Java Interview Questions n Answers - An interviewhelper.org blog

Do objects stored in a HTTP Session need to be serializable Or can it

2009-03-14T01:26:00.000-07:00

Question :Do objects stored in a HTTP Session need to be serializable? Or can it
store any object? (Servlets)

Answer :Yes, the objects need to be serializable, but only if your servlet container
supports persistent sessions. Most lightweight servlet engines (like
Tomcat) do not support this. However, many EJB-enabled servlet engines
do. Even if your engine does support persistent sessions, it is usually
possible to disable this feature.

What is URL Encoding and URL Decoding (Servlets)

2009-03-14T01:25:00.000-07:00

Question :What is URL Encoding and URL Decoding ? (Servlets)
Answer :URL encoding is the method of replacing all the spaces and other extra characters into their Characters and Decoding is the reverse process converting all Hex Characters back their normal For Example consider this URL, /ServletsDirectory/Hello'servlet/
When Encoded using URLEncoder.encode("/ServletsDirectory/Hello'servlet/") the output is
http%3A%2F%2Fwww.javacommerce.com%2FServlets+Directory%2FHello%27servlet%2FThis back using
URLDecoder.decode("http%3A%2F%2Fwww.javacommerce.com%2FServlets+Directory%2FHello%

Can I just abort processing a JSP (Servlets)

2009-03-14T01:23:00.000-07:00

Question :Can I just abort processing a JSP? (Servlets)
Answer :Yes. Because your JSP is just a servlet method, you can just put
(whereever necessary) a < % return; % >

Is it true that servlet containers service each request by creating a new

2009-03-14T01:21:00.000-07:00

Question :Is it true that servlet containers service each request by creating a new
thread? If that is true, how does a container handle a sudden dramatic
surge in incoming requests without significant performance
degradation? (Servlets)

Answer :The implementation depends on the Servlet engine. For each request
generally, a new Thread is created. But to give performance boost, most
containers, create and maintain a thread pool at the server startup time.
To service a request, they simply borrow a thread from the pool and when
they are done, return it to the pool.
For this thread pool, upper bound and lower bound is maintained. Upper
bound prevents the resource exhaustion problem associated with unlimited
thread allocation. The lower bound can instruct the pool not to keep too
many idle threads, freeing them if needed.

What do the differing levels of bean storage (page, session, app) mean (Servlets)

2009-03-14T00:59:00.000-07:00

Question :What do the differing levels of bean storage (page, session, app)
mean? (Servlets)
Answer :page life time - NO storage. This is the same as declaring the variable in
a scriptlet and using it from there.
session life time - request.getSession(true).putValue "myKey", myObj);
application level ?
getServletConfig().getServletContext().setAttribute("myKey ",myObj )
request level - The storage exists for the lifetime of the request, which
may be forwarded between jsp's and servlets

Is there some sort of event that happens when a session object gets

2009-03-14T00:56:00.000-07:00

Question :Is there some sort of event that happens when a session object gets
bound or unbound to the session? (Servlets)

Answer :HttpSessionBindingListener will hear the events When an object is added
and/or remove from the session object, or when the session is invalidated,
in which case the objects are first removed from the session, whether the
session is invalidated manually or automatically (timeout).

What?s the difference between sendRedirect( ) and forward( )

2009-03-14T00:55:00.000-07:00

Question :What?s the difference between sendRedirect( ) and forward( )
methods? (Servlets)

Answer :A sendRedirect method creates a new request (it?s also reflected in
browser?s URL ) where as forward method forwards the same request to
the new target(hence the chnge is NOT reflected in browser?s URL).
The previous request scope objects are no longer available after a redirect
because it results in a new request, but it?s available in forward.
SendRedirectis slower compared to forward.

How many cookies can one set in the response object of the servlet

2009-03-14T00:51:00.000-07:00

Question :How many cookies can one set in the response object of the servlet?
Also, are there any restrictions on the size of cookies? (Servlets)

Answer :If the client is using Netscape, the browser can receive and store 300
total cookies
4 kilobytes per cookie (including name)
20 cookies per server or domain

What is Server Side Push and how is it implemented and when is it

2009-03-14T00:47:00.000-07:00

Question :What is Server Side Push and how is it implemented and when is it
useful? (Servlets)

Answer :Server Side push is useful when data needs to change regularly on the
clients application or browser, without intervention from client. Standard
examples might include apps like Stock's Tracker, Current News etc. As
such server cannot connect to client's application automatically. The
mechanism used is, when client first connects to Server, (Either through
login etc..), then Server keeps the TCP/IP connection open.
It's not always possible or feasible to keep the connection to Server open.
So another method used is, to use the standard HTTP protocols ways of
refreshing the page, which is normally supported by all browsers.

This will refresh the page in the browser automatically and loads the new
data every 5 seconds.

What is HttpTunneling (Servlets)

2009-03-14T00:42:00.000-07:00

Question :What is HttpTunneling? (Servlets)
Answer :HTTP tunneling is used to encapsulate other protocols within the HTTP or
HTTPS protocols. Normally the intra-network of an organization is blocked
by a firewall and the network is exposed to the outer world only through a
specific web server port , that listens for only HTTP requests. To use any
other protocol, that by passes the firewall, the protocol is embedded in
HTTP and send as HttpRequest.

The code in a finally clause will never fail to execute, right (Servlets)

2009-03-14T00:40:00.000-07:00

Question :The code in a finally clause will never fail to execute, right ? (Servlets)
Answer :Using System.exit(1); in try block will not allow finally code to execute.

How can a servlet refresh automatically if some new data has entered the database (Servlets)

2009-03-14T00:38:00.000-07:00

Question :How can a servlet refresh automatically if some new data has entered the
database? (Servlets)
Answer :You can use a client-side Refresh or Server Push

Can we use the constructor, instead of init(), to initialize servlet (Servlets)

2009-03-14T00:37:00.000-07:00

Question :Can we use the constructor, instead of init(), to initialize servlet? (Servlets)
Answer :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 I send user authentication information while

2009-03-14T00:36:00.000-07:00

Question :How can I send user authentication information while
makingURLConnection? (Servlets)

Answer :You'll want to use HttpURLConnection.setRequestProperty and set all the
appropriate headers to HTTP authorization.

