SCR JavaDoc Tags
scr goal of the
maven-scr-plugin looks for the following JavaDoc tags when building component descriptors:
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
|name||Fully qualified name of the Java class||no||
||Defines the Component name also used as the PID for the Configuration Admin Service|
||no||--||--||Whether Declarative Services descriptor is generated or not. If this parameter is not set or set to
|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
||--||Whether the component is enabled when the bundle starts|
||--||Whether the component is a factory component|
||--||Whether the component is immediately activated|
||no||--||--||Whether any service, property and reference declarations from base classes should be inherited by this class.|
||no||--||--||Whether Metatype Service data is generated or not. If this parameter is not set or set to
||This is generally used as a title for the object described by the meta type. This name may be localized by prepending a
||This is generally used as a description for the object described by the meta type. This name may be localized by prepending a
||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:
||no||component.policy||--||The configuration policy for this component:
||no||component.activate||--||The name of the component activation method.|
||no||component.deactivate||--||The name of the component deactivation method.|
|modified||--||no||component.modified||--||The name of the component modified method.|
Abstract Service Descriptions¶
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 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
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.
|name||The name of constant||yes||
||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
||The value of the property. If the property type is not
||The type of the property value. This must be one of
||The label to display in a form to configure this property. This name may be localized by prepending a
||A descriptive text to provide the client in a form to configure this property. This name may be localized by prepending a
|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
|cardinality||Depends on property value(s)||no||--||
||Defines the cardinality of the property and its collection type. If the cardinality is negative, the property is expected to be stored in a
|options||--||no||--||See below||See below for a description of the
|values*||--||no||--||See below||See below for a description of parameters starting with
||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
<properties>elements referring to bundle entries is not currently supported.
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.
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
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
Generally the value of a property is scalar, that is a property has a single value such as
"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
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
<provide> elements of the component declaration. See section 112.4.6, Service Elements, in the OSGi Service Platform Service Compendium Specification for more information.
|interface||All implemented interfaces||no||
||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
||Whether the component is registered as a
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
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.
|name||Name of the field||yes||
||The local name of the reference. If the
|interface||Type of the field||yes||
||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
||The cardinality of the service reference. This must be one of
||The dynamicity policy of the reference. If
||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|
||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
||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
||The strategy used for this reference, one of
- If you define a reference on a field with the strategy
eventand there is no bind or unbind method, the plugin will create the necessary methods.