Thursday, 22 September 2011

SOA ,OSB,REST and Middleware Related Stuff

Basic Fault Handling in SOA 11g

In this post, I am going to illustrate the basics of fault handling in Oracle SOA 11g.For the sake of illustration, I am going to create a a sample application.So , let's get started.

In Oracle SOA 11g, faults can be categorized broadly into two categories:- System Faults and Custom Faults.So, let us get started to see how it works.In this first example, we are going to see how faults are propagated.

First,open JDev and create a new SOA Application and a SOA project, select empty composite template.Now drag and drop a  BPEL process onto your composite application.Name it FaultHandlerBPEL and choose synchronous template;leave the default input and output and make sure the "Expose as SOAP service" check box is checked.


 Hit ok once you are done.In the FaultHandlerBPEL process, we are going to handle the faults.Drag another BPEL process.Name it FaultThrowerBPEL.Like before, choose synchronous template and accept the default input and output.However, do not expose this BPEL process .i.e. the check box "Expose as SOAP service" should be unchecked.


As the name implies, the FaultThrowerBPEL process throws a fault Now wire the FaultHandlerBPEL to the FaultThrowerBPEL process.Your composite should look like the following image:-



Now, double click on the FaultThrowerBPEL process to open the BPEL process editor.Now,drag a Throw activity between the receive and reply activity.Name the activity ThrowFault.






Now double click on the Throw activity.A window will pop up.Click on the magnifying glass as shown in the image below to select the fault.



In the fault chooser window, expand the System Faults node and select remoteFault.Hit ok once you are done.



This will bring you back to the previous window.Now click on the green plus sign to add a fault variable as shown in the image below:-


Accept the default name and scope in the variable creation window.Hit Ok twice to come back to the BPEL process.


So in the previous steps, what we have done is we have created a throw activity which throws a remoteFault.While throwing the fault, we have also specified a fault variable.Using the throw activity, we can throw system faults and custom faults.However, the custom faults are discussed later.So, if you are familiar with java, up to now we have written something like this:-

     throw new Exception();

Notice that, once we create a fault variable, a new WSDL file is added to our project.The name of the WSDL file is RuntimeFault.wsdl.The wsdl file is a simple one which contains a message on which the fault variable is based on.It is important to mention here that in SOA 11g, the fault variables must be WSDL message based,be that a custom fault variable or a system fault variable.

Now, drag and drop an Assign activity just before the Throw activity.Name it AssignFaultDetails.The BPEL file should look like the following image:-


Now double click on the assign activity.Add a copy operation.



Choose expression on the from side and enter the string '007'.On the to side,expand the FaultVar node and select the code  part.


Hit Ok once you are done.Now,add another copy operation.On the from side, select expression and enter the string 'My Fault Summary'.On the to side, expand the FaultVar node and select the summary part
.

Add another copy operation.Like before, on the from side select expression and enter the string 'My Fault Details'.On the two side, expand the FaultVar node and select detail node.Hit Ok twice to complete the Assign activity.

So the assign activity populates the fault variable with some dummy data before the fault is thrown. This completes our FaultThrowerBPEL process.

Next open the composite.xml and double click on the FaultHandlerBPEL to open the BPEL editor.Next, drag and drop an Invoke activity onto the BPEL process between the Receive and Reply activity.Double click on the invoke activity.Enter the name InvokeFaultThrower.Next click on the magnifying glass beside the Partner  Link as indicated in the following image:-





The partner link chooser dialog opens.Select the FaultThrowerBPEL.faultthrowerbpel_client partner link and hit ok.




Back in the invoke dialog, create input and output variables.Choose the default name.Your BPEL process should look like the following image.


Add an Assign activity before the invoke activity.Name it initialize variable.Create a copy operation as shown in the follwing image:-
Hit Ok twice to come back to the BPEL process.Add another activity after the Invoke activity and before the Reply activity.Call it IntializeOutput.Create a new copy operation as shown in the following image:-


Hit Ok twice to come back to the BPEL process.Now click on the validate icon on the upper left corner of the BPEL process as shown on the image below:-


All the warning signs from the BPEL process should disappear now.If you test the process now and invoke the FaultHandlerBPEL, when executing the invoke activity InvokeFaultThrower, a fault is going to be thrown.This is because the FaultThrowerBPEL is going to be invoked which is going to throw a remoteFault.As we do not have any catch or catchAll activity in the FaultThrowerBPEL, the fault is going to be propagated to the FaultHandlerBPEL.

