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The @Bean annotation is used to declare a method that returns an object that should be registered as a bean in the application context. The @ConditionalOnBean annotation is used to specify a condition for the bean creation based on the presence or absence of other beans in the application context. The name attribute of this annotation can be used to specify the bean name or names that must be present or absent for the condition to match. However, this approach is less flexible than using the value or type attribute, which can specify the bean class or classes that must be present or absent for the condition to match. Therefore, it is recommended to use @ConditionalOnBean(DataSource.class) instead of @ConditionalOnBean(name= “dataSource”) for greater flexibility.

The JdbcTemplate class is a Spring class that simplifies the use of JDBC and helps to avoid common errors. It executes core JDBC workflow, leaving application code to provide SQL and extract results. To create a JdbcTemplate object, we need to pass a DataSource object as a constructor argument. The DataSource interface is a Java interface that represents a factory of connection objects. In this code, the jdbcTemplate() method takes a DataSource object as a parameter and returns a new JdbcTemplate object. This method is annotated with @Bean and @ConditionalOnBean(name= “dataSource”), which means that it will only create a JdbcTemplate bean when there is already a bean named dataSource in the application context.

Constructor injection is one of the ways to inject dependencies into a bean using its constructor parameters. Since Spring 4.3, if a bean has only one constructor, the @Autowired annotation can be omitted and Spring will use that constructor by default.

Constructor injection is generally recommended over field injection because it makes the dependencies of a bean explicit and immutable. It also facilitates unit testing because it allows us to easily provide mock dependencies through constructor arguments.

REST stands for Representational State Transfer, which is an architectural style for designing web services that adhere to certain principles. One of these principles is statelessness, which means that each request from a client to a server must contain all the information necessary to understand the request, and that no session state is maintained on the server side. Another principle is uniform interface, which means that clients and servers communicate using a standardized protocol, such as HTTP, and use its features, such as headers and status codes, to exchange information about the resources and their representations.

B. A HelloService bean will be created from the helloService() method only when there is no other HelloService bean in the ApplicationContext.

This is true because the @ConditionalOnMissingBean annotation on the helloService() method indicates that this method will only be invoked to create a HelloService bean if there is no existing HelloService bean in the application context. This is a common way to provide a default bean that can be overridden by the user’s own bean definition.

D. This auto-configuration class is used only when the HelloService.class is on the classpath.

This is true because the @ConditionalOnClass annotation on the HelloAutoConfig class indicates that this class will only be loaded and processed by Spring Boot if the HelloService.class is present on the classpath. This is a common way to enable auto-configuration for a specific library or feature only when it is available.

C. Dependencies between application components can be managed external to the components.

This is true because dependency injection allows the application components to declare their dependencies without creating or obtaining them directly. Instead, the dependencies are provided by an external entity, such as the Spring container, which can read the configuration from XML files, annotations, or Java code1.

D. Configuration can be externalized and centralized in a small set of files.

This is true because dependency injection enables the separation of concerns between the application logic and the configuration. The configuration can be stored in a small number of files that can be easily changed without affecting the source code2.

F. Dependency injection facilitates loose coupling between components.

This is true because dependency injection reduces the direct dependencies between components, making them more reusable and testable. It also allows for easier substitution of different implementations of the same interface3.

Spring and Spring Boot provide various annotations and utilities to support testing of different layers of the application. To create an ApplicationContext for integration tests, we can use either @SpringBootTest or @SpringJUnitConfig annotations. The former is a specialized annotation that also provides additional features such as auto-configuration, web environment emulation, and test properties management. The latter is a general-purpose annotation that combines @ContextConfiguration and @ExtendWith(SpringExtension.class) annotations.

To perform slice testing, which focuses on testing a specific layer or feature of the application in isolation, we can use annotations such as @WebMvcTest, @DataJpaTest, @RestClientTest, etc. These annotations will only load the relevant beans for the tested slice and mock or stub the other dependencies.

A. Locale

This is true because the Locale argument can be used to resolve the current locale that the client is using, based on the Accept-Language header or a cookie1.

B. Principal

This is true because the Principal argument can be used to access the currently authenticated user, if any1.

F. HttpSession

This is true because the HttpSession argument can be used to access the current session, if any1. Note that this argument is not required and will be null if a session does not exist.

This is true because the default scope of a bean in Spring is singleton, which means that only one instance of the bean will be created and shared by the entire application context. The @Bean annotation on the accountRepository() method indicates that this method will return a bean that will be managed by Spring. However, this method will not be called every time the bean is needed, but only once when the bean is first created. Therefore, only one AccountRepository bean will be instantiated and injected into the TransferService and AccountService beans.

@DirtiesContext @Test void testProcessWhichDirtiesAppCtx() { // some logic that results in the Spring container being dirtied } Dirty the context after the current test method.

The @Value annotation can be used to inject values from external sources into fields, constructor parameters, or method parameters. To inject a system property, the annotation can use either the ${…} placeholder syntax or the #{…} SpEL expression syntax. The former is simpler and more concise, while the latter is more powerful and flexible. Both syntaxes can access the systemProperties map, which contains all the system properties as key-value pairs.

A. @Configuration This annotation indicates that the class has @Bean definition methods and may be processed by the Spring container to generate bean definitions and service requests for those beans at runtime. B. @ComponentScan This annotation configures component scanning directives for use with @Configuration classes. Provides support parallel with Spring XML's context:component-scan element.

B. If an embedded database is on the classpath, it will be used to configure a DataSource by default.

This is true because the @DataJpaTest annotation enables auto-configuration of an embedded database if one is available on the classpath, such as H2, HSQLDB, or Derby. This allows the test to run with a temporary and isolated database that can be configured with test data.

D. It auto-configures a TestEntityManager bean.

This is true because the @DataJpaTest annotation provides a TestEntityManager bean that can be used to perform common JPA operations in the test. The TestEntityManager is an alternative to the standard EntityManager that provides some convenience methods and exception translation.