The Multi-Sandbox capability of the MicroEJ Core Engine allows a main application (called Standalone Application) to install and execute at runtime additional applications (called sandboxed applications).

The MicroEJ Core Engine implements the [KF] specification. A Kernel is a Standalone Application generated on a Multi-Sandbox-enabled platform. A Feature is a sandboxed application generated against a Kernel.

A sandboxed application may be dynamically downloaded at runtime or integrated at build-time within the executable application.

Note that the Multi-Sandbox is a capability of the MicroEJ Core Engine. The MicroEJ Simulator always runs an application as a Standalone Application.

Functional Description

The Multi-Sandbox process extends the overall process described in the overview of the platform process.

Multi-Sandbox Process

Multi-Sandbox Process

Once a Kernel has been generated, additional MicroEJ Application code (Feature) can be built against the Kernel by :

  • Creating one launch configuration per feature.
  • Setting the Settings field in the Execution tab of each feature launch configuration to Build Dynamic Feature.
  • Setting the Kernel field in the Configuration tab of each feature launch configuration to the .

using the MicroEJ Application launch named Build Dynamic Feature. The binary application file produced ( is compatible only for the Kernel on which it was generated. Generating a new Kernel requires that you generate the Features again on this Kernel.

The Features built can be deployed in the following ways:

  • Downloaded and installed at runtime by software. Refer to the [KF] specification for ej.kf.Kernel install APIs.
  • Linked at build-time into the executable application. Features linked this way are then called Installed Features. The Kernel should have been generated with options for dimensioning the maximum size (code, data) for such Installed Features. Features are linked within the Kernel using the Firmware linker tool.

Firmware Linker

A MicroEJ tool is available to link Features as Installed Features within the executable application. The tool name is Firmware Linker. It takes as input the executable application file and the Feature binary code into which to be linked. It outputs a new executable application file, including the Installed Feature. This tool can be used to append multiple Features, by setting as the input file the output file of the previous pass.

Memory Considerations

Multi-Sandbox memory overhead of MicroEJ Core Engine runtime elements are described in the table below.

Multi-Sandbox Memory Overhead
Runtime element Memory Description
Object RW 4 bytes
Thread RW 24 bytes
Stack Frame RW 8 bytes
Class Type RO 4 bytes
Interface Type RO 8 bytes



Multi-Sandbox is an additional module, disabled by default.

To enable Multi-Sandbox of the MicroEJ Core Engine, in the platform configuration file, check Multi Applications.


The KF API Module must be added to the module.ivy of the MicroEJ Application project to use [KF] library.

<dependency org="ej.api" name="kf" rev="1.4.4"/>

This library provides a set of options. Refer to the chapter Application Options which lists all available options.