webxml

Web.xml is the deployment descriptor for a Java web application, used to configure how a servlet container should deploy and run the app. It is located in the WEB-INF directory as WEB-INF/web.xml and is read when the application is deployed or started. The descriptor defines the components and settings that govern the application’s behavior, including servlets, filters, listeners, and various environment and security configurations.

The file specifies how the application’s components are wired together and how they respond to requests. Common configurations include servlet definitions and mappings, filter declarations and mappings, and listener registrations. It can also declare context parameters, init parameters for individual components, environment entries, and resource references. Additional sections may define welcome files, error pages, and security constraints such as login configurations and access restrictions.

Structure and elements can vary by the version of the servlet specification. The root element is typically <web-app>, with a version attribute (for example, 2.5, 3.0, or 3.1) and, in newer environments, an XML namespace. Early deployments used a DTD, while newer ones use XML schemas. Since Servlet 3.0, some configurations can be achieved with annotations in the code, which can reduce or even replace the need for web.xml. Nevertheless, web.xml remains a portable, centralized way to manage deployment details, and is still widely used in Jakarta EE and Java EE applications for compatibility and explicit control over container behavior.