What is needed for Spring MVC to work?

To run Spring MVC, the following are necessary:

1. Web server: A servlet container such as Apache Tomcat, Jetty, or Undertow for deploying the web application.
2. Spring configuration:
   • XML configuration or Java configuration (using annotations) defining Spring components (controllers, services, repositories, etc.) and their relationships.
   • Configuration of DispatcherServlet in the web.xml file or using Java configuration (AbstractAnnotationConfigDispatcherServletInitializer). DispatcherServlet acts as the front controller of Spring MVC, delegating request processing to appropriate handlers.
3. Maven/Gradle dependencies: Including necessary dependencies in the build file (pom.xml or build.gradle):
   • spring-webmvc: The core dependency for Spring MVC.
   • Dependencies for views (Thymeleaf, JSP, FreeMarker, etc.) when using templating engines.
   • Dependencies for validation (e.g., Hibernate Validator).
   • Dependencies for JSON/XML processing (e.g., Jackson or JAXB).
4. Controllers: Classes annotated with @Controller or @RestController, containing methods marked with @RequestMapping, @GetMapping, @PostMapping, etc., to handle incoming HTTP requests.

Example of minimal Java configuration:

// WebMvcConfig.java
@Configuration
@EnableWebMvc
@ComponentScan(basePackages = "com.example.controller")
public class WebMvcConfig implements WebMvcConfigurer {
    // Additional configuration if needed (e.g., ViewResolver setup)
}

Example of configuring DispatcherServlet using Java configuration:

// AppInitializer.java
public class AppInitializer extends AbstractAnnotationConfigDispatcherServletInitializer {

    @Override
    protected Class<?>[] getRootConfigClasses() {
        return null; // No root contexts
    }

    @Override
    protected Class<?>[] getServletConfigClasses() {
        return new Class<?>[]{WebMvcConfig.class}; // Spring MVC configuration
    }

    @Override
    protected String[] getServletMappings() {
        return new String[]{"/"}; // Map DispatcherServlet to root URL
    }
}

Example of a simple controller:

// HelloController.java
@Controller
public class HelloController {

    @GetMapping("/hello")
    public String hello(@RequestParam(name = "name", required = false, defaultValue = "World") String name, Model model) {
        model.addAttribute("name", name);
        return "hello"; // View name (e.g., hello.jsp or hello.html)
    }
}

In summary, Spring MVC is launched by deploying a web application (JAR or WAR) containing all necessary components and configuration on a web server. DispatcherServlet is initialized at startup and begins processing incoming web requests, directing them to the appropriate controllers based on mappings.