JSP Interview Questions

What are implicit objects? List them?

Certain objects that are available for the use in JSP documents without being declared first. These objects are parsed by the JSP engine and inserted into the generated servlet. The implicit objects re listed below

• request
• response
• pageContext
• session
• application
• out
• config
• page
• exception

Difference between forward and sendRedirect?

When you invoke a forward request, the request is sent to another resource on the server, without the client being informed that a different resource is going to process the request. This process occurs completly with in the web container.

When a sendRedirtect method is invoked, it causes the web container to return to the browser indicating that a new URL should be requested. Because the browser issues a completly new request any object that are stored as request attributes before the redirect occurs will be lost. This extra round trip a redirect is slower than forward.

Explain the life-cycle mehtods in JSP?

The JspPage interface declares only two mehtods - jspInit() and jspDestroy() that must be implemented by all JSP pages regardless of the client-server protocol. However the JSP specification has provided the HttpJspPage interfaec specifically for the JSp pages serving HTTP requests.

This interface declares one method _jspService().
The jspInit()- The container calls the jspInit() to initialize te servlet instance.It is called before any other method, and is called only once for a servlet instance.

The _jspservice()- The container calls the _jspservice() for each request, passing it the request and the response objects.
The jspDestroy()- The container calls this when it decides take the instance out of service. It is the last method called n the servlet instance.

What are the different scope valiues for the ?

The different scope values for are

1. page
2. request
3.session
4.application

What is a Expression?

An expression tag contains a scripting language expression that is evaluated, converted to a String, and inserted where the expression appears in the JSP file. Because the value of an expression is converted to a String, you can use an expression within text in a JSP file.

Like
<%= someexpression %>
<%= (new java.util.Date()).toLocaleString() %>
You cannot use a semicolon to end an expression

What is a Declaration?

A declaration declares one or more variables or methods for use later in the JSP source file.

A declaration must contain at least one complete declarative statement. You can declare any number of variables or methods within one declaration tag, as long as they are separated by semicolons. The declaration must be valid in the scripting language used in the JSP file.

<%! somedeclarations %>
<%! int i = 0; %>
<%! int a, b, c; %>

How can I implement a thread-safe JSP page?

You can make your JSPs thread-safe by having them implement the SingleThreadModel interface.

This is done by adding the directive <%@ page isThreadSafe="false" %>within your JSP page. With this, instead of a single instance of the servlet generated for your JSP page loaded in memory, you will have N instances of the servlet loaded and initialized, with the service method of each instance effectively synchronized.

What's a better approach for enabling thread-safe servlets and JSPs?

The SingleThreadModel technique is easy to use, and works well for low volume sites, it does not scale well. If you anticipate your users to increase in the future, you may be better off implementing explicit synchronization for your shared data. The key however, is to effectively minimize the amount of code that is synchronzied so that you take maximum advantage of multithreading.

What is the difference between jsp and servlet life cycles?

Servlet's life cycle start with the following steps.
servlet's object is created
servlets init() method is there where the servlet is initialized it needs arguments Servlet Config's object
Servlets service() method where all work is done then
Servlet's destroy() method that's the end of servlet.

where as in jsp's life cycle first .jsp is converted to .class that is servlet and then follow the same step's of servlet...that means after jsp in translated to servlet it behave in the same way as servlet.

What is the different between _jspInit() and jspInit()?

when a JSP page transalated into a Servlet then jspInit() method is converted to _jspInit(). We can override _jspInit() and _jspDestry() but we can't override _jspService() method.

What is a output comment?
A comment that is sent to the client in the viewable page source.The JSP engine handles an output comment as uninterpreted HTML text, returning the comment in the HTML output sent to the client. You can see the comment by viewing the page source from your Web browser.

What is a Hidden Comment?
A comments that documents the JSP page but is not sent to the client. The JSP engine ignores a hidden comment, and does not process any code within hidden comment tags.

A hidden comment is not sent to the client, either in the displayed JSP page or the HTML page source. The hidden comment is useful when you want to hide or "comment out" part of your JSP page.

What is a Expression?

An expression tag contains a scripting language expression that is evaluated, converted to a String, and inserted where the expression appears in the JSP file. Because the value of an expression is converted to a String, you can use an expression within text in a JSP file.

What is a Declaration?

A declaration declares one or more variables or methods for use later in the JSP source file.
A declaration must contain at least one complete declarative statement. You can declare any number of variables or methods within one declaration tag, as long as they are separated by semicolons. The declaration must be valid in the scripting language used in the JSP file.

How does JSP handle run-time exceptions?

You can use the errorPage attribute of the page directive to have uncaught run-time exceptions automatically forwarded to an error processing page.

