W/系统错误：java.io.IOException:权限被拒绝
发生这种情况是因为您在Android 8/9/10上创建文件到外部存储。
如果您的targetSdk为23或更高，则应动态请求权限。要了解更多信息：在运行时请求权限
要获取文件路径，您可以使用Context.getExternalFilesDir（）/Context.getExternalCacheDir（），例如，字符串路径=Context.getExternalCacheDir（）+“文件.文本”; File file=new如果文件路径为“Android/data/app package/file name”，则不需要权限
与Android文档中一样，您需要写入外部存储，必须在清单文件中请求WRITE_EXTERNAL_STORAGE权限：

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

如果您使用API 23（Marshmallow）和更高版本，则需要在运行时请求权限，因为这是一个危险的权限。

if (ContextCompat.checkSelfPermission(
        CONTEXT, Manifest.permission.REQUESTED_PERMISSION) ==
        PackageManager.PERMISSION_GRANTED) {
    // You can use the API that requires the permission.
    performAction(...);
} else if (shouldShowRequestPermissionRationale(...)) {
    // In an educational UI, explain to the user why your app requires this
    // permission for a specific feature to behave as expected. In this UI,
    // include a "cancel" or "no thanks" button that allows the user to
    // continue using your app without granting the permission.
    showInContextUI(...);
} else {
    // You can directly ask for the permission.
    // The registered ActivityResultCallback gets the result of this request.
    requestPermissionLauncher.launch(
            Manifest.permission.REQUESTED_PERMISSION);
}

参考源链接
参考文献
make file to external

编辑答案

Intent intent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);
startActivityForResult(intent, 0);

@Override
public void onActivityResult(int requestCode, int resultCode, Intent data) {        
    switch (requestCode){
        case 0:
            if (resultCode == Activity.RESULT_OK){
                Bitmap thumbnail = (Bitmap) data.getExtras().get("data");
                SaveImage(thumbnail);                    
            }
            break;
    }
}

private static void SaveImage(Bitmap finalBitmap) {

    String root = Environment.getExternalStorageDirectory().getAbsolutePath();
    File myDir = new File(root + "/saved_images");
    myDir.mkdirs();

    String fname = "Image-"+ Math.random() +".jpg";
    File file = new File (myDir, fname);
    if (file.exists ()) file.delete ();
    try {
        FileOutputStream out = new FileOutputStream(file);
        finalBitmap.compress(Bitmap.CompressFormat.JPEG, 90, out);
        out.flush();
        out.close();

    } catch (Exception e) {
        e.printStackTrace();
    }
}

我以前也遇到过这个问题，似乎在AndroidManifest.xml文件下的Application标记中添加以下内容可以解决这个问题：

<application
    ...
    android:requestLegacyExternalStorage="true">
</application>