JSP, Servlets Interview questions

Here you can find out a list of interview questions for jsp and servlets. These questions are often asked by the interviewer for jsp interview and servlet interview. We put our maximum effort to make this answers error free. But still there might be some errors. If you feel out any answer given for any question is wrong, please, please inform us by clicking on report bug button provided below. In this section we are offering interview questions for JSP and Servlets only. Since JSP and Servlets are almost identical technology, there is only one section for both JSP and Servlet interview questions. If you need interview questions for any other java related technologies , please check the relevant sections.

you need to define three separate components: the tag handler class that defines the tag's behavior .encapsulating complex behavior into simple and accessible forms. SMTP etc. beans cannot. URL rewriting. FTP. Beans have a standard format for Java classes. 4 5 Q A .the tag library descriptor file that maps the XML element names to the tag implementations and the JSP file that uses the tag library JavaBeans are Java utility classes you defined. but beans can be used in all JSP 1. Hidden form fields What mechanisms are used by a Servlet Container to maintain session information? Cookies.x versions. HttpSession. Custom tags are available only in JSP 1. 2 Q A 3 Q A Q A What are the different ways for session tracking? Cookies. You use tags Custom tags and beans accomplish the same goals -. Custom tags usually define relatively selfcontained behavior. Custom tags require quite a bit more work to set up than do beans. its attributes and its body are interpreted. But a servlet can support any protocol like HTTP. Complex operations can be reduced to a significantly simpler form with custom tags than with beans. and then group your tags into collections called tag libraries that can be used in any number of JSP files. and HTTPS protocol information are used to maintain session information Difference between GET and POST In GET your entire form submission can be encapsulated in one URL. To use custom JSP tags.1 Q A What is the difference between JSP and Servlets ? JSP is used mainly for presentation only. What is difference between custom JSP tags and beans? Custom JSP tag is a tag you defined. A JSP can only be HttpServlet that means the only supported protocol in JSP is HTTP. You define how a tag. URL rewriting. There are several differences: Custom tags can manipulate JSP content.1 and later. whereas beans are often defined in one servlet and used in a different servlet or JSP page.

The original reason for init() was that ancient versions of Java couldn·t dynamically invoke constructors with arguments. scriptlets. What is servlet context ? The servlet context is an object that contains a information about the Web application and container. to initialize servlet? Yes. The data is not visible on the URL and it is more secure. and set and store attributes that other servlets in the context can use. expressions. query length is limited to 255 characters. so there was no way to give the constructor a ServletConfig. How many JSP scripting elements are there and what are they? There are three scripting language elements: declarations. a servlet can log events. So you won·t have access to a ServletConfig or ServletContext. not secure. That no longer applies. But you will not get the servlet specific things from constructor. Can we use the constructor. the inclusion is performed just once during the 7 Q A 8 Q A 9 Q A Q A 10 12 Q A 13 Q A . What is a servlet ? servlet is a java program that runs inside a web container. obtain URL references to resources. quick and easy. faster. The data is submitted as part of URL. Using the context. 6 Q A What is session? The session is an object used by a servlet to track a user's interaction with a Web application across multiple HTTP requests. What is servlet mapping? The servlet mapping defines an association between a URL pattern and a servlet. instead of init(). but servlet containers still will only call your no-arg constructor. The session is stored on the server. In POST data is submitted inside body of the HTTP request. This way. How do I include static files within a JSP page? Static resources should always be included using the JSP include directive. The mapping is used to map requests to Servlets.like a hyperlink.

getRequestDispatcher()? In request. Create an instance :. 14 Q A How can I implement a thread-safe JSP page? You can make your JSPs thread-safe adding the directive <%@ page isThreadSafe="false" % > within your JSP page. Page compilation: page is compiled into a class file Page loading : This class file is loaded. What are the lifecycle of JSP? When presented with JSP page the JSP engine does the following 7 phases. expression is evaluated each time the page is accessed.getRequestDispatcher(path) in order to create it we need to give the absolute path of the resource. 17 Q A What are context initialization parameters? Context initialization parameters are specified by the <contextparam> in the web.xml file. What is a Expression? Expressions are act as place holders for language expression.Instance of servlet is created jspInit() method is called _jspService is called to handle service calls _jspDestroy is called to destroy it when the servlet is not required. This will be included in the service method of the generated servlet.getRequestDispatcher() and context.translation phase. o 15 Q A 16 Q A o o o o o o Page translation: -page is parsed. and a java file which is a servlet is created.getRequestDispatcher(path) in order to create it we need to give the relative path of the resource. A declaration must contain at least one complete 18 Q A 19 Q A . But in resourcecontext. What is a Declaration? It declares one or more variables or methods for use later in the JSP source file. these are initialization parameter for the whole application. What is the difference in using request.

