Struts
1. What is MVC? Model-View-Controller (MVC) is a design pattern put together to help control change. MVC decouples interface from business logic and data.
• Model: The model contains the core of the application's functionality. The model encapsulates the state of the application. Sometimes the only functionality it contains is state. It knows nothing about the view or controller.
• View: The view provides the presentation of the model. It is the look of the application. The view can access the model getters, but it has no knowledge of the setters. In addition, it knows nothing about the controller. The view should be notified when changes to the model occur.
• Controller: The controller reacts to the user input. It creates and sets the model.
2. What is a framework?
A framework is made up of the set of classes which allow us to use a library in a best possible way for a specific requirement.
3. What is Struts framework?
Struts framework is an open-source framework for developing the web applications in Java EE, based on MVC-2 architecture. It uses and extends the Java Servlet API. Struts is robust architecture and can be used for the development of application of any size. Struts framework makes it much easier to design scalable, reliable Web applications with Java.
4. What are the components of Struts?
Struts components can be categorize into Model, View and Controller:
• Model: Components like business logic /business processes and data are the part of model.
• View: HTML, JSP are the view components.
• Controller: Action Servlet of Struts is part of Controller components which works as front controller to handle all the requests.
5. What are the core classes of the Struts Framework?
Struts is a set of cooperating classes, servlets, and JSP tags that make up a reusable MVC 2 design.
• JavaBeans components for managing application state and behavior.
• Event-driven development (via listeners as in traditional GUI development).
• Pages that represent MVC-style views; pages reference view roots via the JSF component tree.
6. What is ActionServlet?
ActionServlet is a simple servlet which is the backbone of all Struts applications. It is the main Controller component that handles client requests and determines which Action will process each received request. It serves as an Action factory – creating specific Action classes based on user’s request.
7. What is role of ActionServlet?
ActionServlet performs the role of Controller:
• Process user requests
• Determine what the user is trying to achieve according to the request
• Pull data from the model (if necessary) to be given to the appropriate view,
• Select the proper view to respond to the user
• Delegates most of this grunt work to Action classes
Is responsible for initialization and clean-up of resources
8. What is the ActionForm?
ActionForm is javabean which represents the form inputs containing the request parameters from the View referencing the Action bean.
9. What are the important methods of ActionForm?
The important methods of ActionForm are : validate() & reset().
10. Describe validate() and reset() methods?
validate () : Used to validate properties after they have been populated; Called before FormBean is handed to Action. Returns a collection of ActionError as ActionErrors. Following is the method signature for the validate() method.
public ActionErrors validate (ActionMapping mapping, HttpServletRequest request)
reset(): reset() method is called by Struts Framework with each request that uses the defined ActionForm. The purpose of this method is to reset all of the ActionForm's data members prior to the new request values being set.
public void reset() {}
11. What is ActionMapping?
Action mapping contains all the deployment information for a particular Action bean. This class is to determine where the results of the Action will be sent once its processing is complete.
12. How is the Action Mapping specified?
We can specify the action mapping in the configuration file called struts-config.xml. Struts framework creates ActionMapping object from <ActionMapping> configuration element of struts-config.xml file
<action-mappings>
<action path="/submit"
name="submitForm"
input="/submit.jsp"
scope="request"
validate="true">
<forward name="success" path="/success.jsp"/>
<forward name="failure" path="/error.jsp"/>
</action>
</action-mappings>
13. What is role of Action Class?
An Action Class performs a role of an adapter between the contents of an incoming HTTP request and the corresponding business logic that should be executed to process this request.
14.In which method of Action class the business logic is executed ?
In the execute() method of Action class the business logic is executed.
public ActionForward execute(
ActionMapping mapping,
ActionForm form,
HttpServletRequest request,
HttpServletResponse response)
throws Exception ;
execute() method of Action class:
• Perform the processing required to deal with this request
• Update the server-side objects (Scope variables) that will be used to create the next page of the user interface
• Return an appropriate ActionForward object
15. What design patterns are used in Struts? S
truts is based on model 2 MVC (Model-View-Controller) architecture. Struts controller uses the command design pattern and the action classes use the adapter design pattern. The process() method of the RequestProcessor uses the template method design pattern. Struts also implement the following J2EE design patterns.
• Service to Worker
• Dispatcher View
• Composite View (Struts Tiles)
• Front Controller
• View Helper
• Synchronizer Token
16.Can we have more than one struts-config.xml file for a single Struts application?
Yes, we can have more than one struts-config.xml for a single Struts application. They can be configured as follows:
<servlet>
<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,
/WEB-INF/struts-admin.xml,
/WEB-INF/struts-config-forms.xml
</param-value>
</init-param>
.....
<servlet>
17.What is the directory structure of Struts application?
The directory structure of Struts application :
18. What is the difference between session scope and request scope when saving formbean ?
When the scope is request, the values of formbean would be available for the current request.
When the scope is session, the values of formbean would be available throughout the session.
19. What are the important tags of struts-config.xml?
The five important sections are:
19. What are the important tags of struts-config.xml?
The five important sections are in above picture:----->
20.What are the different kinds of actions in Struts?
