Generating Java classes for the Azure AD Graph API

NOTE: I’ve since abandoned this avenue to generate pojos for the GraphAPI service. The Restlet Generator simply has too many issues in the resulting output (i.e. not handling package names properly, generics issues, not dealing with Edm.[types] etc). However this still may be of use to someone who wants to explore it further

Recently had to write some code to talk to the Azure AD Graph API. This is a REST based API that exchanges data via typical JSON payloads. For those having to a Java client to talk to this, a good starting point is taking a look at this sample API application to get your feet wet. However to those familiar in Java, this code is less that desirable;  however it has no dependencies which is nice.

When coding something against a REST service its often nice to have a set of classes that you can marshal to/from the JSON payloads to you are interacting with.  Behind the scenes it appears that this Azure Graph API is an OData app, which does present “$metadata” about itself… cool! So now we can generate some classes…..

https://graph.windows.net/YOUR_TENANT_DOMAIN/$metadata

OR

https://graphregistry.cloudapp.net/GraphRegistry.svc/YOUR_TENANT_DOMAIN/$metadata

So what can we use to generate some Java classes against this? Lets use the Restlet OData Extension. This Restlet extension can generate code off OData schema documents.  You will want to follow these instructions as well for the code generation.

IMPORTANT: You will also need a fork/version of Restlet that incorporates this pull request fix for a NullPointer that you will encounter with the code generation. (The bug exists in Restlet 2.2.1)

The command I ran to generate the Java classes for all the Graph API entities was as follows (run this from WITHIN the lib/ directory in the extracted Restlet zip/tarball you downloaded). In the command below, do NOT specify “$metadata” in the Generator URI as the tool appends that automatically.

java -cp org.restlet.jar:org.restlet.ext.xml.jar:org.restlet.ext.atom.jar:org.restlet.ext.freemarker.jar:org.restlet.ext.odata.jar:org.freemarker_2.3/org.freemarker.jar org.restlet.ext.odata.Generator https://graph.windows.net/YOUR_TENANT_DOMAIN/ ~/path/to/your/target/output/dir

Pitfalls:

  •  If you run the command and get the error “Content is not allowed in prolog.” (which I did). There might be some extra characters that are being prepended to the starting “<edmx:Edmx”  in the “$metadata” schema document that this endpoint is returning. If this is the case do the following:
    • Download the source XML $metadata document to your hard-drive
    • Open it up in a editor and REMOVE the “<?xml version=”1.0″ encoding=”utf-8″?>” that precedes the first “<edmx…” element
    • Next, just to ensure there are no more hidden chars at the start of the document, open up a hex editor on the document to get rid of any other hidden chars that precede the first “<edmx…”  element.
    • Save the changes locally, and fire-up a local webserver (or a webserver that lives anywhere) and set it up so that http://yourwebserver/whatever/$metadata will serve up that XML file.
    • Then proceed to alter the Restlet Generator command above to reference this modified URI as appropriate. Remember that you do NOT specify “$metadata” in the Generator URI as the tool appends that automatically.
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