Request parameter How to find whether a parameter exists in the request object (Servlets)

2009-03-14T00:34:00.000-07:00

Question :Request parameter How to find whether a parameter exists in the request
object? (Servlets)

Answer :1.boolean hasFoo = !(request.getParameter("foo") == null ||
request.getParameter("foo").equals(""));
2. boolean hasParameter =
request.getParameterMap().contains(theParameter);
(which works in Servlet 2.3+)

Assume an application needs security permissions granted before the

2009-03-14T00:29:00.000-07:00

Question :Assume an application needs security permissions granted before the
application can talk to the database. How
do you go about setting the permissions? Give an example of setting the
permission in Tomcat and stand alone
java programme. (Security)

Answer :In Tomcat:
Add security permission to catalina.policy file located under
/conf/ Add the following lines
grant codeBase "file:${catalina.home}/webapps/MyContext/-"
{
permission java.security.AllPermission;
};
In stand alone java application:
Create a .policy file that points to the code base where the application
resides.
grant codebase "file:c:/source/java/-"
{
permission java.security.AllPermission;
};
java -Djava.security.policy=.policy com.test.MyClass

Can RMI and Corba based applications interact (RMI)

2009-03-14T00:27:00.000-07:00

Question :Can RMI and Corba based applications interact ? (RMI)
Answer :Yes they can. RMI is available with IIOP as the transport protocol instead
of JRMP.

Does RMI-IIOP support code downloading for Java objects sent by value

2009-03-14T00:25:00.000-07:00

Question :Does RMI-IIOP support code downloading for Java objects sent by value
across an IIOP connection in the same way as RMI does across a JRMP
connection? (RMI)

Answer :Yes. The JDK 1.2 support the dynamic class loading.

Does RMI-IIOP support dynamic downloading of classes (RMI)

2009-03-14T00:23:00.000-07:00

Question :Does RMI-IIOP support dynamic downloading of classes? (RMI)
Answer :No, RMI-IIOP doesn't support dynamic downloading of the classes as it is
done with CORBA in DII (Dynamic Interface Invocation).Actually RMI-IIOP
combines the usability of Java Remote Method Invocation (RMI) with the
interoperability of the Internet Inter-ORB Protocol (IIOP).So in order to
attain this interoperability between RMI and CORBA,some of the features
that are supported by RMI but not CORBA and vice versa are eliminated
from the RMI-IIOP specification.

How many types of protocol implementations does RMI have (RMI)

2009-03-14T00:21:00.000-07:00

Question :How many types of protocol implementations does RMI have? (RMI)
Answer :RMI has at least three protocol implementations: Java Remote Method
Protocol(JRMP), Internet Inter ORB Protocol(IIOP), and Jini Extensible
Remote Invocation(JERI). These are alternatives, not part of the same
thing, All three are indeed layer 6 protocols for those who are still speaking
OSI reference model.

Considering a=4 and b=10. Can you swap the values without using any

2009-03-14T00:18:00.000-07:00

Question :Considering a=4 and b=10. Can you swap the values without using any
temp variable? The final output should be a=10 and b=4. (Other)

Answer :a = a + b // 4 + 10 = 14
b = a - b // 14 - 10 = 4
a = a - b // 14 - 4 = 10
b = 4
a = 10

how to make default checkbox selecte(in struts) (Other)

2009-03-14T00:16:00.000-07:00

Question :how to make default checkbox selecte(in struts) (Other)
Answer :useing the set and get methods it can be done.

Write a query for getting the second maximum marks of students from

2009-03-14T00:15:00.000-07:00

Question :Write a query for getting the second maximum marks of students from
students table? (Other)

Answer :select max(marks) from students where marks <(select max(marks)
from students)

Considering a=4 and b=10. Can you swap the values without using any

2009-03-14T00:13:00.000-07:00

What are the two important TCP Socket classes (Networking)

2009-03-14T00:12:00.000-07:00

Question :What are the two important TCP Socket classes? (Networking)
Answer :Socket and ServerSocket. ServerSocket is used for normal two-way
socket communication. Socket class allows us to read and write through
the sockets. getInputStream() and getOutputStream() are the two
methods available in Socket class.

What is the difference between URL instance and URLConnection

2009-03-14T00:11:00.000-07:00

Question :What is the difference between URL instance and URLConnection
instance? (Networking)

Answer :A URL instance represents the location of a resource, and a
URLConnection instance represents a link for accessing or communicating
with the resource at the location.

What information is needed to create a TCP Socket (Networking)

2009-03-14T00:09:00.000-07:00

Question :What information is needed to create a TCP Socket? (Networking)
Answer :The Local System?s IP Address and Port Number. And the Remote
System's IPAddress and Port Number.

How do I convert a numeric IP address like 192.18.97.39 into a hostname

2009-03-14T00:08:00.000-07:00

Question :How do I convert a numeric IP address like 192.18.97.39 into a hostname
like java.sun.com? (Networking)

Answer :String hostname =
InetAddress.getByName("192.18.97.39").getHostName();

Why would a client application use JTA transactions (JTA)

2009-03-14T00:05:00.000-07:00

Question :Why would a client application use JTA transactions? (JTA)

Answer :One possible example would be a scenario in which a client needs to
employ two (or more) session beans, where each session bean is deployed
on a different EJB server and each bean performs operations against
external resources (for example, a database) and/or is managing one or
more entity beans. In this scenario, the client's logic could required an allor-
nothing guarantee for the operations performed by the session beans;
hence, the session bean usage could be bundled together with a JTA
UserTransaction object.
In the previous scenario, however, the client application developer should
address the question of whether or not it would be better to encapsulate
these operations in yet another session bean, and allow the session bean to
handle the transactions via the EJB container. In general, lightweight clients
are easier to maintain than heavyweight clients. Also, EJB environments are
ideally suited for transaction management.
...
Context c = new InitialContext(); UserTransaction ut =
(UserTransaction) c.lookup("java:comp/UserTransaction");
ut.begin(); // perform multiple operations...
ut.commit()
...

How can we access a Vector from one jsp page to another jsp page. You

2009-03-13T23:44:00.010-07:00

Question :How can we access a Vector from one jsp page to another jsp page.? You
also need to restrict a third jsp page from having access to this
Vector. (JSP)

Answer :If you use session.setAttribute("key","value"); then the object that is put
into the session is available till the session is timed out. In this case
if you need to restrict the vector in third jsp page, put it in request scope
e.g. request.setAttribute("key", "value"); By this way your object
is available till your request has been processed.

