刚开始觉得简单，不就是找到u盘路径，打开文件写入文件

 fun getUsbPath(): String? {val usbRoot = File("/mnt/media_rw")if (usbRoot.exists() && usbRoot.isDirectory()) {val usbFiles = usbRoot.listFiles()if (usbFiles != null && usbFiles.size > 0) {return usbFiles[0].absolutePath}}return ""}fun copyFileToUsb( sourcePath: String?, usbPath: String?):Int {val sourceFile = File(sourcePath,DB_NAME)try {val uPath = File(usbPath+"/Download")Log.d("validate", "DataMngActivity usbPath : $usbPath/Download")if (!uPath.exists()) {uPath.createNewFile() // 创建文件夹}val usbFile = File(usbPath+"/Download/"+DB_NAME)FileInputStream(sourceFile).use { fis ->FileOutputStream(usbFile).use { fos ->val buffer = ByteArray(1024)var length: Intwhile (fis.read(buffer).also { length = it } > 0) {fos.write(buffer, 0, length)}fos.getFD().sync();return 0;}}} catch (e: IOException) {e.printStackTrace()// Handle exception}return 1;}

另外在配上权限啥的，谁知道不插u盘，其他系统文件路径可以，换了u盘报没权限，几次搜索发现android11后有些权限用法不管用了 

Runtime.getRuntime().exec（"cp 也不行

后来发现一个能行的办法

 FireflyApi2.getInstance().execSuCmd("cp "+rootPath_Db+"/"+DB_NAME+" "+f+"/"+DB_NAME);