throttledoutputstream.java

java高级使用教程 全书一共分六章

// ThrottledOutputStream - output stream with throttling
//
// Copyright (C)1996,1998 by Jef Poskanzer <[e-mail]>. All rights reserved.
//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions
// are met:
// 1. Redistributions of source code must retain the above copyright
//    notice, this list of conditions and the following disclaimer.
// 2. Redistributions in binary form must reproduce the above copyright
//    notice, this list of conditions and the following disclaimer in the
//    documentation and/or other materials provided with the distribution.
//
// THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
// ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
// IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
// ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
// FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
// DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
// OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
// HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
// LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
// OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
// SUCH DAMAGE.
//
// Visit the ACME Labs Java page for up-to-date versions of this and other
// fine Java utilities: http://www.acme.com/java/

package Acme.Serve;

import java.io.*;
import java.util.*;

/// Output stream with throttling.
// <P>
// Restricts output to a specified rate.  Also includes a static utility
// routine for parsing a file of throttle settings.
// <P>
// <A HREF="/resources/classes/Acme/Serve/ThrottledOutputStream.java">Fetch the software.</A><BR>
// <A HREF="/resources/classes/Acme.tar.gz">Fetch the entire Acme package.</A>

public class ThrottledOutputStream extends FilterOutputStream
    {

    /// Parses a standard throttle file.
    // <P>
    // A throttle file lets you set maximum byte rates on filename patterns.
    // The format of the throttle file is very simple.  A # starts a
    // comment, and the rest of the line is ignored.  Blank lines are ignored.
    // The rest of the lines should consist of a pattern, whitespace, and a
    // number.  The pattern is a simple shell-style filename pattern, using
    // ? and *, or multiple such patterns separated by |.
    // <P>
    // The numbers in the file are byte rates, specified in units of bytes
    // per second.  For comparison, a v.32b/v.42b modem gives about
    // 1500/2000 B/s depending on compression, a double-B-channel ISDN line
    // about 12800 B/s, and a T1 line is about 150000 B/s.
    // <P>
    // Example:
    // <BLOCKQUOTE><PRE>
    // # throttle file for www.acme.com
    // *               100000  # limit total web usage to 2/3 of our T1
    // *.jpg|*.gif     50000   # limit images to 1/3 of our T1
    // *.mpg           20000   # and movies to even less
    // jef/*           20000   # jef's pages are too popular
    // </PRE></BLOCKQUOTE>
    // <P>
    // The routine returns a WildcardDictionary.  Do a lookup in this
    // dictionary using a filename, and you'll get back a ThrottleItem
    // containing the corresponding byte rate.
    public static Acme.WildcardDictionary parseThrottleFile( String filename ) throws IOException
	{
	Acme.WildcardDictionary wcd = new Acme.WildcardDictionary();
	BufferedReader br = new BufferedReader( new FileReader( filename ) );
	while ( true )
	    {
	    String line = br.readLine();
	    if ( line == null )
		break;
	    int i = line.indexOf( '#' );
	    if ( i != -1 )
		line = line.substring( 0, i );
	    line = line.trim();
	    if ( line.length() == 0 )
		continue;
	    String[] words = Acme.Utils.splitStr( line );
	    if ( words.length != 2 )
		throw new IOException( "malformed throttle line: " + line );
	    try
		{
		wcd.put(
		    words[0], new ThrottleItem( Long.parseLong( words[1] ) ) );
		}
	    catch ( NumberFormatException e )
		{
		throw new IOException(
		    "malformed number in throttle line: " + line );
		}
	    }
	br.close();
	return wcd;
	}


    private long maxBps;
    private long bytes;
    private long start;

    /// Constructor.
    public ThrottledOutputStream( OutputStream out, long maxBps )
	{
	super( out );
	this.maxBps = maxBps;
	bytes = 0;
	start = System.currentTimeMillis();
	}

    private byte[] oneByte = new byte[1];

    /// Writes a byte.  This method will block until the byte is actually
    // written.
    // @param b the byte to be written
    // @exception IOException if an I/O error has occurred
    public void write( int b ) throws IOException
	{
	oneByte[0] = (byte) b;
	write( oneByte, 0, 1 );
	}

    /// Writes a subarray of bytes.
    // @param b	the data to be written
    // @param off the start offset in the data
    // @param len the number of bytes that are written
    // @exception IOException if an I/O error has occurred
    public void write( byte b[], int off, int len ) throws IOException
	{
	// Check the throttle.
	bytes += len;
	long elapsed = System.currentTimeMillis() - start;
	long bps = bytes * 1000L / elapsed;
	if ( bps > maxBps )
	    {
	    // Oops, sending too fast.
	    long wakeElapsed = bytes * 1000L / maxBps;
	    try
		{
		Thread.sleep( wakeElapsed - elapsed );
		}
	    catch ( InterruptedException ignore ) {}
	    }

	// Write the bytes.
	out.write( b, off, len );
	}

    }