Sep 5 2025 note

Java Spring Get

• @GetMapping is a shortcut for @RequestMapping(method = GET, path = …)

@GetMapping({"/health", "/.well-known/health"})
public Map<String, String> health() {
  return Map.of("status","ok","env","dev");
}

• The array means map both routes to this one handler

Build Properties

• Values like groupId, artifactId, version are stored in META-INF/build-info.properties
• META-INF/build-info.properties is generated at build time by the Spring Boot Maven plugin’s build-info goal
• To ensure it’s always there, configure the plugin to run the goal during process-resources in pom.xml
• pluginManagement only declares defaults; it does not execute plugins

Dependency Injection

Without

// Concrete types hard-coded inside Car
class PetrolEngine { void start() { System.out.println("vroom"); } }
class AlloyWheel {}
class LeadAcidBattery {}

class Car {
  private final PetrolEngine engine = new PetrolEngine();
  private final AlloyWheel wheel = new AlloyWheel();
  private final LeadAcidBattery battery = new LeadAcidBattery();

  void start() { engine.start(); }
}

With

class Car {
  private final Engine engine;
  private final Wheel wheel;
  private final Battery battery;

  Car(Engine engine, Wheel wheel, Battery battery) {
    this.engine = engine;
    this.wheel = wheel;
    this.battery = battery;
  }
  void start() { engine.start(); }
}

Store environment values (env, port, dry_run, timezone) in .properties file

about pluginManagement

<build> 
  <pluginManagement>
    <plugin> 
      <groupId>org.springframework.boot</groupId> 
      <artifactId>spring-boot-maven-plugin</artifactId>
      <executions> 
        <execution> 
          <id>build-info</id> 
          <phase>process-resources</phase>
          <goals><goal>build-info</goal></goals> 
        </execution>
      </executions> 
   </plugin> 
  </pluginManagement>
</build>

has to be

<build> 
  <plugin> 
    <groupId>org.springframework.boot</groupId> 
    <artifactId>spring-boot-maven-plugin</artifactId>
    <executions> 
      <execution> 
        <id>build-info</id> 
        <phase>process-resources</phase>
        <goals><goal>build-info</goal></goals> 
      </execution>
    </executions> 
  </plugin> 
</build>