = new byte[BOM_SIZE];
int n, unread;
PushbackInputStream pushbackStream = new PushbackInputStream(in, BOM_SIZE);
n = pushbackStream.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) {
pushbackStream.unread(bom, (n - unread), unread);
} else if (unread < -1) {
pushbackStream.unread(bom, 0, 0);
}
// Use given encoding
if (encoding == null) {
internalInputStreamReader = new InputStreamReader(pushbackStream);
} else {
internalInputStreamReader = new InputStreamReader(pushbackStream,
encoding);
}
}
public String getDefaultEncoding() {
return defaultEnc;
}
public String getEncoding() {
return internalInputStreamReader.getEncoding();
}
@Override public void close() throws IOException {
internalInputStreamReader.close();
}
@Override public int read(char[] cbuf, int off, int len) throws IOException {
return internalInputStreamReader.read(cbuf, off, len);
}
}
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