在heroku上部署的Web应用程序中使用Java Sound API

Question

We are working on a project for creating music based on crowd sourcing. People vote for every note until the vote is closed, and then move on to the next vote until the canvas for the music is filled. A similar project is crowdsound, if you want to get an idea of what it looks like.

We've hosted the .war on heroku and we've managed to make everything work, except the sound. Every time we try to call the Java Sound API (we use the midi synthesizer), we get the following error:

2017-03-10T09:49:01.338821+00:00 app[web.1]: javax.sound.midi.MidiUnavailableException: Can not open line
2017-03-10T09:49:01.339228+00:00 app[web.1]:    at com.sun.media.sound.SoftSynthesizer.open(SoftSynthesizer.java:1155)
2017-03-10T09:49:01.339288+00:00 app[web.1]:    at com.sun.media.sound.SoftSynthesizer.open(SoftSynthesizer.java:1066)
2017-03-10T09:49:01.339340+00:00 app[web.1]:    at music.MusicPlayer.run(MusicPlayer.java:99)
2017-03-10T09:49:01.339391+00:00 app[web.1]:    at java.lang.Thread.run(Thread.java:745)
2017-03-10T09:49:01.340759+00:00 app[web.1]: Caused by: java.lang.IllegalArgumentException: No line matching interface SourceDataLine supporting format PCM_SIGNED 44100.0 Hz, 16 bit, stereo, 4 bytes/frame, little-endian is supported.
2017-03-10T09:49:01.340869+00:00 app[web.1]:    at javax.sound.sampled.AudioSystem.getLine(AudioSystem.java:479)
2017-03-10T09:49:01.340924+00:00 app[web.1]:    at javax.sound.sampled.AudioSystem.getSourceDataLine(AudioSystem.java:606)
2017-03-10T09:49:01.340975+00:00 app[web.1]:    at com.sun.media.sound.SoftSynthesizer.open(SoftSynthesizer.java:1095)
2017-03-10T09:49:01.341045+00:00 app[web.1]:    ... 3 more

Does this mean that we cannot use the midi synthesizer in a web app, or is there some way to make this work?

Answer 1

You simply cannot play a sound from a Java WAR, because it's executed on the server side. Additionally, the heroku instance may be lacking the sound hardware altogether.

If you'd like to generate sound that is then served to the web client, you need to either use some MIDI renderer that produces a sound file, and then serve the resulting audio file to the client (eg as WAV file) or simply serve MIDI to the client and have the browser play the MIDI via a library like eg MIDI.js .