Spring在自动装配的bean中自动装配属性

Question

I'm a newbie to Spring. I'm facing a problem with Spring-Boot. I'm trying to autowire a field from an external config file into an autowired bean. I have the following classes

App.java

public class App {

@Autowired
private Service service;

public static void main(String[] args) {

    final SpringApplication app = new SpringApplication(App.class);
    //app.setShowBanner(false);
    app.run();
}

@PostConstruct
public void foo() {
    System.out.println("Instantiated service name = " + service.serviceName);
}
}

AppConfig.java

@Configuration
@ConfigurationProperties
public class AppConfig {

@Bean
public Service service()    {
    return new Service1();
}
}

Service Interface

public interface Service {
    public String serviceName ="";
    public void getHistory(int days , Location location );
    public void getForecast(int days , Location location );
}

Service1

@Configurable
@ConfigurationProperties
public class Service1 implements Service {

@Autowired
@Value("${serviceName}") 
public String serviceName;
//Available in external configuration file.
//This autowiring is not reflected in the main method of the application.



public void getHistory(int days , Location location)
{
    //history code
}

public void getForecast(int days , Location location )
{
    //forecast code
}
}

I'm unable to display the service name variable in the postconstruct method of the App class. Am I doing this right?

Answer 1

You can load properties in different ways:

Imagine the following application.properties which is automatically loaded by spring-boot.

spring.app.serviceName=Boot demo
spring.app.version=1.0.0

1. Inject values using @Value

    @Service public class ServiceImpl implements Service { @Value("${spring.app.serviceName}") public String serviceName; } 

2. Inject values using @ConfigurationProperties

    @ConfigurationProperties(prefix="spring.app") public class ApplicationProperties { private String serviceName; private String version; //setters and getters } 

You can access to this properties from another class using @Autowired

@Service
public class ServiceImpl implements Service {

@Autowired
public ApplicationProperties applicationProperties;

}

As you can notice the prefix will be spring.app then spring-boot will match the properties prefix with that and look for serviceName and version and values will be injected.

Answer 2

Considering you have you class App annotated with @SpringBootApplication and App class in the top package You can put your serviceName inside application.properties and inject it using @Value("${serviceName}") . Do not use @Component on a class if you are already using @Bean on configuration it will clash, and so @Autowired with @Value

See docs for more info

You will end with something like

@Service // @Component specialization
public class Service1 implements Service {

@Value("${serviceName}") 
public String serviceName;
//Available in external configuration file.
//This autowiring is not reflected in the main method of the application.



public void getHistory(int days , Location location)
{
    //history code
}

public void getForecast(int days , Location location )
{
    //forecast code
}
}

No need for @Bean declaration when you have @Component/@Service/@Repository

@Configuration
public class AppConfig {  //other stuff here not duplicated beans  }

And your main class

    package com.app;

    @SpringBootApplication // contains @EnableAutoConfiguration @ComponentScan @Configuration   
    public class App {

    @Autowired
    private Service service;

    public static void main(String[] args) {

        final SpringApplication app = new SpringApplication(App.class);
        //app.setShowBanner(false);
        app.run();
    }

    @PostConstruct
    public void foo() {
        System.out.println("Instantiated service name = " + service.serviceName);
    }
    }