A servlet Filter, a HandlerInterceptor and an @Aspect all run code around a request, but not at the same point. A traced Spring Boot 4.1 app on Tomcat shows the real order, what each can see, and where each one silently fails.
One invoice built three ways in Spring Boot 4.1: OpenPDF 3.0.5, iText Core 9.8.0 (AGPL) and Flying Saucer 10.7.0 rendering a Thymeleaf template. Checks which one shapes Marathi and Hindi correctly (none by default), the OpenPDF switch that does, streaming vs buffered downloads, font subsetting and timings.
A Spring AI streaming chat UI with no React: ChatClient to a Flux of server-sent events, an htmx front end, per-session memory, a Stop button that really cancels the model call, and back-pressure, all measured against a stub OpenAI-compatible server (no real provider was run).
Map, List, record and POJO attributes as JSON columns in Hibernate 7.4: the DDL on PostgreSQL 18 and MySQL 8, native JSONB operators and the question-mark trap, HQL JSON functions, GIN and expression index plans on 50,000 rows, dirty checking, and Jackson 3 vs 2.
A jextract FFM example on a real library: generate SQLite bindings on JDK 25, understand the four arena kinds, move C strings and pointer-to-pointer out-parameters, turn return codes into exceptions, pass a Java lambda as a callback, and see how FFM compares with hand-written JNI in a JMH run.
Point one Spring AI 2.0.2 OpenAiChatModel at Docker Model Runner and at Ollama by changing only base-url and the model name. Same GGUF model, same prompts: decode speed, time to first token, container memory and tool-call success, with transcripts. Measured on a CPU-only shared sandbox with the real docker/model-runner image; GPU and Docker Desktop paths were not measured and the post says so.
Export Excel from Spring Boot without running out of memory: XSSF vs SXSSF measured under a fixed heap (XSSF dies between 50,000 and 100,000 rows in 512 MB), 1,000,000 rows streamed with StreamingResponseBody under 64 MB, sheet rolling at 1,048,576 rows, temp-file cleanup, OpenCSV traps and a file LibreOffice will not open.
A Spring Batch 6 chunk step calls a Spring AI ChatClient for 100,000 generated support tickets. Resilience4j rate limiting and retry, skip-and-record for malformed JSON, a restart after kill -9 in a second JVM that ends byte-identical, and a per-chunk cost ledger, all run against a deterministic simulated model with every number taken from a committed transcript.
Hibernate 7.4 multi-tenancy on Spring Boot 4.1 and PostgreSQL 17, run end to end: @TenantId discriminator vs schema-per-tenant, tenant taken from a signed JWT claim, the search_path leak, one shared pool vs a pool per tenant (measured connection counts), and what happens when no tenant is set.
Three ways to build an LRU cache in Java: LinkedHashMap with accessOrder, HashMap plus a hand-rolled doubly linked list with sentinels, and thread-safe variants (synchronized, ReentrantLock, striping). Includes an O(1) dry-run table, a demo of why ReadWriteLock corrupts the list, a stress test with real assertions, an indicative JMH comparison and Caffeine as the production answer.