How can you configure the integration of an external library or JAR file in Spring to register its classes as beans without using annotations?

To integrate an external library or JAR file into Spring and register its classes as beans without using annotations, you can use XML configuration or Java configuration with explicit bean declarations.

1. XML Configuration: In the applicationContext.xml file, you can explicitly declare beans by specifying the full class names from the external library:

<bean id="externalService" class="com.external.lib.ExternalService" />

2. Java Configuration: Create a configuration class and declare methods annotated with @Bean that return instances of the required classes:

@Configuration
public class ExternalLibConfig {
    @Bean
    public ExternalService externalService() {
        return new ExternalService();
    }
}

If annotations cannot be used at all, you can programmatically register beans using BeanDefinitionRegistry or BeanFactory, but this is rarely needed.

Thus, without annotations, beans can be explicitly declared in XML or Java configuration by specifying classes from external JAR files.