android 11中无法写入和打开文件

Question

在我的应用程序中，按钮事件从服务器返回 PDF 的 base64 字符串。 然后我将这个 base64 写入文件。 并尝试通过外部 PDF 查看器打开它。 它在除 Android 11 之外的 android 设备上运行良好。请参阅下面的代码。

 byte[] decodedContent = android.util.Base64.decode(base64.getBytes(), Base64.DEFAULT);

                try {
                    File path = new File(getApplicationContext().getExternalFilesDir(null).getAbsolutePath(), "PDFData");
                    if (!path.exists()) {
                        path.mkdirs();
                    }
                    file = new File(path,  "myPDF.pdf");


                    outputStream = new FileOutputStream(file);
                    outputStream.write(decodedContent);
                    outputStream.close();
                    Uri targetUri = Uri.fromFile(file);

                    Intent intent = new Intent(Intent.ACTION_VIEW);
                    intent.setDataAndType(targetUri, "application/pdf");
                    intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
                    PackageManager pm = getApplicationContext().getPackageManager();
                    if (pm.resolveActivity(intent, PackageManager.MATCH_DEFAULT_ONLY) == null) {
                        Toast.makeText(getApplicationContext(), "No application found to open PDF, please install one.", Toast.LENGTH_SHORT).show();
                    }
                    else{
                        startActivity(intent);
                    }
                } catch (FileNotFoundException ex) {
                    ex.printStackTrace();
                    Log.d("FileNotFound", "FileNotFoundException");
                } catch (IOException ex) {
                    ex.printStackTrace();
                    Log.d("IOException", "IOException");

                } finally {
                    // Make absolutely certain the outputStream is closed
                    try {
                        Log.d("outputStream", "outputStream");

                        if (outputStream != null) {
                            outputStream.close();
                        }
                    } catch (IOException ex) {
                        ex.printStackTrace();
                    }

以下权限已在清单文件中：

<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
 

请帮我解决一下这个。 提前致谢！