The java.io Package - Readers and Writers

InputStreamReader

• InputStreamReader extends Reader and has one subclass, FileReader
• InputStreamReader reads bytes and translates them to Unicode characters using the specified character encoding or the default system encoding
• the class has two constructors

      InputStreamReader(InputStream in)
      InputStreamReader(InputStream in, String enc)
  

• to use an InputStreamReader you must first create an instance of it for a byte input stream. You can then read the stream using any of the Reader methods.

OutputStreamWriter

• OutputStreamWriter extends Writer and has one subclass, FileWriter
• OutputStreamWriter translates between Unicode characters and bytes using the specified character encoding or the default system encoding
• the class also has two constructors

      OuputStreamWriter(OutputStream out)
      OuputStreamWriter(OutputStream out, String enc)
  

• you use OutputStreamWriter by first creating an instance of it for a byte output stream; you can then write to the stream using an Writer methods.

Character Encoding

• Character encodings specify how 8-bit bytes are translated to 16-bit Unicode
• they are represented by Strings which follow the naming standards set by IANA Character Registry
• every implementation of Java is required to support the following sets:

    US-ASCII     Seven-bit ASCII, a.k.a. ISO646-US, a.k.a. the
                 Basic Latin block of the Unicode character
                 set
    ISO-8859-1  
                 ISO Latin Alphabet No. 1, a.k.a. ISO-LATIN-1
    UTF-8
                 Eight-bit Unicode Transformation Format
    UTF-16BE
                 Sixteen-bit Unicode Transformation Format,
                 big-endian byte order
    UTF-16LE
                 Sixteen-bit Unicode Transformation Format,
                 little-endian byte order
    UTF-16
                 Sixteen-bit Unicode Transformation Format,
                 byte order specified by a mandatory initial
                 byte-order mark (either order accepted on
                 input, big-endian used on output)
  

• specific platforms ie those used in Japan, China, Mid-East, etc, may include other encodings
• the streams are used to read and write data encoded in a character set which is different than the default system encoding
• For example (JPL pg238), to read bytes encoded under ISO 8859-6 for Arabic characters

  public Reader readArabic(String file) throws IOException {
      InputStream fileIn = new FileInputSgream(file);
      return new InputStreamReader(fileIn, "iso-8859-6");
  }