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Java AWT

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And Then There Were Applets
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14.5 Audio in Applications

The rest of this chapter describes how to use audio in your applications. Because the audio support discussed so far has been provided by the browser, applications that don't run in the context of a browser must use a different set of classes to work with audio. These classes are within the sun.audio package. Although the sun.* package hierarchy is not necessarily included by other vendors, the sun.audio classes discussed here are provided with Netscape Navigator 2.0/3.0 and Internet Explorer 3.0. Therefore, you can use these classes within applets, too. This section ends by developing a SunAudioClip class that has an interface similar to the applet's audio interface; you can use it to minimize coding differences between applets and applications.

AudioData

The AudioData class holds a clip of 8000 Hz µLaw audio data. This data can be used to construct an AudioDataStream or ContinuousAudioDataStream, which can then be played with the AudioPlayer. Constructor

public AudioData (byte buffer[])

The AudioData constructor accepts a byte array buffer and creates an instance of AudioData. The buffer should contain 8000 Hz µLaw audio data.

Methods

There are no methods for AudioData.

AudioStream

AudioStream subclasses FilterInputStream, which extends InputStream. Using an InputStream lets you move back and forth (rewind and fast forward) within an audio file, in addition to playing the audio data from start to finish. Constructors

public AudioStream (InputStream in) throws IOException

The AudioStream constructor has InputStream in as its parameter and can throw IOException on error. In the following code, we get an input stream by opening a .au file. Another common way to construct an AudioStream is to use the stream associated with a URL through the URL's openStream() method.

FileInputStream fis = new FileInputStream ("/usr/openwin/demo/sounds/1.au");
AudioStream audiostream = new AudioStream (fis);

or:

AudioStream audiostream = new AudioStream (savedUrl.openStream());

If you are constructing the audio data yourself, you would use a ByteArrayInputStream. Whatever the source of the data, the input stream should provide data in Sun's .au format.

Methods

public int read (byte buffer[], int offset, int length) throws IOException

The read() method for AudioStream reads an array of bytes into buffer. offset is the first element of buffer that is used. length is the maximum number of bytes to read. This method blocks until some input is available. read() returns the actual number of bytes read. If the end of stream is encountered and no bytes were read, read() returns -1. Ordinarily, you read() an AudioStream only if you want to modify the audio data in some way.

public int getLength()

The getLength() method returns the length of the audio data contained within the AudioStream, excluding any header information in the file.

public AudioData getData () throws IOException

The getData() method of AudioStream is the most important and most frequently used. It reads the data from the input stream and creates an AudioData instance. As the following code shows, you can create an AudioStream and get the AudioData with one statement.

AudioData audiodata = new AudioStream (aUrl.openStream()).getData();

AudioDataStream

Constructors

public AudioDataStream (AudioData data)

This constructor creates an AudioDataStream from an AudioData object data. The resulting AudioDataStream is a subclass of ByteArrayInputStream and can be played by the AudioPlayer.start() method.

Methods

There are no methods for AudioDataStream.

ContinuousAudioDataStream

Constructors

public ContinuousAudioDataStream (AudioData data)

This constructor creates a continuous stream of audio from data. The resulting ContinuousAudioDataStream is a subclass of AudioDataStream and, therefore, of ByteArrayInputStream. It can be played by AudioPlayer.start(); whenever the player reaches the end of the continuous audio data stream, it restarts from the beginning.

Methods

public int read ()

This read() method of ContinuousAudioDataStream overrides the read() method in ByteArrayInputStream to rewind back to the beginning of the stream when end-of-file is reached. This method is used by the system when it reads the InputStream; it is rarely called directly. read() never returns -1 since it loops back to the beginning on end-of-file.

public int read (byte buffer[], int offset, int length)

This read() method of ContinuousAudioDataStream overrides the read() method in ByteArrayInputStream to rewind back to the beginning of the stream when end-of-file is reached. This method is used by the system when it reads the InputStream; it is rarely called directly. read() returns the actual number of bytes read. read() never returns -1 since it loops back to the beginning on end-of-file.

