JEE - Spring - Spring Boot

Question 1

What is JEE ?

Answer 1

JEE is Jakarta EE, a java framework to build web applications

Question 2

What are Key components in JEE ?

Answer 2

*Servlets
*JSP : Java ServerPages
*EJB : Enterprise Java Beans
*JMS : Java Message Service
*JTA : Java Transaction API
*JPA : Java Persistence API
*CDI : Context and Dependency Injection
*JAX-RS : Java API for RESTful Web Services
*JAX-WS : Java API for Web Services

Question 3

Why we need application servers ?

Answer 3

JEE applications are deployed and run on application servers that support JEE specifications

Question 4

Give some popular JEE application servers

Answer 4

*Apache Tomcat
*WildFly ( JBoss )
*GlassFish
*WebLogic ( by Oracle )
*WebSphere ( by IBM )

Question 5

What is servlet ?

Answer 5

*Servlet is a JEE server-side component that handle HTTP requests/responses
*Servlet is a class which extends HttpServlet ,redefine methods like doGet(),doPost(),doPut(),doDelete(),doHead() , and make processes on server side after receiving HTTP requests.
*La méthode doX() est exécutée si la requête HTTP est envoyée avec la méthode X.
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method syntax : doGet(req,resp)

Question 6

What are Sevlets lifecycle methods ?

Answer 6

*init() : invoked before app start
*service()
*destroy() : invoked before class object destroyed.

Question 7

What is JSP ?

Answer 7

JSP is a technology that allows embedding java code directly in HTML for generating dynamic content
=> the code in jsp file gets compiled into a servlet by web container ( Tomcat ).

Question 8

What is JPA ?

Answer 8

JPA is a specification for managing relational data in java apps.It provides an Object-Relational Mapping (ORM) mechanism to map java objects to database tables and vice versa
=> JPA eliminates the need for manual JDBC ( Java Database Connectivity ) code and simplifies database interactions.
=> JPA uses Entity Classes to represent database tables.
=> Common annotations : @Entity, @Id , @OneToMany …

Question 9

What is JAX-RS ?

Answer 9

Used for creating RESTful WS, works over HTTP and stateless.REST based on HTTP methods ( GET,POST,PUT,DELETE,OPTIONS,HEAD…)
=> supports different data format : XML , JSON…

Question 10

What is JAX-WS ?

Answer 10

Building SOAP WS. It supports only XML format.

Question 11

What is Socket ?

Answer 11

Socket is an interface for network communication to receive/send data over network. It is commonly used in a client-server architecture where a client connects to a server with IP address and port number.
TCP sockets provide a reliable communication , while UDP sockets offer faster but less reliable communication
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Example of sockets use : web browsers,chat apps, and real-time multiplayer games

Question 12

What are Socket components ?

Answer 12

*IP Address : usually IPv4 or IPv6
*Port Number : port 80 for HTTP, 443 for HTTPS , 3306 for MySQL
*Protocol : TCP or UDP

Question 13

What is Communication Process for Client-Server Model ?

Answer 13

*A client specifies IP address and port number.
*Once connection established , client and server can send/receive data through the socket
=>vice versa ( server instead of client ) for steps above

Question 14

What is HTTP ?

Answer 14

HTTP (HyperText Transfer Protocol) is a protocol to restore data from a server

Question 15

What is CORS ?

Answer 15

CORS ( Cross-Origin Resource Sharing ) is a security feature implemented by web browsers to prevent malicious websites from making unauthorized requests on a different domain ( origin ) than the one from which the page was served.It is a protocol that allows or restrict resources to be accessed by different origin.

Question 16

What is Origin in the context of CORS ?

Answer 16

An origin is defined by the combination of:

Protocol (e.g., HTTP, HTTPS)
Domain (e.g., example.com)
Port (e.g., 8080)

Question 17

Why CORS is needed ?

Answer 17

*Enforce Same-Origin Policy (SOP)
*prevent CSRF (Cross-Site Request Forgery) and XSS (Cross-Site Scripting) attacks

Question 18

What are common CORS headers ?

Answer 18

*Access-Control-Allow-Origin
*Access-Control-Allow-Methods
*Access-Control-Allow-Headers
*Access-Control-Allow-Credentials

Question 19

What are common code status ?

Answer 19

1xx: Informational Responses
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2xx:Successful Reponses
=>200:OK
=>201:CREATED
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3xx :Redirection Responses
=>301:Moved Permanently
=>302:Found (Moved Temporarily)
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4xx:Client Error Reponses
=>400:Bad Request
=>401:Unauthorized
=>403:Forbidden
=>404:Not Found
=>405:Method Not Allowed
=>408:Request Timeout
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5xx:Server Error Responses
=>500:Internal Server Error
=>502:Bad Gateway
=>504:Gateway Timeout

Question 20

What are Cookies ?

Answer 20

Cookie is a small piece of data sent by server and stored on client (browser). The client then send this cookie back to server on subsequent requests to the same domain.

Question 21

What are Cookies key points ?

Answer 21

*Storage : a cookie is stored on client
*Persistence : a cookie can be persistent (stored for a set of duration) or session-based (deleted after browser closed)
*Data size : Small
*Security : less secure (because it is stored on client side , then exposed )
*Use case : used to store user preferences/identication, tracking, simple data…

Question 22

What are Sessions ?

Answer 22

Session is a server-side mechanism that is used to store data about client across multiple HTTP requests .Unlike cookies, session data is stored on server side, and the client use a Session ID (stored in cookie) to identify the session.

Question 23

What are Sessions key points ?

Answer 23

Storage : a session is stored on server side
Persistence : session can last until a user log out or after a period of inactivity
Data Size: Larger
Security : more secure (stored on server , not exposed)
Use cases:Authentication , user data , complex information.
Identification : server identify a session by unique Session ID passed between client and server via cookies or URL parameters.

Question 24

What is CSRF ?

Answer 24

CSRF (Cross-Site Request Forgery) is a type of web security vulnerability that trick a user on performing unintended actions on web apps in which they are authenticated.It exploits the trust of website on user’s browser,and occurs when attacker gets a user to send malicious requests ( like making transaction ) without their knowledge.
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Example of how it works :
Attacker send a malicious form , which victim fill then without knowing (by user) it performs actions like making a transaction.

Question 25

How we prevent CSRF ?

Answer 25

use CSRF synchronizer Token , which is unique , has a period of validity, generated by server and associated with user session

Question 26

What is XSS ?

Answer 26

XSS ( Cross-Site Scripting ) is a type of web security vulnerability that allows attacker to use multiple scripts on web pages viewed by user. It is used for stealing sensitive information like login credentials or cookies , performing actions on behalf of the user or redirecting user to malicious websites.

Question 27

How to prevent XSS ?

Answer 27

*Input validation and sanitization ( prevent special characters like ‘<’ and ‘>’ )
*Use ‘HttpOnly’ and ‘Secure’ flags on cookies
*Avoid embedding javascript code directly on HTML

Question 28

SOAP VS REST ?

Answer 28

SOAP : is a protocol , use only XML
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REST : is an architectural style , use multiple format like XML , JSON …