Dynamic Service Switching in Spring Boot Using spring‑smart‑di

0. Background

When a system integrates multiple service providers for the same functionality, developers often need a fast way to switch providers based on availability or pricing. The traditional approach stores each provider implementation and selects the active one via a configuration point (e.g., a database or Nacos), retrieving the current provider each time a request is processed.

For example, a system may integrate several SMS providers and allow users to switch between them dynamically.

Step 1: Configure the current provider, e.g., sms.impl = "某腾短信".

Step 2: In the sending logic, read sms.impl, obtain the corresponding implementation class, and invoke its method.

void sendSmsTouser(Req req) {
  // 1. Get the current provider name
  String name = get("sms.impl");
  // 2. Retrieve the implementation bean
  SmsService smsService = springContext.getBean(name);
  // 3. Execute the business logic
  smsService.sendMsg(req);
}

Spring's @Autowired can be extended so that the injected bean automatically follows the configuration, eliminating the need to manually fetch the provider each time. This is where spring-smart-di and its AutowiredProxySPI come into play.

1. spring‑smart‑di

spring‑smart‑di extends Spring's @Autowired mechanism, allowing developers to define custom injection logic. It currently provides two annotations: @SmartAutowired and @AutowiredProxySPI. The article focuses on using @AutowiredProxySPI for dynamic switching.

2. Quick Start

Add the Maven dependency:

<dependency>
    <groupId>io.github.burukeyou</groupId>
    <artifactId>spring-smart-di-all</artifactId>
    <version>0.2.0</version>
</dependency>

Enable the feature on a Spring configuration class with @EnableSmartDI.

2.1 @EnvironmentProxySPI Annotation

@EnvironmentProxySPI

marks a configuration point that determines how to obtain the concrete implementation class, typically from an environment variable.

@EnvironmentProxySPI("${sms.impl}")
public interface SmsService {
}

@BeanAliasName("某腾短信服务")
@Component
public class ASmsService implements SmsService {}

@BeanAliasName("某移短信服务")
@Component
public class BSmsService implements SmsService {}

2.2 Configuring the Active Provider

Specify the active provider in a configuration file (e.g., application.yml); the value can be a bean alias, component name, or fully qualified class name.

sms:
  impl: 某移短信服务

2.3 Using @AutowiredProxySPI

Inject the service just like a regular @Autowired field:

// Dependency injection
@AutowiredProxySPI
private SmsService smsService;

Changing the ${sms.impl} value updates the injected proxy in real time without restarting the application.

2.4 Defining Custom Configuration Points

While @EnvironmentProxySPI reads from environment variables, developers can create custom annotations (e.g., @DBProxySPI) to fetch configuration from a database. The custom annotation is marked with @ProxySPI and points to a factory that implements the retrieval logic.

@Inherited
@Target({ElementType.FIELD,ElementType.METHOD,ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@ProxySPI(DbProxyFactory.class) // specify config retrieval logic
public @interface DBProxySPI {
    String value();
}

@Component
public class DbProxyFactory implements AnnotationProxyFactory<DBProxySPI> {
    @Autowired
    private SysConfigMapper sysConfigDao;

    @Override
    public Object getProxy(Class<?> targetClass, DBProxySPI spi) {
        // Retrieve implementation name from DB based on annotation value
        String configName = sysConfigDao.getConfig(spi.value());
        return springContext.getBean(configName);
    }
}

@DBProxySPI("${sms.impl}")
public interface SmsService {}

Project repository: https://github.com/burukeYou/spring-smart-di