☕ Java & Spring — The Modern Learning Roadmap

A curated, opinionated path from zero to production-grade Java and Spring Boot — refreshed for Java 25 (LTS) and Spring Boot 4 / Spring Framework 7.

Whether you're writing your first main method or hardening a microservice for production, this repo maps what to learn, in what order, with the best free resource for each step. Every link is hand-picked; the roadmap is kept current with the modern Java platform (records, sealed types, pattern matching, virtual threads) and the Spring Boot 3/4 generation.

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🗺️ The Roadmap at a Glance

flowchart TD
    A["1 · Java Fundamentals"] --> B["2 · Object-Oriented Programming"]
    B --> C["3 · Core APIs & Intermediate Java"]
    C --> D["4 · Modern Java (14 → 25)"]
    D --> E["5 · Advanced Java & the JVM"]
    C --> F["6 · Testing"]
    E --> G["7 · Clean Code, SOLID & Design Patterns"]
    F --> G
    C --> H["8 · Build Tools"]
    G --> I["9 · Databases & Persistence"]
    I --> J["10 · Jakarta EE & Servlets"]
    J --> K["11 · Spring Framework & Spring Boot"]
    H --> K
    K --> L["12 · Cloud-Native, Microservices & Spring AI"]
    L --> M["13 · Practice, Projects & Roadmaps"]

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🧭 How to Use This Guide

• Follow the chapters in order if you're new — each builds on the last.
• Jump to a chapter if you're filling gaps (the roadmap above shows dependencies).
• Look for these markers on individual resources:
  • 🎥 video · 📖 deep-read / official docs · ⚡ quick reference · 🧪 hands-on · ⭐ start here · 🆕 modern (Java 17+ / Spring Boot 3+)
• LTS-first mindset: target Java 21 or Java 25 and Spring Boot 4.x for anything new. Older material is still valuable for concepts — just prefer modern syntax when you code.

📚 Table of Contents

1. Fundamentals of Java
2. Object-Oriented Programming
3. Core APIs & Intermediate Java
4. Modern Java (14 → 25)
5. Advanced Java & the JVM
6. Testing
7. Clean Code, SOLID & Design Patterns
8. Build Tools
9. Databases & Persistence
10. Jakarta EE & Servlets
11. Spring Framework & Spring Boot
12. Cloud-Native, Microservices & Spring AI
13. Practice, Projects & Roadmaps

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🌱 Chapter 1: Fundamentals of Java

Goal: read, write, and run simple Java programs. Understand types, control flow, and errors.

⭐ Start here: dev.java — the official learning portal from Oracle · The Java Tutorials (Oracle)

1.1 Primitives & Variables

• Primitive Data Types in Java
• 📖 Primitive Data Types (Oracle Tutorial)
• 🆕 var — Local Variable Type Inference (Java 10+)

1.2 Operators & Conditionals

• Java Control Structures
• Convention: avoid ! in if conditions
• The switch Statement
• 🆕 Switch Expressions (Java 14+) · see also Chapter 4

1.3 Loops

• A Guide to Java Loops

1.4 Strings

• String vs. StringBuilder vs. StringBuffer
• Guide to the Java String API
• 🆕 Text Blocks — multi-line strings (Java 15+)

1.5 Exception Handling

• Exception Handling in Java
• Checked vs. Unchecked Exceptions
• throw vs. throws
• Creating a Custom Exception

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🧱 Chapter 2: Object-Oriented Programming

Goal: model problems with classes and objects; master the four pillars.

2.1 Classes, Interfaces, Abstract Classes & Access Modifiers

• Object-Oriented Programming in Java
• Concrete Classes
• 9 Rules About Constructors in Java
• Everything You Need to Know About Interfaces
• Abstract Class vs. Interface
• Access Modifiers Explained
• Access Modifiers with Examples

2.2 Encapsulation

• What Is Encapsulation — the What, Why & How

2.3 Abstraction

• What Is Abstraction in Java
• Abstract Class in Java

2.4 Inheritance

• What Is Inheritance
• 12 Rules & Examples About Inheritance
• Inheritance vs. Composition (prefer composition!)

