Java Interview Questions and Answers
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What is BDK?-
BDK, Bean Development Kit is a tool that enables to create,
configure and connect a set of set of Beans and it can be used to test Beans
without writing a code.
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What is JSP?-
JSP is a dynamic scripting capability for web pages that allows Java as well as
a few special tags to be embedded into a web file (HTML/XML, etc). The suffix
traditionally ends with .jsp to indicate to the web server that the file is a
JSP files. JSP is a server side technology - you can’t do any client side
validation with it. The advantages are: a) The JSP assists in making the HTML
more functional. Servlets on the other hand allow outputting of HTML but it is
a tedious process. b) It is easy to make a change and then let the JSP
capability of the web server you are using deal with compiling it into a
servlet and running it.
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What are JSP scripting
elements?-
JSP scripting elements lets to insert Java code into the servlet that will be
generated from the current JSP page. There are three forms: a) Expressions of
the form <%= expression %> that are evaluated and inserted into the
output, b) Scriptlets of the form<% code %>that are inserted into the
servlet’s service method, and c) Declarations of the form <%! Code %>that
are inserted into the body of the servlet class, outside of any existing
methods.
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What are JSP Directives?-
A JSP directive affects the overall structure of the servlet class. It usually
has the following form:<%@ directive attribute=”value” %> However, you
can also combine multiple attribute settings for a single directive, as
follows:<%@ directive attribute1=”value1? attribute 2=”value2? . . .
attributeN =”valueN” %> There are two main types of directive: page, which
lets to do things like import classes, customize the servlet superclass, and
the like; and include, which lets to insert a file into the servlet class at
the time the JSP file is translated into a servlet
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What are Predefined
variables or implicit objects?-
To simplify code in JSP expressions and scriptlets, we can use eight
automatically defined variables, sometimes called implicit objects. They are
request, response, out, session, application, config, pageContext, and page.
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What are JSP ACTIONS?-
JSP actions use constructs in XML syntax to control the behavior of the servlet
engine. You can dynamically insert a file, reuse JavaBeans components, forward
the user to another page, or generate HTML for the Java plugin. Available
actions include: jsp:include - Include a file at the time the page is
requested. jsp:useBean - Find or instantiate a JavaBean. jsp:setProperty - Set
the property of a JavaBean. jsp:getProperty - Insert the property of a JavaBean
into the output. jsp:forward - Forward the requester to a newpage. Jsp: plugin
- Generate browser-specific code that makes an OBJECT or EMBED
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How do you pass data
(including JavaBeans) to a JSP from a servlet?-
(1) Request Lifetime: Using this technique to pass beans, a request dispatcher
(using either “include” or forward”) can be called. This bean will disappear
after processing this request has been completed. Servlet: request.
setAttribute(”theBean”, myBean); RequestDispatcher rd = getServletContext().
getRequestDispatcher(”thepage. jsp”); rd. forward(request, response); JSP
PAGE:<jsp: useBean id=”theBean” scope=”request” class=”. . . . . ” />(2)
Session Lifetime: Using this technique to pass beans that are relevant to a
particular session (such as in individual user login) over a number of
requests. This bean will disappear when the session is invalidated or it times
out, or when you remove it. Servlet: HttpSession session = request.
getSession(true); session. putValue(”theBean”, myBean); /* You can do a request
dispatcher here, or just let the bean be visible on the next request */ JSP
Page:<jsp:useBean id=”theBean” scope=”session” class=”. . . ” /> 3)
Application Lifetime: Using this technique to pass beans that are relevant to
all servlets and JSP pages in a particular app, for all users. For example, I
use this to make a JDBC connection pool object available to the various
servlets and JSP pages in my apps. This bean will disappear when the servlet
engine is shut down, or when you remove it. Servlet: GetServletContext().
setAttribute(”theBean”, myBean); JSP PAGE:<jsp:useBean id=”theBean”
scope=”application” class=”. . . ” />
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How can I set a cookie
in JSP?-
response. setHeader(”Set-Cookie”, “cookie string”); To give the response-object
to a bean, write a method setResponse (HttpServletResponse response) - to the
bean, and in jsp-file:<% bean. setResponse (response); %>
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How can I delete a
cookie with JSP?-
Say that I have a cookie called “foo, ” that I set a while ago & I want it
to go away. I simply: <% Cookie killCookie = new Cookie(”foo”, null);
KillCookie. setPath(”/”); killCookie. setMaxAge(0); response.
addCookie(killCookie); %>
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How are Servlets and JSP
Pages related?-
JSP pages are focused around HTML (or XML) with Java codes and JSP tags inside
them. When a web server that has JSP support is asked for a JSP page, it checks
to see if it has already compiled the page into a servlet. Thus, JSP pages
become servlets and are transformed into pure Java and then compiled, loaded
into the server and executed.
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