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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.

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>1.8.0</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)
• 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")
• managedservice : set the Managed Service PID. (optional, default = no PID (i.e. the managed service will not be exposed)).
• factoryMethod : set the factory-method. The specified method must be a static method and return a pojo object.(optional, default = iPOJO uses the 'regular' constructor).
• publicFactory : set if the component type is public. (optional, default = true).

@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)
• strategy : the service object creation strategy. Possible values : SINGLETON, SERVICE, METHOD, INSTANCE or the strategy class name. With SINGLETON there is only one POJO per component instance, SERVICE means OSGi Service factory, METHOD delegates the creation to the factory-method of the component, INSTANCE creates one service object per requiring instance. For other strategies, specify the qualified name of the CreationStrategy class. (optional, default = SINGLETON)
• properties : array containing @StaticServiceProperties defining service properties not attached to fields.

<div class="box">
	<div class="box-blue-header">
	<div class="box-blue-title">
		<img src="http://people.apache.org/~clement/ipojo/site/information.gif"> <b>OSGi Service Factory</b>
	</div>
	</div>
	<div class="box-blue-content">
The <tt>SERVICE</tt> strategy refers to the OSGi service factory. So, one service object per asking bundle will be created.
	</div>
	<div class="box-blue-footer"></div>
</div>

<div class="box">
	<div class="box-blue-header">
	<div class="box-blue-title">
		<img src="http://people.apache.org/~clement/ipojo/site/information.gif"> <b>Changes between the 1.0.0 and the 1.2.0</b>
	</div>
	</div>
	<div class="box-blue-content">
The <tt>factory</tt> attribute became <tt>strategy</tt>. A third policy is now available (<tt>instance</tt>) allowing to create one service object per asking instance. Moreover, it is also possible to indicates the <tt>CreationStrategy</tt> class name. 
	</div>
	<div class="box-blue-footer"></div>
</div>

@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")
• Defaultimplementation: 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
• Specification : the required service specification. This attribute is required for Collection field. (optional, default = annotated field type).
• Proxy : enables / disables the proxy injection (enabled by default)

@ServiceProperty

Goal: Defines a service property
Target: Field
Attributes:

• name: property name (optional, default=field name
• value: property value (optional, default=no value)
• mandatory : is the property mandatory? (optional, default=false)

<div class="box">
	<div class="box-blue-header">
	<div class="box-blue-title">
		<img src="http://people.apache.org/~clement/ipojo/site/information.gif"> <b>Mandatory property</b>
	</div>
	</div>
	<div class="box-blue-content">
A mandatory property must receive a value either from the component type description (<tt>value</tt> attribute, or the instance configuration.
	</div>
	<div class="box-blue-footer"></div>
</div>

@ServiceController

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

• value : the default value. If set to false, it disables the initial exposition
• specification : set the target of the controller, must be an exposed service interface. By default, the controller targets all services.

@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)
• mandatory : is the property mandatory? (optional, default=false)

<div class="box">
	<div class="box-blue-header">
	<div class="box-blue-title">
		<img src="http://people.apache.org/~clement/ipojo/site/information.gif"> <b>Field and Method</b>
	</div>
	</div>
	<div class="box-blue-content">
If another property with the same name is defined the method or the field is added to the existing property.
	</div>
	<div class="box-blue-footer"></div>
</div>

@Updated

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

@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

@Modified

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

@PostRegistration

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

@PostUnregistration

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

@Instantiate

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

• name: the instance name (optional)

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).
• specification : the required service specification. This attribute is required for Collection field. (optional, default = annotated field type).
• proxy : Inject a proxy instead of the real object. This allows passing this reference to collaborators. (Default = false)

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:

• 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.

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:

• it does not support configuration
• it does not allow naming
• the instance is created in the global scope (so no composition)

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.