We can use the java.net.URLConnection and java.net.URL classes to open a standard HTTP connection and "tunnel" to the web server. The server then passes this information to the servlet in the normal way. Basically, the applet pretends to be a web browser, and the servlet doesn't know the difference. As far as the servlet is concerned, the applet is just another HTTP client.
What Is An Applet? Should Applets Have Constructors?
Applets are small programs transferred through Internet, automatically installed and run as part of web-browser. Applets implements functionality of a client. Applet is a dynamic and interactive program that runs inside a Web page displayed by a Java-capable browser. We dont have the concept of Constructors in Applets. Applets can be invoked either through browser or through Appletviewer utility provided by JDK.
How Will You Initialize An Applet?
Write my initialization code in the applets init method or applet constructor.
How To Insert Your Applets Into Frontpage?
1. Place the .class file in the directory containing the HTML document into which you want to insert the applet.
2. Copy the <applet>...</applet> tag from your applet implementation or examples to the clipboard.
3. In FrontPage select the "HTML" tab from the lower left hand corner.
4. Paste the <applet>...</applet> tag in an appropriate place between the <body> and </body> tags. You'll find a gray box with the aqua letter "J" in the "Normal" view indicating the the applet tag has been inserted.
5. To see the applet appearance select the "Preview" tab.
In Our Urls And In The Text Of The Buttons We Have Comma. Its Causing An Error. Is There A Way To Change The Delimiting Character For The Menu Arguments?
Since 2.00 version our applets support an user-defined delimiter for the menu arguments. To modify the default delimiter add the following parameter (you can use any character as a delimiter)
<param name="delimiter" value="~">
and use it within "menuItems"
<param name="menuItems" value="
{Home~http://www.wisdomjobs.com.com/index.php}
{Features,Setup~http://www.wisdomjobs.com/}
">
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| Kofax Most Frequently Asked Latest Advanced Java Interview Questions Answers |
What Is The Order Of Method Invocation In An Applet?
- public void init() : Initialization method called once by browser.
- public void start() : Method called after init() and contains code to start processing. If the user leaves the page and returns without killing the current browser session, the start () method is called without being preceded by init ().
- public void stop() : Stops all processing started by start (). Done if user moves off page.
- public void destroy() : Called if current browser session is being terminated. Frees all resources used by applet.
methods in the life cycle of an Applet
- init() method - called when an applet is first loaded. This method is called only once in the entire cycle of an applet. This method usually intialize the variables to be used in the applet.
- start( ) method - called each time an applet is started.
- paint() method - called when the applet is minimized or refreshed. This method is used for drawing different strings, figures, and images on the applet window.
- stop( ) method - called when the browser moves off the applets page.
- destroy( ) method - called when the browser is finished with the applet.
When an applet begins, the AWT calls the following methods, in this sequence
init()
start()
paint()
When an applet is terminated, the following sequence of method calls takes place
stop()
destroy()
How Do Applets Differ From Applications?
Following are the main differences
Application: Stand Alone, doesnt need web-browser.
Applet: Needs no explicit installation on local machine. Can be transferred through Internet on to the local machine and may run as part of web-browser.
Application: Execution starts with main() method. Doesnt work if main is not there.
Applet: Execution starts with init() method.
Application: May or may not be a GUI.
Applet: Must run within a GUI (Using AWT). This is essential feature of applets.
Can We Pass Parameters To An Applet From Html Page To An Applet? How?
We can pass parameters to an applet using <param> tag in the following way
<param name=param1″ value=value1″>
<param name=param2″ valuevalue2″>
Access those parameters inside the applet is done by calling getParameter() method inside the applet. Note that getParameter() method returns String value corresponding to the parameter name.
How Do We Read Number Information From My Applets Parameters, Given That Applets Getparameter() Method Returns A String?
Use the parseInt() method in the Integer Class, the Float(String) constructor or parseFloat() method in the Class Float, or the Double(String) constructor or parseDoulbl() method in the class Double.
How Can I Arrange For Different Applets On A Web Page To Communicate With Each Other?
Name your applets inside the Applet tag and invoke AppletContexts getApplet() method in your applet code to obtain references to the other applets on the page.
