create own data centers). What's Context and how does it correlate to
View (seems Context aims to provide the basic abstraction layer to the
whole cloud provider features).
As regards this: you're looking at a transitional phase, which
unfortunately complicates things a bit ;-)
As described in the ContextBuilder Javadoc [1], there are basically
two things you can work with in jclouds: a specific API, or a portable
View. As explained in the Javadoc, the relationship can be
one-to-many: some APIs support both blobstore as well as compute
functionality, for example. But in most cases, the link is one-to-one.
When you use a context builder to get an *instance* of an API, it is
wrapped in a context object that basically represents this
instantiation. The "new style" is to use the ApiContext [2], but users
will not often see that as the encouraged style is to use the
ContextBuilder to go straight to the API object via
ContextBuilder.buildApi [3]. Users can still get at the context object
through ContextBuilder.build [4] if they really want to, though.
Which context a particular type of API should use is indicated by the
ApiMetadata, by the way [5].
Now to Views. First, the views that a given API supports are also
determined by the ApiMetadata [6, 7]. To get a view rather than an API
object, users should call ContextBuilder.buildView [8], specifying the
view type desired. Obviously, the system will complain if the view
type is not one of the ones declared in the metadata.
Because views provide an abstraction layer, there is sometimes the
need to get back to the underlying API in order to do API- or
provider-specific stuff (your choice: if you know you're talking at
AWS EC2 through a ComputeServiceContext, you can decide to get just
the generic EC2Api, or the provider-specific AWSEC2Api). This is
achieved using View.unwrapApi [9] to get the API object, or
View.unwrap if you really want the context object (so View.unwrapApi
and View.unwrap basically mirror ContextBuilder.buildApi vs.
ContextBuilder.build).
If all this was clear already, great, and apologies for the
repetition. Otherwise, hope this helps!
ap
[1] http://javadocs.jclouds.cloudbees.net/org/jclouds/ContextBuilder.html
[2] http://javadocs.jclouds.cloudbees.net/org/jclouds/rest/ApiContext.html
[3]
http://javadocs.jclouds.cloudbees.net/org/jclouds/ContextBuilder.html#buildApi(java.lang.Class)
[4]
http://javadocs.jclouds.cloudbees.net/org/jclouds/ContextBuilder.html#build(com.google.common.reflect.TypeToken)
[5]
http://javadocs.jclouds.cloudbees.net/org/jclouds/apis/ApiMetadata.html#getContext()
[6]
http://javadocs.jclouds.cloudbees.net/org/jclouds/apis/ApiMetadata.html#getViews()
[7]
https://github.com/jclouds/jclouds/blob/master/apis/atmos/src/main/java/org/jclouds/atmos/AtmosApiMetadata.java#L87
[8]
http://javadocs.jclouds.cloudbees.net/org/jclouds/ContextBuilder.html#buildView(java.lang.Class)
[9]
http://javadocs.jclouds.cloudbees.net/org/jclouds/View.html#unwrapApi(java.lang.Class)
[10]
http://javadocs.jclouds.cloudbees.net/org/jclouds/View.html#unwrap(com.google.common.reflect.TypeToken)
