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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.

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

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

What are the lifecycle of JSP? When presented with JSP page the JSP engine does the following 7 phases. What is a Declaration? It declares one or more variables or methods for use later in the JSP source file. Page compilation: page is compiled into a class file Page loading : This class file is loaded. But in resourcecontext.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.xml file. This will be included in the service method of the generated servlet. 17 Q A What are context initialization parameters? Context initialization parameters are specified by the <contextparam> in the web. 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. Create an instance :. What is a Expression? Expressions are act as place holders for language expression.getRequestDispatcher()? In request. expression is evaluated each time the page is accessed. What is the difference in using request.getRequestDispatcher() and context. and a java file which is a servlet is created.getRequestDispatcher(path) in order to create it we need to give the absolute path of the resource.getRequestDispatcher(path) in order to create it we need to give the relative path of the resource. these are initialization parameter for the whole application. A declaration must contain at least one complete 18 Q A 19 Q A . o 15 Q A 16 Q A o o o o o o Page translation: -page is parsed.translation phase.

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

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

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. //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. the page implicit object page is equivalent to "this". scriptlets. You can put a return statement to abort JSP processing. Q How many JSP scripting elements and what are they? A There are three scripting elements in JSP . 0). 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. Q Can we implement an interface in JSP ? A No.0."no-store"). When you try to send a redirect status. //HTTP 1."no-cache"). and returns a reference to the servlet generated by the JSP page. your HTTP server cannot send it right now if it hasn't .1 response. expressions.setHeader("Pragma".0 response. This happens because HTTP specification force the header to be set up before the lay out of the page can be shown. 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. Cookies are used for session tracking. They are declarations.setHeader("Cache-Control".setDateHeader ("Expires". //HTTP 1.34 Q Can I just abort processing a JSP? A Yes.

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

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. then Server keeps the TCP/IP connection open.<META HTTP-EQUIV="Refresh" CONTENT="5. when client first connects to Server. c) Servlet collaboration . without intervention from client. which should not exceed more than 4K.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. You can see the comment by viewing the page source from your Web browser. The mechanism used is. The JSP engine handles an output comment as un interpreted HTML text. 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. which is normally supported by all browsers. 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 . 48 Q What is client side refresh? A The standard HTTP protocols ways of refreshing the page. 52 Q What is a Hidden Comment A . URL=/servlet/MyServlet/">This will refresh the page in the browser automatically and loads the new data every 5 seconds.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. The only limit is the Session ID length . returning the comment in the HTML output sent to the client.

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

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

where the return type of parameter is String. What JSP lifecycle methods we can override? You cannot override the _jspService() method within a JSP page. A session time out value of zero or less in DD means that the session will never expire. To specify session will never expire programmatically it must be negative value. Eg: synchronized (getServletContext ()) { // do whatever you want with thread safe context. You are supposed to use JSPWriter object (given to you in the form of the implicit object out) only for replying to clients.A The return type of attribute is object. 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. You can however. But there is no setters available for setting a parameter. But in programmatically it is specified in seconds. We have a method setAttribute to set an attribute. 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>. override the jspInit() and jspDestroy() methods within a JSP page. 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. Can we use ServletOutputStream object from a JSP page? No. 65 Q A 66 Q A 67 Q A 68 Q A 69 Q A 70 Q A 71 Q A .

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

or when the session is invalidated.jsp<> <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.<servlet-name>test. in which case the objects are first removed from the session. JRun 80 Q A 81 Q A 82 Q A 83 Q A 84 Q A . Applets must have graphical user interfaces whereas servlets have no graphical user interfaces. How many cookies can one set in the response object of the servlet? Also. 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. What are the different web servers available name few of them? Tomcat. whether the session is invalidated manually or automatically (timeout). the browser can receive and store 300 total cookies and 4 kilobytes per cookie. Java Web Server. What is the difference between an applet and a servlet? Servlets run inside a web server and applets run inside web browsers. 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. are there any restrictions on the size of cookies? If the client is using Netscape. which event will get notified ? HttpSessionBindingListener will get notified When an object is added and/or removed from the session object.jsp</servlet-name> <jsp-file>test.

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

How do you communicate between the servlets? We can communicate between servlets by using RequestDespatcher interface and servlet chaining. In servlet chaining. 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. 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). 93 Q A 94 Q A 95 Q A 96 Q A 97 Q A 98 Q A . The public folder contains the static resources of the web application. Socket Communication and RMI Communication Can we call a servlet with parameters in the URL? Yes. which calls a service method of the servlet.default behavior described with setMaxAge. one servlet·s output is the input of next servlet. classes directory (where we keeps all our classes and servlets) and lib directory (where we keeps all our jar files).xml (the deployment descriptor). getSecure method returns the value of the 'secure' flag. the web server will start a new thread and the request is assigned to a thread. What is Servlet chaining? Servlet chaining is a technique in which two or more servlets can cooperate in servicing a single request. This process continues until the last servlet is reached. Its output is then sent back to the client. Explain the directory structure of a web application? The directory structure of a web application consists of two parts. WEB-INF folder consists of web. A private directory called WEB-INF and a public resource directory which contains files server to public. We are achieving Servlet Chaining with the help of RequestDispatcher. 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 servlet specification defines the <load-on-startup> element.99 Q A What is pre initialization of a servlet? A container doesn't initialize the servlets when it starts up. which can be specified in the deployment descriptor to make the servlet container load and initialize the servlet as soon as it starts up. Even the server-side utility classes are not considered web components. 102 Q How HTTP Servlet handles client requests? A An HTTP Servlet handles client requests through its service method. The name of deployment descriptor of a web application is web. ServletInputStream. It provides an output stream. 104 Q What is the container? AA container is a runtime support of a system-level entity. 107 Q How can I print the stack trace of an exception from a JSP page? Q A . the protocol (scheme) being used by the client. The input stream.xml. 106 Q What is deployment descriptor? A A deployment descriptor is an XML based file which describes a web application's deployment settings. What are the uses of ServletResponse interface? A ServletResponse allows the servlet to set the content length and MIME type of that response. 100 What are the uses of ServletRequest? The ServletRequest gives information such as the names of the parameters passed by the client. and threading. security. Static HTML pages and applets are not considered as web components by J2EE specification. deployment. Containers provide components with services such as lifecycle management. and the names of the remote host that made the request and the server that received it. It initializes a servlet when it receives a request for that servlet first time. ServletOutputStream and a Writer through which the servlet can send data. The process of loading a servlet before any request comes in is called preloading or pre initializing a servlet. The service method supports standard HTTP client requests by dispatching each request to a method designed to handle that request. This is called lazy loading. 103 Q Is HTML page a web component? A No. 105 Q What is the web container? A Servlet and JSP containers are collectively referred to as Web containers.

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

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