How do I use a scriptlet to initialize a newly instantiated bean?
A jsp:useBean action may optionally have a body. If the body is specified, its contents will be automatically invoked when the specified bean is instantiated. Typically, the body will contain scriptlets or jsp:setProperty tags to initialize the newly instantiated bean, although you are not restricted to using those alone.

What's a better approach for enabling thread-safe servlets and JSPs? SingleThreadModel Interface or Synchronization?
Although the SingleThreadModel technique is easy to use, and works well for low volume sites, it does not scale well. If you anticipate your users to increase in the future, you may be better off implementing explicit synchronization for your shared data. The key however, is to effectively minimize the amount of code that is synchronzied so that you take maximum advantage of multithreading.
Also, note that SingleThreadModel is pretty resource intensive from the server\'s perspective. The most serious issue however is when the number of concurrent requests exhaust the servlet instance pool. In that case, all the unserviced requests are queued until something becomes free which results in poor performance. Since the usage is non-deterministic, it may not help much even if you did add more memory and increased the size of the instance pool.

What is the difference b/w variable declared inside a declaration part and variable declared in scriplet part?
Variable declared inside declaration part is treated as a global variable.that means after convertion jsp file into servlet that variable will be in outside of service method or it will be declared as instance variable.And the scope is available to complete jsp and to complete in the converted servlet class.where as if u declare a variable inside a scriplet that variable will be declared inside a service method and the scope is with in the service method.

What are the lifecycle of JSP?
A When presented with JSP page the JSP engine does the following 7 phases.

• Page translation: -page is parsed, and a java file which is a servlet is created.
• Page compilation: page is compiled into a class file.
• Page loading : This class file is loaded.
• Create an instance :- Instance of servlet is created
• jspInit() method is called
• _jspService is called to handle service calls
• _jspDestroy is called to destroy it when the servlet is not required.

What is the difference between JSP and Servlets ?
A JSP is used mainly for presentation only. A JSP can only be HttpServlet that means the only supported protocol in JSP is HTTP. But a servlet can Support any protocol like HTTP, FTP,SMTP etc.

What is difference between custom JSP tags and beans?
A Custom JSP tag is a tag you defined. You define how a tag, its attributes and its body are interpreted, and then group your tags into collections called tag libraries that can be used in any number of JSP files. To use custom JSP tags, you need to define three separate components: the tag handler class that defines the tag's behavior ,the tag library descriptor file that maps the XML element names to the tag implementations and the JSP file that uses the tag library JavaBeans are Java utility classes you defined.

Beans have a standard format for Java classes. You use tags Custom tags and beans accomplish the same goals -- encapsulating complex behavior into simple and accessible forms. There are several differences:Custom tags can manipulate JSP content; beans cannot. Complex operations can be reduced to a significantly simpler form with custom tags than with beans. Custom tags require quite a bit more work to set up than do beans.

Custom tags usually define relatively self-contained behavior, whereas beans are often defined in one servlet and used in a different servlet or JSP page. Custom tags are available only in JSP 1.1 and later, but beans can be used in all JSP 1.x versions.

How many JSP Scripting elements are there and what are they?
A There are three scripting language elements: declarations, scriptlets, expressions.

How do I include static files within a JSP page?
A Static resources should always be included using the JSP include directive. This way, the inclusion is performed just once during the translation phase.

What is difference between custom JSP tags and beans?
Custom JSP tag is a tag you defined. You define how a tag, its attributes and its body are interpreted, and then group your tags into collections called tag libraries that can be used in any number of JSP files. Custom tags and beans accomplish the same goals – encapsulating complex behavior into simple and accessible forms. There are several differences:

• Custom tags can manipulate JSP content; beans cannot.
• Complex operations can be reduced to a significantly simpler form with custom tags than with beans.
• Custom tags require quite a bit more work to set up than do beans.
• Custom tags usually define relatively self-contained behavior, whereas beans are often defined in one servlet and used in a different servlet or JSP page.
• Custom tags are available only in JSP 1.1 and later, but beans can be used in all JSP 1.x versions.

What is JSP technology?
Java Server Page is a standard Java extension that is defined on top of the servlet Extensions. The goal of JSP is the simplified creation and management of dynamic Web pages. JSPs are secure, platform-independent, and best of all, make use of Java as a server-side scripting language.

What is JSP page?
A JSP page is a text-based document that contains two types of text: static template data, which can be expressed in any text-based format such as HTML, SVG, WML, and XML, and JSP elements, which construct dynamic content.

