Spring Framework

Bean in Spring Boot

Spring Context is the corner stone of Spring, it represents Spring Container of Dependency Injection. It’s the power house of initiating and wiring.

@Configuration is equivalent to the Configuration.xml, it use the class style to store the Java Bean definition.

In @Configuration we define the bean explicitly using @Bean annotation, we can use name and scope.

@Bean(name = "foo")
public Foo foo() {
   return new Foo(); // add any customized initiate step here.
}

Another way to add the bean to context is using Spring Boot auto scan with these annotation @Component , @Repository, @Service and @Controller etc.

Here’s the difference among the 4 annotations:

@Component is the basic version with Bean auto scan and registration.
@Controller special form of @Component, which has exact same function. And it also indicate it’s the controller in Spring MVC, which provide the routing and wiring up services.
@Service, @Repository are also the special form of @Component is service and persistent layer.

When it comes to Dependency Injection stage, we can add them into the constructor (e.g. @RequiredArgsConstructor) or use the field dependency injection.

And check here to see why the constructor way is better.

For the field injection. there are 3 different choices, all of them support field and setter injection. And the details are:

@Resource: resolves dependencies by name first.
@Inject: resolve dependencies by type as default.
@Autowired: similar as @Inject, and it’s part of the Spring framework. reference

Configuration @SpringBootApplication is the composed annotation, actually it includes the following annotations:

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan

Then all the @Component will be scanned and put it as bean in Context, @Autowired will help to initiate the bean and dependency injection.

And if we need to scan package not in default component scanning, we need to explicitly to add @ComponentScan annotation.

@ConfigurationProperties Spring Boot 2.2 will add the corresponding field as bean into the application context.

then the config can be got from the either the application config or Spring Boot Admin

Constructor @RequiredArgsContructor will generate a contructor with final fields. If customed logic is needed (e.g. setup a custom mapping for later usage), we need to create a explicit constructor manually.

Properties

https://docs.spring.io/spring-boot/docs/current/reference/html/application-properties.html

Spring Profile

The Spring profile can selectively enable part of the application, and help use the segregate the configuration for different environments.

JPA With Spring Boot’s help, all the manual tedious works will be saved, e.g. setup the DB driver, open and close DB, SQL statement, convert result set to objects, etc. As a result, we can concentrate on the business logic.

DAO and Enity

JUnit Test

Actuator

Auctuator module provide production ready features, like monitoring, health, metrics gathering. To use that, we could just add spring-boot-starter-actuator in the dpendency.

And we could use endpoint private/actuator/refresh to refresh the config

Links/ Pagination

HATEOAS is a standard/way to do the links in JAVA.

REST architectural style lets you use hypermedia links in the response contents so that the client can dynamically navigate to the appropriate resource by traversing the hypermedia links.

"_links": {
        "first": {
            "href": "http://localhost:8080/api/albums-list?page=0&size=2&sort=title,desc"
        },
        "prev": {
            "href": "http://localhost:8080/api/albums-list?page=0&size=2&sort=title,desc"
        },
        "self": {
            "href": "http://localhost:8080/api/albums-list?page=1&size=2&sort=title,desc"
        },
        "next": {
            "href": "http://localhost:8080/api/albums-list?page=2&size=2&sort=title,desc"
        },
        "last": {
            "href": "http://localhost:8080/api/albums-list?page=4&size=2&sort=title,desc"
        }
    }

Log config

Data Access