Servlets

Question 1

What is a servlet?

Answer 1

- A servlet is a Java programming language class that is used to extend the capabilities of
servers that host applications accessed by means of a request-response
programming model.

Question 2

What is J2EE?

Answer 2

• J2EE stands for Java Platform Enterprise Edition. It is a collection of Java APIs used to write server-side applications.

Question 3

What is the Lifecycle of a Servlet?

Answer 3

1) Servlet class is loaded
2) Servlet instance is created
3) Init method is invoked
4) Service method is invoked
5) Destroy method is invoked

Question 4

App Server vs Web Server

Answer 4

• A Web server exclusively handles HTTP requests, whereas an application server serves business logic to application programs through any number of protocols.

Question 5

What is XML?

Answer 5

• Stands for Extensible Markup Language

- It defines set of rules for encoding documents in a format that is both human-readable and machine readable

Question 6

What is JAXB?

Answer 6

• Stands for Java Architecture for XML Binding

- It is used to convert Java Object to XML and XML to Java Objects.

Question 7

What is Marshalling?

Answer 7

• The process of transforming the memory representation of an object to a data format suitable for storage or transmission.

Question 8

What is Unmarshalling?

Answer 8

• The process of transforming a representation of an object that was used for
  storage or transmission to a representation of the object that is executable.

Question 9

What is MVC?

Answer 9

• Represents Model, View, Controller.

MVC is an architectural pattern that separates an application into three main
components:

• Model - all data related logic.
• View - all UI related logic.
• Controller - handles all business logic and incoming requests.

Question 10

What is the deployment descriptor?

Answer 10

• In J2EE, a deployment descriptor describes how a component should be deployed.
• An example of a “deployment descriptor” is the web.xml.

Question 11

What are the important tags you need to include in the web.xml?

Answer 11

• web-app
• servlet, servlet-name, servlet-class
• servlet-mapping, servlet-name, url-pattern
• init-param, param-name, param-value
• context-param, param-name, param-value

Question 12

Eager Loading vs Lazy Loading

Answer 12

• Lazy loading - a servlet is not loaded when server is starting and loaded only when the servlet receives a request.
• Eager Loading - servlet loads while server is starting.

Question 13

URL vs URI vs URN

Answer 13

• URL (Uniform Resource Locator) - identifies the location of the resource and how to access it.
• URI (Uniform Resource Identifier) - identifies a resource by name, location, or both.
• URN (Uniform Resource Name) - identifies a resource by name in a given
  namespace but does not specify how to obtain it.

Question 14

What are the method signatures of doGet() and doPost()?

Answer 14

• Protected void doGet(HttpServletRequest req, HttpServletResponse res) extends
  IOException, ServletException.
• Protected void doPost(HttpServletRequest req, HttpServletResponse res) extends
  IOException, ServletException.

Question 15

Init, Service and Destroy, how many times do they execute?

Answer 15

• The init and destroy method is called once.

- The service method is called for every request the servlet receives.

Question 16

doGet vs doPost vs GET vs POST

Answer 16

• doGet handles all GET requests while doPost handles all POST requests
• GET HTTP requests supplies all required data in the URL while POST HTTP requests
  supplies all required data in the request/message body

Question 17

Another name for web.xml?

Answer 17

• Web application deployment descriptor

Question 18

How do I declare a Servlet?

Answer 18

servlet tag
servlet-name servlet1 /servlet-name
servlet-class com.xx.servClass /servlet-class
/servlet

Question 19

How does Error Handling work on JEE?

Answer 19

• Handle the error on the server side with try-catch or throws.
• Return status codes to the front-end depending on errors or lack thereof

Question 20

How to maintain user state?

Answer 20

• Cookies initialized when the user logs in.
• Send the session id from the cookie in HTTP requests.
• Access the HttpSession object from the request object using the getSession()
  method.

Question 21

What are filters?

Answer 21

• A filter in the context of java servlets is an object that performs filtering tasks on either the request to a resource or on the response from a resource

Question 22

What is a thread pool?

Answer 22

• Object pools are used in java for storage of objects that we want to use
  dynamically.