You can specify that a bean should be injected with a specific qualifier when there are multiple candidates by using the @Qualifier annotation in Spring. This annotation helps Spring identify which candidate bean should be injected into the target. The other options, such as @Inject and @Autowired, are used for dependency injection but do not directly deal with qualifier-based injection. The application.properties file is typically used for configuration and not for specifying bean injection.

In a Spring Boot project, you use the spring-boot-maven-plugin to create an executable JAR or WAR file. This plugin provides features like packaging your application with all its dependencies and specifying the main class to run when the JAR is executed. It simplifies the process of creating self-contained, executable Spring Boot applications.

To implement a custom error response structure in Spring Boot when an exception occurs, you can configure a custom ErrorAttributes bean. This bean allows you to control the error response structure. The other options don't provide a direct mechanism for customizing the error response structure.

When testing service layer components in Spring Boot, you can use the @MockBean annotation to mock dependencies and avoid loading the complete ApplicationContext. This helps in isolating the unit under test.

The purpose of password encoding in Spring Security is to prevent password exposure. Storing passwords in plaintext is a security risk, so Spring Security encourages password encoding (hashing) to store passwords securely. This way, even if the password database is compromised, attackers cannot easily retrieve the original passwords. Password encoding is not meant to obfuscate passwords but to securely store them and prevent unauthorized access to plaintext passwords.

By default, Spring Security handles password encoding using BCrypt. BCrypt is a secure and commonly used password hashing algorithm that helps protect user passwords. Spring Security's default behavior is to use BCrypt encoding to securely store and verify passwords, enhancing the security of user authentication. The other options are not the default mechanisms used by Spring Security for password encoding.

In Spring Boot, the @PostMapping annotation is used to map HTTP POST requests onto specific handler methods in a controller class. When you apply this annotation to a method, it tells Spring that this method should be invoked when an HTTP POST request with a matching URL is received. It's a key annotation for handling POST requests in a RESTful API.

To implement a complex request mapping strategy with custom conditions, you would typically need to create a custom RequestMappingHandlerMapping. This allows you to define intricate conditions and behaviors for mapping requests to controller methods. Using annotations or configuration properties alone may not provide the level of customization needed for complex mappings. A separate utility class may not integrate seamlessly with Spring Boot's request handling mechanism.

In Spring Boot, the primary annotation used to mark the main class of your application is @SpringBootApplication. This annotation not only marks the class as the main entry point but also enables various Spring Boot features like auto-configuration, component scanning, and more. It's the starting point for your Spring Boot application.

Application properties in Spring Boot can be overridden for different environments by using environment-specific property files. By naming these files application-{profile}.properties (e.g., application-dev.properties for the 'dev' profile), Spring Boot can load the properties specific to the active profile, allowing you to configure different settings for each environment. This is a key feature for maintaining configurations across various deployment scenarios.