223 lines
8.2 KiB
Java
223 lines
8.2 KiB
Java
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/*
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* Copyright (c) 1995, 2013, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation. Oracle designates this
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* particular file as subject to the "Classpath" exception as provided
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* by Oracle in the LICENSE file that accompanied this code.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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package sun.misc;
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import java.io.OutputStream;
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import java.io.ByteArrayOutputStream;
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import java.io.InputStream;
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import java.io.PushbackInputStream;
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import java.io.ByteArrayInputStream;
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import java.io.IOException;
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import java.nio.ByteBuffer;
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/**
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* This class defines the decoding half of character encoders.
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* A character decoder is an algorithim for transforming 8 bit
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* binary data that has been encoded into text by a character
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* encoder, back into original binary form.
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*
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* The character encoders, in general, have been structured
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* around a central theme that binary data can be encoded into
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* text that has the form:
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*
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* <pre>
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* [Buffer Prefix]
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* [Line Prefix][encoded data atoms][Line Suffix]
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* [Buffer Suffix]
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* </pre>
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*
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* Of course in the simplest encoding schemes, the buffer has no
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* distinct prefix of suffix, however all have some fixed relationship
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* between the text in an 'atom' and the binary data itself.
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*
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* In the CharacterEncoder and CharacterDecoder classes, one complete
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* chunk of data is referred to as a <i>buffer</i>. Encoded buffers
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* are all text, and decoded buffers (sometimes just referred to as
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* buffers) are binary octets.
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*
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* To create a custom decoder, you must, at a minimum, overide three
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* abstract methods in this class.
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* <DL>
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* <DD>bytesPerAtom which tells the decoder how many bytes to
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* expect from decodeAtom
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* <DD>decodeAtom which decodes the bytes sent to it as text.
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* <DD>bytesPerLine which tells the encoder the maximum number of
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* bytes per line.
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* </DL>
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*
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* In general, the character decoders return error in the form of a
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* CEFormatException. The syntax of the detail string is
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* <pre>
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* DecoderClassName: Error message.
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* </pre>
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*
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* Several useful decoders have already been written and are
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* referenced in the See Also list below.
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*
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* @author Chuck McManis
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* @see CEFormatException
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* @see CharacterEncoder
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* @see UCDecoder
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* @see UUDecoder
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* @see BASE64Decoder
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*/
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public abstract class CharacterDecoder {
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/** Return the number of bytes per atom of decoding */
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abstract protected int bytesPerAtom();
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/** Return the maximum number of bytes that can be encoded per line */
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abstract protected int bytesPerLine();
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/** decode the beginning of the buffer, by default this is a NOP. */
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protected void decodeBufferPrefix(PushbackInputStream aStream, OutputStream bStream) throws IOException { }
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/** decode the buffer suffix, again by default it is a NOP. */
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protected void decodeBufferSuffix(PushbackInputStream aStream, OutputStream bStream) throws IOException { }
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/**
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* This method should return, if it knows, the number of bytes
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* that will be decoded. Many formats such as uuencoding provide
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* this information. By default we return the maximum bytes that
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* could have been encoded on the line.
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*/
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protected int decodeLinePrefix(PushbackInputStream aStream, OutputStream bStream) throws IOException {
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return (bytesPerLine());
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}
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/**
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* This method post processes the line, if there are error detection
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* or correction codes in a line, they are generally processed by
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* this method. The simplest version of this method looks for the
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* (newline) character.
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*/
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protected void decodeLineSuffix(PushbackInputStream aStream, OutputStream bStream) throws IOException { }
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/**
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* This method does an actual decode. It takes the decoded bytes and
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* writes them to the OutputStream. The integer <i>l</i> tells the
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* method how many bytes are required. This is always <= bytesPerAtom().
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*/
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protected void decodeAtom(PushbackInputStream aStream, OutputStream bStream, int l) throws IOException {
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throw new CEStreamExhausted();
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}
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/**
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* This method works around the bizarre semantics of BufferedInputStream's
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* read method.
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*/
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protected int readFully(InputStream in, byte buffer[], int offset, int len)
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throws java.io.IOException {
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for (int i = 0; i < len; i++) {
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int q = in.read();
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if (q == -1)
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return ((i == 0) ? -1 : i);
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buffer[i+offset] = (byte)q;
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}
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return len;
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}
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/**
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* Decode the text from the InputStream and write the decoded
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* octets to the OutputStream. This method runs until the stream
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* is exhausted.
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* @exception CEFormatException An error has occurred while decoding
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* @exception CEStreamExhausted The input stream is unexpectedly out of data
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*/
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public void decodeBuffer(InputStream aStream, OutputStream bStream) throws IOException {
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int i;
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int totalBytes = 0;
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PushbackInputStream ps = new PushbackInputStream (aStream);
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decodeBufferPrefix(ps, bStream);
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while (true) {
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int length;
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try {
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length = decodeLinePrefix(ps, bStream);
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for (i = 0; (i+bytesPerAtom()) < length; i += bytesPerAtom()) {
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decodeAtom(ps, bStream, bytesPerAtom());
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totalBytes += bytesPerAtom();
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}
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if ((i + bytesPerAtom()) == length) {
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decodeAtom(ps, bStream, bytesPerAtom());
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totalBytes += bytesPerAtom();
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} else {
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decodeAtom(ps, bStream, length - i);
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totalBytes += (length - i);
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}
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decodeLineSuffix(ps, bStream);
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} catch (CEStreamExhausted e) {
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break;
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}
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}
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decodeBufferSuffix(ps, bStream);
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}
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/**
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* Alternate decode interface that takes a String containing the encoded
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* buffer and returns a byte array containing the data.
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* @exception CEFormatException An error has occurred while decoding
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*/
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public byte decodeBuffer(String inputString)[] throws IOException {
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byte inputBuffer[] = new byte[inputString.length()];
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ByteArrayInputStream inStream;
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ByteArrayOutputStream outStream;
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inputString.getBytes(0, inputString.length(), inputBuffer, 0);
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inStream = new ByteArrayInputStream(inputBuffer);
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outStream = new ByteArrayOutputStream();
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decodeBuffer(inStream, outStream);
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return (outStream.toByteArray());
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}
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/**
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* Decode the contents of the inputstream into a buffer.
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*/
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public byte decodeBuffer(InputStream in)[] throws IOException {
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ByteArrayOutputStream outStream = new ByteArrayOutputStream();
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decodeBuffer(in, outStream);
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return (outStream.toByteArray());
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}
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/**
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* Decode the contents of the String into a ByteBuffer.
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*/
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public ByteBuffer decodeBufferToByteBuffer(String inputString)
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throws IOException {
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return ByteBuffer.wrap(decodeBuffer(inputString));
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}
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/**
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* Decode the contents of the inputStream into a ByteBuffer.
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*/
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public ByteBuffer decodeBufferToByteBuffer(InputStream in)
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throws IOException {
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return ByteBuffer.wrap(decodeBuffer(in));
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}
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}
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