variable or expressions that are valid in the page scripting language. config. without the client being informed that a different resource is going to process the request. exception Q What's the difference between forward and sendRedirect? A forward is server side redirect and sendRedirect is client side redirect. response. Q What are the implicit objects? A Certain objects that are available for the use in JSP documents without being declared first. This will be included in the declaration section of the generated servlet. application. pageContext. you can declare variables to use later in the file. session. out.declarative statement. session. The implicit objects are: request. request. This will become the part of generated servlet's service method. Q A 21 22 23 24 . use any of the JSP implicit objects or any object declared with a <jsp:useBean>. When a sendRedirect method is invoked. the request is sent to another resource on the server. or tags. it is. write expressions valid in the page scripting language. The declaration must be valid in the scripting language used in the JSP file. Generally a scriptlet can contain any java code that are valid inside a normal java method. Q What are the different scopes available ? A page. 20 What is a Scriptlet? A scriptlet can contain any number of language statements. application Q Is JSP extensible ? A Yes. which are encapsulated in tag libraries. JSP technology is extensible through the development of custom actions. You can declare any number of variables or methods within one declaration tag. These objects are parsed by the JSP engine and inserted into the generated servlet. it causes the web container to return to the browser indicating that a new URL should be requested. page. Client can disable sendRedirect. This process occurs completely with in the web container And then returns to the calling method. Because the browser issues a completely new request any object that are stored as request attributes before the redirect occurs will be lost. Within scriptlet tags. When you invoke a forward request. as long as semicolons separate them. This extra round trip a redirect is slower than forward.

Q What are two different types of Servlets ? A GenericServlet and HttpServlet.. We cannot have a dynamic filename for directive include. We can aslo pass parameters to <jsp:include 26 27 28 29 30 32 33 . either directly or. finally it executes the destroy() method when server removes the servlet. by extending a class that implements it such as HttpServlet. Q What is the difference between <%@ include . Here the included file will be processed as a separate file and the response will be included.25 Q What's the Servlet Interface? A The central abstraction in the Servlet API is the Servlet interface. HttpServlet supports only HTTP protocol. It is something like inline inclusion. HttpServlet is used to implement HTTP protocol. Q Can we call destroy() method on servlets from service method ? A Yes. The contents of the file will get included on Translation phase.> (directive include) and <jsp:include> ? A @ include is static include. it executes the service method. By extending GenericServlet we can write a servlet that supports our own custom protocol or any other protocol. Then when a client makes a request. more commonly. Q What is the difference between GenericServlet and HttpServlet? A GenericServlet supports any protocol. It is inline inclusion. Q Can we write a constructor for servlet ? A Yes.where as Generic servlet can implement any protocol. the container will throw an exception. But the container will always call the default constructor only. Q What is the need of super. This init() method will be executed only once during the life time of a servlet.. If there is no ServletConfig our servlet will not have any servlet nature. All servlets implement this interface. the server loads and initializes the servlet by calling the init method. We can have a dynamic filename for <jsp:include>.init (config) in servlets ? A Then only we will be able to access the ServletConfig from our servlet. Q What is the life cycle of servlet? A Each servlet has the same life cycle: first. <jsp:include> is dynamic include. If default constructor is not present .

