How to migrate a legacy application on servlets to Spring Boot? Describe the main steps.

Translating a legacy servlet application to Spring Boot involves several key steps:

1. Creating a Spring Boot project

   • Use Spring Initializr or a similar tool to create a basic project.

2. Migrating configuration

   • Replace web.xml with Spring Boot configuration (automatic server setup).
   • Configure application.properties or application.yml for parameters.

3. Migrating servlets and filters

   • Rewrite servlets as @RestController or @Controller with methods annotated with @RequestMapping.
   • Filters can be registered via @Bean or annotations.

4. Transferring business logic

   • Extract logic from servlets into services (@Service).

5. Managing dependencies

   • Add necessary Spring Boot Starter dependencies (web, data, security, etc.).

6. Testing and debugging

   • Run the application and verify correct operation.

Example of a simple controller replacing a servlet:

@RestController
public class HelloController {
    @GetMapping("/hello")
    public String hello() {
        return "Hello from Spring Boot!";
    }
}

Thus, you gradually replace the outdated architecture with a modern one using Spring Boot, simplifying configuration and improving support.