Servlet Hierarchy

Core Interfaces and Classes

• javax.servlet.Servlet interface (Root interface)
  • void init(ServletConfig config) throws ServletException
  • void service(ServletRequest req, ServletResponse resp) throws IOException, ServletException
  • void destroy()
• GenericServlet (Abstract class)
  • Protocol-independent servlet
  • Base class for all servlets
• HttpServlet (Abstract class)
  • HTTP-based servlet class
  • User-defined servlets inherit from this
  • Overrides service() method
  • Provides HTTP method handlers: doGet(), doPost(), doPut(), doDelete(), doHead(), doTrace(), doOptions()

HttpServletRequest Interface

Key Features

• Inherits from ServletRequest interface
• Created by web server for each request
• Represents HTTP request body and headers

Request Parameters

// Single value (textbox, radiobutton, dropdown)
String paramValue = req.getParameter("param-name");

// Multiple values (checkboxes, listbox)
String[] paramValues = req.getParameterValues("param-name");

Request Headers

// Single header value
String headerValue = req.getHeader("header-name");
String contentType = req.getHeader("Content-Type");

// Multiple header values
String[] headerValues = req.getHeaderValues("header-name");

File Upload

InputStream in = req.getInputStream();

HttpServletResponse Interface

Key Features

• Inherits from ServletResponse interface
• Created by web server for each request