What are the differences between a web server and an application server?

A web server handles HTTP requests by serving static content (HTML, CSS, JS, images). An application server provides a runtime environment for dynamic content and business logic, typically supporting a broader range of protocols and services (e.g., EJB, JMS).

Main differences:

• Functionality: The web server focuses on delivering static content. The application server provides an environment for executing business logic and dynamic content.
• Protocols: The web server primarily works with HTTP. The application server supports multiple protocols, including HTTP, RMI, JMS.
• API: The application server implements a broader range of APIs (e.g., Java EE - EJB, JMS, JTA). The web server may only support Servlets and JSP.
• Complexity: Application servers are more complex and resource-intensive compared to web servers.
• Examples:
  • Web servers: Apache HTTP Server, Nginx.
  • Application servers: Apache Tomcat (can operate as a web server and servlet container), JBoss/WildFly, Oracle WebLogic Server.

Often, an application server includes web server functions, allowing it to handle static content as well as perform dynamic logic.

// Example of handling an HTTP request by a web server
// The web server simply returns index.html to the client
// (pseudo-code)
if (request.getMethod().equals("GET") && request.getPath().equals("/")) {
    response.sendStaticFile("index.html");
}

// Example of handling a request by an application server
// The application server executes business logic, retrieves data from the database
// and generates a dynamic HTML response
// (pseudo-code)
if (request.getMethod().equals("GET") && request.getPath().equals("/products")) {
    ProductService productService = lookup("ProductService"); // Using EJB or another service
    List<Product> products = productService.getAllProducts();
    String dynamicHtml = generateProductListHtml(products); // Dynamic content generation
    response.sendDynamicContent(dynamicHtml);
}