JSP Java Interview Questions | Eklavya Online

JSP Java Interview Questions

A JavaBeans component that corresponds to a JSP page that includes JavaServer Faces components. The backing bean defines properties for the components on the page and methods that perform processing for the component. This processing includes event handling, validation, and processing associated with navigation.

  • JSP files,
  • class files for servlets,
  • GIF and HTML files, and
  • a Web deployment descriptor.

Web modules are packaged as JAR files with a .war (Web ARchive) extension.

Here is the sample code that makes use of the default compareTo( ) provided in the String class as it implements the Comparable interface and the Collections utility class that provides a sorting method, which internally uses the efficient “merge sort” algorithm.

import java.util.Arrays;

import java.util.Collections;

import java.util.List;

 

public class Sort1 {

public static void main(String[] args) {

List<string> values = Arrays.asList(“JEE”, “Java”, “Servlets”, “JMS”, “JNDI”, “JDBC”, “JSP”, “EJB”);

Collections.sort(values); // uses the default compareTo(String anotherString)  in the String class

System.out.println(values);

}

}

Output:

[EJB, JDBC, JEE, JMS, JNDI, JSP, Java, Servlets]

Yes, 2 things — firstly, the above sort is case sensitive, that is the uppercase takes priority over lowercase pushing ‘Java’ after ‘JSP’. Secondly, if the collection had any null values, it will throw a NullpointerException.

These two issues can be rectified by providing a custom sorting implementation that ignores case and handles null values by pushing them to the end. The Collections class’s sort method takes a Comparator implementation as a second argument. In the code below, the Comparator has been implemented as an anonymous inner class. The compare(…) method will be called a number of times by the Collections.sort(list, comparator).

import java.util.Arrays;

import java.util.Collections;

import java.util.Comparator;

import java.util.List;

 

public class Sort2 {

 

public static void main(String[] args) {

List<String> values = Arrays.asList(“JEE”, “Java”, null,  “Servlets”, null, “JMS”, “JNDI”, “JDBC”, “JSP”, null,”EJB”);

 

//The comparator is defined as an anonymous inner class, but it can be

//defined in its own class. Handles nulls and ignores case

Collections.sort(values, new Comparator<String>() {

 

@Override

public int compare(String o1, String o2) {

//push the null values to the end

if(o1 == null){

if(o2 == null) {

return 0;

}

return 1;

}

else if(o2 == null){

return -1;

}

return o1.compareToIgnoreCase(o2);

}

}); // anonymous inner class end

 

System.out.println(values);

}

}

Any number of Comparator classes can be created to sort them differently as shown below.

import java.util.Comparator;

 

public class JavaTechnologyComparator implements Comparator<JavaTechnology> {

 

@Override

public int compare(JavaTechnology t1, JavaTechnology t2) {

 

//handle null values here

Integer rank1 = t1.getRank();

Integer rank2 = t2.getRank();

int rankVal = rank1.compareTo(rank2);

int nameVal = t1.getName().toLowerCase().compareTo(t2.getName().toLowerCase());

 

//if same rank, then sort by name

if(rankVal == 0){

return nameVal;

}

//else sort by rank

return rankVal ;

}

}

Now, the Sort3Test class has been slightly modified to use a Comparator.

import java.util.Collections;

import java.util.List;

 

public class Sort3Test {

public static void main(String[] args) {

 

JavaTechnology jt1 = new JavaTechnology(“JEE”, 1);

JavaTechnology jt2 = new JavaTechnology(“Java”, 1);

JavaTechnology jt3 = new JavaTechnology(“Servlets”, 2);

JavaTechnology jt4 = new JavaTechnology(“JSP”, 2);

JavaTechnology jt5 = new JavaTechnology(“JNDI”, 3);

JavaTechnology jt6 = new JavaTechnology(“EJB”, 4);

JavaTechnology jt7 = new JavaTechnology(“JMS”, 5);

 

List<JavaTechnology> values = Arrays.asList(jt1, jt2, jt3, jt4, jt5, jt6, jt7);

 

Collections.sort(values, new JavaTechnologyComparator());

// invokes the compare(…) in JavaTechnologyComparator

// a number of times

System.out.println(values);

}

}

The output will be:

[(Java , 1), (JEE , 1), (JSP , 2), (Servlets , 2), (JNDI , 3), (EJB , 4), (JMS , 5)]

This should now enable you to sort any Java objects.