2.5 Polymorphism

• What Is Polymorphism

2.6 Overloading & Overriding

• What Is Overloading
• 12 Rules of Overriding
• Overriding vs. Overloading
• Covariant Return Types
• Method Hiding

2.7 Keywords, Members & Data Objects

• Default & Private Methods in Interfaces
• Static & Default Methods in Interfaces
• The this Keyword
• Type Casting
• The static Keyword
• The final Keyword
• Static Blocks
• Static Imports
• Pass-by-Value vs. Pass-by-Reference in Java
• Wrapper Classes & Autoboxing
• JavaBeans
• What Is a JavaBean, exactly? (StackOverflow)
• POJO Classes
• A Guide to Java Enums
• Overriding toString()
• The equals() and hashCode() Contracts
• BigDecimal and BigInteger
• Java Serialization
• Everything About Java Serialization
• Why implement Serializable? (StackOverflow)
• 🆕 Records — concise immutable data carriers (Java 14+)

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🔧 Chapter 3: Core APIs & Intermediate Java

Goal: fluently use the standard library — collections, generics, streams, and functional Java.

3.1 Collections Framework

• ⭐ What Is the Java Collections Framework

Fig: Collections Framework hierarchy. Source: javatpoint

List

• List Tutorial & Examples
• Sorting Lists
• Sorting a List by Multiple Attributes
• Convert an Iterator to a List
• Get a Random Element from a List
• Partition a List
• Remove All Nulls from a List
• Remove Duplicates from a List
• Check If Two Lists Are Equal
• Find an Element in a List
• UnsupportedOperationException on Lists
• Copy a List to Another List
• Remove All Occurrences of a Value
• Add Multiple Items to an ArrayList
• Remove the First Element
• Ways to Iterate Over a List
• Intersection of Two Lists
• Count Duplicate Elements in an ArrayList
• Differences Between Two Lists
• Reversing a Linked List
• Assert Two Lists Equal Ignoring Order

Set

• Set Tutorial & Examples
• Guide to TreeSet
• Guide to HashSet

Map

• Guide to HashMap
• HashMap Under the Hood
• Guide to TreeMap
• TreeMap vs. HashMap
• Store Duplicate Keys in a Map
• Initialize a HashMap
• Merge Two Maps (Java 8)
• Sort a HashMap
• Compare Two HashMaps
• Using Map.Entry
• Working with Maps Using Streams
• Iterate Over a Map

Conversions & utilities

• Convert Between an Array and a List
• Convert Between an Array and a Set
• Convert Between a List and a Set
• Convert a Map to an Array, List or Set
• Convert a List to a Map
• Map to String Conversion
• Arrays.asList vs. new ArrayList(Arrays.asList())
• Collect Stream Elements into a List
• stream().forEach() vs. forEach()
• A Guide to the Java Iterator
• Time Complexity of Java Collections
• 🆕 Sequenced Collections (Java 21+)

3.2 Generics

• A Guide to Java Generics
• Generics Wildcards (Jenkov)
• Type Parameter vs. Wildcard

3.3 Lambdas, Functional Interfaces & Streams

• ⭐ Lambda Expressions Quick Start (Oracle)
• Functional Interfaces in Java
• Java Streams Explained (JRebel)
• A Comprehensive Guide to Java Streams
• Java Streams by Example (Capital One)
• A Guide to Java Collectors
• 🎥 Streams — video series (Java Brains)
• 🧪 Modern Java by Example (winterbe/java8-tutorial)
• 🆕 Stream Gatherers — custom intermediate ops (Java 24+)

3.4 Optional

• Optionals (winterbe)
• A Guide to Optional

3.5 Annotations & Reflection

• Java Reflection Tutorial (Jenkov)
• A Guide to Java Reflection
• 📖 Annotations (Oracle Tutorial)
• Common Java Annotations
• 🎥 Creating a Custom Annotation (video)
• Java Annotation Processing
• Annotations (winterbe)
• @Deprecated Examples
• @Override Examples
• @SuppressWarnings Examples
• Annotation Processing Under the Hood

3.6 Date & Time API

• The java.time Date/Time API (winterbe)
• Introduction to the Java 8 Date/Time API

3.7 Command-Line Tools

• Command-Line Tools for Java

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🚀 Chapter 4: Modern Java (14 → 25)

Goal: write idiomatic modern Java. These features define how professional code looks today — favour them over legacy patterns.