The following are the contents of test.jsp

2009-03-13T23:44:00.009-07:00

Question :The following are the contents of test.jsp

Welcome to my web page
This example demonstrates the output of test.jsp

<%! String name=request.getParameter(``name``); %>
Name is <%=name %>

If the user types http://localhost:8080/test.jsp?name=JavaGalaxy, What
will the output be? (JSP)

Answer :Compilation error as all the implict objects (request,session,out,...) are
not available in
declarative part.Since we are trying to declare
name=request.getParameter("name")
it gives us compilation error as stating undefined variable or class name :
request

a.jsp

2009-03-13T23:44:00.008-07:00

Question :a.jsp
<%!
int x = 10;
%>
b.jsp
<%@ include file="a.jsp" %>
<%
int x = 20;
out.println("x:"+x);
%>
When the above programme is invoked as http://localhost:8080/b.jsp,
what is the output? (JSP)

Answer :Compiler error as x is already initialised.
When a.jsp file is included in b.jsp, all the variables of a.jsp are also
invoked
in b.jsp.

How do you print the contents of a.jsp in b.jsp. How do you include the

2009-03-13T23:44:00.007-07:00

Question :How do you print the contents of a.jsp in b.jsp. How do you include the
file? (JSP)
Answer :a.jsp
<%!
public int i=10;
%>
b.jsp
<%@ include file="a.jsp" %>
<%
out.println(i);
%>
do not use as this will include the file at runtime where as the above
includes (directive include) the file at compile time

How do you precompile a jsp page (JSP)

2009-03-13T23:44:00.006-07:00

Question :How do you precompile a jsp page? (JSP)
Answer :To precompile a JSP page, access the page with a query string of ?
jsp_precompile
http://www.javagalaxy.com:8080/RMI/index.jsp?jsp_precompile
the jsp page will not get executed by this action.

What is the difference between a tag handler and a tag handler

2009-03-13T23:44:00.005-07:00

Question :What is the difference between a tag handler and a tag handler
class? (JSP)
Answer :The only difference between a tag handler and a tag handler class is that
a tag handler is written in JSP syntax, while a tag handler class is written
in the Java language.

What is the difference between page and request scopes (JSP)

2009-03-13T23:44:00.004-07:00

Question :What is the difference between page and request scopes? (JSP)
Answer :If you specify scope as Page then its life span is until page is displayed or
control is forwarded to a new page. Accessibility is current page only.
But if u specify as Request, its life span is until the request has been
completely processed and the response has been sent back to the user.
Accessibility is current page and any included or for-warded pages

How do you prevent the Creation of a Session in a JSP Page and

2009-03-13T23:44:00.003-07:00

Question :How do you prevent the Creation of a Session in a JSP Page and
why? (JSP)

Answer :By default, a JSP page will automatically create a session for the request
if one does not exist. However, sessions consume resources and if it is not
necessary to maintain a session, one should not be created. For example,
a marketing campaign may suggest the reader visit a web page for more
information. If it is anticipated that a lot of traffic will hit that page, you
may want to optimize the load on the machine by not creating useless
sessions.
The page directive is used to prevent a JSP page from automatically
creating a session:
<%@ page session="false">

How can my JSP page communicate with an EJB Session Bean? (JSP)

2009-03-13T23:44:00.002-07:00

Question :How can my JSP page communicate with an EJB Session Bean? (JSP)
Answer :The following is a code snippet that demonstrates how a JSP page can
interact with an EJB session bean:
<%@ page import="javax.naming.*, javax.rmi.PortableRemoteObject,
foo.AccountHome, foo.Account" %>
<%!
//declare a "global" reference to an instance of the home interface of the
session bean
AccountHome accHome=null;
public void jspInit() {
//obtain an instance of the home interface
InitialContext cntxt = new InitialContext( );
Object ref= cntxt.lookup("java:comp/env/ejb/AccountEJB");
accHome =
(AccountHome)PortableRemoteObject.narrow(ref,AccountHome.class);
}
%>
<%
//instantiate the session bean
Account acct = accHome.create();
//invoke the remote methods
acct.doWhatever(...);
// etc etc...
%>

How do you pass an InitParameter to a JSP? (JSP)

2009-03-13T23:44:00.001-07:00

Question :How do you pass an InitParameter to a JSP? (JSP)
Answer :The JspPage interface defines the jspInit() and jspDestroy() method which
the page writer can use in their pages and are invoked in much the same
manner as the init() and destory() methods of a servlet. The example page
below enumerates through all the parameters and prints them to the
console.
<%@ page import="java.util.*" %>
<%!
ServletConfig cfg =null;
public void jspInit(){
ServletConfig cfg=getServletConfig();
for (Enumeration e=cfg.getInitParameterNames(); e.hasMoreElements();)
{
String name=(String)e.nextElement();
String value = cfg.getInitParameter(name);
System.out.println(name+"="+value);
}
}
%>

How can I get to print the stacktrace for an exception occuring within my

2009-03-13T23:35:00.000-07:00

Question :How can I get to print the stacktrace for an exception occuring within my
JSP page? (JSP)

Answer :By printing out the exception's stack trace, you can usually diagonse a
problem better when debugging JSP pages. By looking at a stack trace, a
programmer should be able to discern which method threw the exception
and which method called that method. However, you cannot print the
stacktrace using the JSP out implicit variable, which is of type JspWriter.
You will have to use a PrintWriter object instead. The following snippet
demonstrates how you can print a stacktrace from within a JSP error page:
<%@ page isErrorPage="true" %>
<%
out.println("
");
PrintWriter pw = response.getWriter();
exception.printStackTrace(pw);
out.println("
");
%>

How can I prevent the word "null" from appearing in my HTML input text

2009-03-13T06:53:00.000-07:00

Question :How can I prevent the word "null" from appearing in my HTML input text
fields when I populate them with a resultset that has null values? (JSP)

Answer :You could make a simple wrapper function, like
<%!
String blanknull(String s) {
return (s == null) ? "" : s;
}
%>
then use it inside your JSP form, like

