Front Controller in Struts2
In the Struts2 framework, the Front Controller design pattern is implemented through its core servlet: org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter. This servlet acts as the entry point for handling all incoming requests to a Struts2 web application. It intercepts requests, processes them through a series of interceptors and actions, and manages the flow of control throughout the application.
Table of Contents
Java Example
In a typical web.xml configuration for a Struts2 application, you’ll find the StrutsPrepareAndExecuteFilter configured as the front controller:
xml
<web-app>
<!-- Struts2 Filter Configuration -->
<filter>
<filter-name>struts2</filter-name>
<filter-class>org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>struts2</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
<!-- Other configurations -->
</web-app>
Detailed Explanation
- 1. StrutsPrepareAndExecuteFilter : This filter intercepts every request (/* in the example) and is responsible for initializing the Struts2 framework, preparing necessary objects for request processing, and executing the appropriate action. It coordinates the flow by invoking interceptors, executing actions, and handling results.
- 2. Role as Front Controller : As per the Front Controller pattern, StrutsPrepareAndExecuteFilter centralizes request handling and routing in a Struts2 application. It ensures that all requests go through a single point of entry, where the framework’s components (actions, interceptors, results) are invoked in a controlled sequence.
Benefits
- Centralized Request Handling : Promotes consistency and reduces duplication of request handling logic across the application.
- Interception and Flow Control : Facilitates the use of interceptors for cross-cutting concerns such as logging, validation, and authentication without coupling these concerns with business logic.
- Configuration Flexibility : Allows customization and configuration of interceptors, actions, and results through XML (struts.xml) and annotations, providing flexibility in application behavior.
Conclusion
The StrutsPrepareAndExecuteFilter class serves as the Front Controller in Struts2, adhering to the Front Controller design pattern by centralizing request processing and ensuring a consistent flow of control throughout the application. This approach enhances maintainability, scalability, and modularity in Struts2-based web applications.