The different kinds of actions in Struts are:
• ForwardAction
• IncludeAction
• DispatchAction
• LookupDispatchAction
• SwitchAction
21. What is DispatchAction?
The DispatchAction class is used to group related actions into one class. Using this class, you can have a method for each logical action compared than a single execute method. The DispatchAction dispatches to one of the logical actions represented by the methods. It picks a method to invoke based on an incoming request parameter. The value of the incoming parameter is the name of the method that the DispatchAction will invoke.
22. How to use DispatchAction?
To use the DispatchAction, follow these steps :
• Create a class that extends DispatchAction (instead of Action)
• In a new class, add a method for every function you need to perform on the service – The method has the same signature as the execute() method of an Action class.
• Do not override execute() method – Because DispatchAction class itself provides execute() method.
• Add an entry to struts-config.xml
23.What is the use of ForwardAction?
The ForwardAction class is useful when you’re trying to integrate Struts into an existing application that uses Servlets to perform business logic functions. You can use this class to take advantage of the Struts controller and its functionality, without having to rewrite the existing Servlets. Use ForwardAction to forward a request to another resource in your application, such as a Servlet that already does business logic processing or even another JSP page. By using this predefined action, you don’t have to write your own Action class. You just have to set up the struts-config file properly to use ForwardAction.
24. What is IncludeAction?
The IncludeAction class is useful when you want to integrate Struts into an application that uses Servlets. Use the IncludeAction class to include another resource in the response to the request being processed.
25.What is the difference between ForwardAction and IncludeAction?
The difference is that you need to use the IncludeAction only if the action is going to be included by another action or jsp. Use ForwardAction to forward a request to another resource in your application, such as a Servlet that already does business logic processing or even another JSP page.
26.What is LookupDispatchAction?
The LookupDispatchAction is a subclass of DispatchAction. It does a reverse lookup on the resource bundle to get the key and then gets the method whose name is associated with the key into the Resource Bundle.
27.What is the use of LookupDispatchAction?
LookupDispatchAction is useful if the method name in the Action is not driven by its name in the front end, but by the Locale independent key into the resource bundle. Since the key is always the same, the LookupDispatchAction shields your application from the side effects of I18N.
28.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.
29.What is SwitchAction?
The SwitchAction class provides a means to switch from a resource in one module to another resource in a different module. SwitchAction is useful only if you have multiple modules in your Struts application. The SwitchAction class can be used as is, without extending.
30.What if <action> element has <forward> declaration with same name as global forward?
In this case the global forward is not used. Instead the <action> element’s <forward> takes precendence.
.What is DynaActionForm?
A specialized subclass of ActionForm that allows the creation of form beans with dynamic sets of properties (configured in configuration file), without requiring the developer to create a Java class for each type of form bean.
32.What are the steps need to use DynaActionForm?
Using a DynaActionForm instead of a custom subclass of ActionForm is relatively straightforward. You need to make changes in two places:
• In struts-config.xml: change your <form-bean> to be an org.apache.struts.action.DynaActionForm instead of some subclass of ActionForm
<form-bean name="loginForm" >
<form-property name="userName" />
<form-property name="password" />
</form-bean>
• In your Action subclass that uses your form bean:
o import org.apache.struts.action.DynaActionForm
o downcast the ActionForm parameter in execute() to a DynaActionForm
o access the form fields with get(field) rather than getField()
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.apache.struts.action.Action;
import org.apache.struts.action.ActionForm;
import org.apache.struts.action.ActionForward;
import org.apache.struts.action.ActionMapping;
import org.apache.struts.action.ActionMessage;
import org.apache.struts.action.ActionMessages;
import org.apache.struts.action.DynaActionForm;
public class DynaActionFormExample extends Action {
public ActionForward execute(ActionMapping mapping, ActionForm form,
HttpServletRequest request, HttpServletResponse response)
throws Exception {
DynaActionForm loginForm = (DynaActionForm) form;
ActionMessages errors = new ActionMessages();
if (((String) loginForm.get("userName")).equals("")) {
errors.add("userName", new ActionMessage(
"error.userName.required"));
}
if (((String) loginForm.get("password")).equals("")) {
errors.add("password", new ActionMessage(
"error.password.required"));
}
...........
33.How to display validation errors on jsp page?
<html: errors/> tag displays all the errors. <html: errors/> iterates over ActionErrors request attribute.
34. What are the various Struts tag libraries?
The various Struts tag libraries are:
• HTML Tags
• Bean Tags
• Logic Tags
• Template Tags
• Nested Tags
• Tiles Tags
35.What is the use of <logic:iterate>?
<logic:iterate> repeats the nested body content of this tag over a specified collection.
<table border=1>
<logic:iterate id="customer" name="customers">
<tr>
<td><bean:write name="customer" property="firstName"/></td>
<td><bean:write name="customer" property="lastName"/></td>
<td><bean:write name="customer" property="address"/></td>
</tr>
</logic:iterate>
</table>
36.What are differences between <bean:message> and <bean:write>
<bean:message>: is used to retrive keyed values from resource bundle. It also supports the ability to include parameters that can be substituted for defined placeholders in the retrieved string.
