java - 无法从 TargetDataLine 读取

Question

因此，我一直致力于学习型项目，从线路中获取音频数据并将其呈现到我的扬声器。现在，我已经到了最后一根稻草和最后几行代码，我不知道什么会先发生。设置两条数据线后，我尝试将 TargetDataLine 读入字节数组，编译器抛出一个 nullPointerException。错误被跟踪到 Stream.java:138，即 public static void play()。我也不确定我的 Thread 是否设置正确，但让我们现在试着专注于手头的主题。我基本上只是在尝试阅读 Line In 并将其写入 Speakers，任何建议都很好。

代码:

package moshi;

import javax.sound.sampled.AudioFormat;
import javax.sound.sampled.AudioSystem;
import javax.sound.sampled.Line;
import javax.sound.sampled.LineUnavailableException;
import javax.sound.sampled.Mixer;
import javax.sound.sampled.SourceDataLine;
import javax.sound.sampled.TargetDataLine;

/**
 * @author KN
 * @version 1.0 Build 1 October 25, 2013
 * 
 *          This concurrent process sets up and controls the streaming of audio
 *          data via input and output buffers.
 * 
 * @see {@link Thread}, {@link AudioSystem}, {@link TargetDataLine},
 *      {@link SourceDataLine}
 */

public class Stream extends Thread {

    /** The {@link AudioFormat} used in encoding/decoding streaming audio data */
    public final static AudioFormat audioFormat = new AudioFormat(44100, 8, 1, true, true);

    /**
     * {@link String} describing the name of the audio device to be used.
     * <p>
     * Example: "Line In", "Microphone"
     */
    private static String INPUT = "Line In";
    /**
     * {@link String} describing the name of the audio device to be used.
     * <p>
     * Example: "Speakers", "Line Out"
     */
    private static String OUTPUT = "Speakers";

    /**
     * {@link #PROCESSING_BUFFER} is a buffer used for receiving audio data
     * 
     * @see TargetDataLine
     */
    private static TargetDataLine PROCESSING_BUFFER;
    /**
     * {@link #RENDERING_BUFFER} is a buffer used for writing audio data
     * 
     * @see SourceDataLine
     */
    private static SourceDataLine RENDERING_BUFFER;
    /** {@link Integer} specifying the buffer sizes in bytes */
    private static int BUFFER_SIZE = 2048;
    /** {@link Byte[]} for holding raw audio data */
    private static byte[] READ_BUFFER;

    /**
     * Initiates the audio hardware read/write buffers into
     * {@link TargetDataLine}s and {@link SourceDataLine}s respectively.
     * 
     * @see {@link TargetDataLine}, {@link SourceDataLine}
     */
    public Stream() {
        setProcessingBuffer();
        setRenderingBuffer();
    }

    /**
     * Queries input Lines and stores the {@link TargetDataLine} at
     * {@link #PROCESSING_BUFFER}
     * 
     * @see {@link AudioSystem}, {@link Line}, {@link TargetDataLine},
     *      {@link Mixer}
     */
    private void setProcessingBuffer() {
        final Mixer.Info[] mixerInfos = AudioSystem.getMixerInfo();
        for (final Mixer.Info info : mixerInfos) {
            final Mixer mixer = AudioSystem.getMixer(info);
            final Line.Info[] targetLineInfos = mixer.getTargetLineInfo();
            for (final Line.Info targetLineInfo : targetLineInfos) {
                if (targetLineInfo.getLineClass() == javax.sound.sampled.TargetDataLine.class
                        && info.getName().startsWith(Stream.INPUT)) {
                    try {
                        Stream.PROCESSING_BUFFER = (TargetDataLine) mixer.getLine(targetLineInfo);
                        System.out.println(targetLineInfo.getLineClass() + ": " + info.getName() + " ["
                                + Stream.PROCESSING_BUFFER + "]");
                    } catch (LineUnavailableException e) {
                        e.printStackTrace();
                    }
                } else {
                }
            }
        }
    }

