+ * Since in general it is not possible to predict the number of characters to be read from the + * {@link Reader} to satisfy a read request on the {@link ReaderInputStream}, all reads from + * the {@link Reader} are buffered. There is therefore no well defined correlation + * between the current position of the {@link Reader} and that of the {@link ReaderInputStream}. + * This also implies that in general there is no need to wrap the underlying {@link Reader} + * in a {@link java.io.BufferedReader}. + *
+ * {@link ReaderInputStream} implements the inverse transformation of {@link java.io.InputStreamReader}; + * in the following example, reading from in2 would return the same byte + * sequence as reading from in (provided that the initial byte sequence is legal + * with respect to the charset encoding): + *
+ * InputStream in = ... + * Charset cs = ... + * InputStreamReader reader = new InputStreamReader(in, cs); + * ReaderInputStream in2 = new ReaderInputStream(reader, cs);+ * {@link ReaderInputStream} implements the same transformation as {@link java.io.OutputStreamWriter}, + * except that the control flow is reversed: both classes transform a character stream + * into a byte stream, but {@link java.io.OutputStreamWriter} pushes data to the underlying stream, + * while {@link ReaderInputStream} pulls it from the underlying stream. + *
+ * Note that while there are use cases where there is no alternative to using + * this class, very often the need to use this class is an indication of a flaw + * in the design of the code. This class is typically used in situations where an existing + * API only accepts an {@link InputStream}, but where the most natural way to produce the data + * is as a character stream, i.e. by providing a {@link Reader} instance. An example of a situation + * where this problem may appear is when implementing the {@link javax.activation.DataSource} + * interface from the Java Activation Framework. + *
+ * Given the fact that the {@link Reader} class doesn't provide any way to predict whether the next + * read operation will block or not, it is not possible to provide a meaningful + * implementation of the {@link InputStream#available()} method. A call to this method + * will always return 0. Also, this class doesn't support {@link InputStream#mark(int)}. + *
+ * Instances of {@link ReaderInputStream} are not thread safe.
+ * *
+ * @since 2.0
+ */
+public class ReaderInputStream extends InputStream {
+ private static final int DEFAULT_BUFFER_SIZE = 1024;
+
+ private final Reader reader;
+ private final CharsetEncoder encoder;
+
+ /**
+ * CharBuffer used as input for the decoder. It should be reasonably
+ * large as we read data from the underlying Reader into this buffer.
+ */
+ private final CharBuffer encoderIn;
+
+ /**
+ * ByteBuffer used as output for the decoder. This buffer can be small
+ * as it is only used to transfer data from the decoder to the
+ * buffer provided by the caller.
+ */
+ private final ByteBuffer encoderOut;
+
+ private CoderResult lastCoderResult;
+ private boolean endOfInput;
+
+ /**
+ * Construct a new {@link ReaderInputStream}.
+ *
+ * @param reader the target {@link Reader}
+ * @param encoder the charset encoder
+ * @since 2.1
+ */
+ public ReaderInputStream(Reader reader, CharsetEncoder encoder) {
+ this(reader, encoder, DEFAULT_BUFFER_SIZE);
+ }
+
+ /**
+ * Construct a new {@link ReaderInputStream}.
+ *
+ * @param reader the target {@link Reader}
+ * @param encoder the charset encoder
+ * @param bufferSize the size of the input buffer in number of characters
+ * @since 2.1
+ */
+ public ReaderInputStream(Reader reader, CharsetEncoder encoder, int bufferSize) {
+ this.reader = reader;
+ this.encoder = encoder;
+ this.encoderIn = CharBuffer.allocate(bufferSize);
+ this.encoderIn.flip();
+ this.encoderOut = ByteBuffer.allocate(128);
+ this.encoderOut.flip();
+ }
+
+ /**
+ * Construct a new {@link ReaderInputStream}.
+ *
+ * @param reader the target {@link Reader}
+ * @param charset the charset encoding
+ * @param bufferSize the size of the input buffer in number of characters
+ */
+ public ReaderInputStream(Reader reader, Charset charset, int bufferSize) {
+ this(reader,
+ charset.newEncoder()
+ .onMalformedInput(CodingErrorAction.REPLACE)
+ .onUnmappableCharacter(CodingErrorAction.REPLACE),
+ bufferSize);
+ }
+
+ /**
+ * Construct a new {@link ReaderInputStream} with a default input buffer size of
+ * 1024 characters.
