Overview of the Fraclet Annotation Framework

Fraclet is both an implementation of the Fractal specifications conformed to the level 0.1, and an annotation framework for the Fractal component model. Fraclet is composed of several annotations and plugins to generate automatically various artifacts required by the Fractal component model. Annotations provide a way to describe the component meta-information directly in the source code of the content class. Fraclet plugins generate either Fractal component glue, FractalADL definitions or Monolog configurations.

This approach has several benefits:

• You don't have to worry about out dating deployment meta-data whenever you touch the code. The deployment meta-data is continuously integrated.
• Working with only one file per component gives you a better overview of what you're doing. If your component consists of several files, it's easy to lose track. If you have ever written an Enterprise Java Bean, you know what we mean. A single EJB can typically consists of 7 or more files. With Fraclet you only maintain one of them, and the rest is generated.
• You dramatically reduce development time, and can concentrate on business logic, while Fraclet generates 60% of the code for you.

Two implementations of the Fraclet annotation framework exist: Fraclet XDoc and Fraclet Annotation.

• Fraclet XDoc uses the XDoclet generation engine to produce the various artifacts required by the Fractal component model.
• Fraclet-Annotation uses the Spoon transformation tool to enhance the handwritten program code with the non-functional properties of the component model.

Table of Contents

1. Fraclet XDoc: An XDoclet2 plugin for Fractal
2. Fraclet Annotation: A Java 5 annotation support for Fractal
3. Fraclet Availability
4. Dissemination

1. Fraclet XDoc: An XDoclet2 plugin for Fractal

Fraclet uses the XDoclet2 as annotation parser and generation engine.

XDoclet is an open source code generation engine. It enables Attribute-Oriented Programming for java. In short, this means that you can add more significance to your code by adding meta data (attributes) to your java sources. This is done in special JavaDoc tags. This use of JavaDoc tags for attributes formed the original ideas for Java 5 Annotations.

XDoclet2 is the next generation of this technology. Based on Generama, it uses standard template engines such as Velocity and Freemarker for generation of text-oriented output, and Jelly for XML output. The function of XDoclet2 is to seed the generation contexts for these template engines.

XDoclet2 is supported by XDoclet2 plugins, which provide task-specific generation functionality.

This part describes the features of this XDoclet2 plugin for Fractal, and the way to use them.

1. Available Annotations
2. Available Plugins
3. Revisiting the HelloWorld Example

1.1 Available Annotations

Some annotations have been defined in order to describe the component meta-information. The list below describes these annotations.

The @provides annotation

Details:

This class annotation adds the name information to the definition of a Fractal interface. This name is required by the Fractal component model to identify the interfaces required and provided by a Fractal component. This annotation can also override the associated interface signature to introduce interface meta-information at the class level.

Parameters:

Examples:

/** @provides name=m */
public interface Main { ... }

/** @provides name=r signature=java.lang.Runnable */
public class Client implements Runnable { ... }
                

The @component annotation

Details:

This class annotation allows the developer to describe the description of the controller part that should be associated to the content part of the Fractal component.

Parameters:

Example:

/** @component controller=primitive */
public class Client implements Runnable { ... }

/** @component controller=primitive template=primitiveTemplate */
public class Client implements Runnable { ... }
                

The @data annotation

Details:

This class annotation provides a way to define a data used by a Fractal component.

Example:

/** @data */                
public class Message {
  ...
}
                

The @monolog.handler annotation

Details:

This class annotation allows the developer to describe a Monolog handler specific to the Fractal component. The available annotation attributes support the various properties that can be defined in a Monolog configuration file.

Parameters:

Example:

/** @monolog.handler name=clientHandler output=System.err pattern="%-5l [%h] <%t> %m%n" */
public class Client implements Runnable { ... }
                

The @attribute annotation

Details:

This field annotation describes a Fractal attribute. A Fractal attribute is a Java attribute whose value can be configured and introspected from the Fractal component. Fractal attributes are managed by the attribute control feature of the Fractal component model.

Parameters:

Example:

public class Client implements Runnable {
  /** @attribute name=count value=2 */
  protected int counter; // field should be declared as protected or public.

  /** @attribute argument=client-prefix */
  protected String pref;

  /** @attribute */
  protected String suffix;

  ...
}
                

The @requires annotation

Details:

This field annotation describes a Fractal binding. A Fractal binding is a Java attribute representing a client interface. Fractal bindings are managed by the binding control feature of the Fractal component model.

Parameters:

Example:

public class Client implements Runnable {
  /** @requires name=s signature=Service cardinality=collection */
  protected Map servers = new HashMap(); // collections are stored in a map

  /** @requires */
  protected Service service;

  ...
}
                

The @control annotation

Details:

This field annotation provides a way to refer a control interface provided by the controller part of the associated Fractal component.

Parameters:

Example:

public class Client implements Runnable {
  /** @control name=name-controller */
  protected NameController nc; // field should be declared as protected or public.

  /** @control  */
  protected Component self;

  ...
}
                

The @logger annotation

Details:

This field annotation provides a way to define a Monolog logger to log the execution of the Fractal component.

