Spring Boot

Key Concepts

• @EnableAutoConfiguration

  • Configure beans according to the jars under classpath

• Spring Bean Life Cycle

spring bean life cycle - start up

• This 3 step happens in the Bean Creation Life-Cycle Callback:

  • When an object constructor is done, @PostConstruct will be called.

  • If InitializingBean is implemented, then afterPropertiesSet() will be called. InitializingBean is for Spring Boot to assign attributes with @Autowired.

  • If bean definition contains init-method or @Bean(initmethod="..") then it calls the init method.

spring bean life cycle - shut down

• Running logic on startup

  • implements ApplicationListener run logic after the Spring context has been initialized

  • implements CommandLineRunner receives arguments with String

  • implements ApplicationRunner receives arguments with ApplicationArguments

Spring Cloud

• Quickly enable and configure the common patterns between Spring Boot applications and build large distributed systems.

  • Eureka - Service Discovery

    • Analogy: ECS / API Gateway + Lambda

  • Feign - Declarative HTTP Client

    • Analogy: Route53 / ELB

  • Ribbon - Load balancing

    • Analogy: ELB

  • Hystrix - Circuit Breaker

    • Analogy: AWS App Mesh

  • Zuul - Intelligent Routing

    • Analogy: AWS API Gateway

Automatic Test Implementation

• Unit Tests

  • Declare test target and dependent members (with Mock / Spy)

  • Declare setUp with @Before to:

    • Initializing mocking with MockitoAnnotations.initMocks(this);

      • Or adding @RunWith(MockitoJUnitRunner.class) on class level

    • Assigning test target with constructor approach

      • Or adding @InjectMocks to test target

  • Within tests

    • Setting up given, when then for the mocks

    • Asserting value of results

    • Verifying execution times

    • Asserting arguments in methods invoked with ArgumentCaptor

• Integration Tests

  • Annotations on class level

    • RunWith(SpringRunner.class) for JUnit to invoke the runner

    • Load related components with:

      • @SpringBootTest for looking for a main configuration class (one with @SpringBootApplication for instance), and using it to start a Spring application context.

      • @DataJpaTest for testing JPA repository layer

      • @WebMvcTest(XXController.class) for testing controller layer

  • Declare test target with @Autowired

  • Declare dependent members with @MockBean to add mocking to Spring application context (optional)

  • PS. Spring Boot would initialize embedded DB with below files:

    • schema.sql

    • data.sql

Interesting topics

• Why @Autowired HttpServletRequest is thread safe

  • @Autowired private HttpServletRequest request;

  • request = WebApplicationContextUtils.RequestObjectFactory

  • WebApplicationContextUtils.RequestObjectFactory.getObject() = WebApplicationContextUtils.currentRequestAttributes().getRequest()

  • WebApplicationContextUtils.currentRequestAttributes() = RequestContextHolder.currentRequestAttributes()

  • RequestContextHolder.currentRequestAttributes() is stored in ThreadLocal requestAttributesHolder;

• @Bean

  • lite: with @Component or event without it. Beans would be created by every invocation.

  • standard: with @Configuration. the bean (proxy created with CGLIB) is created when invoked at first time and subsequent invocations would return the same bean.

Reference

• Create your own Spring Boot Starter