org.apache.commons.io.input

Class ReaderInputStream

  • All Implemented Interfaces:
    Closeable, AutoCloseable


    public class ReaderInputStreamextends InputStream
    InputStream implementation that reads a character stream from a Reader and transforms it to a byte stream using a specified charset encoding. The stream is transformed using a CharsetEncoder object, guaranteeing that all charset encodings supported by the JRE are handled correctly. In particular for charsets such as UTF-16, the implementation ensures that one and only one byte order marker is produced.

    Since in general it is not possible to predict the number of characters to be read from the Reader to satisfy a read request on the ReaderInputStream, all reads from the Reader are buffered. There is therefore no well defined correlation between the current position of the Reader and that of the ReaderInputStream. This also implies that in general there is no need to wrap the underlying Reader in a BufferedReader.

    ReaderInputStream implements the inverse transformation of 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);
    ReaderInputStream implements the same transformation as OutputStreamWriter, except that the control flow is reversed: both classes transform a character stream into a byte stream, but OutputStreamWriter pushes data to the underlying stream, while 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 InputStream, but where the most natural way to produce the data is as a character stream, i.e. by providing a Reader instance. An example of a situation where this problem may appear is when implementing the DataSource interface from the Java Activation Framework.

    Given the fact that the 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 InputStream.available() method. A call to this method will always return 0. Also, this class doesn't support InputStream.mark(int).

    Instances of ReaderInputStream are not thread safe.

    Since:
    2.0
    See Also:
    WriterOutputStream
    • Constructor Detail

      • ReaderInputStream

        public ReaderInputStream(Reader reader,                 CharsetEncoder encoder,                 int bufferSize)
        Construct a new ReaderInputStream.
        Parameters:
        reader - the target Reader
        encoder - the charset encoder
        bufferSize - the size of the input buffer in number of characters
        Since:
        2.1
      • ReaderInputStream

        public ReaderInputStream(Reader reader,                 Charset charset,                 int bufferSize)
        Construct a new ReaderInputStream.
        Parameters:
        reader - the target Reader
        charset - the charset encoding
        bufferSize - the size of the input buffer in number of characters
      • ReaderInputStream

        public ReaderInputStream(Reader reader,                 Charset charset)
        Construct a new ReaderInputStream with a default input buffer size of 1024 characters.
        Parameters:
        reader - the target Reader
        charset - the charset encoding
      • ReaderInputStream

        public ReaderInputStream(Reader reader,                 String charsetName,                 int bufferSize)
        Construct a new ReaderInputStream.
        Parameters:
        reader - the target Reader
        charsetName - the name of the charset encoding
        bufferSize - the size of the input buffer in number of characters
      • ReaderInputStream

        public ReaderInputStream(Reader reader,                 String charsetName)
        Construct a new ReaderInputStream with a default input buffer size of 1024 characters.
        Parameters:
        reader - the target Reader
        charsetName - the name of the charset encoding
    • Method Detail

      • read

        public int read(byte[] b,       int off,       int len)         throws IOException
        Read the specified number of bytes into an array.
        Overrides:
        read in class InputStream
        Parameters:
        b - the byte array to read into
        off - the offset to start reading bytes into
        len - the number of bytes to read
        Returns:
        the number of bytes read or -1 if the end of the stream has been reached
        Throws:
        IOException - if an I/O error occurs
      • read

        public int read(byte[] b)         throws IOException
        Read the specified number of bytes into an array.
        Overrides:
        read in class InputStream
        Parameters:
        b - the byte array to read into
        Returns:
        the number of bytes read or -1 if the end of the stream has been reached
        Throws:
        IOException - if an I/O error occurs
      • read

        public int read()         throws IOException
        Read a single byte.
        Specified by:
        read in class InputStream
        Returns:
        either the byte read or -1 if the end of the stream has been reached
        Throws:
        IOException - if an I/O error occurs

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