14-MoreOnConfiguration

Question 1

Ways to read a property from the application.properties

Answer 1

1. Using @Value(“${propertyName}”)
2. @Autowired Environment env;
   then: env.getProperty(“propertyName”);

Question 2

How to use @Value to set a default value if property not found?

Answer 2

@Value(“${propertyName: default Value}”)

Question 3

What properties are loaded into Spring Environment?

Answer 3

1. Environment variables i.e. system environment variables
2. Java system properties
3. Additional resources added by:
   @Configuration
   @PropertySource(“classpath:/com/app.properties”)
   @PropertySource(“file:/config/local.properties”)
   class Config {}
4. ## Properties configured with @TestPropertySource will have higher precedence than those loaded from the OS’s env or Java system propertiesNote that if the same property is defined in both files, the value in the last one seen wins

Question 4

What class does evaluate @Value expression?

Answer 4

PropertySourcesPlaceHolderConfigurer

It extends BFPP (BeanFactoryPostProcessor)

Question 5

How to declare a BFPP bean method?

Answer 5

BFPP bean method must be static so that it can load before all other beans e.g.
@Configuration
class Config {
@Bean
public static PropertySourcesPlaceHolderConfigurer method() {}
}

Question 6

What happens if using @Profile annotation on configuration class?

Answer 6

Everything (e.g. bean) in configuration belongs to the profile

Question 7

How to enable a bean excepts 1 profile?

Answer 7

@Profile(“!profileName”)
@Bean
BeanType method() {}

Question 8

Ways to activate some profiles?

Answer 8

1. -Dspring.profiles.active=p1,p2
2. System.setProperty(“spring.profiles.active”, “p1,p2”)
3. In application.properties
   spring.profiles.active=p1,p2
4. Create applicationContext manually then set:
   applicationContext.getEnvironment().setActiveProfiles(“p1,p2”);
5. In test
   @ActiveProfiles(“p1,p2”)
   class TestClass {}

Question 9

Ways to create an ApplicationContext manually

Answer 9

1. new ClassPathXmlApplicationContext(“config.xml”)
2. ## new AnnotationConfigApplicationContext(ConfigClass.class)Note: WebApplicationContext is an interface

Question 10

How to control property files loaded using @Profile?

Answer 10

@Configuration
@Profile(“local”)
@PropertyResouce(“file.properties”)
class Config {}

Question 11

Expressions language implemented in Spring

Answer 11

1. SpEL (start with #)

2. Unified Expression Language used by JSP and JSF (start with $)

Question 12

How to set (daily.limit * 2) using @Value?

Answer 12

Must use SpEL, not work for Unified EL
e.g. @Value("#{new Integer(environment["daily.limit"] * 2}")

Question 13

Ways to set fall-back value using @Value?

Answer 13

1. SpEL @Value(“#{environment[‘daily.limit’] ?: 100000}”)

2. Unified EL @Value(“${daily.limit : 100000}”)

Question 14

List out default implicit references in SpEL?

Answer 14

1. environment
2. systemProperties
3. systemEnvironment

Question 15

What do SpEL expressions starting with $ reference?

Answer 15

Properties in the application environment

–> seem they mean syntax of Unified Expression Language is also supported in SpEL