Spring Framework

Question 1

What is Spring?

Answer 1

Spring is a framework for building Java applications

Question 2

How can a configuration class import another configuration class?

Answer 2

@Import({a.class, b.class})

Question 3

What is the default scope of a bean?

Answer 3

Singleton

Question 4

How can you change the scope of a bean?

Answer 4

@Scope(...)

Question 5

Describe how a prototype bean works

Answer 5

A new bean is created anytime it is referenced

Question 6

How can you autowire a dependency only if it exists?

Answer 6

@Autowired(required=false)

Question 7

For non-Spring Boot applications, if @Component is used, what other annotation must be used on the configuration class?

Answer 7

@ComponentScan(…)

Question 8

What problem occurs in the following code and how can you fix it?

@Component("myService")
class MyServiceImpl implements MyService {
@Autowired
MyServiceImpl(MyRepository myRepository) {...}
}
---------------------------------------------------------------------------
@Component("jdbcMyRepository")
class JdbcMyRepository implements MyRepository {...}
---------------------------------------------------------------------------
@Component("jpaMyRepository")
class JpaMyRepository implements MyRepository {...}

Answer 8

Ambiguity problem since MyServiceImpl(MyRepository ...) does not know which implementation to use. This can be solved by:

MyServiceImpl(@Qualifier("jpa") MyRepository myRepository) {...}
-----------------------------------------------------------------------------------------
@Component("jpaMyRepository")
@Qualifier("jpa") // or @Primary
class JpaMyRepository implements MyRepository {...}

Question 9

1. Where can @Value be used?
2. Is @Value implemented by BeanFactoryPostProcessor or BeanPostProcessor?

Answer 9

1. Fields and parameters
2. Both, its value is resolved by BeanFactoryPostProcessor and injected by BeanPostProcessor for fields and setter methods

Question 10

1. What is the difference between standard beans and @Lazy beans?

Answer 10

1. Standard beans are instantiated eagerly at application startup and @Lazy beans are instantiated only when they are referenced (e.g. ApplicationContext.getBean(…) is used)

Question 11

What are the 6 stereotype annotations?

Answer 11

1. @Component
2. @Configuration
3. @Controller
4. @RestController
5. @Repository
6. @Service

Question 12

True or false:

ApplicationContext is a subtype of BeanFactory

Answer 12

True

Question 13

Describe the 5 different phases of a Spring bean’s lifecycle

Answer 13

1. Load and process bean definitions through BeanFactoryPostProcessor
2. Instantiate beans
3. Initialize bean through BeanPostProcessor
4. Use beans through @Autowired
5. Destroy beans through ApplicationContext.close()

Question 14

1. When using a method to define a bean, how is its type and name determined?
2. When using a class to define a bean, how is its type and name determined?

Answer 14

1. Type = method return type
   Name = method name
2. Type = class
   Name = class name

Question 15

The Environment bean has access to the 3 following property sources…

Answer 15

1. JVM system properties
2. System environment properties
3. Property files (if appropriate configuration is used)

Question 16

What are the 2 different ways to access property values inside a configuration class?

@PropertySource(...)
@Configuration
public class MyConfig {...}

Answer 16

1. Environment Bean
2. @Value(…)

Question 17

When might you need to use @PropertySource(…)?

Answer 17

When you need to access the properties of a file (Spring Framework)

When you need to access the properties of a file that is not located in application.properties (Spring Boot)

Question 18

True or False

@Profile(…) can be used on both bean class and bean method definitions

Answer 18

True

Question 19

What is a bean?

Answer 19

A bean is an object managed by the Spring IOC container (ApplicationContext)

Question 20

Should a bean method definition return an interface type or a class type?

Answer 20

Interface type

Always remember, “depend on abstractions, not concretions”

Question 21

What is a Project Object Model?

Answer 21

POM is an xml file containing all the information Maven needs to build an application

Question 22

BeanPostProcessor

1. What does it do?
2. How can you implement your own?

Answer 22

1. BeanPostProcessor can modify an instantiated bean before and/or after initialization
2. Define your own BeanPostProcessor bean class

Question 23

Which bean is responsible for creating bean proxies?

Answer 23

BeanPostProcessor

Question 24

What does @Autowired do?

Answer 24

Injects dependencies by type

Question 25

Describe how "Lite" mode works

Answer 25

`@Configuration(proxyBeanMethods = false)` Lite mode is when a configuration class is not CGLIB proxied and, therefore, bean method definitions cannot call other bean method definitions to facilitate dependency injection. Normal dependency injection must be conducted

Question 26

# @ComponentScan Should you be as specific as possible when defining which packages to scan for?

Answer 26

Yes. This will avoid unnecessary scanning

Question 27

# @PostConstruct and @PreDestroy 1. What access modifier can be used? 2. What must they return? 3. What parameters must they define?

Answer 27

``` @Component public class MyBean { @PostConstruct [any] void init() {...} @PreDestroy [any] void cleanup() {...} } ```

Question 28

# @PostConstruct and @PreDestroy When do they execute?

Answer 28

1. @PostConstruct executes at startup after all dependencies are injected 2. @PreDestroy executes at shutdown prior to bean destruction

Question 29

# True or False An ApplicationContext cannot be created in any environment

Answer 29

False

Question 30

# True or False Singleton beans should be used as stateful beans and prototype beans should be used as stateless beans

Answer 30

False

Question 31

When a singleton bean uses a prototype bean as a dependency, what is the behavior of that prototype bean?

Answer 31

Only a single instance of the prototype bean will ever be created

Question 32

What are the 2 primary bean scopes?

Answer 32

1. Singleton = 1 instance 2. Prototype = new instance per use

Question 33

# True or False Bean overriding can occur in any environment

Answer 33

False. Only in test environments

Question 34

Is `@Configuration` CGLIB or JDK proxied?

Answer 34

CGLIB proxied. This is because CGLIB is used for classes that don't implement an interface

Question 35

Create a custom annotation composed of both @Service and @Transactional

Answer 35

@Target(ElementType.TYPE) @RetentionPolicy(RetentionPolicy.RUNTIME) @Transactional(timeout=60) @Service public @interface MyTransactionalService {...}

Question 36

# What does the following code mean? `@Value("${user.age : 18")`

Answer 36

If the user.age property does not have a value, use 18 as default

Question 37

What are the 3 different ways to implement bean post-construct behavior?

Answer 37

1. @Bean(initMethod="methodName") 2. @PostConstruct on bean class method 3. Bean class implements InitializingBean

Question 38

What are the 3 different ways to implement bean pre-destroy behavior?

Answer 38

1. @Bean(destroyMethod="methodName") 2. @PreDestroy on class bean method 3. Class bean implements DisposableBean

Question 39

When using both XML and Java configuration at the same time, which one is processed first?

Answer 39

Java configuration is processed first. This means XML configuration will override Java configuration

Question 40

Which annotation can be used to define multiple bean aliases?

Answer 40

`@Bean(name={"name1", "name2", ...})`

Question 41

Which annotation can be used to import XML configuration files into a Java configuration class?

Answer 41

`@ImportResource(locations=String[])`

Question 42

How does the Spring IoC Container work?

Answer 42

The container takes in your POJOs and configuration metadata and creates a fully configured application ready for use

Question 43

Are POM dependencies added to the classpath?

Answer 43

Yes