Add rest-client-test module: @RestClientTest on Boot 4.1, Jackson 3 by default, and the RestClient-vs-RestTemplate root-URI matching trap (post #49)

rest-client-test/src/main/java/com/ankurm/restclienttest/EmployeeClient.java

@@ -0,0 +1,35 @@
+package com.ankurm.restclienttest;
+
+import org.springframework.stereotype.Service;
+import org.springframework.web.client.RestClient;
+
+/**
+ * Fetches employee data from the external HR system using Spring's fluent {@code RestClient} -
+ * the recommended approach for new client code. Every successful fetch is audited through
+ * {@link EmployeeAuditLogger}, a plain collaborator bean unrelated to REST at all.
+ *
+ * <p>The client builds itself from an injected {@code RestClient.Builder}, the same shape as
+ * {@link EmployeeTemplateClient}'s {@code RestTemplateBuilder} constructor - this is what lets
+ * {@code @RestClientTest} wire a mocked client straight in, with no separate {@code RestClient}
+ * bean required (see {@link EmployeeHttpInterface} for the one case that does need one).</p>
+ */
+@Service
+public class EmployeeClient {
+
+    private final RestClient restClient;
+    private final EmployeeAuditLogger auditLogger;
+
+    public EmployeeClient(RestClient.Builder restClientBuilder, EmployeeAuditLogger auditLogger) {
+        this.restClient = restClientBuilder.baseUrl("http://hr-api.example.com").build();
+        this.auditLogger = auditLogger;
+    }
+
+    public Employee getEmployeeById(Integer id) {
+        Employee employee = restClient.get()
+                .uri("/employees/{id}", id)
+                .retrieve()
+                .body(Employee.class);
+        auditLogger.logFetch(id);
+        return employee;
+    }
+}