国外的一些struts面试题（3）

Question: Why cant we overide create method in StatelessSessionBean?
Answer:  From the EJB Spec : - A Session bean's home interface defines one or morecreate(…) methods. Each create method must be named create and must match one of the ejbCreate methods defined in the enterprise Bean class. The return type of a create method must be the enterprise Bean's remote interface type. The home interface of a stateless session bean must have one create method that takes no arguments.
Question: Is struts threadsafe?Give an example?
Answer:  Struts is not only thread-safe but thread-dependant. The response to a request is handled by a light-weight Action object, rather than an individual servlet. Struts instantiates each Action class once, and allows other requests to be threaded through the original object. This core strategy conserves resources and provides the best possible throughput. A properly-designed application will exploit this further by routing related operations through a single Action.
Question: Can we Serialize static variable?
Answer:  Serialization is the process of converting a set of object instances that contain references to each other into a linear stream of bytes, which can then be sent through a socket, stored to a file, or simply manipulated as a stream of data. Serialization is the mechanism used by RMI to pass objects between JVMs, either as arguments in a method invocation from a client to a server or as return values from a method invocation. In the first section of this book, There are three exceptions in which serialization doesnot necessarily read and write to the stream. These are
1. Serialization ignores static fields, because they are not part of any particular object's state.
2. Base class fields are only handled if the base class itself is serializable.
3. Transient fields. There are four basic things you must do when you are making a class serializable. They are:
1. Implement the Serializable interface.
2. Make sure that instance-level, locally defined state is serialized properly.
3. Make sure that superclass state is serialized properly.
4. Override equals( )and hashCode( ).
it is possible to have control over serialization process. The class should implement Externalizable interface. This interface contains two methods namely readExternal and writeExternal. You should implement these methods and write the logic for customizing the serialization process …. (Source: http://www.oreilly.com/catalog/javarmi/chapter/ch10.html)
Question: What are the uses of tiles-def.xml file, resourcebundle.properties file, validation.xml file?
Answer:  tiles-def.xml is is an xml file used to configure tiles with the struts application. You can define the layout / header / footer / body content for your View. See more at http://www.roseindia.net/struts/using-tiles-defs-xml.shtml.
The resourcebundle.properties file is used to configure the message (error/ other messages) for the struts applications.
The file validation.xml is used to declare sets of validations that should be applied to Form Beans. Fpr more information please visit http://www.roseindia.net/struts/address_struts_validator.shtml.
Question: What is the difference between perform() and execute() methods?
Answer:  Perform method is the method which was deprecated in the Struts Version 1.1.  In Struts 1.x, Action.perform() is the method called by the ActionServlet. This is typically where your business logic resides, or at least the flow control to your JavaBeans and EJBs that handle your business logic. As we already mentioned, to support declarative exception handling, the method signature changed in perform. Now execute just throws Exception. Action.perform() is now deprecated; however, the Struts v1.1 ActionServlet is smart enough to know whether or not it should call perform or execute in the Action, depending on which one is available.
Question: What are the various Struts tag libraries?
Answer:  Struts is very rich framework and it provides very good and user friendly way to develop web application forms. Struts provide many tag libraries to ease the development of web applications. These tag libraries are:
* Bean tag library - Tags for accessing JavaBeans and their properties.
* HTML tag library - Tags to output standard HTML, including forms, text boxes, checkboxes, radio buttons etc..
* Logic tag library - Tags for generating conditional output, iteration capabilities and flow management
* Tiles or Template tag library - For the application using tiles
* Nested tag library - For using the nested beans in the application
Question: What do you understand by DispatchAction?
Answer:  DispatchAction is an action that comes with Struts 1.1 or later, that lets you combine Struts actions into one class, each with their own method. The org.apache.struts.action.DispatchAction class allows multiple operation to mapped to the different functions in the same Action class.
For example:
A package might include separate RegCreate, RegSave, and RegDelete Actions, which just perform different operations on the same RegBean object. Since all of these operations are usually handled by the same JSP page, it would be handy to also have them handled by the same Struts Action.
A very simple way to do this is to have the submit button modify a field in the form which indicates which operation to perform.
<html:hidden property=”dispatch” value=”error”/>
<SCRIPT>function set(target) {document.forms[0].dispatch.value=target;}</SCRIPT>
<html:submit onclick=”set('save');”>SAVE</html:submit>
<html:submit onclick=”set('create');”>SAVE AS NEW</html:submitl>
<html:submit onclick=”set('delete);”>DELETE</html:submit>
Then, in the Action you can setup different methods to handle the different operations, and branch to one or the other depending on which value is passed in the dispatch field.
String dispatch = myForm.getDispatch();
if (”create”.equals(dispatch)) { …
if (”save”.equals(dispatch)) { …
The Struts Dispatch Action [org.apache.struts.actions] is designed to do exactly the same thing, but without messy branching logic. The base perform method will check a dispatch field for you, and invoke the indicated method. The only catch is that the dispatch methods must use the same signature as perform. This is a very modest requirement, since in practice you usually end up doing that anyway.
To convert an Action that was switching on a dispatch field to a DispatchAction, you simply need to create methods like this
public ActionForward create(
ActionMapping mapping,
ActionForm form,
HttpServletRequest request,
HttpServletResponse response)
throws IOException, ServletException { …
public ActionForward save(
ActionMapping mapping,
ActionForm form,
HttpServletRequest request,
HttpServletResponse response)
throws IOException, ServletException { …
Cool. But do you have to use a property named dispatch? No, you don't. The only other step is to specify the name of of the dispatch property as the “parameter” property of the action-mapping. So a mapping for our example might look like this:
<action
path=”/reg/dispatch”
type=”app.reg.RegDispatch”
name=”regForm”
scope=”request”
validate=”true”
parameter=”dispatch”/>
If you wanted to use the property “o” instead, as in o=create, you would change the mapping to
<action
path=”/reg/dispatch”
type=”app.reg.RegDispatch”
name=”regForm”
scope=”request”
validate=”true”
parameter=”o”/>
Again, very cool. But why use a JavaScript button in the first place? Why not use several buttons named “dispatch” and use a different value for each?
You can, but the value of the button is also its label. This means if the page designers want to label the button something different, they have to coordinate the Action programmer. Localization becomes virtually impossible. (Source: http://husted.com/struts/tips/002.html).
Question: How Struts relates to J2EE?
Answer: Struts framework  is built on J2EE technologies (JSP, Servlet, Taglibs), but it is itself not part of the J2EE standard.
Question: What is Struts actions and action mappings?
Answer: A Struts action is an instance of a subclass of an Action class, which implements a portion of a Web application and whose perform or execute method returns a forward.
An action can perform tasks such as validating a user name and password.
An action mapping is a configuration file entry that, in general, associates an action name with an action. An action mapping can contain a reference to a form bean that the action can use, and can additionally define a list of local forwards that is visible only to this action.
An action servlet is a servlet that is started by the servlet container of a Web server to process a request that invokes an action. The servlet receives a forward from the action and asks the servlet container to pass the request to the forward's URL. An action servlet must be an instance of an org.apache.struts.action.ActionServlet class or of a subclass of that class. An action servlet is the primary component of the controller.