<bean:message key="prompt.customer.firstname"/>
<bean:write>: is used to retrieve and print the value of the bean property. <bean:write> has no body.
<bean:write name="customer" property="firstName"/>
37.How the exceptions are handled in struts?
Exceptions in Struts are handled in two ways:
• Programmatic exception handling :
Explicit try/catch blocks in any code that can throw exception. It works well when custom value (i.e., of variable) needed when error occurs.
• Declarative exception handling: You can either define <global-exceptions> handling tags in your struts-config.xml or define the exception handling tags within <action></action> tag. It works well when custom page needed when error occurs. This approach applies only to exceptions thrown by Actions.
<global-exceptions>
<exception key="some.key"
path="/WEB-INF/errors/null.jsp"/>
</global-exceptions>
or
<exception key="some.key"
path="/WEB-INF/somepage.jsp"/>
38.What is difference between ActionForm and DynaActionForm?
• An ActionForm represents an HTML form that the user interacts with over one or more pages. You will provide properties to hold the state of the form with getters and setters to access them. Whereas, using DynaActionForm there is no need of providing properties to hold the state. Instead these properties and their type are declared in the struts-config.xml
• The DynaActionForm bloats up the Struts config file with the xml based definition. This gets annoying as the Struts Config file grow larger.
• The DynaActionForm is not strongly typed as the ActionForm. This means there is no compile time checking for the form fields. Detecting them at runtime is painful and makes you go through redeployment.
• ActionForm can be cleanly organized in packages as against the flat organization in the Struts Config file.
• ActionForm were designed to act as a Firewall between HTTP and the Action classes, i.e. isolate and encapsulate the HTTP request parameters from direct use in Actions. With DynaActionForm, the property access is no different than using request.getParameter( .. ).
• DynaActionForm construction at runtime requires a lot of Java Reflection (Introspection) machinery that can be avoided.
39.How can we make message resources definitions file available to the Struts framework environment?
We can make message resources definitions file (properties file) available to Struts framework environment by adding this file to struts-config.xml.
<message-resources parameter="com.login.struts.ApplicationResources"/>
40.What is the life cycle of ActionForm?
The lifecycle of ActionForm invoked by the RequestProcessor is as follows:
• Retrieve or Create Form Bean associated with Action
• "Store" FormBean in appropriate scope (request or session)
• Reset the properties of the FormBean
• Populate the properties of the FormBean
• Validate the properties of the FormBean
• Pass FormBean to Action
How you will handle errors and exceptions in Struts?
An efficient error and exception handling makes an application behave gracefully under abnormal conditions.Struts has errors and exception handling done in different ways.The form validations using Struts require a proper mechanism.For handling errors in Struts,it has two objects ActionError andActionErrors.Whenever a form is submitted then cotroller receives request and then create ActionForm object which calls reset() method and stores ActionForm object to required scope and then it loads ActionForm object from request and calls validate() method.If validate method fails then errors are displayed on the form itself through <html:errors> tags.
Exception Handling can be done in following ways:
-try-catch block within
-Using declarative exception handling.In struts-config.xml we can declare on which type of exception, a request should be redirected to.
Use Global Exceptions tag in struts-config.xml
<global-exceptions>
<exception key="errors.MyException" path="/myExcption.jsp"/>
So whenever MyException occurs then Struts framework will display 'myException.jsp' page.
The interpretation of this is that if MyException is caught by Struts' ActionServlet then it should redirect to myExcption.jsp. The key is as usual a pointer to the message resource file
How does Validator framework work in Struts ?
The Validator framework is an open source project and is part of the Jakarta Commons subproject. The Commons project was created for the purpose of providing reusable components like the Validator. Other well-known Commons components include BeanUtils, Digester, and the Logging framework.It was first released in November 2002.
Validator framework consists of the following components:-
-Validators
-Configuration Files
-Resource Bundle
-JSP Custom Tags
-Validator Form Classes
Validators are Java classes which execute validation rule.The framework knows how to invoke a Validator class based on its method signature, as defined in a configuration file. Typically, each Validator provides a single validation rule, and these rules can be chained together to form a more complex set of rules.
Configuration Files:There are two configuration files
-validator.xml and
-validator-rules.xml
validator-rules.xml contains all possible validations available to an application. These validations are present as definitions in this file. The controlling document of Validator-rules.xml is Validator-rules_1_1.dtd.All the elements defined in this file are defined according to the above DTD.
The required validation is applied to mandatory fields, such as employee id(one example).The has many attributes. These attributes are,Name,Classname,MethodMethodparams,Msg
A simple validator-rule.xml file.click here.
Another configuration file is validation.xml file.It is where you couple the individual Validators defined in the validator-rules.xml to components within your application. Since we are talking about using the Validator with Struts, the coupling occurs between the Validators and Struts ActionForm classes.ActionForm also provide a convenient spot to validate the user input before passing it to the business layer. Here is a simple validation.xml file.
Resource Bundle: Resource Bundle forms the base of localization. The error messages created when a rule fails come from the resource bundles. For the common Validators provided by the Validator framework, the default messages can be placed in the Struts application's message resources. Some of these messages are:
#Error messages used by the Validator
errors.required={0} is required.
errors.minlength={0} can not be less than {1} characters.
errors.maxlength={0} can not be greater than {1} characters.
errors.invalid={0} is invalid.