39 40 41 Q What is the meaning of response has already been committed error? A You will get this error only when you try to redirect a page after you already have flushed the output buffer.setHeader("Cache-Control". your HTTP server cannot send it right now if it hasn't . They are declarations.setDateHeader ("Expires". //prevents caching at the proxy server %> 35 36 37 38 Q How to refer the "this" variable within a JSP page? A Under JSP 1."no-store"). Q How do I prevent the output of my JSP or Servlet pages from being cached by the browser? A By setting appropriate HTTP header attributes we can prevent caching by the browser <% response. You can put a return statement to abort JSP processing. This happens because HTTP specification force the header to be set up before the lay out of the page can be shown. //HTTP 1. the page implicit object page is equivalent to "this". 0). When you try to send a redirect status.0 response. scriptlets. Q What are the parameters for service method ? A ServletRequest and ServletResponse Q What are cookies ? A Cookies are small textual information that are stored on client computer.1 response. Q Can we implement an interface in JSP ? A No."no-cache"). Cookies are used for session tracking.0.setHeader("Pragma".34 Q Can I just abort processing a JSP? A Yes. and returns a reference to the servlet generated by the JSP page. expressions. //HTTP 1. Q How many JSP scripting elements and what are they? A There are three scripting elements in JSP .

its contents will be automatically invoked when the specified bean is instantiated (Only at the time of instantiation. reuse JavaBeans components. The suffix must ends with .jsp. Simply it is giving the error due to the specification of HTTP 1.1 42 Q How do I use a scriptlet to initialize a newly instantiated bean? A A jsp:useBean action may optionally have a body. 43 Q What is JSP? A JSP is a server side scripting technology. The ServletContext gives information about the container. The servlet engine implements the ServletConfig interface in order to pass configuration information to a servlet. 44 Q What are JSP Actions? A JSP actions use constructs in XML syntax to control the behavior of the servlet engine. It also provides standard way for servlets to write events to a log file. You can dynamically insert a file.0 and 1. etc). although you are not restricted to using those alone. The server passes an object that implements the ServletConfig interface to the servlet's init() method. jsp:forward and Jsp: plugin 45 Q What is the difference between ServletContext and ServletConfig? A The ServletConfig gives the information about the servlet initialization parameters. If the body is specified. jsp:setProperty. JSP allows Java as well as a few special tags to be embedded into a web file (HTML/XML. or generate HTML for the Java plugin.finished to set up the header. 46 Q How can a servlet refresh automatically? . Available actions include: jsp:include. The ServletContext interface provides information to servlets regarding the environment in which they are running. jsp:getProperty. jsp:useBean. forward the user to another page.) Typically. the body will contain scriptlets or jsp:setProperty tags to initialize the newly instantiated bean.

52 Q What is a Hidden Comment A . The only limit is the Session ID length . which should not exceed more than 4K. which is normally supported by all browsers.requires to communicate with each other by sharing specific information (through method invocation) 51 Q What is a output comment? A A comment that is sent to the client in the viewable page source.<META HTTP-EQUIV="Refresh" CONTENT="5. The mechanism used is. You can see the comment by viewing the page source from your Web browser. returning the comment in the HTML output sent to the client. then Server keeps the TCP/IP connection open. 48 Q What is client side refresh? A The standard HTTP protocols ways of refreshing the page. without intervention from client. URL=/servlet/MyServlet/">This will refresh the page in the browser automatically and loads the new data every 5 seconds.A We can use a client-side Refresh or Server Push 47 Q What is Server side push? A Server Side push is useful when data needs to change regularly on the clients application or browser.allows to gain access to the other currently loaded servlets and perform certain tasks (through the ServletContext object) b) Servlet reuse allows the servlet to reuse the public methods of another servlet. c) Servlet collaboration . 50 Q Why should we go for inter servlet communication? A The three major reasons to use inter servlet communication are: a) Direct servlet manipulation . The JSP engine handles an output comment as un interpreted HTML text. when client first connects to Server. 49 Q What is the Max amount of information that can be saved in a Session Object ? A There is no such limit on the amount of information that can be saved in a Session Object.