How Do I Select A Url From My Applet And Send The Browser To That Page?
Ask the applet for its applet context and invoke showDocument() on that context object.
URL targetURL;
String URLString
AppletContext context = getAppletContext();
try
{
targetURL = new URL(URLString);
}
catch (MalformedURLException e)
{
// Code for recover from the exception
}
context. showDocument (targetURL);
Can Applets On Different Pages Communicate With Each Other?
Use the getSize() method, which the Applet class inherits from the Component class in the Java.awt package. The getSize() method returns the size of the applet as a Dimension object, from which you extract separate width, height fields. The following code snippet explains this
Dimension dim = getSize();
int appletwidth = dim.width();
int appletheight = dim.height();
Which Classes And Interfaces Does Applet Class Consists?
Applet class consists of a single class, the Applet class and three interfaces: AppletContext, AppletStub, and AudioClip.
What Is Appletstub Interface?
The applet stub interface provides the means by which an applet and the browser communicate. Your code will not typically implement this interface.
What Are The Applets Information Methods?
The following are the Applets information methods: getAppletInfo() method: Returns a string describing the applet, its author, copyright information, etc. getParameterInfo() method: Returns an array of string describing the applets parameters.
What Are The Steps Involved In Applet Development?
Following are the steps involved in Applet development
- Create/Edit a Java source file. This file must contain a class which extends Applet class.
- Compile your program using javac
- Execute the appletviewer, specifying the name of your applets source file or html file. In case the applet information is stored in html file then Applet can be invoked using java enabled web browser.
Which Method Is Used To Output A String To An Applet? Which Function Is This Method Included In?
drawString( ) method is used to output a string to an applet. This method is included in the paint method of the Applet.
When Is Update Method Called?
Whenever a screen needs redrawing (e.g., upon creation, resizing, validating) the update method is called. By default, the update method clears the screen and then calls the paint method, which normally contains all the drawing code.
What Is A Message Driven Bean, What Functions Does A Message Driven Bean Have And How Do They Work In Collaboration With Jms?
Message driven beans are the latest addition to the family of component bean types defined by the EJB specification. The original bean types include session beans, which contain business logic and maintain a state associated with client sessions, and entity beans, which map objects to persistent data. Message driven beans will provide asynchrony to EJB based applications by acting as JMS message consumers. A message bean is associated with a JMS topic or queue and receives JMS messages sent by EJB clients or other beans. Unlike entity beans and session beans, message beans do not have home or remote interfaces. Instead, message driven beans are instantiated by the container as required. Like stateless session beans, message beans maintain no client-specific state, allowing the container to optimally manage a pool of message-bean instances. Clients send JMS messages to message beans in exactly the same manner as they would send messages to any other JMS destination. This similarity is a fundamental design goal of the JMS capabilities of the new specification. To receive JMS messages, message driven beans implement the javax.jms.MessageListener interface, which defines a single onMessage() method. When a message arrives, the container ensures that a message bean corresponding to the message topic/queue exists (instantiating it if necessary), and calls its onMessage method passing the client’s message as the single argument. The message bean’s implementation of this method contains the business logic required to process the message. Note that session beans and entity beans are not allowed to function as message beans.
How Does Concurrency Work For Message-driven Beans?
The way concurrency is achieved for Queues is by spawning one JMSSession per MDB instance in the pool. Since JMSSessions are processed in parallel by JMS, concurrency is obtained naturally this way and JMS takes care of delivering the message to, at most, one listener. If an MDB is deployed to multiple servers in a cluster, JMSSessions are created for each MDB instance on each server and load balancing will be done across them. For Topics in WebLogic JMS 6.1, there is one JMSSession per bean instance in the pool. Because of the way Topics work, the session, and thus every bean instance, receives a copy of each message published on that Topic. (There was also a problem that caused parallel processing not to work correctly. This has been fixed for WLS 6.0 Service Pack 1.) Within a single server, one topic consumer is used to pass out messages to multiple threads to get the concurrency while producing only a single copy of each message. You can configure multiple MDBs to listen on the same topic and each MDB will receive a copy of every message. When using multiple servers, each server gets its own consumer and therefore its own copy of each message. It is not currently possible to share a consumer across multiple servers. If you want a message to be processed by exactly one MDB, use a queue. One customer had an example where topic MDBs are needed in which there will be multiple implementations of the MDBs listening on the same topic. In other words, more than one MDB with a different implementation may be subscribing to the same topic. The client has no advanced way of knowing how many different kinds of MDBs may be listening on the same topic, but it is possible for there to be more than one listener, therefore topics, not queues. For each kind of MDB listening on the topic, the message is delivered exactly once (i.e., the message will be delivered exactly once to an instance in each named MDB pool listening on the topic).
