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SAF 1 requires Action classes to extend an abstract base class. A common problem in SAF 1 is programming to abstract classes instead of interfaces.

An SAF 2 Action may optionally implement an Action interface, along with other interfaces to enable optional and custom services. SAF 2 provides a base ActionSupport class to implement commonly used interfaces. Albeit, the Action interface is not required. Any POJO object with a execute signature can be used as an Action object.

SAF 1 Actions must be thread-safe because there will only be one instance of a class to handle all requests. The singleton strategy places restrictions on what can be done with SAF 1 Actions. Action resources must be thread-safe or synchronized.

SAF 2 Action objects are instantiated for each request, so there are no thread-safety issues. In practice, servlet containers generate many throw-away objects per request, and one more object does not impose a performance penality or impact garbage collection.

SAF 1 Actions have dependencies on the servlet API since the HttpServletRequest and HttpServletResponse is passed to the execute method when an Action is invoked.

SAF 2 Actions are not tied to a container. Most often the servlet contexts are represented as simple Maps, allowing the Action to be tested in isolation. SAF 2 Actions can still access to the request and response, when needed. Other architectural elements reduce or eliminate the need to access the HttpServerRequest directly.

A major hurdle to testing SAF 1 Actions is that the execute method exposes the Servlet API. A third-party extension, Struts TestCase, offers a set of mock object for SAF 1.

SAF 2 Actions can be tested by instantiating the Action, setting properties, and invoking methods. Dependency Injection support can make testing even simpler.

SAF 1 uses an ActionForm object to capture input, which can create a lot of extra classes. DynaBeans are often used as an alternative to creating conventional ActionForm classes.

SAF 2 allows you to have all of your properties directly accessible on your Action as regular JavaBean properties, including rich object types which can have their own properties which can be accessed from the taglibs. SAF 2 also supports the ActionForm pattern, as well as POJO form objects and POJO Actions. which allow you to have a rich Object type or domain object as your form bean, with its properties directly accessible to the web page, rather than accessing them as sub-properties of a property of the Action.

SAF 1 integrates with JSTL, so it uses the JSTL EL. The EL has basic object graph traversal, but relatively weak collection and indexed property support.

SAF 2 uses OGNL which is a powerful and flexible expression language SAF 2 can also use JSTL.

SAF 1 uses the standard JSP mechanism for binding objects into the page context for access.

SAF 2 sets up a ValueStack which the taglibs access to dynamically find values without tightly coupling your view to the types it is rendering. This strategy allows reuse of views across a range of types which have the same properties.

SAF 1 ActionForm properties are usually all Strings. SAF 1 uses Commons-Beanutils for type conversion. Converters are per-class, and not configurable per instance.

SAF 2 uses OGNL for type conversion with added converters provided for all basic types.

SAF 1 supports manual validation via a validate method on the ActionForm, or through an extension to the Commons Validator. Classes can have different validation contexts for the same class, but cannot chain to validations on sub-objects.

SAF 2 supports manual validation via the validate method and the XWork Validation framework. The Xwork Validation Framework supports chaining validation into sub-properties using the validations defined for the properties class type and the validation context.

SAF 1 supports separate Request Processors (lifecycles) for each module, but all the Actions in the module must share the same lifecycle.

SAF 2 supports creating different lifecycles on a per Action basis via Interceptor Stacks. Various stacks can be created and used with various Actions, as needed.