Modularizing Web Services Management with AOP María Agustina Cibrán, Bart Verheecke { Maria.Cibran, System and Software Engineering Lab Vrije Universiteit Brussel ECOOP Workshop

Introduction –Web Services –Aspect Oriented Programming Web Services Management Layer –Architecture –JAsCo Technology –Redirection Mechanism and Hot Swapping –Service Management Conclusions Overview

Introduction Web Services –Independent modules Described, published, localised and invoked over a network using XML-standards –Integrated in client-applications using the Wrapper Approach Automatically generate client-stub and treat service as an internal component Used in Visual Studio.NET, Bea Web Logic, etc

Introduction Problem Statement –Services are hard-wired in application How to adapt to changes? What if service or network fails? How to deal with other service related issues? –Checking of availability, switching to other services, dealing with billing, security, logging, etc –Needs to be provided manually by the programmer –Results scattered and tangled in the application  Use AOP to achieve better separation of concerns

Introduction Aspect Oriented Programming (AOP) –Tyranny of the dominant decomposition Impossible to modularize some concerns (e.g. logging) using current software engineering methodologies such as OO. As a result code gets scattered all over the system AOP Concepts –Modularize these concerns in Aspects –An aspect defines a set of join points –Weavers to weave aspect logic in the core application

Web Services Management Layer The Wrapper Approach

Web Services Management Layer Introducing the WSML to decouple Web Services from the client-application

Web Services Management Layer Use the WSML to deal with all web service related issues

Web Services Management Layer Core Functionality –Decoupling of Services from application Redirection of application requests to service invocations –Hot-Swapping Switch between services at runtime –Advanced Service Selection and Monitoring Select services based on business driven requirements –Service Management Security, logging, billing, transaction management, etc

Web Services Management Layer Use of JAsCo Technology –Dynamic Aspect Oriented Language –Introduces two new concepts: Aspect Beans: –specify crosscutting behaviour in a reusable manner: »When the normal execution of a method should be intercepted »what extra behaviour should be executed at those points. Connectors: –Specify deployment details: »where the crosscutting behaviour should be deployed.

Web Services Management Layer

Hotel Service Example

Web Services Management Layer Code Example 1 1. Class ListAvailableHotelsAspect { 2. hook RedirectionHook { 3. RedirectionHook(method(..args)){ 4. execute(method); 5. } 6. replace() { 7. return specificMethod(args); 8. } 9. abstract public String specificMethod(args); 10. } 11. } Redirection Aspect for the request ListHotels One Aspect for each request Hook specifying to replace method (..args) with specificMethod (args) specificMethod is specified in the connector

Web Services Management Layer Code Example 1 1. static connector HotelServiceC_listHotels { 2. ListAvailableHotelsAspect.RedirectionHook redirectionhook = new 3. ListAvailableHotelsAspect.RedirectionHook(List listHotels(args)){ 4. public String specificMethod(args) { 5. try { 6. Stub stub = new Stub (WebServiceC); 7. result = stub.listAvailableHotels(args); 8. return result; 9. } 10. catch (ServiceUnavailableException e) { 11.WSML.failureNotification ("WebServiceC"); 12.return asi.HotelServiceASI.listHotels (args); 13. } 14. } 15. } 16. redirectionhook.replace(); 17. } Connector for WebService C Connector for each Service Invocation specificMethod with actual service call Hook instantiation

class BillingPerUse { hook BillingHook { private int total = 0; private int cost = 0; public void setCost(int aCost){ cost = aCost; } private void pay(){ total = total + cost; } BillingHook(method (Date d1,Date d2,CityCode cc)) { call(method); } after() { pay(); } Web Services Management Layer Code Example 2 Service Management: Billing Aspect Billing Aspect to bill each time a service is invoked Billing hook

Web Services Management Layer Code Example 2 Service Management: Billing Aspect Same connector before, now extended with billing hook Instantiation of the billing hook static connector HotelServiceC_listHotels { … BillingPerUse.BillingHook billPerUse = new BillingPerUse.BillingHook (List listHotels(args)); billPerUse.setCost(2); redirectionhook.replace(); billPerUse.after(); }

Conclusions AOP is suited to modularize Web Service related issues Use JAsCo to dynamically hot-swap between services and allow runtime management More flexible applications that can easily adapt to changes in the environment