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This article demonstrates how to implement a correct waitlist auto-promotion system for limited-capacity events using Spring Boot, MySQL InnoDB row locks, and database transactions to atomically handle cancellations and promotions without race conditions, ensuring the first waitlisted user always gets the freed spot.
This article demonstrates how to prevent race conditions between order timeout closure and payment callbacks using atomic conditional UPDATE statements and SELECT FOR UPDATE with a refund outbox pattern, ensuring either payment wins and order becomes PAID, or closure wins and late payments trigger automatic refund compensation.
The article demonstrates how Spring Boot 4.1's new InetAddressFilter.externalAddresses() simplifies SSRF protection for user-supplied URLs, replacing manual IP checks with a centralized HTTP client filter, while also covering URL validation, redirect handling, timeouts, response size limits, and testing strategies to secure link preview and similar features.
This guide demonstrates integrating Passkey/WebAuthn authentication into a Spring Boot application using Spring Security 7.1's built-in support, covering dependency setup, security configuration, frontend JavaScript implementation for credential registration and authentication, database persistence with JDBC repositories, and a migration strategy that retains password login while adding Passkey as a second factor.
The article demonstrates why distributed locks alone fail to guarantee idempotency in Spring Boot order APIs, and presents a three-layer solution combining Idempotency-Key with request fingerprinting, Redis SET NX for fast duplicate interception, and a database unique constraint as the ultimate safeguard against duplicate orders even after crashes or Redis failures.
After an external system hammered a Spring Boot search endpoint causing database connection exhaustion, the author builds a distributed fixed-window rate limiter using Redis and Lua for atomicity, wraps it with an annotation-driven AOP aspect supporting user, IP, API key, and global dimensions, returns proper HTTP 429 with Retry-After, discusses fixed-window limitations versus token bucket and sliding window, and covers fail-open/fail-closed strategies for Redis outages plus monitoring metrics.
The article shows how to handle 10GB file downloads in Spring Boot by replacing in-memory byte[] loading with streaming via FileSystemResource and leveraging Spring MVC's built-in Range request support for resumable downloads, while covering security, immutability, and object storage offloading.
The article explains how to handle duplicate payment callbacks in Spring Boot using database unique constraints, conditional state updates, an outbox pattern for reliable event publishing, and downstream idempotency, ensuring orders are processed exactly once even if the payment platform sends repeated notifications.
The article details refactoring a synchronous Spring Boot Excel import that failed at 100k rows into an async task model with streaming Apache POI SAX parsing, 500-row JDBC batch inserts, row-level error isolation, and SSE real-time progress, eliminating 504 timeouts and duplicate data on retry.
The author evolves a simple Spring Boot file upload to handle 5GB files by implementing 8MB chunked uploads, resumable upload via chunk tracking, instant upload via SHA-256 deduplication, with database schema, REST API design, streaming merge, database-level concurrency control, and automated cleanup of expired uploads.
