Spring boot auto configuration with dependency and without @ComponentScan

问题

Spring boot provides @ComponentScan to find packages to be scanned.

I am building a library which has @RestControllers inside with package com.mylib.controller. There are other classes as well with stereotype annotations in different packages.

So, if some one is developing SpringBoot Application with com.myapp base package. He uses my library in his application. He need to mention @ComponentScan("com.mylib") to discover stereotype components of library.

Is there any way to scan components without including library package in @ComponentScan?

As spring-boot-starter-actuator expose its endpoints just with dependency, without defining @ComponentScan. OR any default package which is scanned regardless of application base package.

回答1:

You could create a Spring Boot Starter in the same style as the Spring Provided Starters. They are essentially a jar'd library with a a spring.factories file pointing to the @Configuration class to load with some other annotations on there to provide overriding/bean back off (@ConditionalOnMissingBean) and generally provide their own @ConfigurationProperties.

Stéphane Nicoll provided an excellent demo of how to build one.

https://github.com/snicoll-demos/hello-service-auto-configuration

It is also documented in the Spring Boot documentation. https://docs.spring.io/spring-boot/docs/current/reference/html/boot-features-developing-auto-configuration.html

The library approach would also work but I see no benefit in not making it a starter. Additionally for any library/starter I'd recommend dropping the @ComponentScan and just defining the beans in a @Configuration. This will work for sterotypes like @RestController etc. will function as normal if you create an @Bean out of it in a configuration.

回答2:

Spring boot starter are special artifacts designed by Spring and used by Spring.
You can check that in the source code that contains mainly a
spring.provides file :

provides: spring-boot-actuator,micrometer-core

I don't know the exact way to process in the same way as Spring Boot Starter but as probably acceptable workaround, you could define in your jar a @Configuration class that specifies @ComponentScan("com.mylib").

 @Configuration
 @ComponentScan("com.mylib")
 public class MyLibConfig {
     //...
 }

In this way, clients of the jar need "only" to import the @Configuration class :

@Import(MyLibConfig.class)
@Configuration
public class ClientConfig{
  //...
}

来源：https://stackoverflow.com/questions/48808752/spring-boot-auto-configuration-with-dependency-and-without-componentscan