The parameter in place of {0} and {1} is inserted automatically by the framework when the rules fail. These values are corresponding to the parameters comes from the Validator-rules.xml and validation.xml files.
JSP Custom Tags
Like errors and javascript Struts HTML tags required in case of validations. The former is for server-side validation while the latter is for client side validation.
Validator Form Class
In Struts data is passed from the JSP page (view layer) to Action class (controller layer) by means of ActionForm objects. The standard Struts ActionForm won't suffice to impose validation framework.The specially designed classes for this purpose come quite handy. It comes in two varieties- ValidatorForm and DynaValidatorForm. The former is used in place of ActionForm while the latter is used with the DynaActionForm. Whatever the variety being used, two methods used forperforming validation which are present in both of them are- reset() and validate().
Integrating validator to Struts is done by introducing the following piece of data inside strust-config.xml:
The Validator framework is easily extensible and the effort required is minimal.
-Create your own validation classes.
-Hook it up inside validation-rules.xml file
Apart from using in Struts application,the Validator framework can be used as a separate unit for validation of applications.
How to handle duplicate submits in Struts?
The duplicate form submission occurs
-When a user clicks the Submit button more than once before the response is sent back or
- When a client accesses a view by returning to a previously bookmarked page.
It may result in inconsistent transactions and must be avoided.In Struts this problem can be handled by using the saveToken() and isTokenValid() methods of Action class.saveToken() method creates a token (a unique string) and saves that in the user's current session, while isTokenValid() checks if the token stored in the user's current session is the same as that was passed as the request parameter.
It can be done by loading JSP through an Action and before loading the JSP call saveToken() to save the token in the user session. When the form is submitted, check the token against that in the session by calling isTokenValid().
public ActionForward submitOrder(ActionMapping mapping,
ActionForm form,
HttpServletRequest request,
HttpServletResponse response) throws Exception
{
try
{
// check the token. Proceed only if token is valid
if(isTokenValid(request,true)) {
//implement order submit functionality here
} else {
return mapping.findForward("failure");
}
}
catch(Exception ex){//exception}
}
What is DispatchAction?
org.apache.struts.actions.DispatchAction is responsible for
-Dispatches to a public method named on a request parameter
-Method name corresponds to the 'parameter' property of corresponding ActionMapping
-useful when multiple similar actions are to be clubbed within a singe Action class in order to simplify the design.
If you want to to insert,update and delete all actions on a database from a JSP with the same Action class in such case it will come quite handy.
Here is how this JSP looks like:
<html:form action="/saveSubscription">
<html:submit>
<bean:message key="insert"/>
</html:submit>
<html:submit>
<bean:message key="update"/>
</html:submit>
<html:submit>
<bean:message key="delete"/>
</html:submit>
</html:form>
To configure the use of this action in your struts-config.xml file, create an entry like this:
<action path="/saveSubscription" name="subscriptionForm" scope="request" input="/subscription.jsp" parameter="submit"/>
It will use the value of the request parameter named "submit" to pick the appropriate "execute" method, which must have the same signature (other than method name) of the standard Action.execute method. For example, you might have the following three methods in the same action:
* public ActionForward delete(ActionMapping mapping, ActionForm form, HttpServletRequest request, HttpServletResponse response) throws Exception
* public ActionForward insert(ActionMapping mapping, ActionForm form, HttpServletRequest request, HttpServletResponse response) throws Exception
* public ActionForward update(ActionMapping mapping, ActionForm form, HttpServletRequest request, HttpServletResponse response) throws Exception
In our JSP, we can refer to the buttons in the usual way.Later, when the user selects a button, the form will pass the submit parameter, along with whatever message is Struts finds for "insert" or "delete" in the resource bundle.
Using the conventional DispatchAction, this approach would be problematic, not necessarily each message will map to a valid Java identifier. This is where the magic of the LookupDispatchAction comes into play.
When you create your LookupDispatchAction subclass, along with the methods for the dispatch operations you must also implement a getKeyMethodMap method. This is a "hotspot" that the LookupDispatchAction will call.
Here's an example of the methods you might declare in your subclass:
protected Map getKeyMethodMap(ActionMapping mapping,
ActionForm form,
HttpServletRequest request) {
Map map = new HashMap();
map.put("button.add", "add");
map.put("button.delete", "delete");
return map;
}
Internally, the base action will lookup the messages for 'insert' and 'delete', and match those against the submit parameter. When it finds a match, it will then use either "insert" or "delete" to call the corresponding methods.
So while the LookupDispatchAction means adding an extra method to your Action, it lets you skip putting a JavaScript in your form.
Both the DispatchAction and LookupDispatchAction are an excellent way to streamline your Struts action classes, and group several related operations into a single umbrella action. So, how many dispatch actions do you need? Can you use a dispatch action to collect everything into a single action?
In practice, you can easily use one dispatch action for any forms that share a common validation. It is not advisable to have sharing of dispatch action between different form beans, or form beans that are validated differently,as it can start to make things harder rather than simpler. But the use of a dispatch action can easily half or quarter the number of action classes in most Struts application.
