Storage-Get-Started

Overview

MicroEJ multisandbox firmware demos disable access to the file system in the application context. To store/retrieve information you should use a service provided by the firmware. This service is called Storage and like any other services it can be retrieved by using the default ServiceLoader (if you want more information about Service, please read the firmware documentation).

Storage storage = ServiceLoaderFactory.getServiceLoader().getService(Storage.class);

This service is based on key/value principle. The value is Java’s InputStream and the keys are Java’s String (with some restrictions on the allowed characters, see the javadoc).

Usage

Store data

The store method needs an input stream and a key. During the method execution the given input stream is entirely read, closed and stored in the underlying file system (can be volatile or not depend on your firmware).

String key = "MY_DATA"; //$NON-NLS-1$
try (ByteArrayInputStream bais = new ByteArrayInputStream("mydata".getBytes())) { //$NON-NLS-1$
    storage.store(key, bais);
} catch (IOException e) {
    e.printStackTrace();
}

Retrieve data

Call the load method with the same key used to store the data, to retrieve it.

try (InputStream stream = storage.load(key)) {
    // Do something with the input stream.
} catch (IOException e) {
    e.printStackTrace();
}

The application must close the input stream when it is no longer needed.

List all stored data

An application can list all stored data by calling the getIds method. This method returns all data key’s already stored.

try {
    for (String k : storage.getIds()) {
        System.out.println("Data available " + k);
    }
} catch (IOException e) {
    e.printStackTrace();
}

Delete data

Call the remove method with the data key’s to remove it.

try {
    storage.remove(key);
} catch (IOException e) {
    e.printStackTrace();
}

Run on MicroEJ Simulator

1. Right Click on the project
2. Select Run as -> MicroEJ Application
3. Select your virtual device.
4. Press Ok

Run on device

Build

1. Right Click on the example
2. Select Run as -> Run Configuration
3. Select MicroEJ Application configuration
4. Click on New launch configuration icon
5. In Execution tab
   1. In Target frame, in Platform field, select the relevant virtual device.
   2. In Execution frame
      1. Select Execute on Device
      2. In Settings field, select Local Deployment(…)
6. In Configurations tab, set the options of the deployment
7. Press Apply
8. Press Run

Requirements

This example has been tested on:

• MicroEJ SDK 5.1
• With a BLACK-ESP32WROVER-RQQAW board virtual device

Dependencies

All dependencies are retrieved transitively by Ivy resolver.

Source

N/A

Restrictions

None.