JSP Interview Questions

1. How do i include static files within a jsp page ?

This is static include.. you can just include using below code

<%@ include file="header.jsp" %>

or

<%@ include file="footer.html" %>

Dynamic include you can do like below

<jsp:include page="header.jsp"/>

or

 you can pass parameter also

<jsp:include page="header.jsp">

<jsp:param name="title" value="Java Interview Questions"/>

</jsp:include>

2.Difference between static include and dynamic include in JSP ?

          The syntax for static include is <%@ include file=?filename.jsp? %> and the syntax for dynamic include is <jsp:include page=?filename.jsp? />

Static include is an inline inclusion. i.e., the contents of the file will be included at translation phase. It's something like a copy and paste .

In case of dynamic include the response of the file will be included to the original response at runtime. The file will be processed separately and only the response will become the part of the original files response.

Static include cannot accept a parameter (What this parameter will do even if are passing it?). But dynamic include can accept a parameter. (Here we have some one to do something  on the parameter).

Dynamic include

<jsp:include page="masterTemplate.jsp" flush="true">

<jsp:param name="rColumn" value="rightDisplay.jsp" />

<jsp:param name="mColumn" value="AlertBody.jsp" />

<jsp:param name="title" value="Alerts" />

</jsp:include>

we are passing parameters.

3. which situation you use static include and dynamic include in jsp?

static include : Contents are static like

<%@ include file="header.jsp"%> ..Not changing frequently. Don't need to pass parameter.

For example.

a.jsp contain <%@ include file="header.jsp"%> then all the codes of header.jsp is included in a.jsp.

dynamic include : Need to pass parameter. Need to execute every time. Dynamic content. Excecute the included jsp and only ouput is pasted to main jsp

For example..

a.jsp contain following code

<jsp:include page="masterTemplate.jsp" flush="true">

<jsp:param name="rColumn" value="rightDisplay.jsp" />

<jsp:param name="mColumn" value="AlertBody.jsp" />

<jsp:param name="title" value="Alerts" />

</jsp:include>

masterTemplate.jsp execute and output is pasted to a.jsp.

4.Explain the life-cycle mehtods in JSP?

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.

5.   How many JSP scripting elements and what are they?

   

There are three scripting language elements:

--declarations

<%!

int i=8;

%>

--scriptlets

<% Java Code Logic

i=i+29;

%>

--expressions

<%= i %> - This will display the value of i.

6. What is a Expression,Declaration,Scriptlet in jsp?

expression

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

<%= emp.getName()%>

<%= (new java.util.Date()).toLocaleString() %>

You cannot use a semicolon to end an expression.

All the expression code is converting to servlet. All the expressions go to inside service() method of the convert servlet.

Declaration

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

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

<%! int i = 0; %>

<%! int a, b, c; %

You can add method to declaration part.

<%!

public String trimData(String str){

return str.trim();

}

%>

You can call the method within the jsp.

All the declaration code is converting to servlet. If you add method , the method is in convert servlet. All varibales are instance variable in the convert servlet.

Scriptlet

Scriptlet code is like java logic. you can declare varibales in the scriptlet and do the logic.

All the Scriptlet go to inside service() method of the convert servlet.

<%

int n=10;

for(int i=0;i<n;i++){

}

%>

7.What is a Visible and Hidden Comment in jsp?

On view source (browser) the Hidden Comment is not visible to end user.

On view source (browser) the Visible Comment is visible to end user.

Examples

<%-- This comment will not be visible in the page source --%>

<!-- This comment will visible in the page source -->

8.What are implicit objects in JSP?

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

Ø  request

Ø  response

Ø  pageContext

Ø  session

Ø  application

Ø  out

Ø  config

Ø  page

Ø  exception

9.What are the different scope valiues for the <jsp:useBean>?

Scopes are

page - with in the same page

request - after forward or include also you will get the request scope data.

session - after senRedirect also you will get the session scope data. All data stored in session is available to end user till session closed or browser closed.

application - Data will be available through out the application. One user can store data in application scope and other can get the data from application scope.

10.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.

11.How does JSP handle run-time exceptions?

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

For example:

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: isErrorPage=true.

the Throwable object describing the exception may be accessed within the error page via the exception implicit object.

12. What's the Difference between Forward and Include?

The <jsp:forward> action enables you to forward the request to a static HTML file, a servlet, or another JSP.

<jsp:forward page="url" />

The JSP that contains the <jsp:forward> action stops processing, clears its buffer, and forwards the request to the target resource. Note that the calling JSP should not write anything to the response prior to the <jsp:forward> action.

You can also pass additional parameters to the target resource using the <jsp:param> tag.

<jsp:forward page="test.htm" >

<jsp:param name="name1" value="value1" />

<jsp:param name="name2" value="value2" />

</jsp:forward>

In this example, test.jsp can access the value of name1 using request.getParameter("name1").

