In Spring Boot, the @WebMvcTest annotation is used to simulate HTTP requests and test the web layers (controllers) without starting a full web server. It focuses on testing the web-related components of your application.

To handle validation errors globally across a Spring Boot application in a centralized manner, you should define a global exception handler using the @ControllerAdvice annotation. This allows you to handle validation errors uniformly across all controllers, promoting code reusability and centralization. Options 1 and 2 are incorrect as they involve handling errors at the controller level, and Option 4 is not recommended as it lacks centralization.

The @PreAuthorize annotation in Spring Security uses SpEL (Spring Expression Language) expressions to define access controls. SpEL allows you to write expressive and dynamic access control expressions based on the current authentication context.

The @RequestMapping annotation is used to map a web request to a specific handler method in a Spring Boot controller. It allows you to specify the URL path, HTTP method, and other parameters to define how the request should be routed to the appropriate method. The other options, such as @ResponseBody, @PostMapping, and @Autowired, serve different purposes in Spring Boot but are not used for request mapping.

In a Spring Boot project, the pom.xml file, which stands for Project Object Model, is used to define the project's dependencies, build configuration, and metadata. It's an XML file that manages project dependencies and configurations, making it a critical component of any Spring Boot project. This file is essential for Maven-based projects.

To implement Two-Factor Authentication in Spring Security, you would typically need to implement custom authentication filters to handle this process. Spring Security does provide support for two-factor authentication, but it often requires customizations based on specific requirements. OAuth2 is a different authentication mechanism and is not related to Two-Factor Authentication. Configuring Spring Boot to use an external OTP service is a specific approach, not a general method for Two-Factor Authentication.

Validation annotations in JSR-303 can be placed both on fields within a class and on method parameters. This flexibility allows you to validate not only the data fields of a class but also method parameters to ensure that the input meets the specified constraints. The other options are not accurate; you can use validation annotations in both scenarios mentioned.

Global Method Security can be optimized by configuring AspectJ security expressions. AspectJ expressions allow fine-grained control over method security, enabling security to be applied across different layers of a Spring application based on conditions defined in expressions.

You can perform unit testing for Spring Boot security configurations by using the @SpringBootTest annotation, which loads the complete Spring application context. This allows you to test the security configurations along with other components. The other options do not specifically target testing security configurations.

In connection pooling, "Maximum Pool Size" refers to the maximum number of connections that the pool can hold at a given time. This value determines the upper limit of connections available to clients. It ensures that the pool doesn't grow indefinitely and helps manage resources efficiently. The maximum pool size should be set carefully to balance resource utilization and performance. It doesn't refer to the size of the database server or the number of database queries allowed.