REST APIs are synchronous — the caller waits for a response. Sometimes you don’t want that. An order creation shouldn’t wait for the inventory system, the notification system, and the analytics system to all respond before confirming to the user. Kafka decouples these concerns. What Kafka Is Kafka is a distributed event streaming platform. It stores events (messages) in an ordered, immutable log. Producers write to Kafka; consumers read from it.

Every application has a class of work that doesn’t fit the request-response model: process 2 million orders overnight, generate 500,000 monthly statements, migrate 10 years of legacy data before Monday morning. This work needs to be reliable, restartable after failures, and fast enough to finish in the available window. That’s what Spring Batch is built for. This article covers what Spring Batch is, when to use it, and how its architecture works.

You want to build a Java web application or REST API. You’ve heard everyone uses Spring Boot. But what is it exactly, and why does it exist? This article answers that — clearly — before writing a single line of code. What Is Spring Boot? Spring Boot is an opinionated framework for building Spring-based Java applications with minimal configuration. Break that down: Spring-based — it sits on top of the Spring Framework, which has been the dominant Java application framework since 2003 Minimal configuration — you describe what you want (a web app, a database connection), and Spring Boot figures out how to set it up Opinionated — it makes sensible default choices so you don’t have to make every decision yourself The one-line version: Spring Boot lets you go from a blank project to a running application in minutes, with production-ready defaults built in.

Most Spring Boot applications need to read and write data to a relational database. Spring Data JPA makes this dramatically simpler by generating the boilerplate data access code for you. This article explains what it is, how it fits together, and how to get started. The Stack: JPA, Hibernate, and Spring Data JPA These three things work together — understanding the layering matters: Your Code (Repository interfaces, @Entity classes) │ ▼ Spring Data JPA (generates repository implementations, adds convenience methods) │ ▼ JPA (Jakarta Persistence API) (standard specification: @Entity, @Id, EntityManager, JPQL) │ ▼ Hibernate (JPA implementation) (translates JPA operations to SQL, manages sessions) │ ▼ JDBC (Java Database Connectivity) (sends SQL to the database) │ ▼ PostgreSQL / MySQL / H2 / etc.

Introduction Two mechanisms let you pass information into and through a Spring Batch job: JobParameters — input values provided at launch time (a date, a file path, a run ID). They are immutable and persisted to BATCH_JOB_EXECUTION_PARAMS. ExecutionContext — a key-value map that steps can read and write during execution. It is persisted after each chunk commit, enabling restartability. Understanding both is essential for building jobs that can be safely re-run, restarted after failure, and parameterised for different data sets.

Introduction Every time Spring Batch runs a job it records the run’s history in a set of relational tables. This metadata is not optional — it is what makes Spring Batch reliable. Without it there would be no restart capability, no duplicate-run prevention, and no audit trail. Understanding the metadata layer is essential for debugging failures, building monitoring dashboards, and designing restartable jobs. In this article you will learn: The role of JobRepository and JobExplorer in the Spring Batch architecture The six metadata tables — their schema, purpose, and relationships How Spring Batch uses these tables to enable restartability How to query batch history directly in MySQL How to access metadata programmatically with JobExplorer Key changes in Spring Batch 5 (removed MapJobRepositoryFactoryBean, new testing approach) All examples use Spring Boot 3.

JPA entity mapping defines how Java objects translate to database tables. Get it right and your schema is clean, performant, and expressive. This article covers every mapping annotation you’ll need. @Entity and @Table @Entity @Table( name = "orders", // table name (default: class name) schema = "commerce", // database schema indexes = { @Index(name = "idx_orders_customer_id", columnList = "customer_id"), @Index(name = "idx_orders_status_created", columnList = "status, created_at") }, uniqueConstraints = { @UniqueConstraint(name = "uq_order_number", columnNames = "order_number") } ) public class Order { // .

JPA makes data access easy — until it silently runs hundreds of queries to load what you think is a single query. This article covers how to find and fix the most common JPA performance problems. Enable Query Logging First You can’t fix what you can’t see. Enable SQL logging before optimizing: logging: level: org.hibernate.SQL: DEBUG org.hibernate.orm.jdbc.bind: TRACE # log bind parameters (Spring Boot 3+) spring: jpa: properties: hibernate: format_sql: true generate_statistics: true # log query count, cache hits, etc.

Derived query methods cover simple cases. Complex filtering, aggregation, and reporting queries need JPQL or native SQL. This article covers both with practical examples. JPQL vs SQL vs Native SQL JPQL Native SQL Writes Entity-oriented (FROM Order o) Table-oriented (FROM orders o) Portability DB-agnostic DB-specific Features Basic SQL + JPA joins Full DB-specific SQL (CTEs, window functions, JSONB) Type-safety Partial None Use for Most queries Reporting, DB-specific features @Query with JPQL public interface OrderRepository extends JpaRepository<Order, UUID> { // Basic JPQL — uses entity/field names, not table/column names @Query("SELECT o FROM Order o WHERE o.

JWT (JSON Web Token) is the standard for stateless REST API authentication. This article builds a complete JWT authentication system — login, token generation, request validation, and token refresh. What is a JWT? A JWT has three base64url-encoded parts separated by dots: eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9 ← Header (algorithm + type) .eyJzdWIiOiJ1c2VyMTIzIiwicm9sZXMiOlsiVVNFUiJdLCJpYXQiOjE3MTQ3MjY0MDAsImV4cCI6MTcxNDczMDAwMH0 ← Payload .SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c ← Signature The payload contains claims: { "sub": "user123", // subject (user identifier) "roles": ["USER"], "iat": 1714726400, // issued at "exp": 1714730000 // expires at } The signature is a HMAC of the header+payload — tamper-proof.