+ *
+ * @param reader the target {@link Reader}
+ * @param charset the charset encoding
+ */
+ public ReaderInputStream(Reader reader, Charset charset) {
+ this(reader, charset, DEFAULT_BUFFER_SIZE);
+ }
+
+ /**
+ * Construct a new {@link ReaderInputStream}.
+ *
+ * @param reader the target {@link Reader}
+ * @param charsetName the name of the charset encoding
+ * @param bufferSize the size of the input buffer in number of characters
+ */
+ public ReaderInputStream(Reader reader, String charsetName, int bufferSize) {
+ this(reader, Charset.forName(charsetName), bufferSize);
+ }
+
+ /**
+ * Construct a new {@link ReaderInputStream} with a default input buffer size of
+ * 1024 characters.
+ *
+ * @param reader the target {@link Reader}
+ * @param charsetName the name of the charset encoding
+ */
+ public ReaderInputStream(Reader reader, String charsetName) {
+ this(reader, charsetName, DEFAULT_BUFFER_SIZE);
+ }
+
+ /**
+ * Construct a new {@link ReaderInputStream} that uses the default character encoding
+ * with a default input buffer size of 1024 characters.
+ *
+ * @param reader the target {@link Reader}
+ */
+ public ReaderInputStream(Reader reader) {
+ this(reader, Charset.defaultCharset());
+ }
+
+ /**
+ * Fills the internal char buffer from the reader.
+ *
+ * @throws IOException
+ * If an I/O error occurs
+ */
+ private void fillBuffer() throws IOException {
+ if (!endOfInput && (lastCoderResult == null || lastCoderResult.isUnderflow())) {
+ encoderIn.compact();
+ int position = encoderIn.position();
+ // We don't use Reader#read(CharBuffer) here because it is more efficient
+ // to write directly to the underlying char array (the default implementation
+ // copies data to a temporary char array).
+ int c = reader.read(encoderIn.array(), position, encoderIn.remaining());
+ if (c == -1) {
+ endOfInput = true;
+ } else {
+ encoderIn.position(position+c);
+ }
+ encoderIn.flip();
+ }
+ encoderOut.compact();
+ lastCoderResult = encoder.encode(encoderIn, encoderOut, endOfInput);
+ encoderOut.flip();
+ }
+
+ /**
+ * Read the specified number of bytes into an array.
+ *
+ * @param b the byte array to read into
+ * @param off the offset to start reading bytes into
+ * @param len the number of bytes to read
+ * @return the number of bytes read or -1
+ * if the end of the stream has been reached
+ * @throws IOException if an I/O error occurs
+ */
+ @Override
+ public int read(byte[] b, int off, int len) throws IOException {
+ if (b == null) {
+ throw new NullPointerException("Byte array must not be null");
+ }
+ if (len < 0 || off < 0 || (off + len) > b.length) {
+ throw new IndexOutOfBoundsException("Array Size=" + b.length +
+ ", offset=" + off + ", length=" + len);
+ }
+ int read = 0;
+ if (len == 0) {
+ return 0; // Always return 0 if len == 0
+ }
+ while (len > 0) {
+ if (encoderOut.hasRemaining()) {
+ int c = Math.min(encoderOut.remaining(), len);
+ encoderOut.get(b, off, c);
+ off += c;
+ len -= c;
+ read += c;
+ } else {
+ fillBuffer();
+ if (endOfInput && !encoderOut.hasRemaining()) {
+ break;
+ }
+ }
+ }
+ return read == 0 && endOfInput ? -1 : read;
+ }
+
+ /**
+ * Read the specified number of bytes into an array.
+ *
+ * @param b the byte array to read into
+ * @return the number of bytes read or -1
+ * if the end of the stream has been reached
+ * @throws IOException if an I/O error occurs
+ */
+ @Override
+ public int read(byte[] b) throws IOException {
+ return read(b, 0, b.length);
+ }
+
+ /**
+ * Read a single byte.
+ *
+ * @return either the byte read or -1 if the end of the stream
+ * has been reached
+ * @throws IOException if an I/O error occurs
+ */
+ @Override
+ public int read() throws IOException {
+ for (;;) {
+ if (encoderOut.hasRemaining()) {
+ return encoderOut.get() & 0xFF;
+ } else {
+ fillBuffer();
+ if (endOfInput && !encoderOut.hasRemaining()) {
+ return -1;
+ }
+ }
+ }
+ }
+
+ /**
+ * Close the stream. This method will cause the underlying {@link Reader}
+ * to be closed.
+ * @throws IOException if an I/O error occurs
+ */
+ @Override
+ public void close() throws IOException {
+ reader.close();
+ }
+}