JSP Interview Questions

JavaServer Pages (JSP) is a technology for developing Webpages that support dynamic content which helps developers insert java code in HTML pages by making use of special JSP tags, most of which start with <% and end with %>.

JSP offer several advantages as listed below -

• Performance is significantly better because JSP allows embedding Dynamic Elements in HTML Pages itself.
• JSP are always compiled before its processed by the server unlike CGI/Perl which requires the server to load an interpreter and the target script each time the page is requested.
• JavaServer Pages are built on top of the Java Servlets API, so like Servlets, JSP also has access to all the powerful Enterprise Java APIs, including JDBC, JNDI, EJB, JAXP etc.
• JSP pages can be used in combination with servlets that handle the business logic, the model supported by Java servlet template engines.

The advantages of JSP are twofold.

First, the dynamic part is written in Java, not Visual Basic or other MS specific language, so it is more powerful and easier to use.

Second, it is portable to other operating systems and non-Microsoft Web servers.

DDL commands are used to modify and edit the structure of a database system. Some of the important commands are-

It is more convenient to write (and to modify!) regular HTML than to have plenty of println statements that generate the HTML. Other advantages are -

• Embedding of Java code in HTML pages.
• Platform independence.
• Creation of database-driven Web applications.
• Server-side programming capabilities.

SSI is really only intended for simple inclusions, not for "real" programs that use form data, make database connections, and the like.

JavaScript can generate HTML dynamically on the client but can hardly interact with the web server to perform complex tasks like database access and image processing etc.

Regular HTML, of course, cannot contain dynamic information.

A JSP Lifecycle consists of following steps -

• Compilation - When a browser asks for a JSP, the JSP engine first checks to see whether it needs to compile the page. If the page has never been compiled, or if the JSP has been modified since it was last compiled, the JSP engine compiles the page.
  • The compilation process involves three steps -
  • Parsing the JSP.
  • Turning the JSP into a servlet.
  • Compiling the servlet.
• Initialization - When a container loads a JSP it invokes the jspInit() method before servicing any requests
• Execution - Whenever a browser requests a JSP and the page has been loaded and initialized, the JSP engine invokes the _jspService() method in the JSP.The _jspService() method of a JSP is invoked once per a request and is responsible for generating the response for that request and this method is also responsible for generating responses to all seven of the HTTP methods ie. GET, POST, DELETE etc.
• Cleanup - The destruction phase of the JSP life cycle represents when a JSP is being removed from use by a container.The jspDestroy() method is the JSP equivalent of the destroy method for servlets.

A scriptlet can contain any number of JAVA language statements, variable or method declarations, or expressions that are valid in the page scripting language.

Following is the syntax of Scriptlet -

<% code fragment %>         

A declaration declares one or more variables or methods that you can use in Java code later in the JSP file. You must declare the variable or method before you use it in the JSP file.

<%! declaration; [ declaration; ]+ ... %>

A JSP expression element contains a scripting language expression that is evaluated, converted to a String, and inserted where the expression appears in the JSP file.

The expression element can contain any expression that is valid according to the Java Language Specification but you cannot use a semicolon to end an expression.

Its syntax is -

<%= expression %>

They are comments that can be viewed in HTML Source File.

Expression tag is used to insert Java values directly in the output. Its syntax is <%=expression%>

It contains a scripting language expression that is evaluated, then converted to a string, and then inserted where the expression comes in JSP file.

Composition has a stronger relationship with the object than Aggregation.

It a JSP tag that encloses Java code in JSP pages. Their syntax is <% %>. Code written in scriptlet executes every time the program is run.

Errorpage attribute is used to uncatch the run-time exceptions forwarded automatically to an error processing page.

It redirects the browser to JSP page error.jsp if any uncaught exception is faces during request handling. It is an error processing page.

Whatever content made in a jsp page goes inside the _jspService() method by the container. If it is override, the compiler gives an error, but the other 2 lifecycles can be easily override. So ‘_’ shows that we cannot override this method.

tag is used to use any java object in the jsp page. Some scope values are :

1. application
2. request
3. page
4. session

The 2 types are :

<%–JSP Comment–%>
<!–HTML comment–>

We can declare static methods with same signature in subclass, but it is not considered overriding as there won’t be any run-time polymorphism. Hence the answer is ‘No’.

JSP directives are messages to JSP Engine. They serve as a message from page to container and control the processing of the entire page. They can set global values like class declaration. They do not produce output and are enclosed in <%@….%>

Page Directives inform the JSP Engine about headers and facilities that the page receives from the environment. It is found at the top of all JSP pages. Its syntax is <%@ page attribute=”value”>

1. Session : It shows if a session data is available to the page.
2. Import : it shows packages that are imported.
3. isELIgnored : It shows whether EL expressions are ignored when JSP translates into a servlet.
4. contentType : it allows the user to specify the content type of page.

The include directive statically inserts the contents of a resource into the current JSP. It helps in the reuse of code without duplication. and includes contents of the file at translation time. Its syntax is as follows <%@ include file=”Filename”%>.

They affect overall runtime behaviour of a page and response sent to the client. They are used to include a file at request time, to instantiate a JavaBean or find one. They are also used to generate a browser-specific code or forward a request to a new page.

It is used to give values to properties of beans that have been referenced beforehand.

…

jsp:setproperty is executed even if a new bean is instantiated or existing bean is found.

By adding at the end of the code, the condition for execution is inverted i.e. It is not executed if existing object was found and only if a new object was instantiated.

It is used to start the static data member. It is executed before classloading.

This action helps in insertion of a specific object in the browser or embed the element needed to specify the running of applet using Java plugin.

Javascript is used for the client-side validation. It takes place within the browser. Javascript is used to submit the form data if validation is successful. Validation errors require no extra network trip because form cannot be submitted.

Validation is also carried out in the server after submission. If validation fails, extra network trip is required to resend the form to the client.

JSP engine translates and compiles a JSP file to a servlet. This servlet moves to the execution phase where requests and responses are handled. They are compiled for the first time they are accessed unless manually compiled ahead of time. The manual or explicit compilation is useful for long and convoluted programs.