What Is The Difference Between Message Driven Beans And Stateless Session Beans?
In several ways, the dynamic creation and allocation of message-driven bean instances mimics the behavior of stateless session EJB instances, which exist only for the duration of a particular method call. However, message-driven beans are different from stateless session EJBs (and other types of EJBs) in several significant ways: Message-driven beans process multiple JMS messages asynchronously, rather than processing a serialized sequence of method calls. Message-driven beans have no home or remote interface, and therefore cannot be directly accessed by internal or external clients. Clients interact with message-driven beans only indirectly, by sending a message to a JMS Queue or Topic.
Only the container directly interacts with a message-driven bean by creating bean instances and passing JMS messages to those instances as necessary. The Container maintains the entire lifecycle of a message-driven bean; instances cannot be created or removed as a result of client requests or other API calls.
Why Does The Option Tag Render Selected=selected Instead Of Just Selected?
Attribute minimization (that is, specifying an attribute with no value) is a place where HTML violates standard XML syntax rules. This matters a lot for people writing to browsers that support XHTML, where doing so makes the page invalid. It's much better for Struts to use the expanded syntax, which works the same on existing browsers interpreting HTML, and newer browsers that expect XHTML-compliant syntax. Struts is following the behavior recommended by the XHTML specification.
Do I Have To Use Jsps With My Application?
The short to this question is: No, you are not limited to JavaServer Pages.
The longer is that you can use any type of presentation technology which can be returned by a web server or Java container. The list includes but is not limited to
* JavaServer Pages,
* HTML pages,
* WML files,
* Java servlets,
* Velocity templates, and
* XML/XLST
Some people even mix and match apparently unrelated technologies, like PHP, into the same web application.
Can I Have An Action Without A Form?
Yes. If your Action does not need any data and it does not need to make any data available to the view or controller component that it forwards to, it doesn't need a form. A good example of an Action with no ActionForm is the LogoffAction in the struts example application
<action path="/logoff"
type="org.apache.struts.webapp.example.LogoffAction">
<forward name="success" path="/index.jsp"/>
</action>
This action needs no data other than the user's session, which it can get from the Request, and it doesn't need to prepare any view elements for display, so it does not need a form.
However, you cannot use the <html:form> tag without an ActionForm. Even if you want to use the <html:form> tag with a simple Action that does not require input, the tag will expect you to use some type of ActionForm, even if it is an empty subclass without any properties.
Can You Give Me A Simple Example Of Using The Requiredif Validator Rule?
First off, there's an even newer Validator rule called validwhen, which is almost certainly what you want to use, since it is much easier and more powerful. It will be available in the first release after 1.1 ships.