How do I have the JSP-generated servlet subclass my own custom servlet

2009-03-13T06:51:00.000-07:00

Question :How do I have the JSP-generated servlet subclass my own custom servlet
class, instead of the default? (JSP)

Answer :One should be very careful when having JSP pages extend custom servlet
classes as opposed to the default one generated by the JSP engine. In
doing so, you may lose out on any advanced optimization that may be
provided by the JSP engine. In any case, your new superclass has to fulfill
the contract with the JSP engine by:
Implementing the HttpJspPage interface, if the protocol used is HTTP, or
implementing JspPage otherwise Ensuring that all the methods in the
Servlet interface are declared final Additionally, your servlet superclass
also needs to do the following:
The service() method has to invoke the _jspService() method
The init() method has to invoke the jspInit() method
The destroy() method has to invoke jspDestroy()
If any of the above conditions are not satisfied, the JSP engine may throw
a translation error.
Once the superclass has been developed, you can have your JSP extend it
as follows:
<%@ page extends="packageName.ServletName" %<

How does a servlet communicate with a JSP page (JSP)

2009-03-13T06:48:00.002-07:00

Question :How does a servlet communicate with a JSP page? (JSP)
Answer :The following code snippet shows how a servlet instantiates a bean and
initializes it with FORM data posted by a browser. The bean is then placed
into the request, and the call is then forwarded to the JSP page, Bean1.jsp,
by means of a request dispatcher for downstream processing.
public void doPost (HttpServletRequest request, HttpServletResponse
response) {
try {
govi.FormBean f = new govi.FormBean();
String id = request.getParameter("id");
f.setName(request.getParameter("name"));
f.setAddr(request.getParameter("addr"));
f.setAge(request.getParameter("age"));
//use the id to compute
//additional bean properties like info
//maybe perform a db query, etc.
// . . .
f.setPersonalizationInfo(info);
request.setAttribute("fBean",f);
getServletConfig().getServletContext().getRequestDispatcher
("/jsp/Bean1.jsp").forward(request, response);
} catch (Exception ex) {
. . .
}
}
The JSP page Bean1.jsp can then process fBean, after first extracting it
from the default request scope via the useBean action.
jsp:useBean id="fBean" class="govi.FormBean" scope="request"/
jsp:getProperty name="fBean" property="name" / jsp:getProperty
name="fBean" property="addr" / jsp:getProperty name="fBean"
property="age" / jsp:getProperty name="fBean"
property="personalizationInfo" /

How can I set a cookie and delete a cookie from within a JSP page (JSP)

2009-03-13T06:48:00.001-07:00

Question :How can I set a cookie and delete a cookie from within a JSP page? (JSP)
Answer :A cookie, mycookie, can be deleted using the following scriptlet:
<%
//creating a cookie
Cookie mycookie = new Cookie("aName","aValue");
response.addCookie(mycookie);
//delete a cookie
Cookie killMyCookie = new Cookie("mycookie", null);
killMyCookie.setMaxAge(0);
killMyCookie.setPath("/");
response.addCookie(killMyCookie);
%>

Is there a way I can set the inactivity lease period on a per-session basis

2009-03-13T06:47:00.000-07:00

Question :Is there a way I can set the inactivity lease period on a per-session basis?
(JSP)

Answer :Typically, a default inactivity lease period for all sessions is set within
your JSP engine admin screen or associated properties file. However, if
your JSP engine supports the Servlet 2.1 API, you can manage the
inactivity lease period on a per-session basis. This is done by invoking the
HttpSession.setMaxInactiveInterval() method, right after the session has
been created. For example:
<%
session.setMaxInactiveInterval(300);
%>
would reset the inactivity period for this session to 5 minutes. The
inactivity interval is set in seconds.

How can I declare methods within my JSP page? (JSP)

2009-03-13T06:46:00.001-07:00

Question :How can I declare methods within my JSP page? (JSP)
Answer :You can declare methods for use within your JSP page as declarations.
The methods can then be invoked within any other methods you declare,
or within JSP scriptlets and expressions.
Do note that you do not have direct access to any of the JSP implicit
objects like request, response, session and so forth from within JSP
methods. However, you should be able to pass any of the implicit JSP
variables as parameters to the methods you declare. For example:
<%!
public String whereFrom(HttpServletRequest req) {
HttpSession ses = req.getSession();
...
return req.getRemoteHost();
}
%>
<%
out.print("Hi there, I see that you are coming in from ");
%>
<%= whereFrom(request) %>
Another Example
file1.jsp:
<%@page contentType="text/html"%>
<%!
public void test(JspWriter writer) throws IOException{
writer.println("Hello!");
}
%>
file2.jsp
<%@include file="file1.jsp"%>

<%test(out);% >

How can I enable session tracking for JSP pages if the browser has

2009-03-13T06:43:00.000-07:00

Question :How can I enable session tracking for JSP pages if the browser has
disabled cookies? (JSP)

Answer :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. Basically, we create a new session
within hello1.jsp and place an object within this session. The user can then
traverse to hello2.jsp by clicking on the link present within the page.Within
hello2.jsp, we simply extract the object that was earlier placed in the
session and display its contents. Notice that we invoke the encodeURL()
within hello1.jsp on the link used to invoke hello2.jsp; if cookies are
disabled, the session ID is automatically appended to the URL, allowing
hello2.jsp to still retrieve the session object.
Try this example first with cookies enabled. Then disable cookie support,
restart the brower, and try again. Each time you should see the
maintenance of the session across pages.
Do note that to get this example to work with cookies disabled at the
browser, your JSP engine has to support URL rewriting.
hello1.jsp
<%@ page session="true" %>
<%
Integer num = new Integer(100);
session.putValue("num",num);
String url =response.encodeURL("hello2.jsp");
%>
hello2.jsp
hello2.jsp
<%@ page session="true" %>
<%
Integer i= (Integer )session.getValue("num");
out.println("Num value in session is "+i.intValue());

How do I use a scriptlet to initialize a newly instantiated bean (JSP)

2009-03-13T06:41:00.000-07:00

Question :How do I use a scriptlet to initialize a newly instantiated bean? (JSP)
Answer :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.
The following example shows the "today" property of the Foo bean
initialized to the current date when it is instantiated. Note that here, we
make use of a JSP expression within the jsp:setProperty action.

