Enabling
JSON based REST Invocation in OSB 11g
Scenario: Service
Provider is migrating from SOAP WS to REST Model. Service Consumer needs to be
updated with REST Clients.
Solution: If all
the communication happens via OSB Layer then SOAP messages can be translated to
JSON messages so that Service Consumer don’t have to modify their WS clients.
In this post, we will discuss on how to leverage Java
Callout capability in OSB to enable JSON based REST Invocation.
On a high level, OSB has two components called Proxy Service
& Business Service
Proxy Service
will define the service with message formats, communication protocols, Message
Flow and target Business Service.
Business Service
holds the information about Service Provider like URL, mode of communication,
authentication mechanism, etc.
Service Consumer will have no idea about to which instance
of Service Provider the request is redirected. It acts as an Abstraction layer,
where service consumer & service provider were not tightly coupled.
Let’s come back to the scope, Enabling JSON based REST
Invocation in OSB.
Ø
If the incoming request is REST message, then it
is straight forward, you can define the proxy service’s service type as
Messaging Service to accept the data as Text and pass it to business service
where URL & corresponding http method will be configured, with which the
request will be sent to the target Service Provider.
Ø
If the incoming request is SOAP message, then
Java callout capability in OSB can be leveraged to convert the SOAP XML message
to JSON message and pass on.
To perform any activity on OSB except read, you need to
create a session which can be activated post your configuration is completed
Create Proxy
Service:
1.
Under Create Resource Field, select Proxy
Service.
2.
Expose the Proxy Service as SOAP Web Service so
that SOAP based Service consumer will communicate to proxy in a seamless manner
(In my case, Service Consumer was SOA BPEL Process).
Click Next, Select Protocol as
http. Endpoint URI will be prepopulated, modify as needed.
3.
Click Last, Let’s skip to last page of this
configuration leaving all other parameters with the default value. Then Click
on Save button.
Before getting into Proxy Service Message Flow, let’s create
the corresponding Business Service,
Create Business
Service:
1.
Under Create Resource, select Business Service.
Enter Service Name
2.
Select Service Type as Messaging Service for
accepting json messages from proxy service. Click Next
3.
Select the Request Message Type & Response
Message Type as Text and Click Next
4.
Select protocol as http and configure the
Endpoint URI & add the same then Click Next
5.
Select the appropriate method as needed. If any basic
authenication needed then configure a service account and tag here. Then Click
Next.
Note: If you want to invoke GET method, then Request Message Type
should be None, because GET method invocation cannot have a body. If you want
to invoke HEAD method, then Response Message Type should be None.
6.
Click Last and save the configuration .
Linking Proxy
Service to Business Service:
Now Proxy service & Business Service is created, In
order to link the proxy service to business service, Click Edit Message Flow
button to create a message flow for this proxy.
·
In the Message flow, add a Route to the service
and click Edit Route
·
Click the link in the Route to field to
configure the corresponding Business Service.
·
In the Request Action section,
External Activity:
Develop an API to convert incoming XML object to JSON String as a static method
which will take apache XMLObject as input param and return String as output. Upload
the JAR file into OSB with all dependency jar files. Hint: Develop the api as
Maven Project to manage dependencies effectively.
·
Click Java
Callout to link to configure the static method in the api. Locate the JAR
& implemented method.
ü
Configure Input Parameter as $body, so that the
entire SOAP Body will be passed as input.
ü
Capture the return parameter (output) in result
variable (run-time variable).
·
Add another action called Replace to replace the body content with temporary result variable
ü
Enter the variable as body
ü
Enter the with value as ‘$result’
·
Add another action called Replace to set the content-type of the request.
ü
Click XPath link and replace it with “./ctx:transport/ctx:request/tp:headers/http:Content-Type”
ü
Enter the variable as outbound
ü
Enter the with value as “<http:Content-Type>application/json</http:Content-Type>”
or ‘application/json’
In case you are
trying to perform GET operation, the default content type of business service
is ‘binary/octet-stream’, so you need to update the content type in proxy
service & send all the headers to business service.
·
Below screenshot will speak about setting up the
Transport Headers (Add an
action->Communication->Transport Headers/Routing options options) for
enabling GET operation with respective Content-type. In case if you need to add
some application data to URI for GET operation, then perform a concat operation
using xquery & update URI field in Routing Options action. The updated URI
will be overridden in the business service.
Likewise, perform the reverse activity to convert the
incoming JSON message to appropriate XML format and set in the body content in
the Response Action Section.
By this way you can enable JSON based REST Invocation in OSB
Layer without impact the service consumer & service provider.
