java - 我需要有关为何为什么要获得NPE以及如何在播放时停止剪辑的帮助

Question

您好，我急切地想寻找一种解决方案，在它已经运行时如何停止我的剪辑。我一直在寻找解决方案已有多少天了，但仍然找不到。请任何知道如何帮助我的人。

这是我的代码

import java.io.BufferedReader;
import java.io.File;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.InetAddress;
import java.net.ServerSocket;
import java.net.Socket;

import javax.sound.sampled.AudioInputStream;
import javax.sound.sampled.AudioSystem;
import javax.sound.sampled.Clip;
import javax.swing.JOptionPane;
import javax.swing.SwingUtilities;

import javazoom.jl.player.Player;

public class server
{
    private static final int PORT = 7777;

    private static ServerSocket serverSocket;
    private static Socket clientSocket;
    private static InputStreamReader inputStreamReader;
    private static BufferedReader bufferedReader;
    private static String message;


    @SuppressWarnings("unused")
    private String filename;  
    private static  Clip clip1;
    private static  Clip clip2;
    private static  Clip clip3;
    private static  Clip clip4;
    private static  Clip clip5;
    private static  Clip clip6;
    static Player player; 

    public server(String filename) {  
        this.filename = filename;  


    }
    public static void main(String[] args) throws Exception

    {


        try
        {
            serverSocket = new ServerSocket(PORT, 0, InetAddress.getLocalHost());

            System.out.println("IP:  " + serverSocket.getInetAddress() + "  Port:  " +  serverSocket.getLocalPort());

        } catch (IOException e)
        {
            System.out.println("Could not listen on port: 7777");
        }

        System.out.println("Server started. Listening to the port 7777");

        while (true)
        {

            try
            {
                clientSocket = serverSocket.accept();
                inputStreamReader = new InputStreamReader(clientSocket.getInputStream());
                bufferedReader = new BufferedReader(inputStreamReader); 
                message = bufferedReader.readLine();


                System.out.println(message);{
                clip1 = null;
                clip2 = null;
                clip3 = null;
                clip4 = null;
                clip5 = null;
                clip6 = null;
                 if (message.equals("rock1")) {

                    AudioInputStream inputStream = AudioSystem.getAudioInputStream(new File("D:/Andrd/Music/TheAll-AmericanRejects-Swing,Swing.wav"));
                      clip4 = AudioSystem.getClip();

                      clip4.open(inputStream);
                      clip4.start(); 
                      SwingUtilities.invokeLater(new Runnable() {
                          public void run() {
                              JOptionPane.showMessageDialog(null, "rock1 song is playing!");
                          }
                      });  
                } else if (message.equals("stop") && clip4 != null && clip4.isRunning()){
                     clip4.stop();
                 }
                 if(message.equals("rock2")) {

                    AudioInputStream inputStream = AudioSystem.getAudioInputStream(new File("D:/Andrd/Music/FallOutBoy-SugarWe'reGoingDownWithLyrics!HQ.wav"));
                        clip5 = AudioSystem.getClip();
                        clip5.open(inputStream);
                       clip5.start();
                       SwingUtilities.invokeLater(new Runnable() {
                           public void run() {
                               JOptionPane.showMessageDialog(null, "rock2 song is playing!");
                           }
                       });
                } else if(message.equals("stop") && clip5 != null && clip5.isRunning()) {
                    clip5.stop();
                }
                 if(message.equals("rock3")) {

                    AudioInputStream inputStream = AudioSystem.getAudioInputStream(new File("D:/Andrd/Music/Fall Out Boy Light Em Up Lyrics.wav"));
                        clip6 = AudioSystem.getClip();
                        clip6.open(inputStream);
                        clip6.start();
                        SwingUtilities.invokeLater(new Runnable() {
                            public void run() {
                                JOptionPane.showMessageDialog(null, "rock3 song is playing!");
                            }
                        });
                 } else if(message.equals("stop") && clip6 !=null && clip6.isRunning()){
                clip6.stop();
            }
                if(message.equals("punk1")){
                    AudioInputStream inputStream = AudioSystem.getAudioInputStream(new File("D:/Andrd/Music/athousandmiles.wav"));
                    clip1 = AudioSystem.getClip();
                    clip1.open(inputStream);
                    clip1.start();
                    SwingUtilities.invokeLater(new Runnable() {
                        public void run() {
                            JOptionPane.showMessageDialog(null, "punk1 song is playing!");
                        }
                    });
             } else if(message.equals("stop") && clip1 !=null && clip1.isRunning()){
            clip1.stop();
        }
                if(message.equals("punk2")){
                    AudioInputStream inputStream = AudioSystem.getAudioInputStream(new File("D:/Andrd/Music/ISSUES - Boyfriend Lyric Video (Punk Goes Pop 5).wav"));
                    clip2 = AudioSystem.getClip();
                    clip2.open(inputStream);
                    clip2.start();
                    SwingUtilities.invokeLater(new Runnable() {
                        public void run() {
                            JOptionPane.showMessageDialog(null, "punk2 song is playing!");
                        }
                    });
             } else if(message.equals("stop") && clip2 !=null && clip2.isRunning()){
            clip2.stop();
        }
                if(message.equals("punk3")){
                    AudioInputStream inputStream = AudioSystem.getAudioInputStream(new File("D:/Andrd/Music/My Chemical Romance - Famous Last Words (Lyrics) - GetThemLyrics.wav"));
                    clip2 = AudioSystem.getClip();
                    clip2.open(inputStream);
                    clip2.start();
                    SwingUtilities.invokeLater(new Runnable() {
                        public void run() {
                            JOptionPane.showMessageDialog(null, "punk3 song is playing!");
                        }
                    });
             } else if(message.equals("stop") && clip3 !=null && clip3.isRunning()){
            clip3.stop();
        }
           }
                inputStreamReader.close();
                clientSocket.close();
            }catch (IOException ex)
            {
                System.out.println("Problem in message reading");
            }


        } 
        }

}

问题是当收到消息“停止”时歌曲没有停止
并且当它收到另一个消息，例如“rock2”时，即使已经有歌曲在播放，它也将继续播放。请帮助我修复此程序。

这是我的java stacktrace控制台:

 Exception in thread "main" java.lang.NullPointerException
    at server.main(server.java:73)

它可以同时播放所有3首歌曲，但无法停止播放，当我尝试发送2条相同的消息时，服务器崩溃并显示上述错误。

Answer 1

菲尔(Phil)的上述评论是正确的。

如果要避免"stop".equals(message)，通常写message.equals("stop")比NullPointerExceptions更安全。

另外，您似乎从未检查过message的有效性。如果没有更多输入，即另一侧刚刚挂断，readLine()返回null。在这种情况下，您可能要等待下一个请求。

[...]
message = bufferedReader.readLine();
// the following line may solve the issue:
if (message == null) continue;

干杯。