Now add a catch all branch.To do this, click on the add catch all branch icon as indicated in the image below:-




A new catch all branch is going to be added to the BPEL process.Expand the catch all activity and drag and drop an Assign activity under the catchAll activity and name it PopulateOutput.The BPEL process should now look like the following image:-





Double click to open the Assign activity and add a copy operation.On the from side select, expression,open the expression builder and enter expression:-

concat(ora:getFaultName(),'::',ora:getFaultAsString())

On the to side, select the result element as shown in the image below:-



The function ora:getFaultName() returns the fault name i.e. remoteFault in this case.The function ora:getFaultAsString() returns the details of the fault which contains all the parts i.e. code, summary and detail.Next drag and drop a Reply activity under the catchAll branch just below the PopulateOutput Asign activity.Your BPEL process should look like the following image:-





Double click to open the Reply activity.Enter replyOutput as the name.Now select the partner link as before.In the partner link chooser, select the faulthandlerbpel_client partner link.Hit ok to comeback to the previous window.


Now click on the magnifying glass beside the Variable chooser as shown in the image below:-








In the variable chooser, choose the output variable.


Hit Ok twice to complete the Reply activity.In the previous steps, we created a catch all branch synonymous to java "catch(Exception e){}".Now,inside the catch all, we have implemented an Assign activity which update the output variable with the details of the fault and a Reply activity which replies to the calling process.

Now deploy and test the service from the EM console.A fault is going to be returned when you invoke the ErrorHandlerBPEL from the EM console.


Returning a fault from a synchronous BPEL process:-

Now we are going to see how we can return a fault from a synchronous BPEL process.To do this, open the FaultThrower BPEL process. Next add a catch branch by clicking on the add catch branch as indicated in the image below:-


Now double click on the catch branch that is created .Now we are going to choose the fault that we intend to catch which is, in this case, a remoteFault.Click on the magnifying glass icon as indicated in the image below to bring up the fault chooser window.



In the fault chooser window, select remoteFault.Hit Ok once you are done.



 Next click on the magnifying glass icon as indicated in the image below to select a fault variable.Here, we are going to reuse the same variable that we created while throwing the fault.Alternatively, you can create a new fault variable by clicking on the green plus icon.In this case, the fault variable is going to be automatically populated when the fault is caught.
.


Next, choose the FaultVar and hit Ok once you are done.Hit Ok again to complete the catch activity.So in java syntax, we have written something like this:-
                       catch(RemoteFault faultVar){}


Now drag and drop a Reply activity under the catch activity.Your BPEL process is going to look like the following image.



Next we are going to configure the reply activity to reply with a fault.Double click on the Reply activity.Enter ReplyFault as name.Choose the faultthrowerbpel_client partner link.Now, select the fault variable as the variable.Next click on the magnifying glass as indicated in the following image  to choose the fault that we intend to return.

In the fault chooser dialog, select remoteFault.Hit Ok once you are done.



The reply activity should look like as shown in the following image.


 Hit Ok to complete the reply activity.The BPEL process should look like the following image.


 Next,we have to configure the operation for the FaultThrower BPEL to indicate that he process can return a fault.To do this, open the FaultThrower.wsdl file and go to source.Notice that the RuntimeFault.wsdl is imported into this WSDL automatically.



Now, add a new fault inside the operation.The fault should be based on the message as defined in the RuntimeFault.wsdl.file.Make sure the namespace is declared.


This completes the BPEL process.Now deploy and test the web service.The behavior is going to be the same;this time though, the fault is caught by the FaultThrowerBPEL.Once caught, the FaultThrowerBPEL replies to the calling BPEL i,e, the FaultHandlerBPEL in this case with a remoteFault.This remoteFault is then caught by the catchAll activity inside the FaultHandlerBPEL.So in java syntax, we are doing something like this in the FaultThrowerBPEL:-


                                ....
                                catch(RemoteFault faultVar){
                                                throw new RemoteFault(faultVar);
                                }

In my next post, I am going to show another powerful fault handling mechanism which is the fault handling framework.Hope this helps.

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