访问共享首选项以进行多部分上传时，Android 上的 Java 错误

Posted 2023-02-19

【中文标题】访问共享首选项以进行多部分上传时，Android 上的 Java 错误

【英文标题】：Java on Android error while accessing shared preference for multi part upload

【发布时间】：2017-11-19 12:36:36

【问题描述】：

请我在这个问题上需要帮助。我正在尝试将文件上传到当前工作正常的远程服务器。我还可以将用户电子邮件保存到共享偏好中。但是在尝试在异步任务中访问电子邮件时。它不断给出错误：

E/androidRuntime：致命异常：AsyncTask #2 java.lang.RuntimeException：执行 doInBackground() 时出错 在 android.os.AsyncTask$3.done(AsyncTask.java:309) 在 java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:354) 在 java.util.concurrent.FutureTask.setException(FutureTask.java:223) 在 java.util.concurrent.FutureTask.run(FutureTask.java:242) 在 android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:234) 在 java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1113) 在 java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:588) 在 java.lang.Thread.run(Thread.java:818) 原因：java.lang.NullPointerException：尝试在空对象引用上调用虚拟方法“java.lang.String android.content.Context.getPackageName()” $1.doInBackground(PASSMobileAudioservice.java:165) 在 android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:234) 在 java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1113) 在 java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:588) 在 java.lang.Thread.run(Thread.java:818)

这是我的代码：

       public class PASSMobileAudioService extends Service implements MediaRecorder.OnInfoListener 

private static Context mContext;
public PASSMobileAudioService(Context mContext) 
    this.mContext = mContext;



        public void uploadAudio(final String existingFileName)  
    this.mFileName = existingFileName;

    new AsyncTask<String, Void, Void>() 

        @Override
        protected Void doInBackground(String... params) 
            HttpURLConnection conn = null;
            DataOutputStream dos = null;
            DataInputStream inStream = null;
            String lineEnd = "\r\n";
            String twoHyphens = "--";
            String boundary = "*****";
            int bytesRead, bytesAvailable, bufferSize;
            byte[] buffer;
            int maxBufferSize = 1 * 1024 * 1024;
            String responseFromServer = "";
            String urlString = Constant.UPLOAD_AUDIO;
            SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(mContext);
            String email = prefs.getString(Constant.USER_EMAIL, "");

            try 
                //------------------ CLIENT REQUEST
                FileInputStream fileInputStream = new FileInputStream(new File(existingFileName));
                // open a URL connection to the Servlet
                URL url = new URL(urlString);
                // Open a HTTP connection to the URL
                conn = (HttpURLConnection) url.openConnection();
                // Allow Inputs
                conn.setDoInput(true);
                // Allow Outputs
                conn.setDoOutput(true);
                // Don't use a cached copy.
                conn.setUseCaches(false);
                // Use a post method.
                conn.setRequestMethod("POST");
                conn.setRequestProperty("Connection", "Keep-Alive");
                conn.setRequestProperty("Content-Type", "multipart/form-data;boundary=" + boundary);
                dos = new DataOutputStream(conn.getOutputStream());

                dos.writeBytes(twoHyphens + boundary + lineEnd);
                dos.writeBytes("Content-Disposition: form-data; name=\"userid=\"" + lineEnd);
                dos.writeBytes("Content-Type: text/plain; charset=US-ASCII" + lineEnd);
                dos.writeBytes("Content-Transfer-Encoding: 8bit" + lineEnd);
                dos.writeBytes(lineEnd);
                dos.writeBytes(email + lineEnd);

                dos.writeBytes(twoHyphens + boundary + lineEnd);
                dos.writeBytes("Content-Disposition: form-data; name=\"sessionid=\"" + lineEnd);
                dos.writeBytes("Content-Type: text/plain; charset=US-ASCII" + lineEnd);
                dos.writeBytes("Content-Transfer-Encoding: 8bit" + lineEnd);
                dos.writeBytes(lineEnd);
                dos.writeBytes(sessionid + lineEnd);

                dos.writeBytes(twoHyphens + boundary + lineEnd);
                dos.writeBytes("Content-Disposition: form-data; name=\"upload\";filename=\"" + existingFileName + "\"" + lineEnd);
                dos.writeBytes(lineEnd);
                // create a buffer of maximum size
                bytesAvailable = fileInputStream.available();
                bufferSize = Math.min(bytesAvailable, maxBufferSize);
                buffer = new byte[bufferSize];
                // read file and write it into form...
                bytesRead = fileInputStream.read(buffer, 0, bufferSize);
                while (bytesRead > 0) 
                    dos.write(buffer, 0, bufferSize);
                    bytesAvailable = fileInputStream.available();
                    bufferSize = Math.min(bytesAvailable, maxBufferSize);
                    bytesRead = fileInputStream.read(buffer, 0, bufferSize);
                
                // send multipart form data necesssary after file data...
                dos.writeBytes(lineEnd);
                dos.writeBytes(twoHyphens + boundary + twoHyphens + lineEnd);
                // close streams
                Log.e("Debug", "File is written");
                fileInputStream.close();
                dos.flush();
                dos.close();
             catch (MalformedURLException ex) 
                Log.e("Debug", "error: " + ex.getMessage(), ex);
             catch (IOException ioe) 
                Log.e("Debug", "error: " + ioe.getMessage(), ioe);
            
            //------------------ read the SERVER RESPONSE
            try 
                inStream = new DataInputStream(conn.getInputStream());
                String str;
                while ((str = inStream.readLine()) != null) 
                    Log.e("Debug", "Server Response " + str);
                
                inStream.close();
             catch (IOException ioex) 
                Log.e("Debug", "error: " + ioex.getMessage(), ioex);
            
            return null;
        
    .execute();

【参考方案1】：

您的根错误消息是Attempt to invoke virtual method 'java.lang.String android.content.Context.getPackageName()' on a null object reference in PASSMobileAudioService.java:165

我假设这条线是：

SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(mContext);

在这种情况下，mContext 为空。

你没有任何其他关于这个类的上下文，所以这就是我能给你的全部内容。确保您的上下文不为空。

【讨论】：

我已经定义了一个上下文，我很惊讶为什么上下文仍然为空。我更新了我的代码，请看一下

我只能假设，因为没有发布完整的代码。附加调试器并逐步执行您的程序以确保。您可以编辑您的原始帖子以显示在此类中定义/分配 mContext 的位置吗？

Hrm，你用非空参数调用构造函数，对吗？

我不太明白你的最后一句话。你能帮我解决这个问题吗

尝试将private static Context mContext;更改为private final Context mContext;