Here is an example of a JavaTechnology custom object that implements a default sorting logic based on the rank (i.e popularity).

public class JavaTechnology implements Comparable<JavaTechnology>{

 

private String name;

private int rank;   // popularity lower value means more popular

 

public JavaTechnology(String name, int rank){

this.name = name;

this.rank = rank;

}

 

//default implementation by rank alone

@Override

public int compareTo(JavaTechnology technology) {

int rank1 = this.rank;

int rank2 = technology.rank;

if (rank1 > rank2){

return +1;

}else if (rank1 < rank2){

return -1;

}else{

return 0;

}

}

 

//required for printing, displaying, etc.

@Override

public String toString() {

return “(” + name + ” , ” + rank + “)”;

}

}

Now, a simple test class

import java.util.Arrays;

import java.util.Collections;

import java.util.List;

 

public class Sort3Test {

 

public static void main(String[] args) {

JavaTechnology jt1 = new JavaTechnology(“JEE”, 1);

JavaTechnology jt2 = new JavaTechnology(“Java”, 1);

JavaTechnology jt3 = new JavaTechnology(“Servlets”, 2);

JavaTechnology jt4 = new JavaTechnology(“JSP”, 2);

JavaTechnology jt5 = new JavaTechnology(“JNDI”, 3);

JavaTechnology jt6 = new JavaTechnology(“EJB”, 4);

JavaTechnology jt7 = new JavaTechnology(“JMS”, 5);

 

List<javatechnology> values = Arrays.asList(jt1, jt2, jt3, jt4, jt5, jt6, jt7);

 

Collections.sort(values); // invokes the compareTo(…) method in JavaTechnology a number of times

 

System.out.println(values);

 

}

 

}

Output:

[(JEE , 1), (Java , 1), (Servlets , 2), (JSP , 2), (JNDI , 3), (EJB , 4), (JMS , 5)]

A vendor that provides the Java classes that implement components’ methods, JSP page definitions, and any required deployment descriptors.

A J2EE component is a self-contained functional software unit that is assembled into a J2EE application with its related classes and files and communicates with other components. The J2EE specification defines the following J2EE components:

  • Application clients and applets are client components.
  • Java Servlet and JavaServer PagesTM (JSPTM) technology components are web components.
  • Enterprise JavaBeansTM (EJBTM) components (enterprise beans) are business components.
  • Resource adapter components provided by EIS and tool vendors.

response. setHeader(”Set-Cookie”, “cookie string”); To give the response-object to a bean, write a method setResponse (HttpServletResponse response) – to the bean, and in jsp-file:<% bean. setResponse (response); %>

JSP is a dynamic scripting capability for web pages that allows Java as well as a few special tags to be embedded into a web file (HTML/XML, etc). The suffix traditionally ends with .jsp to indicate to the web server that the file is a JSP files. JSP is a server side technology – you can’t do any client side validation with it. The advantages are: a) The JSP assists in making the HTML more functional. Servlets on the other hand allow outputting of HTML but it is a tedious process. b) It is easy to make a change and then let the JSP capability of the web server you are using deal with compiling it into a servlet and running it.

JavaServer Pages (JSP) technology is the Java platform technology for delivering dynamic content to web applications in a portable, secure and well-defined way. The JSP Technology allows us to use HTML, Java, JavaScript and XML in a single file to create high quality and fully functionaly User Interface components for Web Applications.

Say that I have a cookie called “foo, ” that I set a while ago & I want it to go away. I simply: <% Cookie killCookie = new Cookie(”foo”, null); KillCookie. setPath(”/”); killCookie. setMaxAge(0); response. addCookie(killCookie); %>

JSP scripting elements lets to insert Java code into the servlet that will be generated from the current JSP page. There are three forms: a) Expressions of the form <%= expression %> that are evaluated and inserted into the output, b) Scriptlets of the form<% code %>that are inserted into the servlet’s service method, and c) Declarations of the form <%! Code %>that are inserted into the body of the servlet class, outside of any existing methods.

JSP pages are focused around HTML (or XML) with Java codes and JSP tags inside them. When a web server that has JSP support is asked for a JSP page, it checks to see if it has already compiled the page into a servlet. Thus, JSP pages become servlets and are transformed into pure Java and then compiled, loaded into the server and executed.

A JSP directive affects the overall structure of the servlet class. It usually has the following form:<%@ directive attribute=”value” %> However, you can also combine multiple attribute settings for a single directive, as follows:<%@ directive attribute1=”value1″ attribute 2=”value2″ . . . attributeN =”valueN” %> There are two main types of directive: page, which lets to do things like import classes, customize the servlet superclass, and the like; and include, which lets to insert a file into the servlet class at the time the JSP file is translated into a servlet

To simplify code in JSP expressions and scriptlets, we can use eight automatically defined variables, sometimes called implicit objects. They are request, response, out, session, application, config, pageContext, and page.

