Flow of Struts Appication

Struts Flow start with ActionServlet then call to process() method of RequestProcessor.

Step 1. Load ActionServlet using load-on-startup and do the following tasks.

Any struts web application contain the ActionServlet configuration in web.xml file.
On load-on-startup the servlet container Instantiate the ActionServlet .
First Task by ActionServlet : The ActionServlet takes the Struts Config file name as an init-param.
At startup, in the init() method, the ActionServlet reads the Struts Config file and load into memory.
Second Task by ActionServlet : If the user types http://localhost:8080/app/submitForm.do in the browser URL bar, the URL will be intercepted and processed by the ActionServlet since the URL has a pattern *.do, with a suffix of "do". Because servlet-mapping is

<servlet-mapping>
<servlet-name>action</servlet-name>
<url-pattern>*.do</url-pattern>
</servlet-mapping>


Third Task by ActionServlet : Then ActionServlet delegates the request handling to another class called RequestProcessor by invoking its process() method.

<servlet-name>action</servlet-name>
<servlet-class>org.apache.struts.action.ActionServlet</servlet-class>
<init-param>
<param-name>config</param-name>
<param-value>/WEB-INF/struts-config.xml</param-value>
</init-param>
<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>action</servlet-name>
<url-pattern>*.do</url-pattern>
</servlet-mapping>

Step 2. ActionServlet calls process() method of RequestProcessor.

The RequestProcessor does the following in its process() method:
a) The RequestProcessor looks up the configuration file for the URL pattern /submitForm (if the URL is http://localhost:8080/app/submitForm.do). and and finds the XML block (ActionMapping).

ActionMapping from struts-config.xml

<action path="/submitForm"
type="com.techfaq.emp.EmpAction"
name="EmpForm"
scope="request"
validate="true"
input="EmpForm.jsp">

<forward name="success" path="success.jsp"/>
<forward name="failure" path="failure.jsp" />
</action>

b) The RequestProcessor instantiates the EmpForm and puts it in appropriate scope – either session or request.
The RequestProcessor determines the appropriate scope by looking at the scope attribute in the same ActionMapping.
c) RequestProcessor iterates through the HTTP request parameters and populates the EmpForm.
d) the RequestProcessor checks for the validateattribute in the ActionMapping.
If the validate is set to true, the RequestProcessor invokes the validate() method on the EmpForm instance.
This is the method where you can put all the html form data validations.
If Validate fail the RequestProcessor looks for the input attribute and return to JSP page mentioned in input tag.
If Validate pass goto next step.
e) The RequestProcessor instantiates the Action class specified in the ActionMapping (EmpAction) and invokes the execute() method on the EmpAction instance.

signature of the execute method is

public ActionForward execute(ActionMapping mapping, ActionForm form, HttpServletRequest request, HttpServletResponse response) throws Exception { //your logic return mapping.findForward("success"); }

f) In return mapping.findForward("success")
RequestProcessor looks for the success attribute and forward to JSP page mentioned in success tag. i.e success.jsp.
In return mapping.findForward("failure")
RequestProcessor looks for the failure attribute and forward to JSP page mentioned in failure tag. i.e. failure.jsp