<%-- scriptlets calling bean setter methods go here --%>

Response has already been commited error. What does it mean (JSP)

2009-03-13T06:38:00.000-07:00

Question :Response has already been commited error. What does it mean? (JSP)
Answer :This error show only when you try to redirect a page after you already
have written something in your page. This happens because HTTP
specification force the header to be set up before the lay out of the page
can be shown (to make sure of how it should be displayed...contenttype="
text/html" or "text/xml" or "plain-text" or "image/jpg", etc...) When
you try to send a redirect status (Number is line_status_402), your HTTP
server cannot send it right now if it hasn't finished to set up the header. If
not starter to set up the header, there are no problems, but if it 's already
begin to set up the header, then your HTTP server expects these headers to
be finished setting up and it cannot be the case if the stream of the page is
not over... In this last case it's like you have a file started with Tag> some output (like testing your
variables...) ... and before you indicate that the file is over (and before the
size of the page can be setted up in the header), you try to send a redirect
status... It s simply impossible due to the specification of HTTP 1.0 and 1.1

How do I use comments within a JSP page? (JSP)

2009-03-13T06:25:00.000-07:00

Question :How do I use comments within a JSP page? (JSP)
Answer :You can use "JSP-style" comments to selectively block out code while
debugging or simply to comment your scriptlets. JSP comments are not
visible at the client. For example:
<%-- the scriptlet is now commented out
<%
out.println("Hello World");
%>
--%>
You can also use HTML-style comments anywhere within your JSP page.
These comments are visible at the client. For example:

Of course, you can also use comments supported by your JSP scripting
language within your scriptlets. For example, assuming Java is the
scripting language, you can have:
<%
//some comment
/**
yet another comment
**/
%>

How do I prevent the output of my JSP or Servlet pages from being

2009-03-13T06:24:00.000-07:00

Question :How do I prevent the output of my JSP or Servlet pages from being
cached by the browser? (JSP)
Answer :You will need to set the appropriate HTTP header attributes to prevent
the dynamic content output by the JSP page from being cached by the
browser. Just execute the following scriptlet at the beginning of your JSP
pages to prevent them from being cached at the browser. You need both
the statements to take care of some of the older browser versions.
<%
response.setHeader("Cache-Control","no-store"); //HTTP 1.1
response.setHeader("Pragma","no-cache"); //HTTP 1.0
response.setDateHeader ("Expires", 0); //prevents caching at the proxy
server
%>

How does JSP handle run-time exceptions (JSP)

2009-03-13T06:23:00.000-07:00

Question :How does JSP handle run-time exceptions? (JSP)
Answer :You can use the errorPage attribute of the page directive to have
uncaught run-time exceptions automatically forwarded to an error
processing page. For example:
<%@ page errorPage="error.jsp" %>
redirects the browser to the JSP page error.jsp if an uncaught exception is
encountered during request processing. Within error.jsp, if you indicate
that it is an error-processing page, via the directive:
<%@ page isErrorPage="true" %>
the Throwable object describing the exception may be accessed within the
error page via the exception implicit object.
Note: You must always use a relative URL as the value for the errorPage
attribute.

How can I implement a thread-safe JSP page? What are the advantages

2009-03-13T06:22:00.000-07:00

Question :How can I implement a thread-safe JSP page? What are the advantages
and Disadvantages of using it? (JSP)
Answer :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. You can typically control the number of instances (N) that
are instantiated for all servlets implementing SingleThreadModel through
the admin screen for your JSP engine.
More importantly, avoid using the <%! DECLARE %> tag for variables. If
you do use this tag, then you should set isThreadSafe to true, as
mentioned above. Otherwise, all requests to that page will access those
variables, causing a nasty race condition.
SingleThreadModel is not recommended for normal use. There are many
pitfalls, including the example above of not being able to use <%! %>.
You should try really hard to make them thread-safe the old fashioned
way: by making them thread-safe

Is JSP technology extensible (JSP)

2009-03-13T06:21:00.002-07:00

Question :Is JSP technology extensible? (JSP)
Answer :YES. JSP technology is extensible through the development of custom
actions, or tags, which are encapsulated in tag libraries

What are the implicit objects (JSP)

2009-03-13T06:21:00.001-07:00

Question :What are the implicit objects? (JSP)
Answer :Implicit objects are objects that are created by the web container and
contain information related to a particular request, page, or application.
They are:
request
response
pageContext
session
application
out
config
page
exception

How can you store international / Unicode characters into a cookie (JSP)

2009-03-13T06:20:00.001-07:00

Question :How can you store international / Unicode characters into a cookie? (JSP)
Answer :One way is, before storing the cookie URLEncode it.
URLEnocder.encoder(str);
And use URLDecoder.decode(str) when you get the stored cookie.

Can I invoke a JSP error page from a servlet? (JSP)

2009-03-13T06:19:00.000-07:00

Question :Can I invoke a JSP error page from a servlet? (JSP)
Answer :Yes, you can invoke the JSP error page and pass the exception object to
it from within a servlet. The trick is to create a request dispatcher for the
JSP error page, and pass the exception object as a
javax.servlet.jsp.jspException request attribute. However, note that you
can do this from only within controller servlets. If your servlet opens an
OutputStream or PrintWriter, the JSP engine will throw the following
translation error:
java.lang.IllegalStateException: Cannot forward as OutputStream or Writer
has already been obtained
The following code snippet demonstrates the invocation of a JSP error page
from within a controller servlet:
protected void sendErrorRedirect(HttpServletRequest request,
HttpServletResponse response, String errorPageURL, Throwable e) throws
ServletException, IOException {
request.setAttribute ("javax.servlet.jsp.jspException", e);
getServletConfig().getServletContext().
getRequestDispatcher(errorPageURL).forward(request, response);
}
public void doPost(HttpServletRequest request, HttpServletResponse
response) {
try {
// do something
} catch (Exception ex) {
try {
sendErrorRedirect(request,response,"/jsp/MyErrorPage.jsp",ex);
} catch (Exception e) {
e.printStackTrace();
}
}
}