JSP actions use constructs in XML syntax to control the behavior of the servlet engine. You can dynamically insert a file, reuse JavaBeans components, forward the user to another page, or generate HTML for the Java plugin. Available actions include: jsp:include – Include a file at the time the page is requested. jsp:useBean – Find or instantiate a JavaBean. jsp:setProperty – Set the property of a JavaBean. jsp:getProperty – Insert the property of a JavaBean into the output. jsp:forward – Forward the requester to a newpage. Jsp: plugin – Generate browser-specific code that makes an OBJECT or EMBED

?– (1) Request Lifetime: Using this technique to pass beans, a request dispatcher (using either “include” or forward”) can be called. This bean will disappear after processing this request has been completed. Servlet: request. setAttribute(”theBean”, myBean); RequestDispatcher rd = getServletContext(). getRequestDispatcher(”thepage. jsp”); rd. forward(request, response); JSP PAGE:<jsp: useBean id=”theBean” scope=”request” class=”. . . . . ” />(2) Session Lifetime: Using this technique to pass beans that are relevant to a particular session (such as in individual user login) over a number of requests. This bean will disappear when the session is invalidated or it times out, or when you remove it. Servlet: HttpSession session = request. getSession(true); session. putValue(”theBean”, myBean); /* You can do a request dispatcher here, or just let the bean be visible on the next request */ JSP Page:<jsp:useBean id=”theBean” scope=”session” class=”. . . ” /> 3) Application Lifetime: Using this technique to pass beans that are relevant to all servlets and JSP pages in a particular app, for all users. For example, I use this to make a JDBC connection pool object available to the various servlets and JSP pages in my apps. This bean will disappear when the servlet engine is shut down, or when you remove it. Servlet: GetServletContext(). setAttribute(”theBean”, myBean); JSP PAGE:<jsp:useBean id=”theBean” scope=”application” class=”. . . ” />

JSP translation is an action that refers to the convertion of the JSP Page into a Java Servlet. This class is essentially a servlet class wrapped with features for JSP functionality.

JSP Scriptlets is a term used to refer to pieces of Java code that can be embedded in a JSP PAge. Scriptlets begins with <% tag and ends with %> tag. Java code written inside scriptlet executes every time the JSP is invoked.

Can contain HTML, JavaScript, XML and Java Code whereas Servlets can contain only Java Code, making JSPs more flexible and powerful than Servlets.

However, Servlets have their own place in a J2EE application and cannot be ignored altogether. They have their strengths too which cannot be overseen.

A language used to write expressions that access the properties of JavaBeans components. EL expressions can be used in static text and in any standard or custom tag attribute that can accept an expression

A tag that references a JSP custom action

Servlets and Java Server Pages are complementary APIs, both providing a means for generating dynamic Web content. A servlet is a Java class implementing the javax.servlet.Servlet interface that runs within a Web or application server’s servlet engine, servicing client requests forwarded to it through the server. A Java Server Page is a slightly more complicated beast. JSP pages contain a mixture of HTML, Java scripts (not to be confused with JavaScript), JSP elements, and JSP directives. The elements in a Java Server Page will generally be compiled by the JSP engine into a servlet, but the JSP specification only requires that the JSP page execution entity follow the Servlet Protocol.

The advantage of Java Server Pages is that they are document-centric. Servlets, on the other hand, look and act like programs. A Java Server Page can contain Java program fragments that instantiate and execute Java classes, but these occur inside an HTML template file and are primarily used to generate dynamic content. Some of the JSP functionality can be achieved on the client, using JavaScript. The power of JSP is that it is server-based and provides a framework for Web application development. Rather than choosing between servlets and Java Server Pages, you will find that most non-trivial applications will want to use a combination of JSP and servlets. In fact, the JSP 1.1 and Servlet 2.2 specifications are based around the concept of the Web application, combining the two APIs into a unified framework.

There are two types of comments are allowed in the JSP. These are hidden and output comments. A hidden comments does not appear in the generated output in the html, while output comments appear in the generated output.

Example of hidden comment:

<%– This is hidden comment –%>

Example of output comment:<!– This is output comment –>

Compilation error, as two variables with same name can’t be declared. This happens because, when a page is included statically, entire code of included page becomes part of the new page. at this time there are two declarations of variable ‘a’. Hence compilation error.

Yes. Preemptive termination of request processing on an error condition is a good way to maximize the throughput of a high-volume JSP engine. The trick (assuming Java is your scripting language) is to use the return statement when you want to terminate further processing.

There are three scripting language elements:

  • Declarations
  • Scriptlets
  • Expressions

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 actionvalue=””/ >

Java Server Pages (JSP) is a platform independent presentation layer technology that comes with SUN s J2EE platform. JSPs are normal HTML pages with Java code pieces embedded in them. JSP pages are saved to *.jsp files. A JSP compiler is used in the background to generate a Servlet from the JSP page.

