How to write a web application in Java?

Developing a web application in Java traditionally involves the following steps:

1. Choosing a framework: The most popular frameworks:

   • Spring: Flexible, includes Spring MVC, Spring Boot for rapid development.
   • Jakarta EE (formerly Java EE): A set of specifications (Servlets, JSP, EJB, JPA, etc.) implemented by application servers (Tomcat, WildFly, GlassFish).
   • Quarkus/Micronaut: Frameworks for native cloud and microservice applications.

2. Setting up the environment:

   • JDK (Java Development Kit).
   • IDE (Integrated Development Environment), such as IntelliJ IDEA, Eclipse, NetBeans.
   • Build system (Maven or Gradle).

3. Project structure: Typical Maven/Gradle project structure:

   ├── src
   │   ├── main
   │   │   ├── java        // Java source code
   │   │   ├── resources   // Configuration files, templates
   │   │   └── webapp      // Web resources (HTML, CSS, JS)
   │   └── test
   │       ├── java        // Tests
   │       └── resources
   └── pom.xml / build.gradle // Build configuration file
   

4. Backend development:

   • Creating RESTful APIs using Spring MVC (@RestController, @RequestMapping) or Jakarta RESTful Web Services (JAX-RS) (@Path, @GET, @POST).
   • Handling HTTP requests and forming responses.
   • Business logic.
   • Interacting with the database using JPA (Java Persistence API) and frameworks like Hibernate or Spring Data JPA.

5. Frontend development (optional, for monoliths):

   • Using JSP (JavaServer Pages) for HTML generation.
   • Templating engines: Thymeleaf, Freemarker.
   • Modern approaches often involve separating backend (REST API) and frontend (React, Angular, Vue.js).

6. Configuration:

   • Managing dependencies in Maven (pom.xml) or Gradle (build.gradle).
   • Server configuration (e.g., application.properties or application.yml for Spring Boot).
   • Database configuration.

7. Build and deployment:

   • Building the project into a WAR (Web Application Archive) or JAR (Executable JAR for Spring Boot).
   • Deploying WAR on application servers (Tomcat, WildFly).
   • Running the executable JAR.

Example of a simple REST controller in Spring Boot:

import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class GreetingController {

    @GetMapping("/greeting")
    public String greet(@RequestParam(value = "name", defaultValue = "World") String name) {
        // Handle request and return string
        return String.format("Hello, %s!", name);
    }
}