How do I instantiate a bean whose constructor accepts parameters using

2009-03-13T06:18:00.000-07:00

Question :How do I instantiate a bean whose constructor accepts parameters using
the useBean tag? (JSP)
Answer :Consider the following bean: package bar;
public class FooBean {
public FooBean(SomeObj arg) {
...
}
//getters and setters here
}
The only way you can instantiate this bean within your JSP page is to use a
scriptlet. For example, the following snippet creates the bean with session
scope:
&l;% SomeObj x = new SomeObj(...);
bar.FooBean foobar = new FooBean(x);
session.putValue("foobar",foobar);
%> You can now access this bean within any other page that is part of the
same session as: &l;%
bar.FooBean foobar = session.getValue("foobar");
%>
To give the bean "application scope", you will have to place it within the
ServletContext as:
&l;%
application.setAttribute("foobar",foobar);
%>
To give the bean "request scope", you will have to place it within the
request object as:
&l;%
request.setAttribute("foobar",foobar);
%>
If you do not place the bean within the request, session or application
scope, the bean can be accessed only within the current JSP page (page
scope).
Once the bean is instantiated, it can be accessed in the usual way:
jsp:getProperty name="foobar" property="someProperty"/ jsp:setProperty
name="foobar" property="someProperty" value="someValue"/

Is there a way to reference the "this" variable within a JSP page? (JSP)

2009-03-13T06:17:00.000-07:00

Question :Is there a way to reference the "this" variable within a JSP page? (JSP)
Answer :Yes, there is. Under JSP 1.0, the page implicit object is equivalent to
"this", and returns a reference to the servlet generated by the JSP page.

How can I get to view any compilation/parsing errors at the client while

2009-03-13T06:16:00.000-07:00

Question :How can I get to view any compilation/parsing errors at the client while
developing JSP pages? (JSP)
Answer :With JSWDK 1.0, set the following servlet initialization property within the
\WEB-INF\servlets.properties file for your application:
jsp.initparams=sendErrToClient=true
This will cause any compilation/parsing errors to be sent as part of the
response to the client.

Can I stop JSP execution while in the midst of processing a request (JSP)

2009-03-13T06:14:00.002-07:00

Question :Can I stop JSP execution while in the midst of processing a request? (JSP)
Answer :Yes. Preemptive termination of request processing on an error condition
is a good way to maximize the throughput of a high-volume JSP engine.
The trick (asuming Java is your scripting language) is to use the return
statement when you want to terminate further processing. For example,
consider:

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

2009-03-13T06:14:00.001-07:00

Question :What's a better approach for enabling thread-safe servlets and JSPs?
SingleThreadModel Interface or Synchronization? (JSP)
Answer :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.

Can you make use of a ServletOutputStream object from within a JSP page (JSP)

2009-03-13T06:13:00.000-07:00

Question :Can you make use of a ServletOutputStream object from within a JSP
page? (JSP)
Answer :No. You are supposed to make use of only a JSPWriter object (given to
you in the form of the implicit object out) for replying to clients. A
JSPWriter can be viewed as a buffered version of the stream object
returned by response.getWriter(), although from an implementational
perspective, it is not. A page author can always disable the default
buffering for any page using a page directive as:
<%@ page buffer="none" %>

Can a JSP page instantiate a serialized bean (JSP)

2009-03-13T06:12:00.000-07:00

Question :Can a JSP page instantiate a serialized bean? (JSP)
Answer :No problem! The useBean action specifies the beanName attribute, which
can be used for indicating a serialized bean. For example:

A couple of important points to note. Although you would have to name
your serialized file "filename.ser", you only indicate "filename" as the value
for the beanName attribute. Also, you will have to place your serialized file
within the WEB-INF\jsp\beans directory for it to be located by the JSP
engine.

How do I perform browser redirection from a JSP page? (JSP)

2009-03-13T06:11:00.000-07:00

Question :How do I perform browser redirection from a JSP page? (JSP)
Answer :You can use the response implicit object to redirect the browser to a
different resource, as:
response.sendRedirect("http://www.foo.com/path/error.html");
You can also physically alter the Location HTTP header attribute, as shown
below:
<%
response.setStatus(HttpServletResponse.SC_MOVED_PERMANENTLY);
String newLocn = "/newpath/index.html";
response.setHeader("Location",newLocn);
%>
You can also use the: Also note
that you can only use this before any output has been sent to the client. I
beleve this is the case with the response.sendRedirect() method as well.
If you want to pass any paramateres then you can pass using page="/servlet/login">
>

How do I include static files within a JSP page (JSP)

2009-03-13T06:10:00.000-07:00

Question :How do I include static files within a JSP page? (JSP)
Answer :Static resources should always be included using the JSP include
directive. This way, the inclusion is performed just once during the
translation phase. The following example shows the syntax:
<%@ include file="copyright.html" %>
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.

What JSP lifecycle methods can I override (JSP)

2009-03-13T06:06:00.000-07:00

Question :What JSP lifecycle methods can I override? (JSP)
Answer :You cannot override the _jspService() method within a JSP page. You can
however, override the jspInit() and jspDestroy() methods within a JSP
page. jspInit() can be useful for allocating resources like database
connections, network connections, and so forth for the JSP page. It is good
programming practice to free any allocated resources within jspDestroy().
The jspInit() and jspDestroy() methods are each executed just once during
the lifecycle of a JSP page and are typically declared as JSP declarations:
<%!
public void jspInit() {
. . .
}
%>
<%!
public void jspDestroy() {
. . .
}
%>

Can a JSP page process HTML FORM data (JSP)

2009-03-13T06:04:00.001-07:00

Question :Can a JSP page process HTML FORM data (JSP)
Answer :Yes. However, unlike servlets, you are not required to implement HTTPprotocol
specific methods like doGet() or doPost() within your JSP page.
You can obtain the data for the FORM input elements via the request
implicit object within a scriptlet or expression as:
<% String item = request.getParameter("item"); int howMany = new Integer(request.getParameter("units")).intValue(); %>
or
<%= request.getParameter("item") %>

Can a JSP page process HTML FORM data (JSP)

2009-03-13T06:04:00.000-07:00

Question :Can a JSP page process HTML FORM data? (JSP)
Answer :Yes. However, unlike servlets, you are not required to implement HTTPprotocol
specific methods like doGet() or doPost() within your JSP page.
You can obtain the data for the FORM input elements via the request
implicit object within a scriptlet or expression as:
<%
String item = request.getParameter("item");
int howMany = new Integer(request.getParameter("units")).intValue();
%>
or
<%= request.getParameter("item") %>

How do I mix JSP and SSI #include? (JSP)

2009-03-13T06:03:00.000-07:00

Question :How do I mix JSP and SSI #include? (JSP)
Answer :If you're just including raw HTML, use the #include directive as usual
inside your .jsp file.