<jsp:include> execute the code and force a flush of the buffer in the output stream.

If a.jsp has the code like

<jsp:include page="template.jsp" flush="true" >

<jsp:param name="name1" value="value1" />

</jsp:include>

then template.jsp execute and the output is placed in a.jsp

13.How you do Session Management in JSP ?

Http protocol is a stateless protocol, that means that it can't persist the data. Http treats each request as a new request so every time you will send a request you will be considered as a new user.

In session management whenever a request comes for any resource, a unique token is generated by the server and transmitted to the client by the response object and stored on the client machine as a cookie. We can also say that the process of managing the state of a web based client is through the use of session IDs. Session IDs are used to uniquely identify a client browser, while the server side processes are used to associate the session ID with a level of access. Thus, once a client has successfully authenticated to the web applicatiion, the session ID can be used as a stored authentication voucher so that the client does not have to retype their login information with each page request. Now whenever a request goes from this client again the ID or token will also be passed through the request object so that the server can understand from where the request is coming.

Session management can be achieved by :

1. Cookies: cookies are small bits of textual information that a web server sends to a browser and that browsers returns the cookie when it visits the same site again. In cookie the information is stored in the form of a name, value pair. By default the cookie is generated. If the user doesn't want to use cookies then it can disable them browser setting.

2. URL rewriting: In URL rewriting we append some extra information on the end of each URL that identifies the session. This URL rewriting can be used where a cookie is disabled. It is a good practice to use URL rewriting. In this session ID information is embedded in the URL, which is recieved by the application through Http GET requests when the client clicks on the links embedded with a page.

3. Hidden form fields: In hidden form fields the html entry will be like this : <input type ="hidden" name ="name" value="">. This means that when you submit the form, the specified name and value will be get included in get or post method. In this session ID information would be embedded within the form as a hidden field and submitted with the Http POST method.

4. HttpSession object :

javax.servlet.http.HttpSession is an interface that provides a way to identify a user across more than one page request or visit to a web site. This is the way mainly used in webapplication. HttpSession object maintain session for you. You don't need to do any session management.

session.setAttribute("name",name);

String name = session.getAttribute("name");

you will get the same value which you have set.

14. How to Disable session in JSP page ?

Disabling the session in some pages will improve the performance of your JSP container.

Every time a JSP is requested, JSP creates an HttpSession object to maintain state for each unique client. The session data is accessible in the JSP as the implicit session object. In JSPs, sessions are enabled by default.

By default <%@ page session="true" %>

Session object uses the server resources. Each session object uses up a small amount of system resources as it is stored on the server side. This also increases the traffic as the session ID is sent from server to client. Client also sends the same session ID along with each request. If some of the JSP pages on your web site are getting millions of hits from internet browser and there is not need to identify the user, so its better to disable the session in that JSP page.

You can tell the container to disable session in the JSP file by setting the session attribute to false. Set the session attribute of the page directive to false.

<%@ page session="false" %>

<%@ page language="java" session="false"%>

<html>

<head>

<title>Session Disabled Example</title>

</head>

<body>

<p>Session is Disabled in this page </p>

</body>

</html>

15. How do you prevent the Creation of a Session in a JSP Page and why?

<%@ page session="false">

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.

16. How to add and delete Cookie in jsp ?

Add Cookie to response object:

Cookie cookie = new Cookie ("name",value);

cookie.setPath("/");

cookie.setDomain(DOMAIN_NAME);

cookie.setMaxAge(2* 7 * 24 * 60 * 60);// 2 week

response.addCookie(cookie);

Get cookie from request object :

Cookie myCookie = null;

Cookie cookies [] = request.getCookies ();

if (cookies != null)

for (int i = 0; i < cookies.length; i++)

{

if (cookies [i].getName().equals ("name")) // the name of the cookie you have added

{

myCookie = cookies[i];

break;

}

}

Delete Cookie:

You can't delete the cookie. just add maxage to 0;

cookie.setMaxAge(0);

cookie.setPath("/");

cookie.setDomain(DOMAIN_NAME);

response.addCookie(cookie);

cookie.setMaxAge(-1) means on browser close cookie will be deleted.

17. How does a servlet communicate with a JSP page?

In the service method

protected void service(HttpServletRequest request,HttpServletResponse response)

        throws ServletException, java.io.IOException {

User user = (User)request.getSession().getAttribute("user");

                

        String imgId = (String)request.getParameter("imgId");

        String path = request.getContextPath()+"/jsp/addnetwork.jsp";

        

        //do some thing

User user = DAO.getUser(imgId);

request.getSession().setAttribute("user",user);    

         response.sendRedirect(path);

}

In the addnetwork.jsp

User user = getAttribute("user);