    /**
     * Queries output Lines and stores the {@link SourceDataLine} at
     * {@link #RENDERING_BUFFER}
     * 
     * @see {@link AudioSystem}, {@link Line}, {@link SourceDataLine},
     *      {@link Mixer}
     */
    private void setRenderingBuffer() {
        final Mixer.Info[] mixerInfos = AudioSystem.getMixerInfo();
        for (Mixer.Info info : mixerInfos) {
            final Mixer mixer = AudioSystem.getMixer(info);
            final Line.Info[] sourceLineInfos = mixer.getSourceLineInfo();
            for (final Line.Info sourceLineInfo : sourceLineInfos) {
                if (sourceLineInfo.getLineClass() == javax.sound.sampled.SourceDataLine.class
                        && info.getName().startsWith(Stream.OUTPUT)) {
                    try {
                        Stream.RENDERING_BUFFER = (SourceDataLine) mixer.getLine(sourceLineInfo);
                        System.out.println(sourceLineInfo.getLineClass() + ": " + info.getName() + " ["
                                + Stream.RENDERING_BUFFER + "]");
                    } catch (LineUnavailableException e) {
                        e.printStackTrace();
                    }
                } else {
                }
            }
        }
    }

    /**
     * Opens buffers {@link #PROCESSING_BUFFER} and {@link #RENDERING_BUFFER}
     * for reading/writing
     */
    public static void play() {
        try {
            if (!Stream.PROCESSING_BUFFER.isOpen()) {
                Stream.PROCESSING_BUFFER.open(Stream.audioFormat);
            }
            if (!Stream.RENDERING_BUFFER.isOpen()) {
                Stream.RENDERING_BUFFER.open(Stream.audioFormat);
                Stream.RENDERING_BUFFER.start();
            }
            while (Stream.RENDERING_BUFFER.isOpen()) {
                Stream.PROCESSING_BUFFER.read(Stream.READ_BUFFER, 0, Stream.BUFFER_SIZE);
                System.out.println(Stream.READ_BUFFER.length);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    /**
     * Stops buffers {@link #PROCESSING_BUFFER} and {@link #RENDERING_BUFFER}
     * from reading/writing
     */
    public static void pause() {
        if (Stream.PROCESSING_BUFFER.isOpen()) {
            Stream.PROCESSING_BUFFER.close();
        }
        if (Stream.RENDERING_BUFFER.isOpen()) {
            Stream.RENDERING_BUFFER.stop();
            Stream.RENDERING_BUFFER.close();
        }
    }

    /** {@inheritDoc} */
    @Override
    public void run() {
    }
}

系统输出和错误堆栈跟踪显示:

interface javax.sound.sampled.TargetDataLine: Line In (Realtek High Definitio [com.sun.media.sound.DirectAudioDevice$DirectTDL@18dd7404]
interface javax.sound.sampled.SourceDataLine: Speakers (Realtek High Definition Audio) [com.sun.media.sound.DirectAudioDevice$DirectSDL@3639b3a2]
java.lang.NullPointerException
    at com.sun.media.sound.DirectAudioDevice$DirectTDL.read(Unknown Source)
    at moshi.Stream.play(Stream.java:138)
    at moshi.Controls$1.actionPerformed(Controls.java:38)
    at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
    at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
    at java.awt.Component.processMouseEvent(Unknown Source)
    at javax.swing.JComponent.processMouseEvent(Unknown Source)
    at java.awt.Component.processEvent(Unknown Source)
    at java.awt.Container.processEvent(Unknown Source)
    at java.awt.Component.dispatchEventImpl(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Window.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
    at java.awt.EventQueue.access$000(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.awt.EventQueue$4.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue.dispatchEvent(Unknown Source)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.run(Unknown Source)

Answer 1

您从未在代码中初始化 READ_BUFFER 变量，您必须以适当的大小实例化它:

READ_BUFFER = new byte[BUFFER_SIZE]; // I guess this was the intended size