InputStreamReader

InputStreamReader is a class in the Java I/O library that acts as a bridge between byte streams and character streams. It reads bytes from an underlying InputStream and decodes them into characters using a specified character set (charset) or the platform default if none is specified. It extends the Reader class and delegates the conversion of bytes to characters according to the chosen encoding.

Constructors of InputStreamReader provide flexibility for encoding choice. It can be created with InputStreamReader(InputStream in), which uses the platform’s default charset; or with InputStreamReader(InputStream in, Charset cs), which accepts a Charset object; or with InputStreamReader(InputStream in, String charsetName), which accepts a charset name and may throw an exception if the encoding is not supported. The encoding determines how bytes are mapped to characters during reading.

Encoding and decoding behavior: InputStreamReader decodes bytes from the underlying stream into characters using the selected charset. The getEncoding() method returns the name of the charset in use or null if the encoding is not known. If the byte sequence cannot be decoded, reading operations may throw exceptions such as MalformedInputException or UnmappableCharacterException, depending on the charset and error handling.

Usage considerations: InputStreamReader is not buffered by itself; for efficient reading, it is common to wrap it in a BufferedReader. When you close the InputStreamReader, the underlying InputStream is closed as well.

See also: java.io.Reader, java.io.BufferedReader, java.nio.charset.Charset.