• Model: The model contains the core of the application's functionality. The model encapsulates the state of the application. Sometimes the only functionality it contains is state. It knows nothing about the view or controller.
• View: The view provides the presentation of the model. It is the look of the application. The view can access the model getters, but it has no knowledge of the setters. In addition, it knows nothing about the controller. The view should be notified when changes to the model occur.
• Controller: The controller reacts to the user input. It creates and sets the model.
2. What is a framework?
A framework is made up of the set of classes which allow us to use a library in a best possible way for a specific requirement.
3. What is Struts framework?
Struts framework is an open-source framework for developing the web applications in Java EE, based on MVC-2 architecture. It uses and extends the Java Servlet API. Struts is robust architecture and can be used for the development of application of any size. Struts framework makes it much easier to design scalable, reliable Web applications with Java.
4. What are the components of Struts?
Struts components can be categorize into Model, View and Controller:
• Model: Components like business logic /business processes and data are the part of model.
• View: HTML, JSP are the view components.
• Controller: Action Servlet of Struts is part of Controller components which works as front controller to handle all the requests.
5. What are the core classes of the Struts Framework?
Struts is a set of cooperating classes, servlets, and JSP tags that make up a reusable MVC 2 design.
• JavaBeans components for managing application state and behavior.
• Event-driven development (via listeners as in traditional GUI development).
• Pages that represent MVC-style views; pages reference view roots via the JSF component tree.
6. What is ActionServlet?
ActionServlet is a simple servlet which is the backbone of all Struts applications. It is the main Controller component that handles client requests and determines which Action will process each received request. It serves as an Action factory – creating specific Action classes based on user’s request.
7. What is role of ActionServlet?
ActionServlet performs the role of Controller:
• Process user requests
• Determine what the user is trying to achieve according to the request
• Pull data from the model (if necessary) to be given to the appropriate view,
• Select the proper view to respond to the user
• Delegates most of this grunt work to Action classes
Is responsible for initialization and clean-up of resources
8. What is the ActionForm?
ActionForm is javabean which represents the form inputs containing the request parameters from the View referencing the Action bean.
9. What are the important methods of ActionForm?
The important methods of ActionForm are : validate() & reset().
10. Describe validate() and reset() methods?
validate () : Used to validate properties after they have been populated; Called before FormBean is handed to Action. Returns a collection of ActionError as ActionErrors. Following is the method signature for the validate() method.
public ActionErrors validate (ActionMapping mapping, HttpServletRequest request)
reset(): reset() method is called by Struts Framework with each request that uses the defined ActionForm. The purpose of this method is to reset all of the ActionForm's data members prior to the new request values being set.
public void reset() {}
11. What is ActionMapping?
Action mapping contains all the deployment information for a particular Action bean. This class is to determine where the results of the Action will be sent once its processing is complete.
12. How is the Action Mapping specified?
We can specify the action mapping in the configuration file called struts-config.xml. Struts framework creates ActionMapping object from <ActionMapping> configuration element of struts-config.xml file
<action-mappings>
<action path="/submit"
name="submitForm"
input="/submit.jsp"
scope="request"
validate="true">
<forward name="success" path="/success.jsp"/>
<forward name="failure" path="/error.jsp"/>
</action>
</action-mappings>
13. What is role of Action Class?
An Action Class performs a role of an adapter between the contents of an incoming HTTP request and the corresponding business logic that should be executed to process this request.
14.In which method of Action class the business logic is executed ?
In the execute() method of Action class the business logic is executed.
public ActionForward execute(
ActionMapping mapping,
ActionForm form,
HttpServletRequest request,
HttpServletResponse response)
throws Exception ;
execute() method of Action class:
• Perform the processing required to deal with this request
• Update the server-side objects (Scope variables) that will be used to create the next page of the user interface
• Return an appropriate ActionForward object
15. What design patterns are used in Struts? S
truts is based on model 2 MVC (Model-View-Controller) architecture. Struts controller uses the command design pattern and the action classes use the adapter design pattern. The process() method of the RequestProcessor uses the template method design pattern. Struts also implement the following J2EE design patterns.
• Service to Worker
• Dispatcher View
• Composite View (Struts Tiles)
• Front Controller
• View Helper
• Synchronizer Token
16.Can we have more than one struts-config.xml file for a single Struts application?
Yes, we can have more than one struts-config.xml for a single Struts application. They can be configured as follows:
<servlet>
<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,
/WEB-INF/struts-admin.xml,
/WEB-INF/struts-config-forms.xml
</param-value>
</init-param>
.....
<servlet>
17.What is the directory structure of Struts application?
The directory structure of Struts application :
18. What is the difference between session scope and request scope when saving formbean ?
When the scope is request, the values of formbean would be available for the current request.
When the scope is session, the values of formbean would be available throughout the session.
19. What are the important tags of struts-config.xml?
The five important sections are:
19. What are the important tags of struts-config.xml?
The five important sections are in above picture:----->
20.What are the different kinds of actions in Struts?