4.1 Language Features Every Modern Java Dev Should Know

• 🆕 Records — immutable data classes
• 🆕 Sealed Classes & Interfaces — controlled hierarchies
• 🆕 Pattern Matching for instanceof
• 🆕 Pattern Matching for switch
• 🆕 Record Patterns — destructuring
• 🆕 Text Blocks — multi-line string literals
• 🆕 Switch Expressions
• 🆕 var — Local Variable Type Inference
• 🆕 Sequenced Collections

4.2 What's New, Version by Version

LTS releases (bold) are what you should target for production: Java 8, 11, 17, 21, 25.

• Java 8 — lambdas, streams, Optional, new Date/Time
• Java 9 — modules (JPMS), var in the REPL, collection factory methods
• Java 10 — var local type inference
• Java 11 — HTTP Client, String methods, run single-file source
• Java 12 · Java 13 · Java 14 — switch expressions, records (preview), text blocks (preview)
• Java 15 — text blocks, sealed classes (preview)
• Java 16 — records & pattern matching for instanceof finalized
• Java 17 — sealed classes finalized; migration guide 8 → 17
• Java 18 — UTF-8 by default, simple web server
• Java 21 — virtual threads, pattern matching for switch, record patterns, sequenced collections
• Java 22 — stream gatherers (preview), unnamed variables
• Java 25 — 🆕 latest LTS: scoped values, compact source files & instance main, structured concurrency
• 📖 Full JDK release/JEP index (OpenJDK)

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⚙️ Chapter 5: Advanced Java & the JVM

Goal: reason about concurrency and understand what happens beneath your code.

5.1 Concurrency — Classic

• Java Thread Programming — all 14 parts (foojay)
• The synchronized Keyword
• The volatile Keyword (Jenkov)
• CompletableFuture
• 📖 Concurrency (Oracle Tutorial)
• Synchronization & Locks (MIT 6.005)
• ReentrantReadWriteLock
• ExecutorService (Jenkov)
• Thread Pools
• ThreadPoolExecutor Example
• Fork/Join Framework

5.2 Concurrency — Modern (Project Loom) 🆕

• ⭐ Difference Between Thread and Virtual Thread
• OpenJDK Project Loom
• Structured Concurrency
• Scoped Values (a modern alternative to ThreadLocal)
• Working with Virtual Threads in Spring

5.3 The JVM: Memory & Garbage Collection

• JVM Garbage Collectors
• Experimental Garbage Collectors (ZGC, Shenandoah)
• Java Memory Management (interview-grade deep dive)

5.4 Miscellaneous Deep Cuts

• Object Ordering: Comparable & Comparator
• Collections & Thread Safety
• 18 Collections & Generics Best Practices
• extends/super Wildcards & the Get-Put Principle
• Generics, Subtyping & the Substitution Principle
• Static vs. Non-Static
• Upcasting & Downcasting

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🧪 Chapter 6: Testing

Goal: a habit, not a chore. Modern Java hiring assumes you can write clean, fast, isolated tests.

6.1 Unit Testing

• ⭐ A Guide to JUnit 5
• Assertions in JUnit 4 and JUnit 5
• Assert an Exception Is Thrown
• Introduction to AssertJ — fluent assertions

6.2 Mocking

• Mockito Series — basics to advanced
• Mockito with JUnit 5 (@ExtendWith)
• JUnit vs. Mockito — what each is for

6.3 Integration Testing with Testcontainers 🆕

• Docker Test Containers in Java Tests
• DB Integration Tests with Spring Boot & Testcontainers
• Built-in Testcontainers Support in Spring Boot (3.1+)
• 📖 Testcontainers — official site

6.4 Testing Spring Applications

• Testing in Spring Boot (see also Chapter 11.10)

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✨ Chapter 7: Clean Code, SOLID & Design Patterns

Goal: write code other humans (and future-you) can change safely.