The example shown below could be coded with validwhen as
<form name="medicalStatusForm">
<field
property="pregnancyTest" depends="validwhen">
<arg0 key="medicalStatusForm.pregnancyTest.label"/>
<var>
<var-name>test</var-name>
<var-value>((((sex == 'm') OR (sex == 'M'))
AND (*this* == null)) OR (*this* != null))</test>
</var>
</field>
Let's assume you have a medical information form
with three fields,
sex, pregnancyTest, and testResult. If sex is 'f' or 'F',
pregnancyTest is required. If pregnancyTest is not blank,
testResult is required. The entry in your validation.xml
file would look like this
<form name="medicalStatusForm">
<field
property="pregnancyTest" depends="requiredif">
<arg0 key="medicalStatusForm.pregnancyTest.label"/>
<var>
<var-name>field[0]</var-name>
<var-value>sex</var-value>
</var>
<var>
<var-name>fieldTest[0]</var-name>
<var-value>EQUAL</var-value>
</var>
<var>
<var-name>fieldValue[0]</var-name>
<var-value>F</var-value>
</var>
<var>
<var-name>field[1]</var-name>
<var-value>sex</var-value>
</var>
<var>
<var-name>fieldTest[1]</var-name>
<var-value>EQUAL</var-value>
</var>
<var>
<var-name>fieldValue[1]</var-name>
<var-value>f</var-value>
</var>
<var>
<var-name>fieldJoin</var-name>
<var-value>OR</var-value>
</var>
</field>
<field
property="testResult" depends="requiredif">
<arg0 key="medicalStatusForm.testResult.label"/>
<var>
<var-name>field[0]</var-name>
<var-value>pregnancyTest</var-value>
</var>
<var>
<var-name>fieldTest[0]</var-name>
<var-value>NOTNULL</var-value>
</var>
</field>
</form>
When Is The Best Time To Validate Input?
This is an excellent question. Let's step back a second and think about a typical mid to large size application. If we start from the back end and work toward the view we have
1) Database: Most modern databases are going to validate for required fields, duplicate records, security constraints, etc.
2) Business Logic: Here you are going to check for valid data relationships and things that make sense for the particular problem you are triing to solve.
... This is where struts comes into the picture, by now the system should be pretty well bulletproof. What we are going to do is make validation friendlier and informative. Rember it is OK to have duplicate validations...
3) ActionErrors validate(ActionMapping map, HttpServletRequest req) is where you can do your validation and feed back to the view, information required to correct any errors. validate is run after the form has been reset and after the ActionForm properties have been set from corresponding view based input. Also remember you can turn validation off with validate="false" in the action mapping in the struts-config.xml. This is done by returning an ActionErrors collection with messages from your ApplicationResources.properties file.
Here you have access to the request so you can see what kinds of action is being requested to fine tune your validations. The <html:error> tag allows you to dump all errors on your page or a particular error associated with a particular property. The input attribute of the struts-config.xml action allows you to send validation errors to a particular jsp / html / tile page.
4) You can have the system perform low level validations and client side feedback using a ValidatorForm or its derivatives. This will generate javascript and give instant feedback to the user for simple data entry errors. You code your validations in the validator-rules.xml file. A working knowledge of regular expressions is necessary to use this feature effectively.
How Can I Avoid Validating A Form Before Data Is Entered?
The simplest way is to have two actions. The first one has the job of setting the form data, i.e. a blank registration screen. The second action in our writes the registration data to the database. Struts would take care of invoking the validation and returning the user to the correct screen if validation was not complete.
The EditRegistration action in the struts example application illustrates this
< action path="/editRegistration">
type="org.apache.struts.webapp.example.EditRegistrationAction"
attribute="registrationForm"
scope="request"
validate="false">
<forward name="success path="/registration.jsp"/>
</action>
When the /editRegistration action is invoked, a registrationForm is created and added to the request, but its validate method is not called. The default value of the validate attribute is true, so if you do not want an action to trigger form validation, you need to remember to add this attribute and set it to false.
Declarative Exception Handling
If you have developed web applications long enough, you will realize a recurring pattern emerges: when the backend (e.g. the EJB tier) throws you an exception, you nearly always need to display an error page corresponding to the type of that exception. Sooner or later, you will come up with a mechanism to use a lookup table (e.g. an HashMap) to lookup an error page from the exception class.
Struts 1.1 now provides a similar but more powerful mechanism to declare exception handling. In Struts 1.1, you can declare in the struts-config.xml the associations between an exception class and an exception handler. Using the default exception handler included in Struts, you can also specify the path of the error pages. With this information, Struts will automatically forward to the specified pages when an uncaught exception is thrown from an Action.
Like other facilities in Struts, the exception handlers are pluggable. You can write and define your own handler classes if needed.
What Is Hibernate?
Hibernate is a powerful, high performance object/relational persistence and query service.
This lets the users to develop persistent classes following object-oriented principles such as association, inheritance, polymorphism, composition, and collections.