Q) Explain the life-cycle methods in JSP?
A) The generated servlet class for a JSP page implements the HttpJspPage interface of the javax.servlet.jsp package. Hte HttpJspPage interface extends the JspPage interface which inturn extends the Servlet interface of the javax.servlet package. the generated servlet class thus implements all the methods of the these three interfaces. 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 interface 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.

Q) What is a Declaration?
A) 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; %>

Q) What is a Scriptlet?
A) A scriptlet can contain any number of language statements, variable or method declarations, or expressions that are valid in the page scripting language. Within scriptlet tags, you can
1.Declare variables or methods to use later in the file (see also Declaration).
2.Write expressions valid in the page scripting language (see also Expression).
3.Use any of the JSP implicit objects or any object declared with a < jsp:useBean> tag.
You must write plain text, HTML-encoded text, or other JSP tags outside the scriptlet. Scriptlets are executed at request time, when the JSP engine processes the client request. If the scriptlet produces output, the output is stored in the out object, from which you can display it.

Q) What are implicit objects? List them?
A) 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 are listed as request , response , pageContext , session , application , out , config , page , exception .

Q) Difference between forward and sendRedirect?
A) 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.

Q) What are the different scope values for the < jsp:useBean>?
A) The different scope values for < jsp:useBean> are
1. page
2. request
3.session
4.application

Q) How can I implement a thread-safe JSP page? What are the advantages and Disadvantages of using it?
A) 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 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 .

Q) What's a better approach for enabling thread-safe servlets and JSPs? SingleThreadModel Interface or Synchronization?
A) 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.

Q) What is a output comment?
A) 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.
JSP Syntax
< !-- comment [ < %= expression %> ] -->
Example 1
< !-- This is a commnet sent to client on
< %= (new java.util.Date()).toLocaleString() %>
-->
Displays in the page source:
< !-- This is a commnet sent to client on January 24, 2004 -->

Q) What is a Expression?
A) 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

Q) What is a Hidden Comment?
A) 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.
You can use any characters in the body of the comment except the closing --%> combination. If you need to use --%> in your comment, you can escape it by typing --%\>.
JSP Syntax
< %-- comment --%>
Examples
< %@ page language="java" %>
< html>
< head>< title>A Hidden Comment < /title>< /head>
< body>
< %-- This comment will not be visible to the colent in the page source --%>
< /body>
< /html>

Q) Is JSP technology extensible?
A) Yes. JSP technology is extensible through the development of custom actions, or tags, which are encapsulated in tag libraries.

Q) How do you pass an InitParameter to a JSP?
A) 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);
}
}
%>

Q) What's Difference between JSP:include action and include directive
A) There are two mechanisms for including another Web resource in a JSP page: the include directive and the jsp:include element.
The include directive is processed when the JSP page is translated into a servlet class. The effect of the directive is to insert the text contained in another file--either static content or another JSP page--in the including JSP page. You would probably use the include directive to include banner content, copyright information, or any chunk of content that you might want to reuse in another page. The syntax for the include directive is as follows:
< %@ include file="filename" %>
The jsp:include element is processed when a JSP page is executed. The include action allows you to include either a static or dynamic resource in a JSP file. The results of including static and dynamic resources are quite different. If the resource is static, its content is inserted into the calling JSP file. If the resource is dynamic, the request is sent to the included resource, the included page is executed, and then the result is included in the response from the calling JSP page. The syntax for the jsp:include element is as follows:
< jsp:include page="includedPage" />

Q) How can my JSP page communicate with an EJB Session Bean?
A) 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...
%>

Q) How do I prevent the output of my JSP or Servlet pages from being cached by the browser?
A) 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
%>

Q) 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?
A) You could make a simple wrapper function, like
< %!
String blanknull(String s) {
return (s == null) ? \"\" : s;
}
%>
then use it inside your JSP form, like
< input type="text" name="lastName" value="< %=blanknull(lastName)% > " >

Q) What is the difference b/w variable declared inside a declaration part and variable declared in scriplet part?
A) 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.

Q) How does JSP handle run-time exceptions?
A) 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\" %> 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.

Q) Is there a way to execute a JSP from the comandline or from my own application?
A) There is a little tool called JSPExecutor that allows you to do just that. The developers (Hendrik Schreiber < hs@webapp.de> & Peter Rossbach < pr@webapp.de> ) aim was not to write a full blown servlet engine, but to provide means to use JSP for generating source code or reports. Therefore most HTTP-specific features (headers, sessions, etc) are not implemented, i.e. no reponseline or header is generated. Nevertheless you can use it to precompile JSP for your website

Q) Response has already been commited error. What does it mean?
A) 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, content-type="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 < HTML Tag> < Some Headers> < Body> some output (like testing your variables.) 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

Q) Is there a way I can set the inactivity lease period on a per-session basis?
A) 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.

Q) How can I set a cookie and delete a cookie from within a JSP page?
A) 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);
%>

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

Q) In the Servlet 2.4 specification SingleThreadModel has been deprecates, why?
A) 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.

Q) 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. 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.

Q) What information is needed to create a TCP Socket?
A) The Local System's IP Address and Port Number. And the Remote System's IPAddress and Port Number.

Q) What are stored procedures? How is it useful?
A) A stored procedure is a set of statements/commands which reside in the database. The stored procedure is precompiled and saves the database the effort of parsing and compiling sql statements everytime a query is run. Each Database has it's 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.

Q) Why does JComponent have add() and remove() methods but Component does not?
A) Because JComponent is a subclass of Container, and can contain other components and jcomponents.

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

Q) How to Retrieve Warnings?
A) 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();
}
}

Q) How many messaging models do JMS provide for and what are they?
A) JMS provide for two messaging models, publish-and-subscribe and point-to-point queuing.

Q) How can I get to print the stacktrace for an exception occuring within my JSP page?
A) 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(" ");
%>

Q) How do I have the JSP-generated servlet subclass my own custom servlet class, instead of the default?
A) 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:
o The service() method has to invoke the _jspService() method
o The init() method has to invoke the jspInit() method
o 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" %>

Q) What Class.forName will do while loading drivers?
A) 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.

Q) How do I use a scriptlet to initialize a newly instantiated bean?
A) 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.
< jsp:useBean id="foo" class="com.Bar.Foo" >
< jsp:setProperty name="foo" property="today"
value="<%=java.text.DateFormat.getDateInstance().format(new java.util.Date()) %> " / >
</jsp:useBean >

Q) How does a servlet communicate with a JSP page?
A) 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" /

Q) How can I enable session tracking for JSP pages if the browser has disabled cookies?
A) 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");
%>
< a href=\'< %=url%> \'> hello2.jsp< /a>
hello2.jsp
< %@ page session="true" %>
< %
Integer i= (Integer )session.getValue("num");
out.println("Num value in session is " + i.intValue());
%>