Normally the intranet is blocked by a firewall and the network is exposed to the outer world only through a specific web server port.SingleThreadModel is pretty resource intensive from web server's perspective. that by passes the firewall. 57 Q What is the difference between ServletContext and PageContext? A ServletContext gives the information about the container and PageContext gives the information about the Request 58 Q Why in Servlet 2.Hidden Comments are JSP comments. In that case. 54 Q What is HttpTunneling? A HTTP tunneling is used to encapsulate other protocols within the HTTP or HTTPS protocols. Because SingleThreadModel is not scalable. The JSP engine ignores a hidden comment.which results in poor performance. all the un serviced requests are queued until something becomes free . The most serious issue is when the number of concurrent requests exhaust the servlet instance pool. 56 Q What is the better way to enable thread-safe servlets and JSPs? SingleThreadModel Synchronization? A The better approach is to use synchronization. that listens for only HTTP requests.4 specification SingleThreadModel has been deprecated? A . 55 Q How to pass information from JSP to included JSP? A By using <jsp:param> tag. Session can store objects and cookies can store only strings. But it is limited in cookie. A comments that documents the JSP page but is not sent to the client. and does not process any code within hidden comment tags. Cookies are faster than session. the protocol is embedded in HTTP and send as HttpRequest. To use any other protocol. Session should work regardless of the settings on the client browser. There is no limit on the amount of data that can be stored on session. 53 Q What are the differences between a session and a cookie? A Session is stored in server but cookie stored in client.

where as context init parameter is for the entire web application.getServletContext () also we will get a ServletContext object. 59 Q How do you pass data (including JavaBeans) to a JSP from a servlet? A By forwarding the request to the servlet ( the data must be there in the request scope) we can pass the data from a JSP to servlet. Context parameters are declared in a tag <context-param> directly inside the <web-app> tag. all the un serviced requests are queued until something becomes free ."value").getInitParamter (´nameµ).getServletContext ().addCookie(killCookie). When the number of concurrent requests exhaust the servlet instance pool. Any servlet or JSP in that web application can access context init parameter. Cookie c = new Cookie("name". 61 Q A How will you delete a cookie? Cookie c = new Cookie ("name". No bodyout side that servlet can access that. This is because a ServletConfig always hold a reference to ServletContext. response.addCookie(c). What are the different ways for getting a servlet context? We will get ServletContext by calling getServletConfig ().getInitParamter (´nameµ) where as method for accessing servlet init parameter is getServletConfig ().which results in poor performance. By calling this. What is the difference between an attribute and a parameter? 62 Q A 63 Q A 64 Q . 60 Q How can I set a cookie? A response. The methods for accessing context init parameter is getServletContext ().setMaxAge(0). It is declared inside the <servlet> tag inside Deployment Descriptor. What is the difference between Context init parameter and Servlet init parameter? Servlet init parameters are for a single servlet only. Also we can use a session to pass the data.SingleThreadModel is pretty resource intensive from web server's perspective. c. null).

65 Q A 66 Q A 67 Q A 68 Q A 69 Q A 70 Q A 71 Q A . Can we use ServletOutputStream object from a JSP page? No. A session time out value of zero or less in DD means that the session will never expire. You can however. How to make a context thread safe? Synchronizing the ServletContext is the only solution to make a ServletContext thread safe. How you can perform browser redirection? We can use the method sendRedirect of HttpServletResponse or forward method of RequestDispatcher. How will you include a static file in a JSP page? You can include a static resource to a JSP using <jsp:directive> or <%@ inlcude>. What JSP lifecycle methods we can override? You cannot override the _jspService() method within a JSP page. override the jspInit() and jspDestroy() methods within a JSP page. To specify session will never expire programmatically it must be negative value. Eg: synchronized (getServletContext ()) { // do whatever you want with thread safe context. But in programmatically it is specified in seconds. You are supposed to use JSPWriter object (given to you in the form of the implicit object out) only for replying to clients. The method to retrieve attribute is getAttribute () where as for parameter is getParamter (). } What is the difference between setting the session time out in deployment descriptor and setting the time out programmatically? In DD time out is specified in terms of minutes only. How can you stop JSP execution in the middle of processing a request? We can use the return statement to stop the processing of JSP.A The return type of attribute is object. We have a method setAttribute to set an attribute. where the return type of parameter is String. But there is no setters available for setting a parameter.

