Module java.base
Package java.io

Class InputStreamReader

java.lang.Object
java.io.Reader
java.io.InputStreamReader
All Implemented Interfaces:
Closeable, AutoCloseable, Readable
Direct Known Subclasses:
FileReader

public class InputStreamReader
extends Reader
An InputStreamReader is a bridge from byte streams to character streams: It reads bytes and decodes them into characters using a specified charset. The charset that it uses may be specified by name or may be given explicitly, or the platform's default charset may be accepted.

Each invocation of one of an InputStreamReader's read() methods may cause one or more bytes to be read from the underlying byte-input stream. To enable the efficient conversion of bytes to characters, more bytes may be read ahead from the underlying stream than are necessary to satisfy the current read operation.

For top efficiency, consider wrapping an InputStreamReader within a BufferedReader. For example:

 BufferedReader in
   = new BufferedReader(new InputStreamReader(System.in));
 

Since:
1.1
See Also:
BufferedReader, InputStream, Charset
  • Constructor Details

    • InputStreamReader

      public InputStreamReader​(InputStream in)
      Creates an InputStreamReader that uses the default charset.
      Parameters:
      in - An InputStream
    • InputStreamReader

      public InputStreamReader​(InputStream in, String charsetName) throws UnsupportedEncodingException
      Creates an InputStreamReader that uses the named charset.
      Parameters:
      in - An InputStream
      charsetName - The name of a supported charset
      Throws:
      UnsupportedEncodingException - If the named charset is not supported
    • InputStreamReader

      public InputStreamReader​(InputStream in, Charset cs)
      Creates an InputStreamReader that uses the given charset.
      Parameters:
      in - An InputStream
      cs - A charset
      Since:
      1.4
    • InputStreamReader

      public InputStreamReader​(InputStream in, CharsetDecoder dec)
      Creates an InputStreamReader that uses the given charset decoder.
      Parameters:
      in - An InputStream
      dec - A charset decoder
      Since:
      1.4
  • Method Details

    • getEncoding

      public String getEncoding()
      Returns the name of the character encoding being used by this stream.

      If the encoding has an historical name then that name is returned; otherwise the encoding's canonical name is returned.

      If this instance was created with the InputStreamReader(InputStream, String) constructor then the returned name, being unique for the encoding, may differ from the name passed to the constructor. This method will return null if the stream has been closed.

      Returns:
      The historical name of this encoding, or null if the stream has been closed
      See Also:
      Charset
    • read

      public int read() throws IOException
      Reads a single character.
      Overrides:
      read in class Reader
      Returns:
      The character read, or -1 if the end of the stream has been reached
      Throws:
      IOException - If an I/O error occurs
    • read

      public int read​(char[] cbuf, int offset, int length) throws IOException
      Reads characters into a portion of an array.
      Specified by:
      read in class Reader
      Parameters:
      cbuf - Destination buffer
      offset - Offset at which to start storing characters
      length - Maximum number of characters to read
      Returns:
      The number of characters read, or -1 if the end of the stream has been reached
      Throws:
      IOException - If an I/O error occurs
      IndexOutOfBoundsException - If off is negative, or len is negative, or len is greater than cbuf.length - off
    • ready

      public boolean ready() throws IOException
      Tells whether this stream is ready to be read. An InputStreamReader is ready if its input buffer is not empty, or if bytes are available to be read from the underlying byte stream.
      Overrides:
      ready in class Reader
      Returns:
      True if the next read() is guaranteed not to block for input, false otherwise. Note that returning false does not guarantee that the next read will block.
      Throws:
      IOException - If an I/O error occurs