iPOJO defines several annotations to help developer to define their components. This page presents an example of iPOJO annotation and describes provided annotations.

Getting iPOJO Annotations:

iPOJO Annotations are defines inside the org.apache.felix.ipojo.annotations project. You can download the Jar file of this project from the download page. Sources are available on the Felix trunk.
Once added to your class path / build path / dependencies, you can use the annotations as normal annotations. These annotations are automatically processed by the iPOJO manipulator.

In Eclipse:

Add the org.apache.felix.ipojo.annotations jar file in your build path. Do not forget to use a Java compiler accepting annotations (1.5 or higher).

In Maven:

Add the following dependency:

<dependency>
      <groupId>org.apache.felix</groupId>
      <artifactId>org.apache.felix.ipojo.annotations</artifactId>
      <version>1.0.0</version>
</dependency>

Moreover, you need to set that the source code and the target code are Java 1.5 code. To achieve this, just add the following plugin in your plugins section:

<plugin>
        <groupId>org.apache.maven.plugins</groupId>
	<artifactId>maven-compiler-plugin</artifactId>
	<configuration>
	  <source>1.5</source>
	  <target>1.5</target>
	</configuration>
</plugin>

In Ant :

Just add the org.apache.felix.ipojo.annotations jar file in your class path.

An example of usage:

To illustrate annotations usage, let taking the tutorial example. In this tutorial, there are two components:

The first one provides the hello service
The second one uses the provided hello service
You can download the archive containing the examples and a preconfigured version of Felix here.

Hello Service Provider

The provider uses two annotations. The "component" annotation is mandatory and defines that the class defines a component type. Then the "provides" annotation just declare that the defined component type provides a service.

package ipojo.example.hello.impl;

import ipojo.example.hello.Hello;

import org.apache.felix.ipojo.annotations.Component;
import org.apache.felix.ipojo.annotations.Provides;

/**
  * Component implementing the Hello service.
 **/
@Component
@Provides
public class HelloImpl implements Hello {
    public String sayHello(String name) { 
     return "hello " + name; 
    }
}

Hello Service Consumer

The Hello Service Consumer use more annotations. First it used the component annotation. To defines its "immediate" behavior, it add the 'immediate' attribute.
Then, it uses the requires annotation to define a service dependency. Finally, it uses the validate and invalidate annotations to define lifecycle callbacks.

package ipojo.example.hello.client;

import org.apache.felix.ipojo.annotations.Component;
import org.apache.felix.ipojo.annotations.Invalidate;
import org.apache.felix.ipojo.annotations.Requires;
import org.apache.felix.ipojo.annotations.Validate;

import ipojo.example.hello.Hello;

@Component(name="AnnotedHelloClient", immediate=true)
public class HelloClient implements Runnable {

@Requires
private Hello[] m_hello; // Service Dependency

private final static int DELAY=10000;
private boolean end;

 public void run() {
    while (!end) {
               try {
		invoke();
                Thread.sleep(DELAY);
              } catch (InterruptedException ie) { }
              /* will recheck end */
     }
}

public void invoke() {
	for (int i = 0; i < m_hello.length; i++) { 
          System.out.println(m_hello[i].
             sayHello("Clement")); 
        }
}

 @Validate
 public void starting() {    
    Thread T = new Thread(this);     
    end = false;     
    T.start(); 
 }

 @Invalidate
 public void stopping() {    
     end = true; 
 }
}

Defined Annotations

This section lists defined annotations and how to use them.

@Component

Goal: Defines a component type
Target: The component implementation class
Attributes:

name : defines the component type name (optional, default = the class name)
factory: defines the factory name (optional, default = "false")
immediate: defines the component type as immediate (optional, default = "false")
architecture: enable the architecture exposition (optional, default = "false")
propagation: enable configuration property propagation (on provided services) (optional, default = "false")

@Provides

Goal: Defines that the component type provide services
Target: The component implementation class
Attributes:

specifications: defines the provided interface (optional, default = all implemented interfaces)
factory: defines the service object creation policy ("SINGLETON" or "SERVICE") (optional, default = "SINGLETON")
[1.1.0-SNAPSHOT] the factory attribute became strategy. A third policy is now available (instance) allowing to create one service object per asking instance. Moreover, it is also possible to indicates the CreationStrategy class name.

Note: "SERVICE" means OSGi service factory.