jspException request attribute.encodeURL() and response.Because JSP is compiled to servlet and all the statements will go inside service method. How will you pass information from JSP to included JSP? By using <%jsp:param> tag. any time you can stop the processing using return statement. By using the methods response. For that you need to create a request dispatcher for the JSP error page. or within JSP scriptlets and expressions. You can configure the DD as follows. and pass the exception object as a javax. 72 Q A How can I invoke a JSP error page from a servlet? You can invoke the JSP error page and pass the exception object to it from within a servlet. If the browser does not support cookies. you need to append the session ID for each and every link that is part of your servlet response.servlet. For URL rewriting to be effective. How does JSP handle runtime exceptions? Using errorPage attribute of page directive JSP handles runtime exceptions.encodeRedirectURL() we can achieve this. or if cookies are disabled. We need to specify isErrorPage=true if the current page is intended to use as a JSP error page. How can we set the inactivity period on a per-session basis? We can set the session time out programmatically by using the method setMaxInactiveInterval() of HttpSession. How can you declare methods in your JSP page? You can declare methods as declarations in your JSP page. you can still use session tracking using URL rewriting. The methods can then be invoked within any other methods you declare.jsp. How do you pass an init parameter to a JSP? You need to configure the DD for passing init parameter to a JSP. <servlet> 73 Q A Q A 74 75 Q A 76 Q A 77 Q A 78 Q A . How can I enable session tracking for JSP pages if the browser has disabled cookies? By default session tracking uses cookies to associate a session identifier with a user.

What are the different web servers available name few of them? Tomcat. which event will get notified ? HttpSessionBindingListener will get notified When an object is added and/or removed from the session object. whether the session is invalidated manually or automatically (timeout). How many cookies can one set in the response object of the servlet? Also. And the no of cookie is restricted to 20 cookies per server or domain When a session object gets added or removed to the session. What is URL Encoding and URL Decoding ? URL encoding is the method of replacing all the spaces and other extra characters into their corresponding Hex Characters and Decoding is the process of converting all Hex Characters back to their normal form.jsp</servlet-name> <jsp-file>test. What is the difference between an applet and a servlet? Servlets run inside a web server and applets run inside web browsers. the browser can receive and store 300 total cookies and 4 kilobytes per cookie. JRun 80 Q A 81 Q A 82 Q A 83 Q A 84 Q A .<servlet-name>test. or when the session is invalidated. Applets must have graphical user interfaces whereas servlets have no graphical user interfaces. Java Web Server. in which case the objects are first removed from the session.jsp<https://www.scribd.com/jsp-name> <init-param> <param-name>Abc</param-name> <param-value>Xyz</param-value> </init-param> </servlet> 79 Q A How can my application get to know when aHttpSession is removed? You can define a class which implements HttpSessionBindingListener and override the valueUnbound() method. are there any restrictions on the size of cookies? If the client is using Netscape.

a negative value is returned. The cookie will expire after that many seconds have passed.85 Q A What is a Java Bean? A Java Bean is a software component that has been designed to be reusable in a variety of different environments. init() is called whenever the servlet is loaded for the first time into the web server. the cookie's purpose will be described using this comment. When init() and Distroy() will be called. What is use of parseQueryString ? It parses a query string and builds a Hashtable of key-value pairs. Destroy will be called whenever the servlet is removed from the web server. Add-on ServletEngine: It is a plug-in to an existing server. If none was specified. What are the different types of ServletEngines? The different types of ServletEngines available are:. Negative values indicate the default behavior. What is the use of setComment and getComment methods in Cookies ? setComment: If a web browser presents this cookie to a user. What is a Session Id? It is a unique id assigned by the server to the user when a user starts a session. getMaxAge : Returns the maximum specified age of the cookie. It adds servlet support to a server that was not originally designed with servlets in mind. indicating the 86 Q A 87 Q A 88 Q A 89 Q A 90 Q A 91 Q A . where the values are arrays of strings. and will be deleted when the browser closes. Why we are used setMaxAge() and getMaxAge() in Cookies ? setMaxAge : Sets the maximum age of the cookie. or null if no such comment has been defined.Standalone ServletEngine: This is a server that includes built-in support for servlets. This is not supported by version zero cookies. getComment: Returns the comment describing the purpose of this cookie. The query string should have the form of a string packaged by the GET or POST method.

