Spring JavaConfig我如何引用为创建新bean而定义的bean

Question

Here's an excerpt from my Applications beans definition, I want to be able to refer to beans that I have defined.

@Configuration
@ComponentScan({"com.abc.config", "com.abc.config.common"})
public class ApplicationConfig {
    @Bean(name = "AWSCredentialsProvider")
    AWSCredentials credentialsProvider() { return new AWSCredentials(/*Omitted*/); }  
    @Bean(name = "DynamoDBClient")
    AmazonDynamoDBClient dynamoDBClient() {
        AmazonDynamoDBClient dynamoDB = new AmazonDynamoDBClient(credentialsProvider());
        return dynamoDB;        
    }  
    @Bean S3Repository s3Repository() {
        AmazonS3 s3 = new AmazonS3Client(credentialsProvider());
        return new S3Repository(s3);
    }  
    @Bean LevelMapper levelMapper() { return new LevelMapper(s3Repository()); }
    @Bean ImageDownloader imageDownloader() { return new ImageDownloader(s3Repository()); }
}

Right now what I'm doing is calling methods like s3Repository() in two places; this way I'll be creating two instances of the repository whereas I would like there to be only one instance across the application. Something like credentialsProvider() is lightweight so I don't mind a new instance being created for every bean.

Answer 1

Actually it will only create one instance of repository. Using s3Repository() in your @Bean annotated method doesn't really call that method, but just tells the spring to inject the already created bean of type (as implied by return type of method) to the LevelMapper and ImageDownloader bean you create. So it will inject the same repository bean instance in both the beans referencing the method.

From this Spring Docs :

All @Configuration classes are subclassed at startup-time with CGLIB. In the subclass, the child method checks the container first for any cached (scoped) beans before it calls the parent method and creates a new instance. Note that as of Spring 3.2, it is no longer necessary to add CGLIB to your classpath because CGLIB classes have been repackaged under org.springframework and included directly within the spring-core JAR.