2009/04/15 - Apache HiveMind has been retired.

<construct
    class="..." autowire-services="..." log-property="..." messages-property="..."
    service-id-property="..." initialize-method="..." error-log-property="..."
    error-handler-property="..." class-resolver-property="...">

    <log/>
    <messages/>
    <service-id/>
    <error-handler/>
    <error-log/>
    <class-resolver/>
    <string>  ... </string>
    <boolean> ... </boolean>
    <configuration> ... </configuration>
    <int> ... </int>
    <long> ... </long>
    <resource> ... </resource>
    <service> ... </service>
    <object> ... </object>
    <null/>

    <event-listener service-id="..." event-type-name="..."/>
    <set property="..." value="..."/>
    <set-configuration property="..." configuration-id="..."/>
    <set-resource property="..." path="..."/>
    <set-service property="..." service-id="..."/>
    <set-object property="..." value="..."/>
</construct> 

construct

Attribute	Required ?	Description
autowire-services	no	If true (the default), then the BuilderFactory will attempt to automatically wire services and some common properties to constructor parameters and to properties of the constructed implementation with setter methods (see notes below).
class	yes	The fully qualified name of the class to instantiate.
class-resolver-property	no	The property to receive the module's ClassResolver.
error-handler-property	no	The name of a property to recieve the module's ErrorHandler instance (which is used to report recoverable errors).
error-log-property	no	The name of a property which will be assigned an ErrorLog instance for the service. An ErrorLog is simply a wrapper around a Log and an ErrorHandler as is the preferred approach.
initialize-method	no	The name of a method (public, no parameters) to invoke after the service is constructed, to allow it to perform any final initializion before being put into use.
log-property	no	The name of a property which will be assigned a org.apache.commons.logging.Log instance for the service. The Log is created from the complete service id (not the name of the class). If ommitted (and autowiring is disabled), no Log will be assigned.
messages-property	no	Allows the Messages for the module to be assigned to a property of the instance.
service-id-property	no	Allows the service id of the constructed service to be assigned to a property of the service implementation.

The remaining elements are enclosed by the <construct> element, and are used to supply constructor parameters and configure properties of the constructed service implementation.

Autowiring

With autowire-services set to true the BuilderFactory can automatically both perform constructor based and setter based dependency injection. It will not only attempt to inject services but also certain common properties. By using standard names (and standard types), the need to specify attributes log-property, error-handler-property, etc. is avoided. Simply declaring a constructor parameter with the correct type or a writable property with the correct name and type is sufficient:

Property name	Property / parameter type
classResolver	ClassResolver
errorHandler	ErrorHandler
errorLog	ErrorLog
log	org.apache.commons.logging.Log
messages	Messages
serviceId	String

Note:

The service id (last entry in above table) will only be automatically injected through a writable property (i.e. setServiceId(String)). This because a constructor parameter of type String is far too common.

As noted the BuilderFactory will also inject services into the constructed service implementation. Through every constructor parameter and writable property whose type is an interface (with the exception of the common parameters / properties listed above) and hasn't been set otherwise the BuilderFactory will attempt to inject a service. This attempt may fail if there is no visible service or more than one visible service implementing the given interface. (Visibility is checked with respect to the module declaring the constructed service's implementation.)

The action taken if the service injection fails (due to one of the reasons given above) depends on the type of dependency injection. For constructor based dependency injection the BuilderFactory will try using a different constructor (see selection details below). If no "working" constructor is found an error is logged. For setter based dependency injection the BuilderFactory will log an error immedeately upon failed injection.

Constructor based dependency injection is enabled with the autowire-services attribute but can be overridden by declaring any constructor parameter elements (see next section). The constructor being used for the constructor based dependency injection has to meet all of the following criteria:

• the constructor is declared as public
• all parameter types are interfaces (including the common types listed above)
• no two parameters are of the same type

All constructors of the service implementation class meeting these criteria (the default constructor is considered as one of these) are ordered by length (given by the number of parameters) and the first of these for which every parameter type either has a matching common property or there is exactly one corresponding visible service available will be invoked. If no such constructor can be found an error is logged. Autowiring may be complicated by the fact that one module may define a service point that will tangentially affect the construction of a service in another module (simply by implementing the same service interface). In this situation, service autowiring can be turned off, by setting the autowire-services attribute to false. Once all properties have been set (possibly by autowiring), an initializer method will be invoked. If the initialize-method attribute is not specified, and the service implementation includes a public method initializeService() (no parameters, returns void), then initializeService() will be invoked as the initializer.

Constructor Parameter Elements

The following table summarizes the elements which can be used to specify constructor parameters for the class to instantiate. These elements can be mixed freely with the properties configuring elements. It is important to know that the number, type, and order of the constructor parameter elements determine the constructor that will be used to instantiate the implementation.

Element	Matched Parameter Type	Passed Parameter Value
error-handler	ErrorHandler	The module's ErrorHandler, user to report recoverable errors.
error-log	ErrorLog	The service's ErrorLog, used to report recoverable errors (this is preferred over using a Log and an ErrorHandler).
log	org.apache.commons.logging.Log	The Log is created from the complete service id (not the name of the class) of the created service.
messages	Messages	The Messages object of the invoking module.
object	variable	As determined by the object translator, this is decidedly free-form. See hivemind.ObjectProviders.
null	any reference type	Always simply null.
service-id	java.lang.String	The service id of the constructed service.
string	java.lang.String	This element's content.
boolean	boolean	This element's content. Must be either "true" or "false".
configuration	java.util.List or java.util.Map	The List / Map of the elements of the configuration specified by this element's content as a configuration id. The id can either by a simple id for a configuration within the same module as the constructed service, or a complete id.
int	int	This element's content parsed as an integer value.
long	long	This element's content parsed as a long value.
resource	Resource	This element's content parsed as a path to a Resource, which is relative to the contributing module's deployment descriptor. If available, a localized version of the Resource will be selected.
service	interface corresponding to specified service	The implementation of the service with the id given in this element's content. The id can either be a simple id for a service within the same module as the constructed service, or a complete id.

Service Property Configuring Elements