How to Dynamically Switch Service Providers in Spring with spring-smart-di

In real-world system development, a common requirement is to integrate multiple service providers for the same functionality, to avoid single points of failure and to optimize costs.

Traditional approach: implement a class for each provider and configure the active provider via a config (database, Nacos). Each call retrieves the config and invokes the corresponding implementation.

Example with multiple SMS providers: configure a property like sms.impl = "某腾短信", then in code retrieve the property and get the bean.

void sendSmsTouser(Req req) {
    // 1. Get current provider name
    String name = get("sms.impl");
    // 2. Get corresponding implementation bean
    SmsService smsService = springContext.getBean(name);
    // 3. Use smsService to send message
    smsService.sendMsg(req);
}

This manual method is cumbersome. spring-smart-di offers a more elegant solution where @Autowired can automatically inject the implementation based on configuration and update when the config changes, using AutowiredProxySPI.

1. Introduction to spring-smart-di

spring-smart-di extends Spring's @Autowired with custom injection logic, providing annotations @SmartAutowired and @AutowiredProxySPI. This article focuses on using AutowiredProxySPI for dynamic provider switching.

2. Quick Start

2.1 Add Dependency

Add the spring-smart-di dependency to your Maven pom.xml:

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

2.2 Enable Feature

Annotate a Spring configuration class with @EnableSmartDI to activate spring-smart-di.

2.3 Use @EnvironmentProxySPI

@EnvironmentProxySPI marks a configuration point that determines how to obtain the concrete implementation, e.g., from an environment variable ${sms.impl}.

@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 {
}

2.4 Configure Current Provider

Set the active provider in application.yml:

sms:
  impl: 某移短信服务

2.5 Inject with @AutowiredProxySPI

Inject the service just like @Autowired:

// Dependency injection
@AutowiredProxySPI
private SmsService smsService;

Changing the ${sms.impl} value updates the injected implementation at runtime without restarting the service.

2.6 Define Custom Configuration Points

@EnvironmentProxySPI is for environment variables. To fetch configuration from a database, define a custom annotation like @DBProxySPI using @ProxySPI and implement a factory that retrieves the bean name from the database.

@Inherited
@Target({ElementType.FIELD, ElementType.METHOD, ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@ProxySPI(DbProxyFactory.class) // specify 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) {
        String configName = sysConfigDao.getConfig(spi.value());
        return springContext.getBean(configName);
    }
}
@DBProxySPI("${sms.impl}")
public interface SmsService {
}

spring-smart-di thus provides a concise and efficient way to handle dynamic switching scenarios, making code more flexible and maintainable.