7.1 Clean Code

• ⭐ Clean Coding in Java
• Clean Code: Naming
• Clean Code: Comments
• Clean Code: Formatting

7.2 SOLID Principles

• ⭐ A Solid Guide to SOLID Principles
• The SOLID Principles in Pictures

7.3 Design Patterns

• ⭐ Refactoring Guru — Design Patterns (illustrated)
• Design Patterns Series (Baeldung)
• Design Principles & Patterns for Highly Concurrent Applications
• 📖 Refactoring Guru — Refactoring Catalog

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🛠️ Chapter 8: Build Tools

Goal: build, test, and package projects reproducibly. Learn one deeply, know the other.

8.1 Maven

• 🎥 Maven — video tutorial (Java Brains)
• 📖 Maven — official Getting Started guide

8.2 Gradle

• 🎥 Gradle for Java Developers (LinkedIn Learning)
• 📖 Getting Started with Gradle (official docs)

8.3 The Wrapper

• Use the Maven/Gradle Wrapper — always commit mvnw/gradlew so builds are reproducible.

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🗄️ Chapter 9: Databases & Persistence

Goal: move data in and out of a relational database, the Java way.

• Introduction to JDBC
• JPA Tutorial
• Learn JPA & Hibernate Series
• The DAO Pattern in Java
• Connection Pooling with HikariCP
• Database Migrations with Flyway

Spring's persistence layer (Spring Data JPA, JdbcTemplate) is covered in Chapter 11.9.

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🌐 Chapter 10: Jakarta EE & Servlets

Goal: understand the web foundation Spring MVC is built on. Note: the javax.* namespace is now jakarta.* (Jakarta EE 9+).

• 🎥 What Is Apache Tomcat?
• What Is a Servlet?
• Lifecycle of a Servlet
• How a Servlet Works
• ServletContext
• Servlet Filters
• What Is a WAR File?
• 🎥 Introduction to Servlets (video)
• Intro to Servlets (Baeldung)
• MVC with Servlets & JSP

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🍃 Chapter 11: Spring Framework & Spring Boot

Goal: build production REST services with Spring Boot 4 / Spring Framework 7. Target Boot 4.x for new work (Boot 3.5 reached end of open-source support on 30 June 2026).

⭐ Start here: Learn Spring Boot Series (Baeldung) · 📖 Spring Boot Reference Docs · 🧪 start.spring.io — bootstrap a project

11.1 Overview of the Spring Framework

• 📖 Spring Framework Overview (current reference)
• Why Choose Spring?
• 🆕 Spring Boot 3 & Spring Framework 6.0 — What's New
• 🆕 Spring Boot 4 & Spring Framework 7 — What's New

11.2 Beans, Inversion of Control & Dependency Injection

• ⭐ Understanding the Core of the Spring Framework
• Spring Bean
• Inversion of Control & Dependency Injection
• What Is Dependency Injection?
• @Autowired — Autowiring
• Spring Bean Annotations
• Field vs. Constructor vs. Setter Injection (StackOverflow)
• @Resource, @Inject & @Autowired
• @Component vs. @Bean (StackOverflow)
• Circular Dependencies in Spring
• UnsatisfiedDependencyException
• Bean Scopes

11.3 Spring MVC & Spring Boot

• ⭐ Spring MVC Tutorial
• The DispatcherServlet
• How @RequestMapping Works (StackOverflow)
• Spring vs. Spring Boot
• 🧪 Building an Application with Spring Boot (official guide)
• @RequestMapping
• @RequestParam
• @Controller vs. @RestController
• View Resolvers
• 🧪 Serving Web Content (official guide)
• 🎥 Spring Framework — video course (Java Brains)

