JSP Interview Questions and Answers

JSP or JavaServer Pages is a software technology used to develop to dynamic interactive web pages based on HTML or XML while controlling the content or appearance of web pages with the use of servlet containers. It has s wide a range of applications and separates business logic from the presentation layer.

Here are a few crucial differences between these two:

• Include directive is processed at the translation time, but include action is processed at the request time.
• Include directive uses both absolute and relative path, whereas include action only uses a relative path.
• Include directive only uses the contents of the resource, while include action process dynamic content resource.

Using JSP has numbers of benefits, such as

• It allows tag-based programming
• Suitable for both Java and non-Java programmers
• Allows developers to use separate presentation logic
• Highly increases readability of code because of tags
• Easy to learn and apply

These are the messages to JSP container, and they provide global information for an entire JSP page. JSP directives are used by developers to give special instruction to a container for translation of JSP to servlet code. These directives can contain many attributes by comma separated as key-value pairs. JSP directives are described in <%@ %> tags.

The session in a JSP page can be disabled by setting the session attributes to false. The following can be exampled to disable the session object using page directive: <%@ page session="false" %>

A JSP custom tag is a user-defined JSP language element. A JSP page which contains a custom tag is generally transcribed into a servlet. Then, the custom tag is converted to operations on an object called a tag handler. The custom tags can be created with JSP tag extensions that let developers insert these new tags directly into a JSP.

JSP is a dynamic content generating webpage scripting language, whereas servlets are programs that operate on a web or application server and act as a middle layer between a request coming from applications on the HTTP server, or a web browser or other HTTP client and database.

The JSP lifecycle methods are as following:

• jspInit() : It operates to initialize the servlet instance. Before calling any other method, its call is made.
• _jspService() : It passes the request and the response subjects. You can’t override the method.
• jspDestroy(): The container calls this when its instance is about to destroy.

Basically, there are two types of comments allowed in the JSP, hidden comments and output comments.

The hidden comments of JSP don’t appear in the generated output in the HTML (ex: <%-- This is hidden comment --%>), while output comments arrear in the generated output ex: <!-- This is output comment -->).

A JSP expression is used to put the Java values directly into the output. It has the form of <%= Java expression %>. JSP scriptlets are more than the simple expression and used to insert complex code into the service() method of the generated servlet. Whereas, a JSP declaration defines fields or methods that get inserted into the main body of the servlet class.