AudioStreamSequence

Constructors

public AudioStreamSequence (Enumeration e)

The constructor for AudioStreamSequence accepts an Enumeration e(normally the elements of a Vector of AudioStreams) as its sole parameter. The constructor converts the sequence of audio streams into a single stream to be played in order. An example follows:

Vector v = new Vector ();
v.addElement (new AudioStream (url1.openStream ());
v.addElement (new AudioStream (url2.openStream ());
AudioStreamSequence audiostream = new AudioStreamSequence (v.elements ());
Methods

public int read ()

This read() method of AudioStreamSequence overrides the read() method in InputStream to start the next stream when end-of-file is reached. This method is used by the system when it reads the InputStream and is rarely called directly. If the end of all streams is encountered and no bytes were read, read() returns -1. Otherwise, read() returns the character read.

public int read (byte buffer[], int offset, int length)

This read() method of AudioStreamSequence overrides the read() method in InputStream to start the next stream when end-of-file is reached. This method is used by the system when it reads the InputStream and is rarely called directly. read() returns the actual number of bytes read. If the end of all streams is encountered and no bytes were read, read() returns -1.

AudioPlayer

The AudioPlayer class is the workhorse of the sun.audio package. It is used to play all the streams that were created with the other classes. There is no constructor for AudioPlayer; it just extends Thread and provides start() and stop() methods. Variable

public final static AudioPlayer player

player is the default audio player. This audio player is initialized automatically when the class is loaded; you do not have to initialize it (in fact, you can't because it is final) or call the constructor yourself.

Methods

public synchronized void start (InputStream in)

The start() method starts a thread that plays the InputStream in. Stream in continues to play until there is no more data or it is stopped. If in is a ContinuousAudioDataStream, the playing continues until stop() (described next) is called.

public synchronized void stop (InputStream in)

The stop() method stops the player from playing InputStream in. Nothing happens if the stream in is no longer playing or was never started.

SunAudioClip Class Definition

The class in Example 14.3 is all you need to play audio files in applications. It implements the java.applet.AudioClip interface, so the methods and functionality will be familiar. The test program in main() demonstrates how to use the class. Although the class itself can be used in applets, provided your users have the sun.audio package available, it is geared towards application users.

Example 14.3: The SunAudioClip Class

import java.net.URL;
import java.io.FileInputStream;
import sun.audio.*;
public class SunAudioClip implements java.applet.AudioClip {
    private AudioData audiodata;
    private AudioDataStream audiostream;
    private ContinuousAudioDataStream continuousaudiostream;
    static int length;
    public SunAudioClip (URL url) throws java.io.IOException {
        audiodata = new AudioStream (url.openStream()).getData();
        audiostream = null;
        continuousaudiostream = null;
    }
    public SunAudioClip (String filename) throws java.io.IOException {
        FileInputStream fis = new FileInputStream (filename);
        AudioStream audioStream = new AudioStream (fis);
        audiodata = audioStream.getData();
        audiostream = null;
        continuousaudiostream = null;
    }
    public void play () {
        audiostream = new AudioDataStream (audiodata);
        AudioPlayer.player.start (audiostream);
    }
    public void loop () {
        continuousaudiostream = new ContinuousAudioDataStream (audiodata);
        AudioPlayer.player.start (continuousaudiostream);
    }
    public void stop () {
        if (audiostream != null)
            AudioPlayer.player.stop (audiostream);
        if (continuousaudiostream != null)
            AudioPlayer.player.stop (continuousaudiostream);
    }
    public static void main (String args[]) throws Exception {
        URL url1 = new URL ("http://localhost:8080/audio/1.au");
        URL url2 = new URL ("http://localhost:8080/audio/2.au");
        SunAudioClip sac1 = new SunAudioClip (url1);
        SunAudioClip sac2 = new SunAudioClip (url2);
        SunAudioClip sac3 = new SunAudioClip ("1.au");
        sac1.play ();
        sac2.loop ();
        sac3.play ();
        try {// Delay for loop
            Thread.sleep (2000);
        } catch (InterruptedException ie) {}
        sac2.stop();
    }
}


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