Parameters:

Example:

public class Client implements Runnable {
  /** @logger name=c handler="clientHandler,fileHandler" */
  protected Logger log; // field should be declared as protected or public.

  /** @logger */
  protected Logger log2;

  ...
}
                

Julia Configuration:

To enable the Monolog support in Julia, the julia.cfg configuration file should be modified to override the lifecycle-controller-impl definition as follows:

...                  
                  
# LifeCycleController implementation (for primitive or composite components)
(lifecycle-controller-impl
  ((org.objectweb.fractal.julia.asm.MixinClassGenerator
        LifeCycleControllerImpl
        org.objectweb.fractal.julia.BasicControllerMixin
        org.objectweb.fractal.julia.UseComponentMixin
        org.objectweb.fractal.julia.control.lifecycle.BasicLifeCycleCoordinatorMixin
        org.objectweb.fractal.julia.control.lifecycle.BasicLifeCycleControllerMixin
        # to check that mandatory client interfaces are bound in startFc:
        org.objectweb.fractal.julia.control.lifecycle.TypeLifeCycleMixin
        # to automatically assign the logger and logger factory:
        org.objectweb.fractal.julia.BasicInitializableMixin
        org.objectweb.fractal.julia.logger.LoggerLifeCycleMixin        
        # to notify the encapsulated component (if present) when its state changes:
        org.objectweb.fractal.julia.control.lifecycle.ContainerLifeCycleMixin
  ) 
        # optional initialization parameter (monolog configuration file name):
        (monolog-conf-file monolog.properties)
  )
)
 
...                                   
                  

AOKell Configuration:

To enable the Monolog support in AOKell, the build.properties configuration file should be modified to activate the feature.loggable.on property as follows:

...
                  
# The loggable feature determines whether primitive components are equipped
# with a monolog logger or not (which is the default case).
# Uncomment the following property for using primitive components equipped
# with a monolog logger.
feature.loggable.on 	true                  

...
                

The @lifecycle annotation

Details:

This method annotation provides a way to define a lifecycle handler supported by the controller part of the associated Fractal component.

Parameters:

Example:

public class Client implements Runnable {
  /** @lifecycle when=start */
  protected void init() {
    System.out.println("Starting the component Client...");
  }

  ...
}
                

1.2 Available Plugins

Some plugins have been defined in order to generate the component artifacts. The list below describes these plugins:

The AttributeControllerPlugin generator

Details:

Generates the <CLASS>Attributes interface associated to a <CLASS> class if it defines at least an attribute using the @attribute annotation.

Usage:

<target name="compile">
  <taskdef name="xdoclet" classname="org.xdoclet.ant.XDocletTask" classpathref="classpath"/>
  <mkdir dir="${gen}"/>
  <xdoclet>

    <fileset dir="${src}" includes="**/*.java" />
    <component destdir="${gen}" classname="org.objectweb.fractal.fraclet.AttributeControllerPlugin"/>
  </xdoclet>
  ...
</target>
                

The PrimitiveComponentPlugin generator

Details:

Generates the Fc<CLASS> class associated to a <CLASS> class. class if it defines either a @attribute, @requires, @control or/and @logger annotation.

Usage:

<target name="compile">
  <taskdef name="xdoclet" classname="org.xdoclet.ant.XDocletTask" classpathref="classpath"/>
  <mkdir dir="${gen}"/>
  <xdoclet>

    <fileset dir="${src}" includes="**/*.java" />
    <component destdir="${gen}" classname="org.objectweb.fractal.fraclet.PrimitiveComponentPlugin"/>
  </xdoclet>
  ...
</target>
                

The PrimitiveDefinitionPlugin generator

Generates the <CLASS>.fractal definition associated to a <CLASS> class (or interface).

Usage:

<target name="compile">
  <taskdef name="xdoclet" classname="org.xdoclet.ant.XDocletTask" classpathref="classpath"/>
  <mkdir dir="${build}"/>
  <xdoclet>
    <fileset dir="${src}" includes="**/*.java" />
    <component destdir="${build}" classname="org.objectweb.fractal.fraclet.PrimitiveDefinitionPlugin"/>

  </xdoclet>
  ...
</target>
                

The CompositeDefinitionPlugin generator

Details:

Generates the <CLASS>Composite.fractal definition associated to a <CLASS> class if it defines at least a @requires annotation.

Usage:

<target name="compile">
  <taskdef name="xdoclet" classname="org.xdoclet.ant.XDocletTask" classpathref="classpath"/>
  <mkdir dir="${build}"/>
  <xdoclet>
    <fileset dir="${src}" includes="**/*.java" />

    <component destdir="${build}" classname="org.objectweb.fractal.fraclet.CompositeDefinitionPlugin"/>
  </xdoclet>
  ...
</target>
                

The MonologConfigurationPlugin generator

Details:

Generates the monolog.properties configuration file for the Monolog tool.

