How to use iPOJO annotations

You can use annotations to define your component types. This page presents supported 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, and do not need to be deployed at runtime.

With Eclipse (or any other IDE)

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).

With Maven

Add the following 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:


With 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.
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="AnnotatedHelloClient", immediate=true)
public class HelloClient implements Runnable {

private Hello[] m_hello;

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

 public void run() {
    while (!end) {
        try {
        } catch (InterruptedException ie) { }

public void invoke() {
    for (int i = 0; i < m_hello.length; i++) { 

 public void starting() {    
    Thread thread = new Thread(this);     
    end = false;     

 public void stopping() {    
     end = true; 

Defined Annotations

This section lists defined annotations and how to use them.


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


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

OSGi Service Factory
The SERVICE strategy refers to the OSGi service factory. So, one service object per asking bundle will be created.


Goal: Defines a service dependency Target: Field, Constructor Parameter Attributes:


Goal: Defines a service property Target: Field Attributes:

Mandatory property
A mandatory property must receive a value either from the component type description (value attribute), or the instance configuration.


Goal: Control the service exposition Target: Field (Boolean) Attributes:


Goal: Defines a property Target: Field, Method, Constructor Parameter Attributes:

Field, Method, Constructor
If another property with the same name is defined, the method or field or constructor argument is added to the existing property.


Goal: Defines method called when a reconfiguration is completed. Target: a method (receiving a dictionary in argument)


Goal: Defines a bind method Target: Method Attributes:


Goal: Defines an unbind method Target: Method Attributes:


Goal: Defines an modified method, called when a bound service is udpated. Target: Method Attributes:


Goal: defines a validate lifecycle callback Target: method


Goal: defines a validate lifecycle callback Target: method


Goal: defines a callback invoked after service registration. The callback must have the following signature : public void name(ServiceReference ref) Target: method


Goal: defines a callback invoked after service unregistration. The callback must have the following signature : public void name(ServiceReference ref) Target: method


Goal: declare a simple instance (this is equivalent to <instance component="..."></instance> Target: class Attribute:

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:

Exposing instances as a JMX MBean (external handler)

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:

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:

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:

Advanced topics and FAQ

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

The @Instantiate annotation allows creating an instance, but this declaration is limited:

To define instances, you should 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.