所以，我一直在从事一个学习型项目，从线路中获取音频数据并将其渲染到我的扬声器。现在，我在我的最后一根稻草和最后几行代码上，我不知道什么会先出现。设置好两条数据线后，我尝试将其读TargetDataLine入字节数组，编译器会抛出nullPointerException. 错误被跟踪到Stream.java:138是public static void play()。我也不确定我Thread的设置是否正确，但现在让我们尝试关注手头的主题。我基本上只是想阅读Line In并将其写入Speakers，任何建议都会很棒。
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() {
}
}
系统的输出和错误堆栈跟踪说：
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)