@Requires

Goal: Defines a service dependency
Target: Field
Attributes:

Filter: defines the LDAP filter (optional)
Optional: defines if the dependency is optional (optional, default = "false")
Id: defines the dependency Id (useful to identify bind & unbind methods) (optional, default = field name) (if a dependency with the same id is already created (by a @bind or @unbind annotation), it merges the dependencies).
Nullable: enable or disable the Null Object injection when the dependency is optional and no providers are available (optional, default = "true")
Default-Implementation: set the Default-Implmentation (optional, by default iPOJO uses a Null object)
Policy: defines the binding policy (accepted value : dynamic, static, dynamic-priority) (optional, default = "dynamic")
Comparator: defines the comparator to use to sort service references (optional, default = OSGi Service Reference Comparator)
From : defines the specific provider to use

@ServiceProperty

Goal: Defines a service property
Target: Field
Attributes:

name: property name (optional, default=field name
value: property value (optional, default=no value)

@Property

Goal: Defines a property
Target: Field or Method
Attributes:

name: property name (optional, default=field name computed by removing "set" from the method name (for instance setFoo(String ff) will get the Foo name))
value: property value (optional, default=no value)

note: if another property with the same name is defined the method or the field is added to the existing property

@Bind

Goal: Defines a bind method
Target: Method
Attributes:

Id: Dependency Id, if the id is already defines in a "@requires " or "@unbind" annotation, it adds this method as a bind method of the already created dependency. (optional, default= no id, compute an id if the method name begin by "bind" (for instance "bindFoo" will have the "Foo" id))
Specification : required dependency (optional)
Aggregate : is the dependency an aggregate dependency (optional, default= "false")
Optional: is the dependency an optional dependency (optional, default= "false")
Filter: dependency LDAP filter (optional)
Policy: defines the binding policy (accepted value : dynamic, static, dynamic-priority) (optional, default = "dynamic")
Comparator: defines the comparator to use to sort service references (optional, default = OSGi Service Reference Comparator)
From : defines the specific provider to use

@Unbind

Goal: Defines an unbind method
Target: Method
Attributes:

Id: Dependency Id, if the id is already defines in a "@requires" or "@bind" annotation, it adds this method as an unbind method of the already created dependency. (optional, default= no id, compute an id if the method name begin by "unbind" (for instance "unbindFoo" will have the "Foo" id))
Specification : required dependency (optional)
Aggregate : is the dependency an aggregate dependency (optional, default= "false")
Optional: is the dependency an optional dependency (optional, default= "false")
Filter: dependency LDAP filter (optional)
Policy: defines the binding policy (accepted value : dynamic, static, dynamic-priority) (optional, default = "dynamic")
Comparator: defines the comparator to use to sort service references (optional, default = OSGi Service Reference Comparator)
From : defines the specific provider to use

@Validate

Goal: defines a validate lifecycle callback
Target: method

@Invalidate

Goal: defines a validate lifecycle callback
Target: method

Temporal Dependencies (external handler)

The temporal dependency handler is an external handler. However, it can be used with an annotation defined in the iPOJO annotations jar file.
The annotation is org.apache.felix.ipojo.handler.temporal.Requires and targets a field.
Attributes:

filter : specify the dependency filter
timeout : specify the dependency timeout (optional)
onTimeout : specify the onTimeout action (null, nullable, empty-array, default-implementation (specify the class name in this case) (optional).

Exposing instances as a JMX MBean (external handler) [New in the 1.1.0-SNAPSHOT version]

The JMX Handler allows exposing an instance as a JMX MBean. To configure the JMX handler directly from your code, three annotations are provided. They are in the org.apache.felix.ipojo.handlers.jmx package

The @org.apache.felix.ipojo.handlers.jmx.Config (@Config if the package it correctly imported) annotation is a type annotation (so placed on the class element. This annotation indicates that the instance will be exposed as an MBean. This annotation supports:

usesMOSGi: set to true to use MOSGi. Otherwise, the MBean will be exposed in the MBean Platform Server (default: false).
objectname: set the MBean objectname. The objectname must follow JMX specification. (default: package-name:factory-name:instance-name)
domain: set the MBean domain. (default: package-name)
name: set the MBean name. (default: instance-name).

The @org.apache.felix.ipojo.handlers.jmx.Property (@Property) annotation is a field annotation indicating that the field is exposed in the MBean. The supported attributes are:

name: set the property name
rights: set the access permission. Possible values are r (read only) and w (read and write). By default, properties are in read-only mode.
notification: enables notification on this property. By default notifications are disabled.

The @org.apache.felix.ipojo.handlers.jmx.Method (@Method) annotation is a method annotation indicating that the method is exposed in the MBean. Only one attribute can be customized:

description: set the method description.

Metadata file and annotation merge

It is possible to defines component type both in the metadata file (in XML) and by using annotation. However, if a component type defined by using annotations has the same name than a type define in the XML file, the XML descriptor override the annotation defined type. However, a warning message is launched during the manipulation.

Instance creation

Annotation can only be used to define component type. To define instances, you need to use the XML descriptor. Instance can refer to annotated types by referring to their names.

<instance component="ipojo.example.hello.impl.HelloImpl"/>
<instance component="AnnotedHelloClient"/>

Using Custom Annotations

External handlers can provides their own annotations. Using these annotations just requires to add them to your build path. To external handlers annotations, please refer to the external handler documentation.