Re: [sca-j] Why is @Property.required attribute MUST be true forconstructor parameter?

[Mike Edwards <mike_edwards@uk.ibm.com>]

Vamsi,

You make a good point in reminding me
that the Java TC has not voted through a resolution to remove the use
of componentType side files for Java
POJOs.  I have now raised a new issue to do this - which will remove

Section 10 entirely.

I note that the Liaison committee posted
a recommendation that implementation types either use pure introspection
OR purely use a side file and never
try to combine the information from two sources.  Java POJOs can have
all
their component type metadata derived
via introspection - as a result side files are not useful and add complexity.


Yours,  Mike.

Strategist - Emerging Technologies, SCA & SDO.
Co Chair OASIS SCA Assembly TC.
IBM Hursley Park, Mail Point 146, Winchester, SO21 2JN, Great Britain.
Phone & FAX: +44-1962-818014    Mobile: +44-7802-467431  
Email:  mike_edwards@uk.ibm.com

From:	C Vamsi <vamsic007@in.ibm.com>
To:	Mike Edwards/UK/IBM@IBMGB
Cc:	sca-j@lists.oasis-open.org
Date:	24/02/2009 10:15
Subject:	Re: [sca-j] Why is @Property.required attribute MUST be true for constructor parameter?

---

Comments inline in <vamsi> tags.

++Vamsi
Apache Tuscany Committer  http://tuscany.apache.org
Apache Geronimo Committer and Member of PMC  http://geronimo.apache.org


                    
                     
                     
          
             Mike Edwards      
                     
                     
             <mike_edwards@uk.  
                     
                    
             ibm.com>      
                     
                     
To 
                    
                  sca-j@lists.oasis-open.org
         
             24/02/2009 15:22    
                     
                cc 
                    
                     
                     
          
                    
                     
                     
  Subject 
                    
                  Re: [sca-j]
Why is                  
                    
                  @Property.required
attribute MUST   
                    
                  be true
for constructor parameter?  
                    
                     
                     
          
                    
                     
                     
          
                    
                     
                     
          
                    
                     
                     
          
                    
                     
                     
          
                    
                     
                     
          




Folks,

When using constructor parameters for injection, there are a couple of
considerations to bear in mind:

1) Each constructor parameter MUST be annotated with either @Reference
or
with @Property, depending
on the type of the parameter.  This is required in order that each
parameter has a NAME which then appears
in the componentType - without this, it is impossible to get a name for
the
constructor parameter (none is
available via introspection)

2) Clearly, each constructor parameter MUST supply a value, even if that
value is NULL.  There is no
avoiding this.  The runtime MUST pass in some value when it invokes
the
constructor.  This is the reason
behind the requirement for required=true on the @Property annotation.  The
using component can set
any value it likes for the property - potentially including "nil"
- but it
must set something.

On the point that Raymond makes that the property value "can be inherited
from the componentType" - this
is not correct.  The componentType is entirely derived from the
implementation itself, not from some other
metadata.  In fact, there is no separate componentType file any longer
for
Java implementations.  So the
<vamsi>
Have we done away with componentType side files for Java implementations?
Is there an issue resolution pending to be applied?  In
sca-javaci-1.1-spec-wd02.pdf, section 10, lines 509 thru 512, I still see
a
description of componentType side file for Java implementations.  What
am I
missing?
</vamsi>
only place for a property value to come from for a constructor parameter
is
from the component configuration
that uses the Java implementation.


Yours,  Mike.

Strategist - Emerging Technologies, SCA & SDO.
Co Chair OASIS SCA Assembly TC.
IBM Hursley Park, Mail Point 146, Winchester, SO21 2JN, Great Britain.
Phone & FAX: +44-1962-818014    Mobile: +44-7802-467431
Email:  mike_edwards@uk.ibm.com


                    
                     
                     
          
 From:     Raymond Feng <rfeng@us.ibm.com>    
                     
      
                    
                     
                     
          
 To:       sca-j@lists.oasis-open.org      
                     
         
                    
                     
                     
          
 Date:     23/02/2009 21:09          
                     
               
                    
                     
                     
          
 Subject:  Re: [sca-j] Why is @Property.required attribute MUST be
true    
           for constructor parameter?    
                     
           
                    
                     
                     
          






My understanding is that @required=true means the property MUST be set
with
a value which can be either configured at the component level or inherited
from the componentType.

For example, if we have a constructor as follows:

public MyServiceImpl(@Property(name="myProp") String myProp)
{
       ...
}

The injection for "myProp" is required no matter what value it
is set.

Thanks,
Raymond



                    
                     
                     
          
 From:   C Vamsi <vamsic007@in.ibm.com>      
                     
       
                    
                     
                     
          
 To:     sca-j@lists.oasis-open.org        
                     
         
                    
                     
                     
          
 Date:   02/23/2009 10:41 AM            
                     
            
                    
                     
                     
          
 Subject [sca-j] Why is @Property.required attribute MUST be true for  
   
 :       constructor parameter?        
                     
             
                    
                     
                     
          







sca-javacaa-1.1-spec-cd02-rev2.doc:

Sec 9.15 @Property

Lines 1622-1623:
required (optional) – specifies whether injection is required, defaults
to
true. For a constructor parameter annotation, this attribute MUST have
the
value true.

Q: Why is, "For a constructor parameter annotation, this attribute
MUST
have the value true." required?

The componentType can define a default value for the property. In this
case, even if a property is not specified in the component definition,
the
runtime will still have a value to pass as an argument to the constructor.


++Vamsi
Apache Tuscany Committer  http://tuscany.apache.org
Apache Geronimo Committer and Member of PMC  http://geronimo.apache.org











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---

Unless stated otherwise above:
IBM United Kingdom Limited - Registered in England and Wales with number 741598.
Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU