refactor(bootstrap): replace PostConstruct validator with ApplicationContextInitializer

bootstrap/src/main/java/com/pablotj/restemailbridge/bootstrap/EnvironmentValidatorInitializer.java

@@ -0,0 +1,29 @@
+package com.pablotj.restemailbridge.bootstrap;
+
+import org.springframework.context.ApplicationContextInitializer;
+import org.springframework.context.ConfigurableApplicationContext;
+
+public class EnvironmentValidatorInitializer implements ApplicationContextInitializer<ConfigurableApplicationContext> {
+
+    @Override
+    public void initialize(ConfigurableApplicationContext ctx) {
+        String[] requiredProperties = {
+                "APP_ENCRYPTION_SECRET",
+                "APP_ALLOWED_ORIGINS",
+                "DB_NAME",
+                "DB_USER",
+                "DB_PASSWORD",
+                "DB_HOST",
+                "DB_PORT",
+                "GMAIL_OAUTH_CLIENT_ID",
+                "GMAIL_OAUTH_CLIENT_SECRET"
+        };
+
+        for (String prop : requiredProperties) {
+            String value = ctx.getEnvironment().getProperty(prop);
+            if (value == null || value.isEmpty()) {
+                throw new IllegalStateException("ERROR: Property '" + prop + "' is not defined or empty");
+            }
+        }
+    }
+}

bootstrap/src/main/java/com/pablotj/restemailbridge/bootstrap/RestEmailBridgeApplication.java

@@ -11,6 +11,8 @@ import org.springframework.data.jpa.repository.config.EnableJpaRepositories;
 public class RestEmailBridgeApplication {
 
     public static void main(String[] args) {
-        SpringApplication.run(RestEmailBridgeApplication.class, args);
+        SpringApplication app = new SpringApplication(RestEmailBridgeApplication.class);
+        app.addInitializers(new EnvironmentValidatorInitializer());
+        app.run(args);
     }
 }