Add filter-interceptor-aop module: servlet Filter vs HandlerInterceptor vs @Aspect on Spring Boot 4.1.2, the real order on Tomcat and MockMvc, error/404/async/body/Security traps

Co-Authored-By: Claude Sonnet 5.5 <[email protected]>
Claude-Session: https://claude.ai/code/session_017ic4b6Kg9RWSTJzyz6KP9X

README.md

@@ -10,6 +10,7 @@ files.
 | Directory | Article | What it demonstrates |
 |---|---|---|
 | [`pdf-invoice/`](pdf-invoice) | [Generate PDF Invoices in Spring Boot: OpenPDF vs iText vs Flying Saucer (HTML to PDF)](https://ankurm.com/spring-boot-generate-pdf-invoice-openpdf-itext-flying-saucer/) | one invoice rendered by OpenPDF 3.0.5, iText Core 9.8.0 (AGPL 3 or commercial) and Flying Saucer 10.7.0 from a Thymeleaf template, with embedded Noto Sans Devanagari: none of the three shapes Marathi/Hindi conjuncts by default (checked by rendering to PNG against a libraqm reference), OpenPDF's `GlyphLayoutManager` does but breaks text extraction until `ActualText` is on, OpenPDF's static `LayoutProcessor` is JVM-global and breaks other writers, Apache FOP on the classpath did not help, streamed vs buffered failure (`200` + curl exit 18 vs `500`), font subsetting, indicative per-invoice timings |
+| [`filter-interceptor-aop/`](filter-interceptor-aop) | [Filter vs HandlerInterceptor vs AOP in Spring Boot 4: Which Runs When](https://ankurm.com/spring-boot-filter-vs-handlerinterceptor-vs-aop-which-runs-when/) | the real order of a servlet filter, a `HandlerInterceptor` and an `@Aspect` printed from a running Tomcat and from MockMvc, the callbacks that still fire (and the ones that do not) after an exception, a 404, a `preHandle` that returns false and an async request, `afterCompletion` seeing `ex=null` after `@ControllerAdvice`, a header added in `postHandle` silently lost, a request body read twice, `ContentCachingResponseWrapper` returning an empty 200, Spring Security 7's chain sitting at order -100, a filter bean running twice, the Framework 7 path-matching removals read with `javap`, and the three self-invocation-style cases an aspect never sees |
 | [`excel-export/`](excel-export) | [Export Excel and CSV from Spring Boot: Streaming 1 Million Rows with Apache POI SXSSF](https://ankurm.com/spring-boot-export-excel-csv-streaming-poi-sxssf/) | XSSF vs SXSSF under a fixed 512 MB heap (XSSF out of memory between 50,000 and 100,000 rows and at 1,000,000 rows even with 3 GB), 1,000,000 rows streamed with `StreamingResponseBody` under a 64 MB heap, sheet rolling at 1,048,576 rows, `compressTempFiles` cutting the spill from 475 MB to 56 MB, OpenCSV swallowing write errors, and an SXSSF file LibreOffice will not open |
 | [`thymeleaf-htmx/`](thymeleaf-htmx) | [Spring Boot 4 + Thymeleaf + htmx: Server-Side CRUD UI in 2026](https://ankurm.com/spring-boot-thymeleaf-htmx-crud-ui/) | one URL answering as full page or fragment on `HX-Request`, a Thymeleaf layout, 422 validation re-render, pagination, inline edit and delete, 10 MockMvc tests plus a headless-Chromium check that observed htmx 2 ignoring a 204 and (without a config tag) a 422 |
 | [`rate-limit/`](rate-limit) | [Rate Limiting Spring Boot APIs with Bucket4j and Redis: Per-User, Per-Key and Global Limits](https://ankurm.com/spring-boot-rate-limiting-bucket4j-redis/) | per-user, per-API-key and global token buckets in a servlet filter on Bucket4j 8.21 (`bucket4j_jdk17-*`), `429` with `Retry-After` and `X-RateLimit-*` headers, two application instances sharing one Redis bucket and 200 concurrent requests letting exactly 20 through, a limit raised in `application.yml` that does not change buckets already stored in Redis until a config version is bumped, a client clock 30 s ahead handing out tokens another instance already spent, and fail-open versus fail-closed when Redis dies |