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

configuration-properties/scripts/demo-metadata-generation.sh

@@ -0,0 +1,51 @@
+#!/usr/bin/env bash
+# Does spring-boot-configuration-processor actually run?
+#
+# Two builds of the SAME sources with the SAME processor jar, differing only in how the
+# processor is declared to the compiler. On JDK 23+ that difference decides whether
+# META-INF/spring-configuration-metadata.json exists at all -- and neither build fails.
+set -euo pipefail
+cd "$(dirname "$0")/.."
+source scripts/env.sh
+
+WORK="${TMPDIR:-/tmp}/configprops-metadata-ab"
+rm -rf "$WORK"; mkdir -p "$WORK/a" "$WORK/b"
+
+PROC_JAR=$(find ~/.m2/repository/org/springframework/boot/spring-boot-configuration-processor \
+             -name 'spring-boot-configuration-processor-*.jar' | sort | tail -1)
+CP=$("$MVN" -B -o -q dependency:build-classpath -Dmdep.outputFile=/dev/stdout 2>/dev/null | tail -1)
+
+SOURCES=$(find src/main/java -name '*.java')
+
+{
+  echo "== is the annotation processor discovered? =="
+  echo
+  java -version 2>&1 | clean | head -1
+  echo "processor jar: $(basename "$PROC_JAR")"
+  echo
+  echo "A) processor on the classpath, javac defaults -- what an <optional> dependency gives you"
+  echo "\$ javac -cp <deps>:spring-boot-configuration-processor.jar -d a \$SOURCES"
+  javac -nowarn -cp "$PROC_JAR:$CP" -d "$WORK/a" $SOURCES 2>&1 | clean | head -3 || true
+  echo "   spring-configuration-metadata.json files produced: \
+$(find "$WORK/a" -name 'spring-configuration-metadata.json' | wc -l)"
+  echo
+  echo "B) identical, plus -proc:full"
+  echo "\$ javac -proc:full -cp <deps>:spring-boot-configuration-processor.jar -d b \$SOURCES"
+  javac -nowarn -proc:full -cp "$PROC_JAR:$CP" -d "$WORK/b" $SOURCES 2>&1 | clean | head -3 || true
+  echo "   spring-configuration-metadata.json files produced: \
+$(find "$WORK/b" -name 'spring-configuration-metadata.json' | wc -l)"
+  echo
+  echo "Both compilations succeed. Only one of them has metadata."
+  echo
+  echo "== what this project's pom does instead =="
+  echo "The processor is declared as an <annotationProcessorPath> on maven-compiler-plugin,"
+  echo "which puts it on javac's --processor-path where discovery is not disabled:"
+  echo
+  echo "\$ mvn clean package && ls target/classes/META-INF/"
+  ls target/classes/META-INF/ 2>/dev/null || echo "(run mvn package first)"
+  echo
+  echo "== the generated metadata, first entries =="
+  python3 -m json.tool target/classes/META-INF/spring-configuration-metadata.json 2>/dev/null \
+    | head -45
+} > docs/output/05-metadata-generation.txt 2>&1
+cat docs/output/05-metadata-generation.txt