Usage:

<target name="compile">
  <taskdef name="xdoclet" classname="org.xdoclet.ant.XDocletTask" classpathref="classpath"/>
  <mkdir dir="${build}"/>
  <xdoclet>
    <fileset dir="${src}" includes="**/*.java" />

    <component destdir="${build}" classname="org.objectweb.fractal.fraclet.MonologConfigurationPlugin"/>
  </xdoclet>
  ...
</target>
                

1.3 Revisiting the HelloWorld Example with Fraclet

This section provides a quick overview of the benefits of Fraclet. It shows that using annotations, Fractal source code becomes more concise and easier to maintain. It shows that using Fractlet, more than 60% of the source code (Java, FractalADL, properties) can be saved.

HelloWorld Implementation

The source code below represents the Java code and the Fraclet annotations written to implement the Client and the Server Fractal components:

/** @provides name=r signature=java.lang.Runnable */
public class Client implements Runnable {
  /** @requires */
  protected Service s ;
          
  /** @attribute value="Hello !" */
  protected String message;
          
  public void run() {
    this.defaut.print(this.message);
  }
}
                          

The Client class defines the Runnable interface as a Fractal interface using the @provides annotation. The attribute s is annoted as a client interface (using @requires), which will be named s as no name parameter is defined. The attribute message is annoted as a Fractal attribute (using @attribute), which will be automatically initialized to "Hello !".

  
/** @provides name=s */
public interface Service {
  void print(String message);
}
                          

The Service interface is annoted with @provides to define the name of the Fractal interface as s.

  
public class Server implements Service {
  /** @attribute */
  protected String header;
                
  /** @attribute */
  protected int counter;
                
  public void print(final String message) {
    for (int i = 0; i < this.counter; i++)
      System.out.println(this.header + message);
  }
}
                        

The Server class inherits automatically from the Service annotations. The header and the counter attributes are defined as Fractal attributes (using @attribute), whose initial value will be defined when the component will be created.

HelloWorld Architecture Definition

The assembly definition below represents the FractalADL assembly defined to describe the HelloWorld Fractal component:

<definition name="HelloWorld" extends="ClientComposite">
  <component name="s" definition="Server('>>',2)"/>

</definition>
                

This definition creates a composite component HelloWorld extending the generated Client abstract definition. Then it specifies that the definition of the component named s is FcServer and that the values of the header and the counter attributes are '>>' and 2, respectively.

Compilation with Ant

The following piece of XML presents the compilation process enhanced with the Fractal plugins.

<project name="helloworld" default="compile">
  ...
  <target name="compile">
    <taskdef name="xdoclet" classname="org.xdoclet.ant.XDocletTask" classpathref="classpath"/>

    <mkdir dir="${gen}"/>
    <mkdir dir="${build}"/>
    <xdoclet>
      <fileset dir="${src}" includes="**/*.java" />
      <component destdir="${gen}" classname="org.objectweb.fractal.fraclet.AttributeControllerPlugin"/>
      <component destdir="${gen}" classname="org.objectweb.fractal.fraclet.PrimitiveComponentPlugin"/>

      <component destdir="${build}" classname="org.objectweb.fractal.fraclet.PrimitiveDefinitionPlugin"/>
      <component destdir="${build}" classname="org.objectweb.fractal.fraclet.CompositeDefinitionPlugin"/>
      <component destdir="${build}" classname="org.objectweb.fractal.fraclet.MonologConfigurationPlugin"/>
    </xdoclet>
    <javac srcdir="${src}:${gen}" destdir="${build}" classpathref="classpath">
      <include name="**/*.java"/>

    </javac>
    <copy todir="${build}">
      <fileset dir="${src}">
        <exclude name="**/*.java"/>
        <exclude name="**/*.html"/>
      </fileset>

    </copy>
  </target>
  ...
</project>
                

Directory Structure

The directory structure below presents the list of compiled, generated and written files when using Fraclet to implement the HelloWorld example:

%example%
  * build/
    - Client.class
    - Client.fractal
    - ClientAttributes.class
    - ClientComposite.fractal
    - FcClient.class
    - FcServer.class
    - HelloWorld.fractal
    - Server.class
    - Server.fractal
    - ServerAttributes.class
    - Service.class
    - Service.fractal
  * generated/
    - ClientAttributes.java
    - FcClient.java
    - FcServer.java
    - ServerAttributes.java
  * src/
    - Client.java
    - HelloWorld.fractal
    - Server.java
    - Service.java
                

4. Dissemination

• R. Rouvoy, N. Pessemier, R. Pawlak, P. Merle, Apports de la programmation par attributs pour le modèle de composants Fractal, at the 5th French speaking days on Component-Oriented Progamming, October 2006 [slides]
• R. Rouvoy, N. Pessemier, R. Pawlak, P. Merle, Using Attribute-Oriented Programming to Leverage Fractal-Based Developments, at the 5th Fractal workshop at ECOOP 2006, July 2006 [slides]
• R. Rouvoy, Fraclet: Making Fractal Developments Easier!, at the Jacquard Research Meeting, January 2006 [slides]