Life-cycle methods of the JSP are:

  1. jspInit(): The container calls the jspInit() to initialize the servlet instance. It is called before any other method, and is called only once for a servlet instance.
  2. _jspService(): The container calls the _jspservice() for each request and it passes the request and the response objects. _jspService() method cann’t be overridden.
  3. jspDestroy(): The container calls this when its instance is about to destroyed.
    The jspInit() and jspDestroy() methods can be overridden within a JSP page.

Implicit objects are the objects available to the JSP page. These objects are created by Web container and contain information related to a particular request, page, or application.

The JSP implicit objects are:

Application, config, exception, out, page, pageContext, request, response andsession.

By setting properties that prevent caching in your JSP Page.They are:

 

<%

response.setHeader(“pragma”,”no-cache”);//HTTP 1.1

response.setHeader(“Cache-Control”,”no-cache”);

response.setHeader(“Cache-Control”,”no-store”);

response.addDateHeader(“Expires”, -1);

response.setDateHeader(“max-age”, 0);

//response.setIntHeader(“Expires”, -1);//prevents caching at the proxy server

response.addHeader(“cache-Control”, “private”);

%>

Because no plug-ins or security policy files are needed on the client systems(applet does). Also, JSP pages enable cleaner and more module application design because they provide a way to separate applications programming from web page design. This means personnel involved in web page design do not need to understand Java programming language syntax to do their jobs.

Custom JSP tag is a tag you defined. You define how a tag, its attributes and its body are interpreted, and then group your tags into collections called tag libraries that can be used in any number of JSP files. To use custom JSP tags, you need to define three separate components:

  • the tag handler class that defines the tag\’s behavior
  • the tag library descriptor file that maps the XML element names to the tag implementations
  • the JSP file that uses the tag library

When the first two components are done, you can use the tag by using taglib directive:

<%@ taglib uri=”xxx.tld” prefix=”…” %>

Then you are ready to use the tags you defined. Let’s say the tag prefix is test:

MyJSPTag or

JavaBeans are Java utility classes you defined. Beans have a standard format for Java classes. You use tags to declare a bean and use to set value of the bean class and use to get value of the bean class.

<%=identifier.getclassField() %>

Custom tags and beans accomplish the same goals — encapsulating complex behavior into simple and accessible forms. There are several differences:

Custom tags can manipulate JSP content; beans cannot.Complex operations can be reduced to a significantly simpler form with custom tags than with beans. Custom tags require quite a bit more work to set up than do beans.Custom tags usually define relatively self-contained behavior, whereas beans are often defined in one servlet and used in a different servlet or JSP page.Custom tags are available only in JSP 1.1 and later, but beans can be used in all JSP 1.x versions.

A JSP scripting element that declares methods, variables, or both in a JSP page.

A text-based document containing static text and JSP elements that describes how to process a request to create a response. A JSP page is translated into and handles requests as a servlet.

A JSP page is a text-based document that contains two types of text: static template data, which can be expressed in any text-based format such as HTML, SVG, WML, and XML, and JSP elements, which construct dynamic content.

  • Efficient: With traditional CGI, a new process is started for each HTTP request. If the CGI program does a relatively fast operation, the overhead of starting the process can dominate the execution time. With servlets, the Java Virtual Machine stays up, and each request is handled by a lightweight Java thread, not a heavyweight operating system process. Similarly, in traditional CGI, if there are N simultaneous request to the same CGI program, then the code for the CGI program is loaded into memory N times. With servlets, however, there are N threads but only a single copy of the servlet class. Servlets also have more alternatives than do regular CGI programs for optimizations such as caching previous computations, keeping database connections open, and the like.
  • Convenient: Hey, you already know Java. Why learn Perl too? Besides the convenience of being able to use a familiar language, servlets have an extensive infrastructure for automatically parsing and decoding HTML form data, reading and setting HTTP headers, handling cookies, tracking sessions, and many other such utilities.
  • Powerful: Java servlets let you easily do several things that are difficult or impossible with regular CGI. For one thing, servlets can talk directly to the Web server (regular CGI programs can’t). This simplifies operations that need to look up images and other data stored in standard places. Servlets can also share data among each other, making useful things like database connection pools easy to implement. They can also maintain information from request to request, simplifying things like session tracking and caching of previous computations.
  • Portable: Servlets are written in Java and follow a well-standardized API. Consequently, servlets written for, say I-Planet Enterprise Server can run virtually unchanged on Apache, Microsoft IIS, or WebStar. Servlets are supported directly or via a plugin on almost every major Web server.
  • Inexpensive: There are a number of free or very inexpensive Web servers available that are good for “personal” use or low-volume Web sites. However, with the major exception of Apache, which is free, most commercial-quality Web servers are relatively expensive. Nevertheless, once you have a Web server, no matter the cost of that server, adding servlet support to it (if it doesn’t come preconfigured to support servlets) is generally free or cheap.

