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SCR JavaDoc Tags

JavaDoc tags are not supported since the Maven SCR Plugin 1.8.0 because annotations are a much more powerful instrument allowing for type safety or supporting JVM based languages such as Groovy and Scala. This page exists to define the support for JavaDoc tags upto Maven SCR Plugin version 1.7.4.

The scr goal of the maven-scr-plugin looks for the following JavaDoc tags when building component descriptors:

scr.component

The scr.component tag is the only required tag. If this tag is not declared in the Java class comment, the class is not declared as a component.

This tag is used to declare the <component> element of the component declaration. See section 112.4.3, Component Element, in the OSGi Service Platform Service Compendium Specification for more information. The required <implementation> element is automatically generated with the fully qualified name of the class containing the scr.component tag.

Supported parameters:

Name Default Value Required SCR Metatype Description
name Fully qualified name of the Java class no component.name OCD.id Defines the Component name also used as the PID for the Configuration Admin Service
ds true no -- -- Whether Declarative Services descriptor is generated or not. If this parameter is not set or set to true the Declarative Services descriptor is generated in the service descriptor file for this component. Otherwise no Declarative Services descriptor is generated for this component.
abstract see description no -- -- This marks an abstract service description which is not added to the descriptor but intended for reuse through inheritance. This attribute defaults to true for abstract classes and false for concrete classes.
enabled true no component.enabled -- Whether the component is enabled when the bundle starts
factory -- no component.factory -- Whether the component is a factory component
immediate -- no component.immediate -- Whether the component is immediately activated
inherit true no -- -- Whether any service, property and reference declarations from base classes should be inherited by this class.
metatype true no -- -- Whether Metatype Service data is generated or not. If this parameter is not set or set to true Metatype Service data is generated in the metatype.xml file for this component. Otherwise no Metatype Service data is generated for this component.
label %<name>.name no -- OCD.name This is generally used as a title for the object described by the meta type. This name may be localized by prepending a % sign to the name.
description %<name>.name no -- OCD.description This is generally used as a description for the object described by the meta type. This name may be localized by prepending a % sign to the name.
create-pid true no service.pid -- Generate the service.pid property if non is declared.
configurationFactory false no -- Designate.factoryPid Is this a configuration factory? (since 1.4.0)

The following attributes are supported since version 1.4.0 of the plugin and required a Declarative Service implementation 1.1:

Name Default Value Required SCR Metatype Description
policy OPTIONAL no component.policy -- The configuration policy for this component: optional, ignore, or require (use lower case words)
activate activate no component.activate -- The name of the component activation method.
deactivate deactivate no component.deactivate -- The name of the component deactivation method.
modified -- no component.modified -- The name of the component modified method.

Abstract Service Descriptions

If the scr.component tag contains the parameter abstract with a value of true, the containing class is regarded as an abstract class. It is not added to the service descriptor and the tags are not validated. The information about this class is added to the bundle. Classes from other bundles (or the same) can extends this abstract class and do not need to specify the references of the abstract class if they set the inherit parameter on the scr.component tag to true.

This allows to create abstract classes which already provide some valuable functionality without having to deal with the details like reference definitions in each and every subclass.

scr.property

The scr.property tag defines properties which are made available to the component through the ComponentContext.getProperties() method. These tags are not strictly required but may be used by components to defined initial configuration. Additionally properties may be set here to identify the component if it is registered as a service, for example the service.description and service.vendor properties.

This tag may be defined in the Java Class comment of the component or in a coment to a field defining a constant with the name of the property.

This tag is used to declare <property> elements of the component declaration. See section 112.4.5, Properties and Property Elements, in the OSGi Service Platform Service Compendium Specification for more information.

Supported parameters:

Name Default Value Required SCR Metatype Description
name The name of constant yes property.name AD.id The name of the property. If this tag is defined on a field with an initialization expression, the value of that expression is used as the name if the field is of type String.
value -- no property.value AD.default The value of the property. If the property type is not String, parsing of the value is done using the valueOf(String) method of the class defined by the property type
type String no property.type AD.type The type of the property value. This must be one of String, Long, Double, Float, Integer, Byte, Char, Boolean and Short.
label %<name>.name no -- AD.name The label to display in a form to configure this property. This name may be localized by prepending a % sign to the name.
description %<name>.description no -- AD.description A descriptive text to provide the client in a form to configure this property. This name may be localized by prepending a % sign to the name.
private Depending on the name no -- See description Boolean flag defining whether a metatype descriptor entry should be generated for this property or not. By default a metatype descriptor entry, i.e. an AD element, is generated except for the properties service.pid, service.description, service.id, service.ranking, service.vendor, service.bundlelocation and service.factoryPid. If a property should not be available for display in a configuration user interface, this parameter should be set to true.
cardinality Depends on property value(s) no -- AD.cardinality Defines the cardinality of the property and its collection type. If the cardinality is negative, the property is expected to be stored in a java.util.Vector (primitive types such as boolean are boxed in the Wrapper class), if the cardinality is positive, the property is stored in an array (primitve types are unboxed, that is Boolean type values are stored in boolean\[\]()). The actual value defines the maximum number of elements in the vector or array, where Integer.MIN*INT describes an unbounded Vector and Integer.MAX*INT describes an unbounded array. If the cardinality is zero, the property is a scalar value. If the defined value of the property is set in the value attribute, the cardinality defaults to 0 (zero for scalar value). If the property is defined in one or more properties starting with values, the cardinality defaults to Integer.MAX_INT, that is an unbounded array.
options -- no -- See below See below for a description of the options parameter.
values* -- no -- See below See below for a description of parameters starting with values.
valueRef -- no -- AD.default A constant containing the value for this property. The constant can either be declared in the same class as this property or in any class that is imported. The type of the property is derived from the constant.
valueRefs -- no -- See below Same as the values attribute with the difference that it acts like the valueRef attribute and the value points to a constants defining the multi value for the property.