The different kinds of actions in Struts are:
• ForwardAction
• IncludeAction
• DispatchAction
• LookupDispatchAction
• SwitchAction
21. What is DispatchAction?
The DispatchAction class is used to group related actions into one class. Using this class, you can have a method for each logical action compared than a single execute method. The DispatchAction dispatches to one of the logical actions represented by the methods. It picks a method to invoke based on an incoming request parameter. The value of the incoming parameter is the name of the method that the DispatchAction will invoke.
22. How to use DispatchAction?
To use the DispatchAction, follow these steps :
• Create a class that extends DispatchAction (instead of Action)
• In a new class, add a method for every function you need to perform on the service – The method has the same signature as the execute() method of an Action class.
• Do not override execute() method – Because DispatchAction class itself provides execute() method.
• Add an entry to struts-config.xml
23.What is the use of ForwardAction?
The ForwardAction class is useful when you’re trying to integrate Struts into an existing application that uses Servlets to perform business logic functions. You can use this class to take advantage of the Struts controller and its functionality, without having to rewrite the existing Servlets. Use ForwardAction to forward a request to another resource in your application, such as a Servlet that already does business logic processing or even another JSP page. By using this predefined action, you don’t have to write your own Action class. You just have to set up the struts-config file properly to use ForwardAction.
24. What is IncludeAction?
The IncludeAction class is useful when you want to integrate Struts into an application that uses Servlets. Use the IncludeAction class to include another resource in the response to the request being processed.
25.What is the difference between ForwardAction and IncludeAction?
The difference is that you need to use the IncludeAction only if the action is going to be included by another action or jsp. Use ForwardAction to forward a request to another resource in your application, such as a Servlet that already does business logic processing or even another JSP page.
26.What is LookupDispatchAction?
The LookupDispatchAction is a subclass of DispatchAction. It does a reverse lookup on the resource bundle to get the key and then gets the method whose name is associated with the key into the Resource Bundle.
27.What is the use of LookupDispatchAction?
LookupDispatchAction is useful if the method name in the Action is not driven by its name in the front end, but by the Locale independent key into the resource bundle. Since the key is always the same, the LookupDispatchAction shields your application from the side effects of I18N.
28.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.
29.What is SwitchAction?
The SwitchAction class provides a means to switch from a resource in one module to another resource in a different module. SwitchAction is useful only if you have multiple modules in your Struts application. The SwitchAction class can be used as is, without extending.
30.What if <action> element has <forward> declaration with same name as global forward?
In this case the global forward is not used. Instead the <action> element’s <forward> takes precendence.
.What is DynaActionForm?
A specialized subclass of ActionForm that allows the creation of form beans with dynamic sets of properties (configured in configuration file), without requiring the developer to create a Java class for each type of form bean.
32.What are the steps need to use DynaActionForm?
Using a DynaActionForm instead of a custom subclass of ActionForm is relatively straightforward. You need to make changes in two places:
• In struts-config.xml: change your <form-bean> to be an org.apache.struts.action.DynaActionForm instead of some subclass of ActionForm
<form-bean name="loginForm" >
<form-property name="userName" />
<form-property name="password" />
</form-bean>
• In your Action subclass that uses your form bean:
o import org.apache.struts.action.DynaActionForm
o downcast the ActionForm parameter in execute() to a DynaActionForm
o access the form fields with get(field) rather than getField()
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.apache.struts.action.Action;
import org.apache.struts.action.ActionForm;
import org.apache.struts.action.ActionForward;
import org.apache.struts.action.ActionMapping;
import org.apache.struts.action.ActionMessage;
import org.apache.struts.action.ActionMessages;
import org.apache.struts.action.DynaActionForm;
public class DynaActionFormExample extends Action {
public ActionForward execute(ActionMapping mapping, ActionForm form,
HttpServletRequest request, HttpServletResponse response)
throws Exception {
DynaActionForm loginForm = (DynaActionForm) form;
ActionMessages errors = new ActionMessages();
if (((String) loginForm.get("userName")).equals("")) {
errors.add("userName", new ActionMessage(
"error.userName.required"));
}
if (((String) loginForm.get("password")).equals("")) {
errors.add("password", new ActionMessage(
"error.password.required"));
}
...........
33.How to display validation errors on jsp page?
<html: errors/> tag displays all the errors. <html: errors/> iterates over ActionErrors request attribute.
34. What are the various Struts tag libraries?
The various Struts tag libraries are:
• HTML Tags
• Bean Tags
• Logic Tags
• Template Tags
• Nested Tags
• Tiles Tags
35.What is the use of <logic:iterate>?
<logic:iterate> repeats the nested body content of this tag over a specified collection.
<table border=1>
<logic:iterate id="customer" name="customers">
<tr>
<td><bean:write name="customer" property="firstName"/></td>
<td><bean:write name="customer" property="lastName"/></td>
<td><bean:write name="customer" property="address"/></td>
</tr>
</logic:iterate>
</table>
36.What are differences between <bean:message> and <bean:write>
<bean:message>: is used to retrive keyed values from resource bundle. It also supports the ability to include parameters that can be substituted for defined placeholders in the retrieved string.
<bean:message key="prompt.customer.firstname"/>
<bean:write>: is used to retrieve and print the value of the bean property. <bean:write> has no body.