A Connection to a database can be established from a jsp page by writing the code to establish a connection using a jsp scriptlets.

Further then you can use the resultset object “res” to read data in the following way.

Yes. However, unlike Servlet, you are not required to implement HTTP-protocol specific methods like doGet() or doPost() within your JSP page. You can obtain the data for the FORM input elements via the request implicit object within a scriptlet or expression as.

Is there a way to reference the “this” variable within a JSP page? Yes, there is. Under JSP 1.0, the page implicit object is equivalent to “this”, and returns a reference to the Servlet generated by the 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.

JSP Custom tags are user defined JSP language elements. JSP custom tags are user defined tags that can encapsulate common functionality. For example you can write your own tag to access the database and performing database operations. You can also write custom tags to encapsulate both simple and complex behaviors in an easy to use syntax. The use of custom tags greatly enhances the functionality and simplifies the readability of JSP pages.

< jsp : useBean > tag is used to use any java object in the jsp page. Here are the scope values for < jsp : useBean > tag:

  • page
  • request
  • session and
  • application

When a JSP include directive is used, the included file’s code is added into the added JSP page at page translation time, this happens before the JSP page is translated into a servlet. While if any page is included using action tag, the page’s output is returned back to the added page. This happens at runtime.

Use the following ways to pass control of a request from one servlet to another or one jsp to another.

  • First is RequestDispatcher object‘s forward method to pass the control.
  • Second is response.sendRedirect method.

YES. JSP technology is extensible through the development of custom actions, or tags,

which are encapsulated in tag libraries.

A JSP declaration, scriptlet, or expression whose syntax is defined by the JSP specification and whose content is written according to the scripting language used in the JSP page. The JSP specification describes the syntax and semantics for the case where the language page attribute is “java”.

A JSP element that gives an instruction to the JSP container and is interpreted at translation time.

The errorPage attribute of the page directive can be used to catch run-time exceptions automatically and then forwarded to an error processing page. You can define the error page to which you want the request forwarded to, in case of an exception, in each JSP Page. Also, there should be another JSP that plays the role of the error page which has the flag isErrorPage set to True.

JSP actions are XML tags that direct the server to use existing components or control the behavior of the JSP engine. JSP Actions consist of a typical (XML-based) prefix of “jsp” followed by a colon, followed by the action name followed by one or more attribute parameters.

There are six JSP Actions:

  • < jsp : include / >
  • < jsp : forward / >
  • < jsp : plugin / >
  • < jsp : usebean / >
  • < jsp : setProperty / >
  • < jsp : getProperty / >
  • <%@ include file=”filename” %> is the JSP include directive.At JSP page translation time, the content of the file given in the include directive is ‘pasted’ as it is, in the place where the JSP include directive is used. Then the source JSP page is converted into a java servlet class. The included file can be a static resource or a JSP page. Generally JSP include directive is used to include header banners and footers.The JSP compilation procedure is that, the source JSP page gets compiled only if that page has changed. If there is a change in the included JSP file, the source JSP file will not be compiled and therefore the modification will not get reflected in the output.
  • <jsp:include page=”relativeURL” /> is the JSP include action element.The jsp:include action element is like a function call. At runtime, the included file will be ‘executed’ and the result content will be included with the soure JSP page. When the included JSP page is called, both the request and response objects are passed as parameters.If there is a need to pass additional parameters, then jsp:param element can be used. If the resource is static, its content is inserted into the calling JSP file, since there is no processing needed.

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

JSP Output Comments are the comments that can be viewed in the HTML source file. They are comments that are enclosed within the < ! – – Your Comments Here – – >

JSP is mostly used to develop the user interface, It plays are role of View in the MVC Model.

  • Cache static data using jspInit() method.
  • Release static data in jspDestroy() method.
  • To concatenate string use, StringBuffer.
  • Do not use println() method.
  • Do not use PrintWriter to send binary data. Use ServletOutputStream.
  • Always flush data in sections.
  • Use getLastModified() method to handle browser and server cache.
  • Use application server cache.
  • Use session in following order: HttpSession, Hidden fields, Cookies, URL rewriting.
  • Always remove HttpSession explicitly.
  • Disable Servlet auto reloading.

We can override jspinit() and jspDestroy() methods but not _jspService().

Typically, a default inactivity lease period for all sessions is set within your JSPengine 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.

