Android DataOutputStream.write（byte []，int，int）'空對象引用

Question

我想從SD卡上傳圖像和音頻文件到服務器。當運行沒有應用程序崩潰，但圖像和音頻上傳適當的方式。當我去服務器，並檢查圖像和音頻，並顯示文件沒有found.Means當我點擊音頻符號嘗試播放服務器上顯示文件未找到。

這裏是我的影像和音頻文件上傳方法

uploadFile(uploadFilePath+""+imagePath , imagePath); 

public int uploadFile(String uploadFileName ,String upLoadImageAudioName) 
    { 
     String fileName = uploadFileName; 
     String baseDir = Environment.getExternalStorageDirectory().getAbsolutePath(); 
     String upLoadFilePath = baseDir+"/classnkk_images/"; 
     HttpURLConnection conn = null; 
     DataOutputStream dos = null; 
     String lineEnd = "\r\n"; 
     String twoHyphens = "--"; 
     String boundary = "*****"; 
     int bytesRead, bytesAvailable, bufferSize; 
     byte[] buffer; 
     int maxBufferSize = 1 * 1024 * 1024; 
     File sourceFile = new File(uploadFileName); 

     if (!sourceFile.isFile()) 
     { 
      Log.e("uploadFile", "Source File not exist :" +upLoadFilePath + "" + upLoadImageAudioName); 
      return 0; 
     } 
     else 
     { 
      try 
      { 
       // open a URL connection to the Servlet 
       FileInputStream fileInputStream = new FileInputStream(sourceFile); 
       URL url = new URL("http://xxxx/xxxx/MobileService.svc/UploadFileStream/"); 

       // Open a HTTP connection to the URL 
       conn = (HttpURLConnection) url.openConnection(); 
       conn.setDoInput(true); // Allow Inputs 
       conn.setDoOutput(true); // Allow Outputs 
       conn.setUseCaches(false); // Don't use a Cached Copy 
       conn.setRequestMethod("POST"); 
       conn.setRequestProperty("Connection", "Keep-Alive"); 
       conn.setRequestProperty("ENCTYPE", "multipart/form-data"); 
       conn.setRequestProperty("Content-Type", "multipart/form-data;boundary=" + boundary); 
       conn.setRequestProperty("uploaded_file", fileName); 

       if(fileName.endsWith(".png")) 
       { 
        dos = new DataOutputStream(conn.getOutputStream()); 
        dos.writeBytes(twoHyphens + boundary + lineEnd); 
        dos.writeBytes("Content-Disposition: form-data; name=\"file_name\";filename=\"" + fileName + "\"" + lineEnd); 
        dos.writeBytes(lineEnd); 
        // Code for sending the image.... 
        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); 

       } 

       if(fileName.endsWith(".mp3")) 
       { 
        dos.writeBytes(twoHyphens + boundary + lineEnd); 
        dos.writeBytes("Content-Disposition: form-data; name=\"file_name_audio\";filename=\""+ fileName + "\"" + lineEnd); 
        dos.writeBytes(lineEnd); 
        // Code for sending the MP3 
        dos.writeBytes(lineEnd); 
        dos.writeBytes(twoHyphens + boundary + twoHyphens + lineEnd); 

       } 
       serverResponseCode = conn.getResponseCode(); 
       String serverResponseMessage = conn.getResponseMessage(); 
       Log.i("uploadFile", "HTTP Response is : " + serverResponseMessage + ": " + serverResponseCode); 
       if(serverResponseCode == 200) 
       {runOnUiThread(new Runnable() { 
         public void run() {} 
        }); 
       } 
       //close the streams // 
       fileInputStream.close(); 
       dos.flush(); 
       dos.close(); 

      } catch (MalformedURLException ex) 
      { 
       ex.printStackTrace(); 
       Log.e("Upload file to server", "error: " + ex.getMessage(), ex); 
      } catch (Exception e) 
      { 
       e.printStackTrace(); 
      } 
      return serverResponseCode; 

     } // End else block 
    } 

這裏是日誌信息，先進

09-23 05:25:45.178 23676-24640/com.example.tazeen.classnkk W/System.err﹕ java.lang.NullPointerException: Attempt to invoke virtual method 'void java.io.DataOutputStream.write(byte[], int, int)' on a null object reference 
09-23 05:25:45.178 23676-24640/com.example.tazeen.classnkk W/System.err﹕ at com.example.tazeen.classnkk.AddPost.uploadFile(AddPost.java:798) 
09-23 05:25:45.178 23676-24640/com.example.tazeen.classnkk W/System.err﹕ at com.example.tazeen.classnkk.AddPost$7$1$1.run(AddPost.java:419) 

感謝。

Answer 1

近代碼的頂部，你有

DataOutputStream dos = null; 

後來

if(fileName.endsWith(".png")) 
{ 
    dos = new DataOutputStream(conn.getOutputStream()); 
    ... 
} 

因此，當文件名以.png格式

後

結束，但仍然要初始化您的DataOutputStream類

if(fileName.endsWith(".mp3")) 
{ 
    dos.writeBytes(twoHyphens + boundary + lineEnd); 
} 

如果文件名以.png結尾，dos會被初始化，但是文件名不能以.mp3結尾，因此當你到達這裏時，dos是空的，因此是錯誤。