Struts work flow:
When user run the Struts Application
first of all controll goes in XML file and find the Action 
Servlet that is main controller class in Struts after that 
control goes in Struts-config.xml and find the Action, find 
the Form bean and execute the action if method execute 
successfully the forward the output at given JSP.

struts work flow begins from jsp pages(when user first hit 
on the submit button),then UR request go and refer in 
struts-config.xml to confirm whether the corresponding  
action class entry has been put and also refer whether the 
corresponding Bean class entry has been put or not,
If the entry Has been identified then that Bean class 
should be populated and then corresponding action class 
also be populated finally ActionForward  instance goes to 
struts-config.xml(GLOBAL-FORWARD).This cyclic process taken 
place for all the request.

1) A request comes in from a Java Server Page into the
ActionServlet.
2) The ActionServlet having already read the
struts-config.xml file, knows which form bean
relates to this JSP, and delegates work to the validate
method of that form bean.
3) The form bean performs the validate method to determine
if all required fields have been entered, and performs
whatever other types of field validations that need to be
performed.
4) If any required field has not been entered, or any field
does not pass validation, the form bean generates
ActionErrors, and after checking all fields returns back to
the ActionServlet.
5) The ActionServlet checks the ActionErrors that were
returned from the form bean’s validate method to determine
if any errors have occurred. If errors have occurred, it
returns to the originating JSP displaying the appropriate
errors.
6) If no errors occurred in the validate method of the form
bean, the ActionServlet passes control to the appropriate
Action class.
7) The Action class performs any necessary business logic,
and then forwards to the next appropriate action (probably
another JSP).

when client makes the request,the request goes to web.xml
files <url-pattern> tag from here it goes to <servlet> tags
<servlet-class> there ActionServlet is loaded into the jvm,
and it is instantiated,initialized with in its init method,
Now the responsibility of  actionServlet is to identify the
request processor,by using <inti-param> tag,after request
processor identified ,ActionServlet creates the instance of
the request processor,on that instance of request processor
calls the process(), as a result request reaches to the
requestprocessor.
 the next responsibility of requestprocessor is to identify
the Action,using the client requestd uri.if client requested
uri and struts-config's path attributes are same then it
checks for the name attribute,if name attribute is found the
it goes to the <form-bean>tag there it check,if found ,sees
whether the form bean instance is available in the request
scope or not ,if found it instance set the request parameter
values by calling setxxx methods.then request reaches to the
  Action. action returns the ActionForward object, using which 
<forward> tag forwards to the appropriate jsp.

1) When a user submitted a jsp page. that page having 
(attribute of )action="login.do". the container will call 
to WEB.XML. in that web.xml thert is two section servlet 
And servlet mapping


2) In servlet mapping it find *.do in the url-pattern. if 
it found to take the name of servlet. and check the 
corresponding class. in the servlet section. that class is 
ActionServlet.
3) ActionServlet is the controller of Struts module 
architecture. in Action servlet having the service method. 
in that method we create RequestPrecessor class instance
4) Service(req,res)
RequestPrecessor rp = new RequestPrecessor();
5) We call a process method of RequestProcessor class 
through the instance rp.process(req,res)
6) In the request processor class have the process method 
with the parameter of req,res. then it has 1 if condition 
in this class. that condition return always true. because 
that is dummy method.
7)Inside that condition ther is 6 steps are processing 
a)Create a action mapping instance in the "Struts-
Config.xml". it will kept all details of the action mapping 
path, value, type forward, validation=true/false, input 
="*.jsp" etc these r created instance 
b)Then it will create Form class instance before it check 
the name of action mapping and form name are coincidence or 
not if it same it will create form instance
c)Then it will go to ActionMapping instace the ris mention 
or not the validate =true/fale if false it will not execute 
the this step else it will execute this step.
d) Then it will create action instance 
e) Next it will take four parameters of execute Method it 
will return ActionErrors instance. if it is not empty. it 
will go to error page other wise it will got to 
corresponding page. else if it is empty if will go further 
and display corresponding value of page in jsp view.This is 
struts flow.