Three new article modules: configuration binding, profiles and config data, Spring AOP

configuration-properties/  @ConfigurationProperties vs @Value on Spring Boot 4.1.1.
  The relaxed-binding matrix is generated by binding each spelling rather than
  transcribed, and re-checked against real processes -- the in-process probe was
  wrong twice before it was right. Records the three findings that came out of it:
  @Value does get relaxed resolution inside Spring Boot (Boot attaches
  ConfigurationPropertySources), the configuration processor silently stops
  generating metadata on JDK 23+ when declared as a plain dependency, and @Valid is
  not what makes nested constraints run.

profiles-and-config/       Precedence, profiles, spring.config.import and config trees.
  /precedence reports every source holding a property in rank order with file and
  line, which turns "my profile file had no effect" into a two-line answer. Also
  pins the counterintuitive one: an imported file outranks the file that imported it.

spring-aop/                Designators, proxy types, and aspects that do not fire.
  One advice per supported designator so the reference table is generated from real
  matches; all fourteen unsupported designators fed to the parser. Two corrections to
  the reference documentation: unsupported designators throw
  UnsupportedPointcutPrimitiveException (extends RuntimeException, not
  IllegalArgumentException), and spring-boot-starter-aop was renamed to
  spring-boot-starter-aspectj in Boot 4.

19 contract tests across the three modules, 15 captured transcripts, all regenerated
by scripts/run-all.sh. Verified on Spring Boot 4.1.1, Spring Framework 7.0.9,
JDK 25.0.4.1.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Gip4srpzMwjgoba6uEfbr5

profiles-and-config/scripts/demo-config-tree.sh

@@ -0,0 +1,66 @@
+#!/usr/bin/env bash
+# Config trees: what a Kubernetes ConfigMap or Secret actually looks like to Spring Boot.
+#
+# A ConfigMap mounted as a volume is not a properties file. Kubernetes writes one file per
+# key, named after the key, containing only the value. `configtree:` is the loader that reads
+# that shape. This script builds the same directory layout on disk, so the demonstration is
+# the real mechanism rather than a description of it.
+set -euo pipefail
+set +m
+cd "$(dirname "$0")/.."
+source scripts/env.sh
+
+TREE="${TMPDIR:-/tmp}/demo-configmap"
+SECRET="${TMPDIR:-/tmp}/demo-secret"
+rm -rf "$TREE" "$SECRET"; mkdir -p "$TREE" "$SECRET"
+
+# Exactly what `kubectl create configmap demo --from-literal=demo.greeting=...` produces
+# once mounted: one file per key, the filename IS the property name.
+printf 'from-configmap-volume'                 > "$TREE/demo.greeting"
+printf 'jdbc:postgresql://configmap-db:5432/o' > "$TREE/demo.datasource-url"
+printf '25'                                    > "$TREE/demo.pool-size"
+# Nested keys use a directory per level, or a dotted filename. Both work.
+mkdir -p "$TREE/demo/nested"
+printf 'from-nested-directory'                 > "$TREE/demo/nested/value"
+# A Secret mount looks identical; only the permissions differ.
+printf 'sk_live_not_a_real_key'                > "$SECRET/demo.api-key"
+
+{
+  echo "== what Kubernetes actually mounts =="
+  echo "\$ find $TREE $SECRET -type f | sort"
+  find "$TREE" "$SECRET" -type f | sort | sed "s|$TREE|<configmap-mount>|;s|$SECRET|<secret-mount>|"
+  echo
+  echo "\$ cat <configmap-mount>/demo.greeting; echo"
+  cat "$TREE/demo.greeting"; echo
+  echo
+  echo "Each file holds a bare value with no trailing newline and no key. There is no"
+  echo "properties syntax to parse -- the filename is the key."
+  echo
+  echo "== importing it =="
+  echo "\$ java -jar $JAR \\"
+  echo "    --spring.config.import=configtree:$TREE/,configtree:$SECRET/"
+  echo
+  start_app "--spring.config.import=configtree:$TREE/,configtree:$SECRET/" > /dev/null
+  report demo.greeting
+  echo
+  echo "  demo.pool-size      = $(curl -s "http://127.0.0.1:${APP_PORT}/precedence?name=demo.pool-size" | python3 -c 'import json,sys; print(json.load(sys.stdin)["effectiveValue"])')"
+  echo "  demo.nested.value   = $(curl -s "http://127.0.0.1:${APP_PORT}/precedence?name=demo.nested.value" | python3 -c 'import json,sys; print(json.load(sys.stdin)["effectiveValue"])')"
+  echo "  demo.api-key        = $(curl -s "http://127.0.0.1:${APP_PORT}/precedence?name=demo.api-key" | python3 -c 'import json,sys; print(json.load(sys.stdin)["effectiveValue"])')"
+  echo
+  echo "A directory under the mount becomes a nested property: demo/nested/value is"
+  echo "demo.nested.value. That is how a ConfigMap with slashes in its keys arrives."
+  echo
+  echo "== the part that surprises people =="
+  echo "An imported config tree outranks application.yaml, but it is still config data,"
+  echo "so it still loses to an environment variable:"
+  echo
+  APP_ENV="DEMO_GREETING=from-environment-variable" \
+    start_app "--spring.config.import=configtree:$TREE/" > /dev/null
+  report demo.greeting
+  echo
+  echo "There is also no such thing as a profile-specific config tree. There is no"
+  echo "<mount>-prod directory convention; a per-environment ConfigMap is a different mount"
+  echo "chosen by the deployment, not by spring.profiles.active."
+  stop_app
+} > docs/output/03-config-tree.txt 2>&1
+cat docs/output/03-config-tree.txt