ReaderInputStream.java

package com.yoursway.utils;

import java.io.IOException;
import java.io.InputStream;
import java.io.Reader;

/**
 * Adapts a <code>Reader</code> as an <code>InputStream</code>. Adapted
 * from <code>StringInputStream</code>.
 * 
 */
public class ReaderInputStream extends InputStream {
    
    /** Source Reader */
    private Reader in;
    
    private String encoding = System.getProperty("file.encoding");
    
    private byte[] slack;
    
    private int begin;
    
    /**
     * Construct a <code>ReaderInputStream</code> for the specified
     * <code>Reader</code>.
     * 
     * @param reader
     *            <code>Reader</code>. Must not be <code>null</code>.
     */
    public ReaderInputStream(Reader reader) {
        in = reader;
    }
    
    /**
     * Construct a <code>ReaderInputStream</code> for the specified
     * <code>Reader</code>, with the specified encoding.
     * 
     * @param reader
     *            non-null <code>Reader</code>.
     * @param encoding
     *            non-null <code>String</code> encoding.
     */
    public ReaderInputStream(Reader reader, String encoding) {
        this(reader);
        if (encoding == null) {
            throw new IllegalArgumentException("encoding must not be null");
        } else {
            this.encoding = encoding;
        }
    }
    
    /**
     * Reads from the <code>Reader</code>, returning the same value.
     * 
     * @return the value of the next character in the <code>Reader</code>.
     * 
     * @exception IOException
     *                if the original <code>Reader</code> fails to be read
     */
    public synchronized int read() throws IOException {
        if (in == null) {
            throw new IOException("Stream Closed");
        }
        
        byte result;
        if (slack != null && begin < slack.length) {
            result = slack[begin];
            if (++begin == slack.length) {
                slack = null;
            }
        } else {
            byte[] buf = new byte[1];
            if (read(buf, 0, 1) <= 0) {
                return -1;
            } else {
                result = buf[0];
            }
        }
        
        return result & 0xFF;
    }
    
    /**
     * Reads from the <code>Reader</code> into a byte array
     * 
     * @param b
     *            the byte array to read into
     * @param off
     *            the offset in the byte array
     * @param len
     *            the length in the byte array to fill
     * @return the actual number read into the byte array, -1 at the end of the
     *         stream
     * @exception IOException
     *                if an error occurs
     */
    public synchronized int read(byte[] b, int off, int len) throws IOException {
        if (in == null) {
            throw new IOException("Stream Closed");
        }
        if (len == 0) {
            return 0;
        }
        while (slack == null) {
            char[] buf = new char[len]; // might read too much
            int n = in.read(buf);
            if (n == -1) {
                return -1;
            }
            if (n > 0) {
                slack = new String(buf, 0, n).getBytes(encoding);
                begin = 0;
            }
        }
        
        if (len > slack.length - begin) {
            len = slack.length - begin;
        }
        
        System.arraycopy(slack, begin, b, off, len);
        
        if ((begin += len) >= slack.length) {
            slack = null;
        }
        
        return len;
    }
    
    /**
     * Marks the read limit of the StringReader.
     * 
     * @param limit
     *            the maximum limit of bytes that can be read before the mark
     *            position becomes invalid
     */
    public synchronized void mark(final int limit) {
        try {
            in.mark(limit);
        } catch (IOException ioe) {
            throw new RuntimeException(ioe.getMessage());
        }
    }
    
    /**
     * @return the current number of bytes ready for reading
     * @exception IOException
     *                if an error occurs
     */
    public synchronized int available() throws IOException {
        if (in == null) {
            throw new IOException("Stream Closed");
        }
        if (slack != null) {
            return slack.length - begin;
        }
        if (in.ready()) {
            return 1;
        } else {
            return 0;
        }
    }
    
    /**
     * @return false - mark is not supported
     */
    public boolean markSupported() {
        return false; // would be imprecise
    }
    
    /**
     * Resets the StringReader.
     * 
     * @exception IOException
     *                if the StringReader fails to be reset
     */
    public synchronized void reset() throws IOException {
        if (in == null) {
            throw new IOException("Stream Closed");
        }
        slack = null;
        in.reset();
    }
    
    /**
     * Closes the Stringreader.
     * 
     * @exception IOException
     *                if the original StringReader fails to be closed
     */
    public synchronized void close() throws IOException {
        if (in != null) {
            in.close();
            slack = null;
            in = null;
        }
    }
}