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Struts has a filter dispatcher. Its fully qualified name is org.apache.struts2.dispatcher.FilterDispatcher. To use it, register it in the deployment descriptor (web.xml file) using this filter and filter-mapping elements.
<filter>
<filter-name>struts2</filter-name>
<filter-class> org.apache.struts2.dispatcher.FilterDispatcher </filter-class>
</filter>
<filter-mapping>
<filter-name>struts2</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
There's a lot that a filter dispatcher in a Model 2 application has to do and Struts' filter dispatcher is by no means an exception. Since Struts has more, actually much more, features to support, its filter dispatcher could grow infinitely in complexity. However, Struts approaches this by splitting task processing in its filter dispatcher into subcomponents called interceptors. The first interceptor you'll notice is the one that populates the action object with request parameters. You'll learn more about interceptors in our later posts.
In a Struts application the action method is executed after the action's properties are populated. An action method can have any name as long as it is a valid Java method name.
An action method returns a String value. This value indicates to Struts where control should be forwarded to. A successful action method execution will forward to a different view than a failed one. For instance, the String "success" indicates a successful action method execution and "error" indicates that there's been an error during processing and an error message should be displayed. Most of the time a RequestDispatcher will be used to forward to a JSP, however JSPs are not the only allowed destination. A result that returns a file for download does not need a JSP. Neither does a result that simply sends a redirection command or sends a chart to be rendered. Even if an action needs to be forwarded to a view, the view may not necessarily be a JSP. A Velocity template or a FreeMarker template can also be used.
<filter>
<filter-name>struts2</filter-name>
<filter-class> org.apache.struts2.dispatcher.FilterDispatcher </filter-class>
</filter>
<filter-mapping>
<filter-name>struts2</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
There's a lot that a filter dispatcher in a Model 2 application has to do and Struts' filter dispatcher is by no means an exception. Since Struts has more, actually much more, features to support, its filter dispatcher could grow infinitely in complexity. However, Struts approaches this by splitting task processing in its filter dispatcher into subcomponents called interceptors. The first interceptor you'll notice is the one that populates the action object with request parameters. You'll learn more about interceptors in our later posts.
In a Struts application the action method is executed after the action's properties are populated. An action method can have any name as long as it is a valid Java method name.
An action method returns a String value. This value indicates to Struts where control should be forwarded to. A successful action method execution will forward to a different view than a failed one. For instance, the String "success" indicates a successful action method execution and "error" indicates that there's been an error during processing and an error message should be displayed. Most of the time a RequestDispatcher will be used to forward to a JSP, however JSPs are not the only allowed destination. A result that returns a file for download does not need a JSP. Neither does a result that simply sends a redirection command or sends a chart to be rendered. Even if an action needs to be forwarded to a view, the view may not necessarily be a JSP. A Velocity template or a FreeMarker template can also be used.
Posted in: Struts 2
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