A Java Servlet is a server-side technology used to extend the capabilities of web servers and provide dynamic content to web applications. Servlets are part of the Java Enterprise Edition (Java EE) platform and are typically used to create web applications that run on web servers.

Here are some key points and concepts related to Java Servlets:

1. Servlet Lifecycle: Servlets have a well-defined lifecycle consisting of three main methods: init(), service(), and destroy(). These methods are called by the servlet container (e.g., Tomcat) at different stages of the servlet’s existence.

2. Servlet Mapping: Servlets are mapped to specific URL patterns in a web application’s deployment descriptor (web.xml) or through annotations in modern Java EE versions. When a matching URL is requested, the servlet container invokes the corresponding servlet.

3. Request and Response Objects: Servlets interact with clients (usually web browsers) through HttpServletRequest and HttpServletResponse objects. These objects provide access to incoming HTTP requests and allow servlets to generate HTTP responses.

4. Handling HTTP Methods: Servlets can handle various HTTP methods such as GET, POST, PUT, DELETE, etc., by overriding the doGet(), doPost(), and other HTTP method-specific methods.

5. Session Management: Servlets can manage user sessions using HttpSession objects. This allows web applications to maintain state information across multiple requests from the same user.

6. Servlet Filters: Servlet filters are components that can intercept requests and responses to perform tasks such as authentication, logging, or data transformation before the request reaches a servlet or after the response is generated.

7. Error Handling: Servlets can handle errors and exceptions using methods like doError() and can be configured to map specific error codes to servlets.

8. Thread Safety: Servlets are generally not thread-safe by default, as a single instance of a servlet can handle multiple requests concurrently. Developers must ensure thread safety when necessary.

9. Deployment: Servlets are typically packaged as WAR (Web Application Archive) files and deployed to a servlet container. Modern Java EE applications may use annotations for configuration instead of a web.xml file.