Add the hexagonal module: Hexagonal Architecture (Ports and Adapters) in Spring Boot 4

hexagonal/persistence-adapter/pom.xml

@@ -0,0 +1,47 @@
+<project xmlns="http://maven.apache.org/POM/4.0.0">
+  <modelVersion>4.0.0</modelVersion>
+
+  <parent>
+    <groupId>com.ankurm</groupId>
+    <artifactId>hexagonal-parent</artifactId>
+    <version>1.0</version>
+  </parent>
+
+  <artifactId>hexagonal-persistence-adapter</artifactId>
+  <packaging>jar</packaging>
+
+  <!-- This is the only module allowed to know a database exists. It depends on hexagonal-core
+       to implement WalletRepository, and on Spring Data JPA to do so for real. -->
+  <dependencies>
+    <dependency>
+      <groupId>com.ankurm</groupId>
+      <artifactId>hexagonal-core</artifactId>
+      <version>1.0</version>
+    </dependency>
+    <dependency>
+      <groupId>org.springframework.boot</groupId>
+      <artifactId>spring-boot-starter-data-jpa</artifactId>
+    </dependency>
+    <dependency>
+      <groupId>com.h2database</groupId>
+      <artifactId>h2</artifactId>
+      <scope>runtime</scope>
+    </dependency>
+    <dependency>
+      <groupId>org.springframework.boot</groupId>
+      <artifactId>spring-boot-starter-test</artifactId>
+      <scope>test</scope>
+    </dependency>
+    <!-- Spring Boot 4 split @DataJpaTest out of spring-boot-test-autoconfigure into its own
+         artifact, alongside the rest of the data/jpa/web slices. Confirmed by unzipping
+         spring-boot-test-autoconfigure-4.1.1.jar (no "jpa" class anywhere in it) and then
+         spring-boot-data-jpa-test-4.1.1.jar, which has
+         org.springframework.boot.data.jpa.test.autoconfigure.DataJpaTest - a new package too,
+         not the old org.springframework.boot.test.autoconfigure.orm.jpa. -->
+    <dependency>
+      <groupId>org.springframework.boot</groupId>
+      <artifactId>spring-boot-data-jpa-test</artifactId>
+      <scope>test</scope>
+    </dependency>
+  </dependencies>
+</project>