Why are JSP pages the preferred API for creating a web-based client program?
Because no plug-ins or security policy files are needed on the client systems(applet does). Also, JSP pages enable cleaner and more module application design because they provide a way to separate applications programming from web page design. This means personnel involved in web page design do not need to understand Java programming language syntax to do their jobs.

Is JSP technology extensible?
YES. JSP technology is extensible through the development of custom actions, or tags, which are encapsulated in tag libraries.
Can we use the constructor, instead of init(), to initialize servlet?
Yes , of course you can use the constructor instead of init(). There’s nothing to stop you. But you shouldn’t. The original reason for init() was that ancient versions of Java couldn’t dynamically invoke constructors with arguments, so there was no way to give the constructur a ServletConfig.

That no longer applies, but servlet containers still will only call your no-arg constructor. So you won’t have access to a ServletConfig or ServletContext.
How can a servlet refresh automatically if some new data has entered the database?
You can use a client-side Refresh or Server Push.

The code in a finally clause will never fail to execute, right?
Using System.exit(1); in try block will not allow finally code to execute.
How many messaging models do JMS provide for and what are they?
JMS provide for two messaging models, publish-and-subscribe and point-to-point queuing.
What information is needed to create a TCP Socket?
The Local Systems IP Address and Port Number. And the Remote System’s IPAddress and Port Number.
What Class.forName will do while loading drivers?
It is used to create an instance of a driver and register it with the DriverManager. When you have loaded a driver, it is available for making a connection with a DBMS.
How to Retrieve Warnings?
SQLWarning objects are a subclass of SQLException that deal with database access warnings. Warnings do not stop the execution of an application, as exceptions do; they simply alert the user that something did not happen as planned. A warning can be reported on a Connection object, a Statement object (including PreparedStatement and CallableStatement objects), or a ResultSet object. Each of these classes has a getWarnings method, which you must invoke in order to see the first warning reported on the calling object
SQLWarning warning = stmt.getWarnings();

if (warning != null) {

while (warning != null)

{ System.out.println("Message: " + warning.getMessage());

System.out.println("SQLState: " + warning.getSQLState());

System.out.print("Vendor error code: ");

System.out.println(warning.getErrorCode());

warning = warning.getNextWarning();

} }

How many JSP scripting elements are there and what are they?
There are three scripting language elements: declarations, scriptlets, expressions.
In the Servlet 2.4 specification SingleThreadModel has been deprecated, why?
Because it is not practical to have such model. Whether you set isThreadSafe to true or false, you should take care of concurrent client requests to the JSP page by synchronizing access to any shared objects defined at the page level.

What are stored procedures? How is it useful?
A stored procedure is a set of statements/commands which reside in the database. The stored procedure is pre-compiled and saves the database the effort of parsing and compiling sql statements everytime a query is run. Each database has its own stored procedure language, usually a variant of C with a SQL preproceesor. Newer versions of db’s support writing stored procedures in Java and Perl too.
Before the advent of 3-tier/n-tier architecture it was pretty common for stored procs to implement the business logic( A lot of systems still do it). The biggest advantage is of course speed. Also certain kind of data manipulations are not achieved in SQL. Stored procs provide a mechanism to do these manipulations. Stored procs are also useful when you want to do Batch updates/exports/houseKeeping kind of stuff on the db. The overhead of a JDBC Connection may be significant in these cases.
How do I include static files within a JSP page?
Static resources should always be included using the JSP include directive. This way, the inclusion is performed just once during the translation phase. Do note that you should always supply a relative URL for the file attribute.

Although you can also include static resources using the action, this is not advisable as the inclusion is then performed for each and every request.
Why does JComponent have add() and remove() methods but Component does not?
because JComponent is a subclass of Container, and can contain other components and jcomponents.

How can I implement a thread-safe JSP page?

You can make your JSPs thread-safe by having them implement the SingleThreadModel interface.

How can I enable session tracking for JSP pages if the browser has disabled cookies?
We know that session tracking uses cookies by default to associate a session identifier with a unique user. If the browser does not support cookies, or if cookies are disabled, you can still enable session tracking using URL rewriting. URL rewriting essentially includes the session ID within the link itself as a name/value pair.However, for this to be effective, you need to append the session ID for each and every link that is part of your servlet response.

Adding the session ID to a link is greatly simplified by means of of a couple of methods: response.encodeURL() associates a session ID with a given URL, and if you are using redirection, response.encodeRedirectURL() can be used by giving the redirected URL as input.

Both encodeURL() and encodeRedirectedURL() first determine whether cookies are supported by the browser; if so, the input URL is returned unchanged since the session ID will be persisted as a cookie. Consider the following example, in which two JSP files, say hello1.jsp and hello2.jsp, interact with each other.