"Is it safe to add password in LoginRequest? Can someone reach the user's request?" Great security question! The answer depends entirely on whether you're using HTTP or HTTPS. With HTTP, anyone on the network can see your password in plain text. With HTTPS, it's encrypted end-to-end. Let's understand the difference and how to secure your login.
"What does ResponseEntity<UnlockResponse> mean? Why can I use <UnlockResponse> here but <LoginResponse> somewhere else?" ResponseEntity is like a delivery box - it's a generic container that can hold any type of content. The <T> is a placeholder that you fill with your specific data type. Let's understand how this "magic" works and why it's incredibly powerful.
In Part 1, we learned why Spring Data JPA repositories must be interfaces. Now let's understand the fundamental difference between classes and interfaces in Java, and when to use each.
In Parts 1 and 2, we learned what interfaces are and when to use them. Now let's dive deep into the OOP principles that make interfaces essential for large-scale applications. This isn't about avoiding code duplication—it's about fundamental software design.
In Parts 1-3, we learned why Spring Data JPA uses interfaces and generates implementations. But here's the critical question: "If implementations need to exist somewhere, aren't we just hiding the work? Someone still has to write the code!" Let's be brutally honest about what frameworks actually save you.
"Why can't I use class instead of interface for UserRepository?" Because Java's type system has strict rules: class extends class, interface extends interface, class implements interface. When you try class UserRepository extends JpaRepository, Java sees JpaRepository is an interface and throws an error. Let's understand the three-level inheritance chain and who implements what.
Trying to create a Spring Data repository by extending JpaRepository with a class instead of an interface? It won't work. Here's why Spring Data JPA requires interfaces and what happens behind the scenes.
"I just added spring-boot-starter-security to my pom.xml and now ALL my endpoints return 401 Unauthorized! I didn't write any security code - why is this happening?" This is Spring Security's "secure by default" philosophy at work. Let's understand why this design choice makes sense and how to configure it.
Your Spring Boot app starts, H2 Console connects, but... where are the tables? Here's how to test if your H2 database is working and fix the most common issue: missing tables.
What if I told you that adding a single annotation to a Java class automatically creates a database table with all the right columns, types, and constraints? Meet @Entity - the annotation that bridges Java objects and database tables.