But it's a little trickier if you want the server to evaluate any JSP code that's
inside the included file. If your data.inc file contains jsp code you will have
to use
<%@ vinclude="data.inc" %>
The is used for including non-JSP files.

How do I include static files within a JSP page (JSP)

2009-03-13T06:02:00.000-07:00

Question :How do I include static files within a JSP page? (JSP)
Answer :Static resources should always be included using the JSP include
directive. This way, the inclusion is performed just once during the
translation phase. The following example shows the syntax: 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.

In the Servlet 2.4 specification SingleThreadModel has been deprecates,

2009-03-13T06:01:00.000-07:00

Question :In the Servlet 2.4 specification SingleThreadModel has been deprecates,
why? (JSP)
Answer :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.

How many JSP scripting elements are there and what are they? (JSP)

2009-03-13T05:59:00.000-07:00

Question :How many JSP scripting elements are there and what are they? (JSP)
Answer :There are three scripting language elements:
declarations
scriptlets
expressions

How can I implement a thread-safe JSP page? (JSP)

2009-03-13T05:58:00.000-07:00

Question :How can I implement a thread-safe JSP page? (JSP)
Answer :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.

How can my application get to know when a HttpSession is

2009-03-13T05:57:00.000-07:00

Question :How can my application get to know when a HttpSession is
removed? (JSP)
Answer :Define a Class HttpSessionNotifier which implements
HttpSessionBindingListener and implement the functionality what you need
in valueUnbound() method.
Create an instance of that class and put that instance in HttpSession.

What is the difference between Model 1 and Model 2 architecture (JSP)

2009-03-13T05:56:00.002-07:00

Question :What is the difference between Model 1 and Model 2 architecture? (JSP)
Answer :In Model 1 there is no Controller and in Model 2 there is a Controller

How do I mix JSP and SSI #include (JSP)

2009-03-13T05:56:00.001-07:00

Question :How do I mix JSP and SSI #include? (JSP)
Answer :If you're just including raw HTML, use the #include directive as usual
inside your .jsp file.

But it's a little trickier if you want the server to evaluate any JSP code
that's inside the included file. Ronel Sumibcay
(ronel@LIVESOFTWARE.COM) says: If your data.inc file contains jsp code
you will have to use
<%@ vinclude="data.inc" %>
The is used for including non-JSP files.

How do you delete a Cookie within a JSP (JSP)

2009-03-13T05:53:00.000-07:00

Question :How do you delete a Cookie within a JSP? (JSP)
Answer :Cookie mycook = new Cookie("name","value");
response.addCookie(mycook);
Cookie killmycook = new Cookie("mycook","value");
killmycook.setMaxAge(0);
killmycook.setPath("/");
killmycook.addCookie(killmycook);

How does JSP handle runtime exceptions (JSP)

2009-03-13T05:52:00.000-07:00

Question :How does JSP handle runtime exceptions? (JSP)
Answer :Using errorPage attribute of page directive and also we need to specify
isErrorPage=true if the current page is intended to URL redirecting of a
JSP.

What is the difference between RequestDispatcher and sendRedirect (JSP)

2009-03-13T05:51:00.000-07:00

Question :What is the difference between RequestDispatcher and sendRedirect? (JSP)
Answer :RequestDispatcher: server-side redirect with request and response
objects.
sendRedirect : Client-side redirect with new request and response objects.

What is the difference between directive include and jsp include? (JSP)

2009-03-13T05:49:00.000-07:00

Question :What is the difference between directive include and jsp include? (JSP)
Answer :<%@ include> : Used to include static resources during translation time.
: Used to include dynamic content or static content during runtime.

How to pass information from JSP to included JSP? (JSP)

2009-03-13T05:48:00.002-07:00

Question :How to pass information from JSP to included JSP? (JSP)
Answer :Using <%jsp:param> tag.

What is the difference in using request.getRequestDispatcher() and

2009-03-13T05:48:00.001-07:00

Question :What is the difference in using request.getRequestDispatcher() and
context.getRequestDispatcher()? (JSP)
Answer :request.getRequestDispatcher(path): In order to create it we need to
give the relative path of the resource
context.getRequestDispatcher(path): In order to create it we need to give
the absolute path of the resource.

What is the difference between ServletContext and PageContext (JSP)

2009-03-13T05:45:00.000-07:00

Question :What is the difference between ServletContext and PageContext? (JSP)
Answer :ServletContext: Gives the information about the container
PageContext: Gives the information about the Request

Can we implement an interface in a JSP (JSP)

2009-03-13T05:43:00.000-07:00

Question :Can we implement an interface in a JSP? (JSP)
Answer :No

What are native methods How do you use them (JNI)

2009-03-13T05:40:00.000-07:00

Question :What are native methods? How do you use them? (JNI)
Answer :Native methods are methods written in other languages like C, C++, or
even assembly language.
You can call native methods from Java using JNI

Is JNDI a protocol Where is it used (JNDI)

2009-03-13T05:37:00.000-07:00

Question :Is JNDI a protocol? Where is it used? (JNDI)
Answer :Yes.HotJava Views 1.1 is using JNDI to access LDAP. Enterprise APIs such
as Enterprise JavaBeans, Java Message Service, JDBC 2.0 make use of
JNDI to for their naming and directory needs. RMI over IIOP applications
can use JNDI to access the CORBA (COS) naming service.

Components of JNDI (JNDI)

2009-03-13T05:36:00.000-07:00

Question :Components of JNDI (JNDI)
Answer :Naming Interface- The naming interface organizes information
hierarchically and maps human-friendly names to addresses or objects that
are machine-friendly. It allows access to named objects through multiple
namespaces.
Directory Interface- JNDI includes a directory service interface that
provides access to directory objects, which can contain attributes, thereby
providing attribute-based searching and schema support
Service Provider Interface- JNDI comes with the SPI, which supports the
protocols provided by third parties.

