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. This is done by adding the directive <%@ page isThreadSafe="false" % > within your JSP page.
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.
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 hello2.jsp
hello2.jsp
<%
Integer i= (Integer )session.getValue("num");
out.println("Num value in session is "+i.intValue());
What are the implicit objects?
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 JSP technology extensible?
Yes. JSP technology is extensible through the development of custom actions, or tags, which are encapsulated in tag libraries.
How can I implement a thread-safe JSP page?
What are the advantages and Disadvantages of using it? - 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
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.
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.
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