Explain the directory structure of a web application? The directory structure of a web application consists of two parts. classes directory (where we keeps all our classes and servlets) and lib directory (where we keeps all our jar files). 93 Q A 94 Q A 95 Q A 96 Q A 97 Q A 98 Q A . one servlet·s output is the input of next servlet. WEB-INF folder consists of web. In servlet chaining. How will you communicate from an applet to servlet? There are three ways to communicate from an applet to servlet and they are: HTTP Communication (Text-based and object-based) . The public folder contains the static resources of the web application. This process continues until the last servlet is reached. which calls a service method of the servlet. getSecure method returns the value of the 'secure' flag. We are achieving Servlet Chaining with the help of RequestDispatcher. How do you communicate between the servlets? We can communicate between servlets by using RequestDespatcher interface and servlet chaining.xml (the deployment descriptor). You can call a servlet with parameters in the URL like ?param=value How do servlets handle multiple simultaneous requests? When a request comes in. What is Servlet chaining? Servlet chaining is a technique in which two or more servlets can cooperate in servicing a single request. Its output is then sent back to the client. the web server will start a new thread and the request is assigned to a thread. 92 Q A What is the use of setSecure() and getSecure() in Cookies ? setSecure method indicates to the web browser that the cookie should only be sent using a secure protocol (https). Socket Communication and RMI Communication Can we call a servlet with parameters in the URL? Yes. A private directory called WEB-INF and a public resource directory which contains files server to public.default behavior described with setMaxAge.

What are the uses of ServletResponse interface? A ServletResponse allows the servlet to set the content length and MIME type of that response. 103 Q Is HTML page a web component? A No.xml. 106 Q What is deployment descriptor? A A deployment descriptor is an XML based file which describes a web application's deployment settings. Containers provide components with services such as lifecycle management. The process of loading a servlet before any request comes in is called preloading or pre initializing a servlet. and the names of the remote host that made the request and the server that received it. which can be specified in the deployment descriptor to make the servlet container load and initialize the servlet as soon as it starts up. the protocol (scheme) being used by the client.99 Q A What is pre initialization of a servlet? A container doesn't initialize the servlets when it starts up. security. 105 Q What is the web container? A Servlet and JSP containers are collectively referred to as Web containers. ServletOutputStream and a Writer through which the servlet can send data. 100 What are the uses of ServletRequest? The ServletRequest gives information such as the names of the parameters passed by the client. The servlet specification defines the <load-on-startup> element. It initializes a servlet when it receives a request for that servlet first time. This is called lazy loading. deployment. 104 Q What is the container? AA container is a runtime support of a system-level entity. The input stream. Even the server-side utility classes are not considered web components. Static HTML pages and applets are not considered as web components by J2EE specification. It provides an output stream. 107 Q How can I print the stack trace of an exception from a JSP page? Q A . and threading. The name of deployment descriptor of a web application is web. The service method supports standard HTTP client requests by dispatching each request to a method designed to handle that request. ServletInputStream. 102 Q How HTTP Servlet handles client requests? A An HTTP Servlet handles client requests through its service method.

getWriter(). We can store any type of objects in session. But application server provides a lot of services like security. the objects need not to be serializable. scalability. You can use this WAR file to deploy your web application. 112 Q What is servlet exception? A It indicates that there is an exception occurred in the servlet. transaction . 110 Q How can you implement singleton pattern in servlets ? A All servlets are singleton only . Application server will be having EJB support where web server don't have an EJB support. It is a compressed version of your web application. Eg: PrintWriter pw = response.A By creating an object of PrintWriter we can print the stack trace in JSP page. 115 Q What is a servlet filter? A . exception. 111 Q What is the difference between an application server and a web server? A Everything in web server must be achieved programmatically. 108 Q Do objects stored in a HTTP Session need to be serializable? Or can it store any object? A No. 113 Q Can we implement Runnable interface from within our servlet? A Our servlet can implement the Runnable interface.printStackTrace(pw). 114 Q What is a WAR file? A WAR stands for Web Archive. 109 Q What is the differecnce between JspWriter and PrintWriter? A JspWriter is buffered. if the servlet is not implementing SingleThreadModel.

Servlet filters are pluggable Web components that allow us to implement preprocessing and post-processing logic in our Web applications. .