What's the difference between JNDI lookup(), list(), listBindings(), and search() (JNDI)

2009-03-13T05:35:00.000-07:00

Question :What's the difference between JNDI lookup(), list(), listBindings(), and
search()? (JNDI)
Answer :lookup() attempts to find the specified object in the given context. I.e., it
looks for a single, specific object and either finds it in the current context
or it fails.
list() attempts to return an enumeration of all of the NameClassPair's of all
of the objects in the current context. I.e., it's a listing of all of the objects
in the current context but only returns the object's name and the name of
the class to which the object belongs.
listBindings() attempts to return an enumeration of the Binding's of all of
the objects in the current context. I.e., it's a listing of all of the objects in
the current context with the object's name, its class name, and a reference
to the object itself.
search() attempts to return an enumeration of all of the objects matching
a given set of search criteria. It can search across multiple contexts (or
not). It can return whatever attributes of the objects that you desire. Etc.
It's by far the most complex and powerful of these options but is also the
most expensive.

What is Context and InitialContext? (JNDI)

2009-03-13T05:33:00.000-07:00

Question :What is Context and InitialContext? (JNDI)
Answer :A context represents a set of bindings within a naming service. A Context
object provides the methods for binding names to objects and unbinding
names from objects, for renaming objects, and for listing the bindings.
JNDI performs all naming operations relative to a context.
The JNDI specification defines an InitialContext class. This class is
instantiated with properties that define the type of naming service in use
(such as provider URL, security, ID and password to use when connecting).

What protocols does JNDI provide an interface to (JNDI)

2009-03-13T05:30:00.000-07:00

Question :What protocols does JNDI provide an interface to? (JNDI)
Answer :JNDI itself is independent of any specific directory access protocol.
Individual service providers determine the protocols to support. JNDI
supports popular protocols, such as LDAP (Light weight Directory Access
Protocol) , NDS(Netscape Directory Service), DNS(Domain Naming
Service), and NIS(Network Information Service), supplied by different
vendors.

How does the Application server handle the JMS Connection (JMS)

2009-03-13T05:28:00.000-07:00

Question:How does the Application server handle the JMS Connection? (JMS)
Answer:- App server creates the server session and stores them in a pool
- Connection consumer uses the server session to put messages in the
session of the JMS.
- Server session is the one that spawns the JMS session.
- Applications written by Application programmers creates the message
listener

Give an example of using the point-to-point model. (JMS)

2009-03-13T05:26:00.000-07:00

Question :Give an example of using the point-to-point model. (JMS)
Answer :The point-to-point model is used when the information is specific to a
single client. For example, a client can send a message for a print out, and
the server can send information back to this client after completion of the
print job.

How does a typical client perform the communication (JMS)

2009-03-13T05:25:00.000-07:00

Question :How does a typical client perform the communication? (JMS)
Answer :1. Use JNDI to locate administrative objects.
1a. Locate a single ConnectionFactory object.
1b. Locate one or more Destination objects.
2. Use the ConnectionFactory to create a JMS Connection.
3. Use the Connection to create one or more Session(s).
4. Use a Session and the Destinations to create the MessageProducers and
MessageConsumers needed.
5. Perform your communication.

What is the Role of the JMS Provider (JMS)

2009-03-13T05:24:00.000-07:00

Question :What is the Role of the JMS Provider? (JMS)
Answer :The JMS provider handles security of the messages, data conversion and
the client triggering. The JMS provider specifies the level of encryption and
the security level of the message, the best data type for the non-JMS
client.

What are the various message types supported by JMS? (JMS)

2009-03-13T05:23:00.000-07:00

Question :What are the various message types supported by JMS? (JMS)
Answer :Stream Messages ? Group of Java Primitives
Map Messages ? Name Value Pairs.
Name being a string
Value being a java primitive
Text Messages ? String messages (since being widely used a separate
messaging Type has been supported)
Object Messages ? Group of serialize able java object
Bytes Message ? Stream of uninterrupted bytes

What are the core JMS-related objects required for each JMS-enabled application (JMS)

2009-03-13T05:21:00.000-07:00

Question :What are the core JMS-related objects required for each JMS-enabled
application? (JMS)
Answer :Each JMS-enabled client must establish the following:
· A connection object provided by the JMS server (the message broker)
· Within a connection, one or more sessions, which provide a context for
message sending and receiving
· Within a session, either a queue or topic object representing the
destination (the message staging area) within the message broker
· Within a session, the appropriate sender or publisher or receiver or
subscriber object (depending on whether the client is a message producer
or consumer and uses a point-to-point or publish/subscribe strategy,
respectively)
Within a session, a message object (to send or to receive)

Why doesn't the JMS API provide end-to-end synchronous message

2009-03-13T05:20:00.000-07:00

Question:Why doesn't the JMS API provide end-to-end synchronous message
delivery and notification of delivery? (JMS)
Answer :Some messaging systems provide synchronous delivery to destinations as
a mechanism for implementing reliable applications. Some systems provide
clients with various forms of delivery notification so that the clients can
detect dropped or ignored messages. This is not the model defined by the
JMS API.
JMS API messaging provides guaranteed delivery via the once-and-onlyonce
delivery semantics of PERSISTENT messages. In addition, message
consumers can insure reliable processing of messages by using either
CLIENT_ACKNOWLEDGE mode or transacted sessions. This achieves
reliable delivery with minimum synchronization and is the enterprise
messaging model most vendors and developers prefer.
The JMS API does not define a schema of systems messages (such as
delivery notifications). If an application requires acknowledgment of
message receipt, it can define an application-level acknowledgment
message.

What is publish/subscribe messaging (JMS)

2009-03-13T05:19:00.000-07:00

Question :What is publish/subscribe messaging? (JMS)
Answer :With publish/subscribe message passing the sending application/client
establishes a named topic in the JMS broker/server and publishes
messages to this queue. The receiving clients register (specifically,
subscribe) via the broker to messages by topic; every subscriber to a topic
receives each message published to that topic. There is a one-to-many
relationship between the publishing client and the subscribing clients.

What are the types of messaging? (JMS)

2009-03-13T05:18:00.000-07:00

Question :What are the types of messaging? (JMS)
Answer :There are two kinds of Messaging.
Synchronous Messaging:
Synchronous messaging involves a client that waits for the server to
respond to a message.
Asynchronous Messaging:
Asynchronous messaging involves a client that does not wait for a message
from the server. An event is used to trigger a message from a server.