What is difference between LookupDispatchAction and DispatchAction?

The difference between LookupDispatchAction and DispatchAction is that the actual method that gets called in LookupDispatchAction is based on a lookup of a key value instead of specifying the method name directly.

Details :

LookupDispatchAction is subclass of DispatchAction.
In case of DispatchAction, you have to declare the method name in the JSP page.
For Example :
http://localhost:8080/emp/empaction.do?step=add // IN CASE OF DispatchAction
here step=add , we are delaring method name in JSP.
or
Add //IN CASE OF DispatchAction
so we can't use localization for button.


To over come both the issues below
a)method name declaration in JSP
b)can't use localization for button
We will go for LookupDispatchAction.

In the LookupDispatchAction :
For example :
If there are three operation like add, delete, update employee.
You can create three different Actions ?
AddEmpAction, DeleteEmpAction and UpdateEmpAction.
This is a valid approach, although not elegant since there might be duplication of code across
the Actions since they are related. LookupDispatchAction is the answer to this
problem. With LookupDispatchAction, you can combine all three Actions into one.

Example :
Step 1.
three buttons might be










//No need method name declaration in JSP . Button name from resource bundle.

Step 2.
In the the Resource Bundle. //Here you can add localization.
button.add=Add
button.delete=Delete
button.update=Update

Step 3.
Implement a method named getKeyMethodMap() in the subclass of the
LookupDispatchAction. The method returns a java.util.Map. The
keys used in the Map should be also used as keys in Message Resource
Bundle.

public class EmpAction extends LookupDispatchAction {

public Map getKeyMethodMap()
{
Map map = new HashMap();
map.put("button.add", "add");
map.put("button.delete", "delete");
map.put("button.update", "update");
}


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

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

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

}

in struts-config.xml

input="/empform.jsp"
type="list.EmpAction"
parameter="step"
scope="request"
validate="false">
path="addEmpSuccess.jsp"
redirect="true"/>
path="deleteEmpSuccess.jsp"
redirect="true"/>
path="updateEmpSuccess.jsp"
redirect="true"/>


for every form submission, LookupDispatchAction does the
reverse lookup on the resource bundle to get the key and then gets the method
whose name is associated with the key from
getKeyMethodmap().


Flow of LookupDispatchAction:
a) Form the button name "Add" get the key "button.add" fro resource bundle.
b) then in the Map getKeyMethodMap() find the value associated with the key "button.add".
c) value from the Map is "add" . then call add() method of the same action class.