11.4 Building REST APIs

• ⭐ REST with Spring Series
• Building a RESTful Web Service (Java config)
• 🧪 Building a RESTful Web Service (official guide)

11.5 Validation

• Validation in Spring Boot

11.6 Exception Handling

• Global Error Handler for a REST API
• Error Handling for REST with Spring (@ControllerAdvice)

11.7 Configuration, Properties & Profiles

• Spring Profiles (JavaDevJournal)
• Spring Profiles (Baeldung)
• The @Value Annotation
• Type-safe @ConfigurationProperties

11.8 JSON, Templates & Serialization

• Jackson ObjectMapper Tutorial
• Spring Template Engines (Thymeleaf, etc.)

11.9 Persistence: Spring JDBC & Spring Data JPA

• JdbcTemplate
• The Persistence Layer with Spring & JPA
• ⭐ The Persistence Layer with Spring Data JPA

11.10 Testing Spring Applications

• ⭐ Testing in Spring Boot
• See also the general Testing chapter (JUnit 5, Mockito, Testcontainers).

11.11 Spring Security 🆕

Spring Security 6 uses the lambda DSL and requires the jakarta.* namespace — many older tutorials are out of date, so prefer the resources below.

• ⭐ Security with Spring Series
• Spring Boot Security Auto-Configuration
• 📖 Spring Security Reference Docs
• 🎥 Spring Security — video series (LinuxTex)

11.12 Actuator & Observability 🆕

• Spring Boot Actuator
• Observability with Spring Boot 3 (Micrometer, tracing)

11.13 Reactive Spring (WebFlux) 🆕

• Guide to Spring WebFlux
• Handling Errors in Spring WebFlux
• Reactor WebFlux vs. Virtual Threads — which to choose

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☁️ Chapter 12: Cloud-Native, Microservices & Spring AI

Goal: take a service beyond localhost — package it, distribute it, observe it, and add AI.

12.1 Microservices with Spring Cloud

• ⭐ Spring Cloud Series
• Spring Cloud Configuration
• 📖 Spring Cloud — project home

12.2 Containerization

• Dockerizing a Spring Boot Application
• 🧪 Spring Boot with Docker (official guide)

12.3 Spring AI 🆕

• ⭐ Spring AI — project home
• 📖 Spring AI Reference — Getting Started
• Getting Started with Model Context Protocol (MCP)

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🎯 Chapter 13: Practice, Projects & Roadmaps

Goal: knowledge only sticks when you build. Pick a track and ship something.

13.1 Visual Roadmaps

• 🗺️ roadmap.sh — Java
• 🗺️ roadmap.sh — Spring Boot

13.2 Coding Practice

• 🧪 Exercism — Java Track (mentored, free)
• 🧪 HackerRank — Java
• 🧪 LeetCode — practice DSA in Java

13.3 Reference & Cheat Sheets

• ⚡ dev.java — official Java resources & guides
• ⚡ Baeldung — full Java & Spring catalogue
• 📖 Official Java SE API Docs
• 📖 Spring Guides — task-focused tutorials

13.4 Project Ideas to Build

Progress from small to production-shaped:

1. CLI to-do app — collections, file I/O, exception handling.
2. REST API for a bookstore — Spring Boot, Spring Data JPA, validation, exception handling, tests.
3. Secured multi-user API — add Spring Security (JWT), profiles, and Testcontainers integration tests.
4. Dockerized microservice — containerize it, add Actuator health checks and observability.
5. AI-assisted feature — add a Spring AI chat/summarize endpoint backed by a model.

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🤝 Contributing

Spotted a dead link, an out-of-date resource, or a missing modern topic? Contributions are very welcome:

1. Open an issue describing the fix or the resource you'd add (with a short note on why it's good).
2. Or submit a pull request — keep link descriptions concise, prefer up-to-date sources, and place the link in the right chapter.

Great additions: modern-Java resources, hands-on tutorials, and anything that replaces an outdated link with a current one.

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Maintained for educational purposes. Curated for Java 25 (LTS) and Spring Boot 4 / Spring Framework 7. Last updated: July 18, 2026.