Servlet technology provides a specification for building web applications in Java. As part of Java EE standards, it enables server-side processing of client requests. The API documentation for Servlet is available in the JavaEE package structure, separate from standard JDK documentation.

Key Characteristics

• Server-side Java components that handle client requests
• Requires implementation of the Servlet interface or extension of helper classes
• Processes requests through the service() method
• Supports configuration through deployment descriptors

Basic Implementation Example

public class BasicServlet extends GenericServlet {
    @Override
    public void service(ServletRequest req, ServletResponse res) 
        throws ServletException, IOException {
        // Request handling logic
    }
}

Servlet Lifecycle and Thread Safety

The Servlet lifecycle consists of three phases:

1. Initialization: When the container loads the Servlet
2. Service: During request processing
3. Destruction: When the container unloads the Servlet

Thread safety considerations:

public class CounterServlet extends HttpServlet {
    private int count; // Potential thread safety issue
    
    protected void doGet(HttpServletRequest req, HttpServletResponse res) {
        count++;
        // Critical section needs synchronization
    }
}

Configuration Methods

Servlets can be configured through:

1. Exact path matching (/example)
2. Directory pattern matching (/path/*)
3. Extension matching (*.action)

Multiple Mapping Example

<servlet-mapping>
    <servlet-name>MultiServlet</servlet-name>
    <url-pattern>/primary</url-pattern>
    <url-pattern>/secondary</url-pattern>
</servlet-mapping>

Servlet Context and Configuration

The ServletContext provides:

• Application-wide initialization parameters
• Resource access methods
• Attriubte sharing across Servlets

// Accessing context parameters
String dbUrl = getServletContext().getInitParameter("databaseUrl");

Annotation-Based Development

Servlet 3.0+ supports annotation configuration:

@WebServlet(
    name = "AnnotatedServlet",
    urlPatterns = {"/annotated"},
    initParams = {
        @WebInitParam(name = "config", value = "value")
    }
)
public class AnnotatedServlet extends HttpServlet {
    // Servlet implementation
}

Practical Application Example

Implementing a student management system:

@WebServlet("/students/add")
public class StudentServlet extends HttpServlet {
    protected void doPost(HttpServletRequest req, HttpServletResponse res) {
        String name = req.getParameter("studentName");
        // Process and store student data
    }
}