判断权限是否开启：

public class NoticePermissionUtil {
 
    private static final String CHECK_OP_NO_THROW = "checkOpNoThrow";
    private static final String OP_POST_NOTIFICATION = "OP_POST_NOTIFICATION";
 
    //调用该方法获取是否开启通知栏权限
    public static boolean isNotifyEnabled(Context context) {
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            return isEnableV26(context);
        } else {
            return isEnabledV19(context);
        }
    }
 
    /**
     * 8.0以下判断
     *
     * @param context api19  4.4及以上判断
     * @return
     */
    private static boolean isEnabledV19(Context context) {
 
        AppOpsManager mAppOps =
                (AppOpsManager) context.getSystemService(Context.APP_OPS_SERVICE);
 
        ApplicationInfo appInfo = context.getApplicationInfo();
        String pkg = context.getApplicationContext().getPackageName();
        int uid = appInfo.uid;
        Class appOpsClass;
 
        try {
            appOpsClass = Class.forName(AppOpsManager.class.getName());
 
            Method checkOpNoThrowMethod =
                    appOpsClass.getMethod(CHECK_OP_NO_THROW,
                            Integer.TYPE, Integer.TYPE, String.class);
 
            Field opPostNotificationValue = appOpsClass.getDeclaredField(OP_POST_NOTIFICATION);
            int value = (Integer) opPostNotificationValue.get(Integer.class);
 
            return ((Integer) checkOpNoThrowMethod.invoke(mAppOps, value, uid, pkg) ==
                    AppOpsManager.MODE_ALLOWED);
        } catch (Exception e) {
            e.printStackTrace();
            return true;
        }
    }
 
 
    /**
     * 8.0及以上通知权限判断
     *
     * @param context
     * @return
     */
    private static boolean isEnableV26(Context context) {
        ApplicationInfo appInfo = context.getApplicationInfo();
        String pkg = context.getApplicationContext().getPackageName();
        int uid = appInfo.uid;
        try {
            NotificationManager notificationManager = (NotificationManager)
                    context.getSystemService(Context.NOTIFICATION_SERVICE);
            @SuppressLint("DiscouragedPrivateApi")
            Method sServiceField = notificationManager.getClass().getDeclaredMethod("getService");
            sServiceField.setAccessible(true);
            Object sService = sServiceField.invoke(notificationManager);
 
            Method method = null;
            if (sService != null) {
                method = sService.getClass().getDeclaredMethod("areNotificationsEnabledForPackage"
                        , String.class, Integer.TYPE);
                method.setAccessible(true);
            }
            return (boolean) method.invoke(sService, pkg, uid);
        } catch (Exception e) {
            return true;
        }
    }
}

目标api小于33，旧版本判断：

NotificationManagerCompat就是NotificationManager兼容性库，适用于旧版平台，使用NotificationManagerCompat来判断是否开启通知权限就行，兼容旧版本。

public class CheckNotifyPermissionUtils {
 
 
    /**
     * 系统层面通知开关有没有开启
     * Build.VERSION.SDK_INT >= 24
     * Build.VERSION.SDK_INT >= 19
     *
     * @param mContext
     * @return
     */
    public static boolean checkNotifyPermission(Context mContext) {
        NotificationManagerCompat manager = NotificationManagerCompat.from(mContext);
        boolean isOpened = manager.areNotificationsEnabled();
        return isOpened;
    }
 
 
    /**
     * 如果通知未打开 跳转到通知设定界面
     * @param mContext
     */
    public static void tryJumpNotifyPage(Context mContext) {
        Intent intent = new Intent();
        try {
            if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
                intent.setAction(Settings.ACTION_APP_NOTIFICATION_SETTINGS);
                intent.putExtra(Settings.EXTRA_APP_PACKAGE, mContext.getPackageName());
            } else if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
                intent.setAction("android.settings.APP_NOTIFICATION_SETTINGS");
                intent.putExtra("app_package", mContext.getPackageName());
                intent.putExtra("app_uid", mContext.getApplicationInfo().uid);
            } else {
                intent.setAction(Settings.ACTION_APPLICATION_DETAILS_SETTINGS);
                intent.addCategory(Intent.CATEGORY_DEFAULT);
                intent.setData(Uri.parse("package:" + mContext.getPackageName()));
            }
            mContext.startActivity(intent);
        } catch (Exception e) {
            intent.setAction(Settings.ACTION_APPLICATION_DETAILS_SETTINGS);
            Uri uri = Uri.fromParts("package", mContext.getPackageName(), null);
            intent.setData(uri);
            mContext.startActivity(intent);
        }
    }
 
}