Cookie mycook = new Cookie(“name”,”value”);

response.addCookie(mycook);

Cookie killmycook = new Cookie(“mycook”,”value”);

killmycook.setMaxAge(0);

killmycook.setPath(“/”);

killmycook.addCookie(killmycook);

A tag library that encapsulates core functionality common to many JSP applications.JSTL has support for common, structural tasks such as iteration and conditionals, tags for manipulating XML documents, internationalization and locale-specific formatting tags, SQL tags, and functions

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.

Both the tags include information from one JSP page in another. The differences are:

< jsp : include page = … >

This is like a function call from one jsp to another jsp. It is executed ( the included page is executed and the generated html content is included in the content of calling jsp) each time the client page is accessed by the client. This approach is useful while modularizing a web application. If the included file changes then the new content will be included in the output automatically.

< % @ include file = … >

In this case the content of the included file is textually embedded in the page that have < % @ include file=”..”> directive. In this case when the included file changes, the changed content will not get included automatically in the output. This approach is used when the code from one jsp file required to include in multiple jsp files.

Java Server Page is a standard Java extension that is defined on top of the servlet Extensions. The goal of JSP is the simplified creation and management of dynamic Web pages. JSPs are secure, platform-independent, and best of all, make use of Java as a server-side scripting language.

A JSP scripting element containing any code fragment that is valid in the scripting language used in the JSP page. The JSP specification describes what is a valid scriptlet for the case where the language page attribute is “java”.

A JSP page written in XML syntax and subject to the constraints of XML documents.

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”).

To “include” another resource with a JSP, you have two options: the include directive and the include action.The include directive executes when the JSP is compiled, which parses any JSP elements in the included file for a static result that is the same for every instance of that JSP. The syntax for the include directive is

<@ include file=”some-filename” %>.

The include action, on the other hand, executes for each client request of the JSP, which means the file is not parsed but included in place. This provides the capability to dynamically change not only the content that you want to include, but also the output of that content. The syntax for the include action is <jsp:include page=”some-filename” flush=”true” />. Note that the flush attribute must always be included (in JSP 1.1) to force a flush of the buffer in the output stream.

You can also pass parameters to the included file using the same process

<jsp:forward> action:

<jsp:include page=”template.htm” flush=”true” >

<jsp:param name=”name1″ value=”value1″ />

</jsp:include>

Expression tag is used to insert Java values directly into the output.

Syntax for the Expression tag is: <%= 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. The most commonly used language is regular Java.

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 requestscope via the useBean action.

  • <jsp:useBean id=”fBean”class=”govi.FormBean” scope=”request”/>
  • <jsp:getPropertyname=”fBean” property=”name”/>
  • <jsp:getProperty name=”fBean” property=”addr”/>
  • <jsp:getProperty name=”fBean” property=”age”/>
  • <jsp:getProperty name=”fBean” property=”personalizationInfo”/>

You first set “Errorpage” attribute of PAGE directory to the name of the error page (ie Errorpage=”error.jsp”)in your jsp page .Then in the error jsp page set “isErrorpage=TRUE”. When an error occur in your jsp page it will automatically call the error page.

There are three scripting language elements:

declarations, scriptlets, expressions.

A source file containing a reusable fragment of JSP code that is translated into a tag handler when a JSP page is translated into a servlet.

A portion of a JSP page that is recognized by a JSP translator. An element can be a directive, an action, or a scripting element.

A container that provides the same services as a servlet container and an engine that interprets and processes JSP pages into a servlet.

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:

  • request :It represents the request made by the client. The request implicit object is generally used to get request parameters, request attributes, header information and query string values.
  • response :The JSP implicit response object is an instance of a java class that implements the javax.servlet.http.HttpServletResponse interface. It represents the response to be given to the client. The response implicit object is generally used to set the response content type, add cookie and redirect the response.
  • pageContext : This is used to access page attributes and also to access all the namespaces associated with a JSP page. The lass or the interface name of the object PageContext is jsp.pageContext. The object PageContext is written: Javax.servlet.jsp.pagecontext The PageContext object has a page scope. It is an instance of the javax.servlet.jsp.PageContext class.
  • session :The session object has a scope of an entire HttpSession. It is an instance of the javax.servlet.http.HttpSession class. It represents the session created for the requesting client, and stores objects between client’s requests. The session object views and manipulates session information, such as the session identifier, creation time, and last accessed time. It also binds objects to a session, so that the user information may persist across multiple user connections.
  • application :The application object has an application scope. It is an instance of the javax.servlet.ServletContext class. It represents the context within which the JSP is executing. It defines a set of methods that a servlet uses to communicate with its servlet container.
  • out :The JSP implicit out object is an instance of the javax.servlet.jsp.JspWriter class. It represents the output content to be sent to the client. The out implicit object is used to write the output content.
  • config :The JSP implicit config object is an instance of the java class that implements javax.servlet.ServletConfig interface. It gives facility for a JSP page to obtain the initialization parameters available.
  • page :The Page object denotes the JSP page, used for calling any instance of a Page’s servlet. The class or the interface name of the Page object is jsp.HttpJspPage. The Page object is written: Java.lang.Object.
  • exception :The JSP implicit exception object is an instance of the java.lang.Throwable class. It is available in JSP error pages only. It represents the occured exception that caused the control to pass to the JSP error page.

