Q1. What is a property placeholder in Spring?
Property placeholder allows you to externalize configuration properties from bean definitions. You define properties in a .properties file and use placeholders like ${db.url} in XML or @Value annotations. Spring resolves them using a PropertySourcesPlaceholderConfigurer.
Q2. How do you use @Value to inject properties?
@Value can inject property values into fields, constructor parameters, or methods. Example: in XML).
@Value("${app.name}")
private String appName;
Q3. What are Spring profiles?
Profiles allow you to register beans conditionally based on the active environment. For example, you can have different datasource configurations for development, testing, and production. Use @Profile on @Bean or @Component to specify which profile the bean belongs to.
Q4. How do you activate a profile?
You can set the active profile programmatically (via ConfigurableEnvironment) or by setting the spring.profiles.active system property (e.g., -Dspring.profiles.active=dev). In Spring Boot, you can also use application.properties: spring.profiles.active=dev.
Q5. What is the use of @PropertySource?
@PropertySource is used to specify the location of property files to be loaded into the Spring Environment. Example:
@Configuration
@PropertySource("classpath:app.properties")
public class AppConfig { ... }