Java IO體系之InputStreamReader

介紹

• 字符輸入流Reader的實現類
• Java IO體系之Reader

繼承關係圖

源碼

package java.io;

import java.nio.charset.Charset;
import java.nio.charset.CharsetDecoder;
import sun.nio.cs.StreamDecoder;


public class InputStreamReader extends Reader {

    private final StreamDecoder sd;

    /**
     * Creates an InputStreamReader that uses the default charset.
     * @param  in   An InputStream
     */
    public InputStreamReader(InputStream in) {
        super(in);
        try {
            sd = StreamDecoder.forInputStreamReader(in, this, (String)null); // ## check lock object
        } catch (UnsupportedEncodingException e) {
            // The default encoding should always be available
            throw new Error(e);
        }
    }

    /**
     * Creates an InputStreamReader that uses the named charset.
     */
    public InputStreamReader(InputStream in, String charsetName)
        throws UnsupportedEncodingException
    {
        super(in);
        if (charsetName == null)
            throw new NullPointerException("charsetName");
        sd = StreamDecoder.forInputStreamReader(in, this, charsetName);
    }

    /**
     * Creates an InputStreamReader that uses the given charset.
     */
    public InputStreamReader(InputStream in, Charset cs) {
        super(in);
        if (cs == null)
            throw new NullPointerException("charset");
        sd = StreamDecoder.forInputStreamReader(in, this, cs);
    }

    /**
     * Creates an InputStreamReader that uses the given charset decoder.
     */
    public InputStreamReader(InputStream in, CharsetDecoder dec) {
        super(in);
        if (dec == null)
            throw new NullPointerException("charset decoder");
        sd = StreamDecoder.forInputStreamReader(in, this, dec);
    }

    /**
     * Returns the name of the character encoding being used by this stream.
     *
     * <p> If the encoding has an historical name then that name is returned;
     * otherwise the encoding's canonical name is returned.
     *
     * <p> If this instance was created with the {@link
     * #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 <code>null</code> if the
     * stream has been closed.
     * </p>
     * @return The historical name of this encoding, or
     *         <code>null</code> if the stream has been closed
     *
     * @see java.nio.charset.Charset
     *
     * @revised 1.4
     * @spec JSR-51
     */
    public String getEncoding() {
        return sd.getEncoding();
    }

    /**
     * Reads a single character.
     *
     * @return The character read, or -1 if the end of the stream has been
     *         reached
     *
     * @exception  IOException  If an I/O error occurs
     */
    public int read() throws IOException {
        return sd.read();
    }

    /**
     * Reads characters into a portion of an array.
     *
     * @param      cbuf     Destination buffer
     * @param      offset   Offset at which to start storing characters
     * @param      length   Maximum number of characters to read
     *
     * @return     The number of characters read, or -1 if the end of the
     *             stream has been reached
     *
     * @exception  IOException  If an I/O error occurs
     */
    public int read(char cbuf[], int offset, int length) throws IOException {
        return sd.read(cbuf, offset, length);
    }

    /**
     * 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.
     *
     * @exception  IOException  If an I/O error occurs
     */
    public boolean ready() throws IOException {
        return sd.ready();
    }

    public void close() throws IOException {
        sd.close();
    }
}

FileReader源碼

package java.io;

/**
 * Convenience class for reading character files.  The constructors of this
 * class assume that the default character encoding and the default byte-buffer
 * size are appropriate.  To specify these values yourself, construct an
 * InputStreamReader on a FileInputStream.
 *
 * <p><code>FileReader</code> is meant for reading streams of characters.
 * For reading streams of raw bytes, consider using a
 * <code>FileInputStream</code>.
 *
 * @see InputStreamReader
 * @see FileInputStream
 *
 * @author      Mark Reinhold
 * @since       JDK1.1
 */
public class FileReader extends InputStreamReader {

   /**
    * Creates a new <tt>FileReader</tt>, given the name of the
    * file to read from.
    *
    * @param fileName the name of the file to read from
    * @exception  FileNotFoundException  if the named file does not exist,
    *                   is a directory rather than a regular file,
    *                   or for some other reason cannot be opened for
    *                   reading.
    */
    public FileReader(String fileName) throws FileNotFoundException {
        super(new FileInputStream(fileName));
    }

   /**
    * Creates a new <tt>FileReader</tt>, given the <tt>File</tt>
    * to read from.
    *
    * @param file the <tt>File</tt> to read from
    * @exception  FileNotFoundException  if the file does not exist,
    *                   is a directory rather than a regular file,
    *                   or for some other reason cannot be opened for
    *                   reading.
    */
    public FileReader(File file) throws FileNotFoundException {
        super(new FileInputStream(file));
    }

   /**
    * Creates a new <tt>FileReader</tt>, given the
    * <tt>FileDescriptor</tt> to read from.
    *
    * @param fd the FileDescriptor to read from
    */
    public FileReader(FileDescriptor fd) {
        super(new FileInputStream(fd));
    }

}