<bean:write name="customer" property="firstName"/>
37.How the exceptions are handled in struts?
Exceptions in Struts are handled in two ways:
• Programmatic exception handling :
Explicit try/catch blocks in any code that can throw exception. It works well when custom value (i.e., of variable) needed when error occurs.
• Declarative exception handling: You can either define <global-exceptions> handling tags in your struts-config.xml or define the exception handling tags within <action></action> tag. It works well when custom page needed when error occurs. This approach applies only to exceptions thrown by Actions.
<global-exceptions>
<exception key="some.key"
path="/WEB-INF/errors/null.jsp"/>
</global-exceptions>
or
<exception key="some.key"
path="/WEB-INF/somepage.jsp"/>
38.What is difference between ActionForm and DynaActionForm?
• An ActionForm represents an HTML form that the user interacts with over one or more pages. You will provide properties to hold the state of the form with getters and setters to access them. Whereas, using DynaActionForm there is no need of providing properties to hold the state. Instead these properties and their type are declared in the struts-config.xml
• The DynaActionForm bloats up the Struts config file with the xml based definition. This gets annoying as the Struts Config file grow larger.
• The DynaActionForm is not strongly typed as the ActionForm. This means there is no compile time checking for the form fields. Detecting them at runtime is painful and makes you go through redeployment.
• ActionForm can be cleanly organized in packages as against the flat organization in the Struts Config file.
• ActionForm were designed to act as a Firewall between HTTP and the Action classes, i.e. isolate and encapsulate the HTTP request parameters from direct use in Actions. With DynaActionForm, the property access is no different than using request.getParameter( .. ).
• DynaActionForm construction at runtime requires a lot of Java Reflection (Introspection) machinery that can be avoided.
39.How can we make message resources definitions file available to the Struts framework environment?
We can make message resources definitions file (properties file) available to Struts framework environment by adding this file to struts-config.xml.
<message-resources parameter="com.login.struts.ApplicationResources"/>
40.What is the life cycle of ActionForm?
The lifecycle of ActionForm invoked by the RequestProcessor is as follows:
• Retrieve or Create Form Bean associated with Action
• "Store" FormBean in appropriate scope (request or session)
• Reset the properties of the FormBean
• Populate the properties of the FormBean
• Validate the properties of the FormBean
• Pass FormBean to Action
How you will handle errors and exceptions in Struts?
An efficient error and exception handling makes an application behave gracefully under abnormal conditions.Struts has errors and exception handling done in different ways.The form validations using Struts require a proper mechanism.For handling errors in Struts,it has two objects ActionError andActionErrors.Whenever a form is submitted then cotroller receives request and then create ActionForm object which calls reset() method and stores ActionForm object to required scope and then it loads ActionForm object from request and calls validate() method.If validate method fails then errors are displayed on the form itself through <html:errors> tags.
Exception Handling can be done in following ways:
-try-catch block within
-Using declarative exception handling.In struts-config.xml we can declare on which type of exception, a request should be redirected to.
Use Global Exceptions tag in struts-config.xml
<global-exceptions>
<exception key="errors.MyException" path="/myExcption.jsp"/>
So whenever MyException occurs then Struts framework will display 'myException.jsp' page.
The interpretation of this is that if MyException is caught by Struts' ActionServlet then it should redirect to myExcption.jsp. The key is as usual a pointer to the message resource file
How does Validator framework work in Struts ?
The Validator framework is an open source project and is part of the Jakarta Commons subproject. The Commons project was created for the purpose of providing reusable components like the Validator. Other well-known Commons components include BeanUtils, Digester, and the Logging framework.It was first released in November 2002.
Validator framework consists of the following components:-
-Validators
-Configuration Files
-Resource Bundle
-JSP Custom Tags
-Validator Form Classes
Validators are Java classes which execute validation rule.The framework knows how to invoke a Validator class based on its method signature, as defined in a configuration file. Typically, each Validator provides a single validation rule, and these rules can be chained together to form a more complex set of rules.
Configuration Files:There are two configuration files
-validator.xml and
-validator-rules.xml
validator-rules.xml contains all possible validations available to an application. These validations are present as definitions in this file. The controlling document of Validator-rules.xml is Validator-rules_1_1.dtd.All the elements defined in this file are defined according to the above DTD.
The required validation is applied to mandatory fields, such as employee id(one example).The has many attributes. These attributes are,Name,Classname,MethodMethodparams,Msg
A simple validator-rule.xml file.click here.
Another configuration file is validation.xml file.It is where you couple the individual Validators defined in the validator-rules.xml to components within your application. Since we are talking about using the Validator with Struts, the coupling occurs between the Validators and Struts ActionForm classes.ActionForm also provide a convenient spot to validate the user input before passing it to the business layer. Here is a simple validation.xml file.
Resource Bundle: Resource Bundle forms the base of localization. The error messages created when a rule fails come from the resource bundles. For the common Validators provided by the Validator framework, the default messages can be placed in the Struts application's message resources. Some of these messages are:
#Error messages used by the Validator
errors.required={0} is required.
errors.minlength={0} can not be less than {1} characters.
errors.maxlength={0} can not be greater than {1} characters.
errors.invalid={0} is invalid.
