Java Tip 24: How to play audio in applications

Here's a step-by-step guide to playing audio files in a Java application

Playing audio files in Java applications is not officially supported in the current release of Java. But fear not, there is a way! This tip will show you how -- starting with a description of the basic steps involved in playing audio clips in Java applets and then moving on to Java application support.

Playing audio clips in applets is quite simple and involves the following steps:

  • Create an AudioClip object
  • Load .au sound file into AudioClip
  • Play sounds once or loop continuously
  • Stop playback

Here's how the code for these steps looks:

import java.applet.*;
AudioClip ac = getAudioClip(getCodeBase(), soundFile);
ac.play();   //play once
ac.stop();   //stop playing
ac.loop();   //play continuously

It would seem logical to use this same code to play audio clips in a Java application. Unfortunately, if you do that you will get errors from the compiler. Why? Because the AudioClip object and the getAudioClip() method are part of the java.applet package -- and are not part of applications. The good news is we can dive down and make things work ourselves.

The trick to solving this problem is to use some undocumented features that are provided by Sun in its JDK. Taking a peek inside the classes.zip file from the Sun JDK (using any of the various zipfile utilities), we find not only the standard Java packages such as java.applet but also sun.audio. (These are in the directory sun/audio.)

The sun.audio package contains everything we need to be able to play audio clips! Here's the code:

import  sun.audio.*;    //import the sun.audio package
import  java.io.*;
//** add this into your application code as appropriate
// Open an input stream  to the audio file.
InputStream in = new FileInputStream(Filename);
// Create an AudioStream object from the input stream.
AudioStream as = new AudioStream(in);         
// Use the static class member "player" from class AudioPlayer to play
// clip.
AudioPlayer.player.start(as);            
// Similarly, to stop the audio.
AudioPlayer.player.stop(as); 

To use a URL as the audio stream source, substitute the following for the input stream and audio stream setup:

AudioStream as = new AudioStream (url.openStream());

Playing the audio stream continuously adds a bit more complexity:

// Create audio stream as discussed previously.
// Create AudioData source.
AudioData data = as.getData();
// Create ContinuousAudioDataStream.
ContinuousAudioDataStream cas = new ContinuousAudioDataStream (data);
// Play audio.
AudioPlayer.player.play (cas);
// Similarly, to stop the audio.
AudioPlayer.player.stop (cas);

And there you have it. Remember, this technique uses undocumented features; there are no guarantees that it will work with anything but the current Sun JDK.

Chong Ser Wah is a consultant at the Competency Centre for Java in Singapore. Check out the center's Java Cup Competition.
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