The element forwards the request object containing the client request information from one JSP file to another file. The target file can be an HTML file, another JSP file, or a servlet, as long as it is in the same application context as the forwarding JSP file.

sendRedirect sends HTTP temporary redirect response to the browser, and browser creates a new request to go the redirected page. The response.sendRedirect also kills the session variables

jspService() method will be written by the container hence any methods which are not to be overridden by the end user are typically written starting with an ‘_’. This is the reason why we don’t override _jspService() method in any JSP page.

Yes. JSP technology lets the programmer to extend the jsp to make the programming more easier. JSP can be extended and custom actions & tag libraries can be developed to enhance/extend its features.

There are two types of comments that are allowed in the JSP. They are hidden and output comments.

A hidden comment does not appear in the generated HTML output, while output comments appear in the generated output.

Example of hidden comment:

< % – – This is a hidden comment – – % >

Example of output comment:

< ! – – This is an output comment – – >

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.

  • Request parameters are the result of submitting an HTTP request with a query string that specifies the name/value pairs, or of submitting an HTML form that specifies the name/value pairs. The name and the values are always strings. For example, when you do a post from html, data can be automatically retrieved by using getParameter(). Parameters are Strings, and generally can be retrieved, but not set.
  • Let’s take a real example, you have one html page named htmland JSP page named Register.jsp. The RegisterForm.html contains a form with few parameters for user registration on web application and those parameters you want to store in database.

<html>

<body>

<form name=”regform” method=”post” action=”../Register.jsp”>

<table ID=”Table1″>

<tr>

<td>

First Name : <input type=”text” name=”FIRSTNAME” size=”25″ value=””>

</td>

</tr>

<tr>

<td>

<input type=”Submit” NAME=”Submit” value=”Submit” >

</td>

</tr>

</table>

</form>

</body>

</html>

When user will enter first name in the text filed and press submit button, it will callRegister.jsp page. Now you want the value entered in text field by user in jsp/servlet so there you use request.getParameter() method.

<%

String lFirstName = request.getParameter(“FIRSTNAME”);

……………….

%>

On the server side, the request.getParameter() will retrieve a value that the client has submitted in the First Name text field. Using this method you can retrive only one value. This method i.e. getParameter method is in ServletRequest interface which is part of javax.servlet package.

Request attributes (more correctly called “request-scoped variables”) are objects of any type that are explicitly placed on the request object via a call to the setAttribute() method. They are retrieved in Java code via the getAttribute() method and in JSP pages with Expression Language references. Always use request.getAttribute() to get an object added to the request scope on the serverside i.e. using request.setAttribute().

Attributes are objects, and can be placed in the request, session, or context objects. Because they can be any object, not just a String, they are much more flexible. You can also set attributes programaticly and retrieve them later. This is very useful in the MVC pattern. For example, you want to take values from database in one jsp/servlet and display them in another jsp. Now you have resultset filled with data ready in servlet then you use setAttributemethod and send this resultset to another jsp where it can be extracted by using getAttributemethod.

Once a servlet gets a request, it can add additional attributes, then forward the request off to another servlet for processing. Attributes allow servlets to communicate with one another.

An include directive tells the JSP engine to include the contents of another file (HTML, JSP, etc.) in the current page. This process of including a file is also called as static include.

Life-cycle methods of the JSP are:

  • jspInit(): The container calls the jspInit() to initialize the servlet instance. It is called before any other method, and is called only once for a servlet instance.
  • _jspService():The container calls the _jspservice() for each request and it passes the request and the response objects. _jspService() method cann’t be overridden.

The container calls this when its instance is about to destroyed.The jspInit() and jspDestroy() methods can be overridden within a JSP page.

No. You are supposed to make use of only a JSPWriter object (given to you in the form of the implicit object out) for replying to clients.

A JSPWriter can be viewed as a buffered version of the stream object returned by response.getWriter(), although from an implementational perspective, it is not.

You can declare methods for use within your JSP page as declarations. The methods can then be invoked within any other methods you declare, or within JSP scriptlets and expressions.

Do note that you do not have direct access to any of the JSP implicit objects like request, response, session and so forth from within JSP methods. However, you should be able to pass any of the implicit JSP variables as parameters to the methods you declare.