The parameter in place of {0} and {1} is inserted automatically by the framework when the rules fail. These values are corresponding to the parameters comes from the Validator-rules.xml and validation.xml files.
JSP Custom Tags
Like errors and javascript Struts HTML tags required in case of validations. The former is for server-side validation while the latter is for client side validation.
Validator Form Class
In Struts data is passed from the JSP page (view layer) to Action class (controller layer) by means of ActionForm objects. The standard Struts ActionForm won't suffice to impose validation framework.The specially designed classes for this purpose come quite handy. It comes in two varieties- ValidatorForm and DynaValidatorForm. The former is used in place of ActionForm while the latter is used with the DynaActionForm. Whatever the variety being used, two methods used forperforming validation which are present in both of them are- reset() and validate().
Integrating validator to Struts is done by introducing the following piece of data inside strust-config.xml:
The Validator framework is easily extensible and the effort required is minimal.
-Create your own validation classes.
-Hook it up inside validation-rules.xml file
Apart from using in Struts application,the Validator framework can be used as a separate unit for validation of applications.
How to handle duplicate submits in Struts?
The duplicate form submission occurs
-When a user clicks the Submit button more than once before the response is sent back or
- When a client accesses a view by returning to a previously bookmarked page.
It may result in inconsistent transactions and must be avoided.In Struts this problem can be handled by using the saveToken() and isTokenValid() methods of Action class.saveToken() method creates a token (a unique string) and saves that in the user's current session, while isTokenValid() checks if the token stored in the user's current session is the same as that was passed as the request parameter.
It can be done by loading JSP through an Action and before loading the JSP call saveToken() to save the token in the user session. When the form is submitted, check the token against that in the session by calling isTokenValid().
public ActionForward submitOrder(ActionMapping mapping,
ActionForm form,
HttpServletRequest request,
HttpServletResponse response) throws Exception
{
try
{
// check the token. Proceed only if token is valid
if(isTokenValid(request,true)) {
//implement order submit functionality here
} else {
return mapping.findForward("failure");
}
}
catch(Exception ex){//exception}
}
What is DispatchAction?
org.apache.struts.actions.DispatchAction is responsible for
-Dispatches to a public method named on a request parameter
-Method name corresponds to the 'parameter' property of corresponding ActionMapping
-useful when multiple similar actions are to be clubbed within a singe Action class in order to simplify the design.
If you want to to insert,update and delete all actions on a database from a JSP with the same Action class in such case it will come quite handy.
Here is how this JSP looks like:
<html:form action="/saveSubscription">
<html:submit>
<bean:message key="insert"/>
</html:submit>
<html:submit>
<bean:message key="update"/>
</html:submit>
<html:submit>
<bean:message key="delete"/>
</html:submit>
</html:form>
To configure the use of this action in your struts-config.xml file, create an entry like this:
<action path="/saveSubscription" name="subscriptionForm" scope="request" input="/subscription.jsp" parameter="submit"/>
It will use the value of the request parameter named "submit" to pick the appropriate "execute" method, which must have the same signature (other than method name) of the standard Action.execute method. For example, you might have the following three methods in the same action:
* public ActionForward delete(ActionMapping mapping, ActionForm form, HttpServletRequest request, HttpServletResponse response) throws Exception
* public ActionForward insert(ActionMapping mapping, ActionForm form, HttpServletRequest request, HttpServletResponse response) throws Exception
* public ActionForward update(ActionMapping mapping, ActionForm form, HttpServletRequest request, HttpServletResponse response) throws Exception
In our JSP, we can refer to the buttons in the usual way.Later, when the user selects a button, the form will pass the submit parameter, along with whatever message is Struts finds for "insert" or "delete" in the resource bundle.
Using the conventional DispatchAction, this approach would be problematic, not necessarily each message will map to a valid Java identifier. This is where the magic of the LookupDispatchAction comes into play.
When you create your LookupDispatchAction subclass, along with the methods for the dispatch operations you must also implement a getKeyMethodMap method. This is a "hotspot" that the LookupDispatchAction will call.
Here's an example of the methods you might declare in your subclass:
protected Map getKeyMethodMap(ActionMapping mapping,
ActionForm form,
HttpServletRequest request) {
Map map = new HashMap();
map.put("button.add", "add");
map.put("button.delete", "delete");
return map;
}
Internally, the base action will lookup the messages for 'insert' and 'delete', and match those against the submit parameter. When it finds a match, it will then use either "insert" or "delete" to call the corresponding methods.
So while the LookupDispatchAction means adding an extra method to your Action, it lets you skip putting a JavaScript in your form.
Both the DispatchAction and LookupDispatchAction are an excellent way to streamline your Struts action classes, and group several related operations into a single umbrella action. So, how many dispatch actions do you need? Can you use a dispatch action to collect everything into a single action?
In practice, you can easily use one dispatch action for any forms that share a common validation. It is not advisable to have sharing of dispatch action between different form beans, or form beans that are validated differently,as it can start to make things harder rather than simpler. But the use of a dispatch action can easily half or quarter the number of action classes in most Struts application.