Struts2 Interceptors

Struts2 provides very powerful mechanism of controlling a request using Interceptors. Interceptors are responsible for most of the request processing. They are invoked by the controller before and after invoking action, thus they sits between the controller and action. Interceptors performs tasks such as Logging, Validation, File Upload, Double-submit guard etc.

lifecycle of Struts2 framework

- Request is generated by user and sent to Servlet container.
- Servlet container invokes FilterDispatcher filter which in turn determines appropriate action.
- One by one Intercetors are applied before calling the Action. Interceptors performs tasks such as Logging, Validation, File Upload, Double-submit guard etc.
- Action is executed and the Result is generated by Action.
- The output of Action is rendered in the view (JSP, Velocity, etc) and the result is returned to the user.

Thus the Struts2 Interceptors removes cross cutting tasks such as logging from action components and create cleaner separation of MVC.

Struts2 comes with default list of Interceptors already configured in the application in struts-default.xml file. We can create our own custom Interceptors and plugin into a Struts2 based web application.

Framework creates an object of ActionInvocation that encapsulates the action and all the interceptors configured for that action. Each interceptors are called before the action gets called. Once the action is called and result is generated, each interceptors are again called in reverse order to perform post processing work. Interceptors can alter the workflow of action. It may prevent the execution of action

Reference:viralpatel