KF

Definitions

Feature Definition Files

A Feature is a group of types, resources and [BON] immutables objects defined using two files that shall be in application classpath:

[featureName].kf, a Java properties file. Keys are described in the “Feature definition file properties” table below.
[featureName].cert, an X509 certificate file that uniquely identifies the Feature

Feature definition file properties
Key	Usage	Description
entryPoint	Mandatory	The fully qualified name of the class that implements `ej.kf.FeatureEntryPoint`
immutables	Optional	Semicolon separated list of paths to [BON] immutable files owned by the Feature. [BON] immutable file is defined by a `/` separated path relative to application classpath
resources	Optional	Semicolon separated list of resource names owned by the Feature. Resource name is defined by `Class.getResourceAsStream(String)`
requiredTypes	Optional	Comma separated list of fully qualified names of required types. (Types that may be dynamically loaded using `Class.forName()`).
types	Optional	Comma separated list of fully qualified names of types owned by the Feature. A wildcard is allowed as terminal character to embed all types starting with the given qualified name (`a.b.C,x.y.*`)
version	Mandatory	String version, that can retrieved using `ej.kf.Module.getVersion()`

Kernel Definition Files

Kernel definition files are mandatory if one or more Feature definition file is loaded and are named kernel.kf and kernel.cert. kernel.kf must only define the version key. All types, resources and immutables are automatically owned by the Kernel if not explicitly set to be owned by a Feature.

Kernel API Definition

Kernel types, methods and static fields allowed to be accessed by Features must be declared in kernel.api file. Kernel API file is an XML file (see example “Kernel API XML Schema” and table “XML elements specification”).

Kernel API XML Schema

<xs:schema xmlns:xs='http://www.w3.org/2001/XMLSchema'>
    <xs:element name='require'>
        <xs:complexType>
            <xs:choice minOccurs='0' maxOccurs='unbounded'>
                <xs:element ref='type'/>
                <xs:element ref='field'/>
                <xs:element ref='method'/>
            </xs:choice>
        </xs:complexType>
    </xs:element>

    <xs:element name='type'>
        <xs:complexType>
            <xs:attribute name='name' type='xs:string' use='required'/>
        </xs:complexType>
    </xs:element>

    <xs:element name='field'>
        <xs:complexType>
            <xs:attribute name='name' type='xs:string' use='required'/>
        </xs:complexType>
    </xs:element>

    <xs:element name='method'>
        <xs:complexType>
            <xs:attribute name='name' type='xs:string' use='required'/>
        </xs:complexType>
    </xs:element>
</xs:schema>

XML elements specification
Tag	Attributes	Description
require		The root element
field		Static field declaration. Declaring a field as a Kernel API automatically sets the declaring type as a Kernel API
field	name	Fully qualified name on the form `[type].[fieldName]`
method		Method or constructor declaration. Declaring a method or a constructor as a Kernel API automatically sets the declaring type as a Kernel API
method	name	Fully qualified name on the form `[type].[methodName]([typeArg1,...,typeArgN) typeReturned`. Types are fully qualified names or one of a base type as described by the Java language (`boolean`, `byte`, `char`, `short`, `int`, `long`, `float`, `double`) When declaring a constructor, `methodName` is the single type name. When declaring a void method or a constructor, `typeReturned` is `void`
type		Type declaration, allowed to be loaded from a Feature using `Class.forName()`
type	name	Fully qualified name on the form `[package].[package].[typeName]`

Access Error Codes

When an instruction is executed that will break a [KF] insulation semantic rule, a java.lang.IllegalAccessError is thrown, with an error code composed of two parts: [source][errorKind].

source: a single character indicating the kind of Java element on which the access error occurred (Table “Error codes: source”)
errorKind: an error number indicating the action on which the access error occurred (Table “Error codes: kind”)

Error codes: source
Ch aracter	Description
A	Error thrown when accessing an array
I	Error thrown when calling a method
F	Error thrown when accessing an instance field
M	Error thrown when entering a synchronized block or method
P	Error thrown when passing a parameter to a method call
R	Error thrown when returning from a method call
S	Error thrown when accessing a static field

Error codes: kind
Id	Description
1	An object owned by a Feature is being assigned to an object owned by the Kernel, but the current context is not owned by the Kernel
2	An object owned by a Feature is being assigned to an object owned by another Feature
3	An object owned by a Feature is being accessed from a context owned by another Feature
4	A synchronize on an object owned by the Kernel is executed in a method owned by a Feature
5	A call to a feature code occurs while owning a Kernel monitor

Loading Features Dynamically

Features may be statically embedded with the Kernel or dynamically built against a Kernel. To build a Feature binary file, select Build Dynamic FeatureMicroEJ PlatformExecution tab. The generated file can be dynamically loaded by the Kernel runtime using ej.kf.Kernel.load(InputStream).