For example:

file1.jsp:

file2.jsp

<%test(out);% >

A Java programming language object that implements the behavior of a custom tag.
If you have any questions that you want answer for – please leave a comment on this page and I will answer them

A scripting element that contains a valid scripting language expression that is evaluated, converted to a String, and placed into the implicit out object.

A user-defined action described in a portable manner by a tag library descriptor and imported into a JSP page by a taglib directive. Custom actions are used to encapsulate recurring tasks in writing JSP pages.

The modern Rich Internet Applications (RIA) use the design concept of “single page web design”, where a single rich page makes ajax based service calls to render different sections of a page instead of the traditional approach of loading a new page of each user action.The “single page web design” can make use of  client side and server side technologies as discussed below. Each approach has its use. It also show

The modern rich single page web applications built today harness the power of dynamically typed and interpreted languages like JavaScript for faster prototyping and increased developer productivity and statically typed Java based frameworks for maintainability, robustness, easier refactoring, and scalability. The modern browsers using faster JavaScript engines and efficient minification of JavaScript files have made client side templating a reality.

The server side templates are such as JSPs, Facelets for JSF, Apache Velocity, tiles, Sitemesh, etc.

The client side templating libraries based on JavaScript include dust.js, underscore.js, mustache.js, etc

The client side and server side templates like Google closure.

Server side templating and data composition 

Generates the markup on the server. For example, returns generated HTML code.

 

Client  side templating and data composition

Generates the markup on the client. More suited for applications that load more data from different back end service providers via ajax. The services could return data in JSON or XML format  and then add the HTML snippets for the new data via the client side templates.

.

Javascript templating is a technique to render templates on client-side (i.e. within the browser) with Javascript using a JSON data retrieved via RESTful web service calls. The template is basically HTML markup, sprayed with tags and variables that will insert values from the JSON data or execute a programming logic.

For example,

  • Import jQuery template library

<script src=”http://code.jquery.com/jquery.min.js” type=”text/javascript”></script>

<script src=”jquery.tmpl.js” type=”text/javascript”></script>

  • Define JSON data to be used to fill the template values. This can be returned from the server via a RESTFul service call.

var carsData = [

{ make: “Toyota”, model: “Camry” },

{ make: “BMW”, model: “3 Series” },

{ make: “Mazda”, model: “3” }

];

  • Define your client side template like

<script id=”carsTemplate” type=”text/html”>

<li><a href=”cars/${make}”>${model}</a></li>

</script>

or the complete HTML code may look like:

<html lang=”en”><head>

<script src=”http://code.jquery.com/jquery.min.js” type=”text/javascript”></script>

<script src=”jquery.tmpl.js” type=”text/javascript”></script>

<script id=”clientTemplate” type=”text/html”>

<li>make: ${make}, model: ${model}</li>

</script></head><body><ul></ul></body></html>

  • Invoking the template enginge (e.g jQuery) plugin to render the template with data

$(“#carsTemplate”).tmpl(carsData).appendTo( “ul” );

The  <li> tags will be appended to the <ul> tag with the retrieved JSON data values.

s the power of JavaScript.

  • Declaring variables in JSP pages are not thread-safe. The declared variables in JSP pages end-up as instance variables in the converted Servlets. <%! Calendar c = Calendar.getInstance(); %>
  • Decalring instance variables in Servlets is not thread safe, as Servlets are inherently multi-threaded and gets accessed by multiple-threads. Same is true for the Actionclasses in the struts framework.
  • Some of the Java standard library classes likeSimpleDateFormat is not thread-safe. Always check the API to see if a particular class is thread-safe. If a particular class or library is not therad-safe, you could do one of three things.

Provide your own wrapper class that decorates the third-party library with proper synchronization.

This is a typical use of the decorator design pattern.

Use an alternative library, which is thread-safe if available.

For example, Joda Time Library.

Use it in a thread-safe manner.

For example, you could use the SimpleDateFormat class as shown below within a ThreadLocal class.

Each thread will have its own instance of the SimpleDateFormat object.

 

public class DateFormatTest

{

//          anonymous inner class. Each thread will have its own copy

 

private final static ThreadLocal<SimpleDateFormat> shortDateFormat

=  new ThreadLocal<SimpleDateFormat>()

{

protected SimpleDateFormat initialValue()

{

return new SimpleDateFormat(“dd/MM/yyyy”);

}

};

 

public Date convert(String strDate)throws ParseException

{

//          get the SimpleDateFormat instance for this thread and parse the date string

 

Date d = shortDateFormat.get().parse(strDate);

return d;

}

}

  • The one that is very popular with the interviewers is writing the singleton classes that are not thread-safe.