终止Java Midi输出

Question

我写了这个简短的程序来学习javax.sound.midi系统。这是使用Java6。输出是预期的(由Sequencer事件触发的一系列System.out.println()字符串)，但问题是，在最后一个声音效果之后，程序停留在循环中，并且没有按预期终止。

有谁能告诉我怎么解决这个问题吗？感谢您的帮助：

import javax.sound.midi.MidiEvent;
import javax.sound.midi.ShortMessage;
import javax.sound.midi.InvalidMidiDataException;
import javax.sound.midi.ControllerEventListener;
import javax.sound.midi.Sequencer;
import javax.sound.midi.MidiSystem;
import javax.sound.midi.Sequence;
import javax.sound.midi.Track;
import javax.sound.midi.InvalidMidiDataException;
import javax.sound.midi.MidiUnavailableException;

class MySound {

    public static MidiEvent makeEvent(int comd, int chan, int one, 
                                      int two, int tick) {
        MidiEvent event = null;

        try {

            ShortMessage a = new ShortMessage();
            a.setMessage(comd, chan, one, two);
            event = new MidiEvent(a, tick);

        } catch (InvalidMidiDataException imde) {

            imde.printStackTrace();
        }       

        return event;
    }
}

class MyControllerListener implements ControllerEventListener {

    public void controlChange(ShortMessage event) {

        System.out.println("la");
    }
}

class SoundEffects {

    public static void main(String[] args) {

        try {

            Sequencer seq = MidiSystem.getSequencer();
            seq.open();

            int[] events = { 127 };

            MyControllerListener mcl = new MyControllerListener();

            seq.addControllerEventListener(mcl, events);

            Sequence s = new Sequence(Sequence.PPQ, 4);

            Track t = s.createTrack();

            for (int i = 5; i < 60; i += 4) {

                t.add(MySound.makeEvent(144, 1, i, 100, i));
                t.add(MySound.makeEvent(176, 1, 127, 0, i));
                t.add(MySound.makeEvent(128, 1, i, 100, i + 2));
            }

            seq.setSequence(s);

            seq.setTempoInBPM(220);

            seq.start();

        } catch (InvalidMidiDataException imde) {

            imde.printStackTrace();

        } catch (MidiUnavailableException mue) {

              mue.printStackTrace();
        }       
    }   
}   

Answer 1

一旦曲目播放完毕，就需要调用seq.close()。这样做的方法是添加一个元消息侦听器，并在遇到类型为0x2F的消息时调用close() (这是非可选的元消息"end of track")。您的代码将如下所示：

        seq.addMetaEventListener(new MetaEventListener() {

            @Override
            public void meta(MetaMessage metaMsg) {
                if (metaMsg.getType() == 0x2F) {
                    seq.close();
                }
            }
        });

请注意，您需要向seq添加final修饰符，以便在匿名接口实现中引用它。

希望这能有所帮助。