Java-ServletInputStream

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

/**
 * Provides an input stream for reading binary data from a client
 * request, including an efficient <code>readLine</code> method
 * for reading data one line at a time. With some protocols, such
 * as HTTP POST and PUT, a <code>ServletInputStream</code>
 * object can be used to read data sent from the client.
 * <p>A <code>ServletInputStream</code> object is normally retrieved via
 * the {@link ServletRequest#getInputStream} method.
 * <p>This is an abstract class that a servlet container implements.
 * Subclasses of this class
 * must implement the <code>java.io.InputStream.read()</code> method.
 * @author 	Various
 * @version 	$Version$
 * @see		ServletRequest
 */

public abstract class ServletInputStream extends InputStream {

    /**
     * Does nothing, because this is an abstract class.
     *
     */
	//抽象类，空构造函数
    protected ServletInputStream() { }

    /**
     * Reads the input stream, one line at a time. Starting at an
     * offset, reads bytes into an array, until it reads a certain number
     * of bytes or reaches a newline character, which it reads into the
     * array as well.
     * <p>This method returns -1 if it reaches the end of the input
     * stream before reading the maximum number of bytes.
     * @param b 		an array of bytes into which data is read
     * @param off 		an integer specifying the character at which this method begins reading
     * @param len		an integer specifying the maximum number of bytes to read
     * @return			an integer specifying the actual number of bytes  read, or -1 if the end of the stream is reached
     * @exception IOException	if an input or output exception has occurred
     */

    public int readLine(byte[] b, int off, int len) throws IOException {

	if (len <= 0) {
	    return 0;
	}
	int count = 0, c;

	while ((c = read()) != -1) {
	    b[off++] = (byte)c;
	    count++;
	    if (c == '\n' || count == len) {
		break;
	    }
	}
	return count > 0 ? count : -1;
    }
}