Spring Boot

Master Class

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Building Your First Web Application
Building Your First Web Application can be
complex:
Web App concepts (Browser, HTML, CSS, Request,
Response, Form, Session, Authentication)
Spring MVC (Dispatcher Servlet, View Resolvers,
Model, View, Controller, Validations ..)
Spring Boot (Starters, Auto Configuration, ..)
Frameworks/Tools (JSP, JSTL, JPA, Bootstrap, Spring
Security, MySQL, H2)
Goal: Build Todo Management Web App with a
Modern Spring Boot Approach
AND explore all concepts in a HANDS-ON way

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Spring Initializr
My favorite place on the internet
Easiest way to create Spring Boot Projects
Remember:
1: SpringBoot: Use latest released version
Avoid M1,M2,M3, SNAPSHOT!
2: Java: Use latest Version
Java uses 6 month release patterns
Spring Boot 3.0+ works on Java 17+
3: Use latest Eclipse Java EE IDE version

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Understanding Logging
logging.level.some.path=debug
logging.level.some.other.path=error
logging.file.name=logfile.log

private Logger logger = LoggerFactory.getLogger(this.getClass());

logger.info("postConstruct");

Knowing what to log is an essential skill to be a great programmer

Spring Boot makes logging easy
spring-boot-starter-logging
Default: Logback with SLF4j
Typical Log Levels: ERROR, WARN, INFO, DEBUG, or TRACE

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Session vs Request Scopes
All requests from browser are handled by our
web application deployed on a server
Request Scope: Active for a single request
ONLY
Once the response is sent back, the request attributes
will be removed from memory
These cannot be used for future requests
Recommended for most use cases
Session Scope: Details stored across multiple
requests
Be careful about what you store in session (Takes
additional memory as all details are stored on server)

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How does Web work?
A: Browser sends a request
HttpRequest
B: Server handles the request
Your Spring Boot Web Application
C: Server returns the response
HttpResponse

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Peek into History - Model 1 Arch.
ALL CODE in Views (JSPs, ...)
View logic
Flow logic
Queries to databases
Disadvantages:
VERY complex JSPs
ZERO separation of concerns
Difficult to maintain

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Peek into History - Model 2 Arch.
How about separating concerns?
Model: Data to generate the view
View: Show information to user
Controller: Controls the flow
Advantage: Simpler to maintain
Concern:
Where to implement common features to all
controllers?

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Model 2 Architecture - Front Controller
Concept: All requests flow into a central
controller
Called as Front Controller
Front Controller controls flow to Controller's
and View's
Common features can be implemented in the Front
Controller

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Spring MVC Front Controller - Dispatcher Servlet
A: Receives HTTP Request
B: Processes HTTP Request
B1: Identifies correct Controller method
Based on request URL
B2: Executes Controller method
Returns Model and View Name
B3: Identifies correct View
Using ViewResolver
B4: Executes view
C: Returns HTTP Response

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Validations with Spring Boot
1: Spring Boot Starter Validation
pom.xml
2: Command Bean (Form Backing Object)
2-way binding (todo.jsp & TodoController.java)
3: Add Validations to Bean
Todo.java
4: Display Validation Errors in the View
todo.jsp

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Slides For Future

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Understanding Component Scan
@SpringBootApplication
@ComponentScan("com.in28minutes.springboot.package1")
@ComponentScan({"com.in28minutes.springboot.package1"
,"com.in28minutes.springboot.package2"})

You can define components using these annotations

@Component, @Controller, @Repository, @Service
How does Spring Framework know which Packages to search for components?
Component Scan
Understanding Component Scan helps you to debug problems (with Spring
and Spring Boot)
@SpringBootApplication defines an automatic component scan
You can customize it by defining additional @ComponentScan
Example Errors:
My URL is not working
No qualifying bean of type found

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Peek into History - Jakarta EE
Java SE: Java Platform, Standard Edition
JDK + JRE
Build and Run Simple Java Applications
Java EE (or J2EE): Build Web Applications
First released in December 1999
Defines Specs: Servlet, JSP, JMS, EJB, JPA, JAX-RS etc..
Was maintained by Oracle
Jakarta EE: New form of Java EE
Oracle moved Java EE to Eclipse Foundation
AND Java EE was renamed to Jakarta EE
Features remain same BUT different ownership
Namespace move from javax to jakarta

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Quick Review : Web App with Spring Boot
HTML: Hyper Text Markup Language
Tags like html, head, body, table, link are part of HTML
CSS: Cascading Style Sheets
Styling of your web page is done using CSS
We used Bootstrap CSS framework
JavaScript: Do actions on a web page
Example: Display a Date Popup (Bootstrap Datepicker)
JSTL: Display dynamic data from model
<c:forEach items="${todos}" var="todo">
Spring form tag library: Data binding-aware tags for handling
form elements
<form:form method="post" modelAttribute="todo">

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Quick Review : Web App with Spring Boot
DispatcherServlet: All requests flow into a central controller
(Front Controller)
View: Show information to user
Controller: Controls the flow
Model: Data to generate the view
Spring Boot Starters: Fast track building apps
Spring Boot Starter Web
Spring Boot Starter Validation
Spring Boot Starter Security
Spring Boot Starter Data JPA

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Spring Boot Auto Configuration Magic - Data JPA
We added Data JPA and H2 dependencies:
Spring Boot Auto Configuration does some magic:
Initialize JPA and Spring Data JPA frameworks
Launch an in memory database (H2)
Setup connection from App to in-memory database
Launch a few scripts at startup (example: data.sql)
Remember - H2 is in memory database
Does NOT persist data
Great for learning
BUT NOT so great for production
Let's see how to use MySQL next!

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Spring and Spring Boot Release Cycles
What is the difference between these?
4.2.0 (SNAPSHOT)
4.4.5 (M3)
4.4.0
Release Number: MAJOR.MINOR.FIX
Spring and Spring Boot Release Cycle:
SNAPSHOT (versions under development) > Mile Stones > Released Version
Recommendation - Do NOT use SNAPSHOTs or M1 or M2 or M3
Prefer released versions!

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Introduction to Functional Programming
Functional Programming: Essential Skill for Java
Programmers today
Lambda Functions
Streams
Filters
Goal: Intro to Functional Programming
7 Steps
~ 30 minutes
Warning: Quick 30 minutes section

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References
| Topic | Reference | |--|:--| |A|B|

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