[ovirt-devel] Fw: Some ideas on oVirt Java SDK

[Michael Pasternak]

Hey Vojtech,

How are you?, please see my reply inline.


>
>    On Friday, November 28, 2014 5:26 PM, Vojtech Szocs <vszocs at redhat.com>
> wrote:
>
>
> Hi guys,
>
> since the initial (small, working & well-tested) version of oVirtJS
> JavaScript SDK is finished [*], I've started working on GWT wrapper
> for oVirtJS.
>
> While analyzing/reverse-engineering oVirt Java SDK, some thoughts
> came to my mind, and I wanted to share them with you.
>
> [*] TODO(vszocs) upload new patchset with all recent changes
>
> First, the way XJC (JAXB binding compiler that generates Java beans
> out of REST XSD schema) is invoked looks a bit weird to me, as Java
> SDK's XsdCodegen does this:
>
>   Runtime.getRuntime().exec(command)
>
> Why not simply use existing Maven plugins to invoke XJC?
> - either: https://github.com/highsource/maven-jaxb2-plugin
>

it was using jaxb to begin with, but Juan has replaced it with XJC,
btw Juan, what was the motivation behind this?
(REST api uses jaxb as well so we used to have 1x1 mappings)


> - or: http://mojo.codehaus.org/jaxb2-maven-plugin/
>

same.


>
> Second, and most importantly, what's the point of having "group"
> entities? I'll give an example - api.xsd contains this:
>
>   <xs:complexType name="DataCenters">
>     <xs:complexContent>
>       <xs:extension base="BaseResources">
>         <xs:sequence>
>           <xs:annotation>
>             <xs:appinfo>
>                 <jaxb:property name="DataCenters"/>
>             </xs:appinfo>
>           </xs:annotation>
>           <xs:element ref="data_center" minOccurs="0"
> maxOccurs="unbounded"/>
>         </xs:sequence>
>       </xs:extension>
>     </xs:complexContent>
>   </xs:complexType>
>
> (Same as above for Hosts, Clusters, VMs, etc.)
>
> This results in following (IMHO rather meaningless) Java class
> being generated by XJC:
>
> public class DataCenters extends BaseResources {
>
>     @XmlElement(name = "data_center")
>     protected List<DataCenter> dataCenters;
>
>     public List<DataCenter> getDataCenters() {
>         if (dataCenters == null) {
>             dataCenters = new ArrayList<DataCenter>();
>         }
>         return this.dataCenters;
>     }
>
>     public boolean isSetDataCenters() {
>         return ((this.dataCenters!= null)&&(!this.dataCenters.isEmpty()));
>     }
>
>     public void unsetDataCenters() {
>         this.dataCenters = null;
>     }
>
> }
>
> Instead, we could use @XmlElementWrapper as described in [1]
> to avoid generating "group" entities altogether.
>
> [1] https://github.com/dmak/jaxb-xew-plugin
>
> The fact that Java SDK provides decorator for each specific
> resource collection (like DataCenters), instead of having ONE
> resource collection type, greatly complicates overall design
> and code-gen aspect.
>

well, i guess now is speaking JS constraints ghost, am i right?,
at any case, the reasons for having decorator per collection are:

1. compliance with REST API (all SDKs and REST api sharing same well know
architecture)
2. "decorator" is a well known and commonly used java design pattern
3. having one resource type serving all collections would create a
bottleneck
(well it might depend on how you implementing it, but still in my view it's
less convenient/readable
than dedicated collection with own context, verbs and behaviour)

after all the purpose of sdk is being java client serving java application
in "Java" way
while JS use-case & paradigms are totally different.


>
> In oVirtJS GWT wrapper, we'll avoid above complication through
> single resource collection type (having common methods like
> get(id), list() etc) for all resources.
>

> Regards,
> Vojtech
> _______________________________________________
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> Devel at ovirt.org
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>
>
>


-- 

Michael Pasternak
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