Notes:

Naming the property

It is important to carefully define the name of properties. By using a constant of the form

/** @scr.property value="default value" */
static final String CONSTANT_NAME = "property.name";

and defining the scr.property tag on this constant, the name of the property is taken from the constant value. Thus it may easily be ensured, that both the property in the descriptor files and the property used by the implementation are actually the same.

The options parameter

Some properties may only be set to a set of possible values. To support user interfaces which provide a selection list of values or a list of checkboxes the option values and labels may be defined as parameters to the scr.property tag. All parameters in the form of name-value pairs occurring after the options parameter are used to build the list of available value options. The parameter name is used as the value while the parameter value is used as the label in the user interface. This label may be prepended with a % sign to localize the string.

The options are written to the metatype.xml file as Option elements inside the AD element defining the property. The name of the parameter will be used for the Option.value attribute while the value of the parameter defines the Option.label attribute.

Please note, that all parameters of the scr.property tag occurring after the options parameter are used to build the options list. Hence no non-option value parameters should actually follow the options parameter.

Multivalue properties

Generally the value of a property is scalar, that is a property has a single value such as true, 5 or "This is a String". Such scalar values are defined with the value parameter of the scr.property tag. In the case of a scalar property value, the cardinality parameter value is assumed to be 0 (zero) unless of course set otherwise.

There may be properties, which have a list of values, such as a list of possible URL mappings for an URL Mapper. Such multiple values are defined in one more parameters whose name starts with values. Each parameter must of course have a unique name which is not in any except to differentiate the parameters.

If the cardinality of the property is not explicilty set with the cardinality property, it defaults to Integer.MAX_INT, i.e. unbound array, if multiple values with a series of values parameters are defined. Otherwise the cardinality parameter may be set for example to a negative value to store the values in a java.util.Vector instead.

scr.service

The scr.service tag defines whether and which service interfaces are provided by the component.

This tag is expected in the Java Class comment of the component.

This tag is used to declare <service> and <provide> elements of the component declaration. See section 112.4.6, Service Elements, in the OSGi Service Platform Service Compendium Specification for more information.

Supported parameters:

Name Default Value Required Descriptor Description
interface All implemented interfaces no provide.interface The name of the service interface provided by the component. This can either be the fully qualified name or just the interface class name if the interface is either in the same package or is imported. If this property is not set provide elements will be generated for all interfaces generated by the class
servicefactory false no service.servicefactory Whether the component is registered as a ServiceFactory or not

Omitting the scr.service tag will just define (and activate if required) the component but not register it as a service. Multiple scr.service tags may be declared each with its own interface. The component is registered as a ServiceFactory if at least on scr.service tag declares the servicefactory parameter as true.

scr.reference

The scr.reference tag defines references to other services made available to the component by the Service Component Runtime.

This tag may be declared in the java Class comment or any Java Field to which it might apply. Depending on where the tag is declared, the parameters may have different default values.

This tag is used to declare <reference> elements of the component declaration. See section 112.4.7, Reference Element, in the OSGi Service Platform Service Compendium Specification for more information.

Supported parameters:

Name Default Value Required Descriptor Description
name Name of the field yes reference.name The local name of the reference. If the scr.reference tag is declared in the class comment, this parameter is required. If the tag is declared in the field comment, the default value for the name parameter is the name of the field
interface Type of the field yes reference.interface The name of the service interface. This name is used by the Service Component Runtime to access the service on behalf of the component. If the scr.reference tag is declared in the class comment, this parameter is required. If the tag is declared in the field comment, the default value for the interface parameter is the type of the field
cardinality 1..1 no reference.cardinality The cardinality of the service reference. This must be one of 0..1, 1..1, 0..n, and 1..n
policy static no reference.policy The dynamicity policy of the reference. If dynamic the service will be made available to the component as it comes and goes. If static the component will be deactivated and re-activated if the service comes and/or goes away. This must be one of static and dynamic
target -- no reference.target A service target filter to select specific services to be made available. In order to be able to overwrite the value of this value by a configuration property, this parameter must be declared. If the parameter is not declared, the respective declaration attribute will not be generated
bind See description no reference.bind The name of the method to be called when the service is to be bound to the component. The default value is the name created by appending the reference name to the string bind. The method must be declared public or protected and take single argument which is declared with the service interface type
unbind See description no reference.unbind The name of the method to be called when the service is to be unbound from the component. The default value is the name created by appending the reference name to the string unbind. The method must be declared public or protected and take single argument which is declared with the service interface type
strategy event no reference.strategy The strategy used for this reference, one of event or lookup

Notes:

Rev. 1438983 by fmeschbe on Sat, 26 Jan 2013 22:54:42 +0000
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