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Servlet - Annotations Servlet - GenericServlet Servlet - HttpServlet Servlet - HTTP Methods Servlet - ServletRequest

Servlet - HttpServlet

📌 What You Will Learn

Understand HttpServlet class hierarchy
Learn the service() → doXxx() dispatch mechanism
See complete working code examples with GET and POST

HttpServlet is the base class for developing HTTP-based servlets. For every HTTP method (GET, POST, etc.), HttpServlet provides a corresponding doXxx() method. This lesson covers HttpServlet lifecycle and complete code examples.

HttpServlet Class Hierarchy

HttpServlet is the child class of GenericServlet and acts as the base class for developing HTTP-based servlets.

Class hierarchy:

ServletConfig (I) → Servlet (I) → Serializable (I)
GenericServlet (AC) → HttpServlet (AC)

For every HTTP method XXX, HttpServlet contains the corresponding doXxx() method:

protected void doXxx(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException

HttpServlet contains 2 service methods:

public void service(ServletRequest req, ServletResponse resp)
protected void service(HttpServletRequest req, HttpServletResponse resp)

HttpServlet Service Methods

Example02

JCode Cell

1
2	public void service(ServletRequest req,ServletResponse resp)throws SE,IOE
3	protected void service(HttpServletRequest req,HttpServletResponse resp)throws SE,IOE
4

Demo: HttpServlet with GET and POST

login.html: Sends POST request to the servlet

login.html Form

Example04

JCode Cell

1
2	<html>
3	<body><h1> This is HttpServletDemo to send Post request</h1>
4	<form action = "/advapps1C/test" method="POST">
5	Enter Name :<input type="text" name="uname"><br/>
6	<input type="submit" value="Login">
7	</form>
8	</body>
9	</html>
10

FirstServlet.java extending HttpServlet

Folder structure: advapps1C/ → login.html, WEB-INF/ → classes/ → FirstServlet.class

If we send a GET request, doGet() method is executed. If we send a POST request, doPost() method is executed.

Example05

JCode Cell

1
2	import javax.servlet.*;
3	import javax.servlet.http.*;
4	import java.io.*;
5	import javax.servlet.annotation.*;
6	@WebServlet("/test")
7	public class FirstSevlet extends HttpServlet
8	{
9	public void doGet(HttpServletRequest req,HttpServletResponse resp) throws ServletException,IOException
10	{
11	PrintWriter out = resp.getWriter();
12	out.println("<h1>This is from doGET()method...</h1>");
13	}
14	public void doPost(HttpServletRequest req,HttpServletResponse resp) throws ServletException,IOException
15	{
16	PrintWriter out = resp.getWriter();
17	out.println("<h1>This is from doPOST()method...</h1>");
18	}
19	}
20

Output


<h1>This is from doGET()method...</h1>
<h1>This is from doPOST()method...</h1>

HttpServlet Lifecycle

The complete request processing flow:

Browser sends HTTP request to the web server
Web server checks if the request is for static or dynamic information
For static information: server provides the response (or 404 if unavailable)
For dynamic information: server forwards to the web container
Container identifies the servlet class based on URL pattern (using web.xml or annotations)
Container checks if a servlet object exists; if not, loads class, instantiates, and calls init()
Container creates ServletRequest and ServletResponse objects and calls public service(SR, SR)
If our class has public service(SR, SR): it's executed directly
If not: HttpServlet's public service() is called, which type-casts and calls protected service(HSR, HSR)
If our class has protected service(HSR, HSR): it's executed directly
If not: HttpServlet's protected service() identifies the HTTP method and invokes the corresponding doXxx() method
If our class has doXxx(): it's executed
If not: HttpServlet's doXxx() returns 405 Method Not Allowed

Method call order:
public service(SR, SR) → protected service(HSR, HSR) → doXxx(HSR, HSR)

Finally, the web container calls destroy() when the servlet is taken out of service.

Servlet Method Override Cases

Case	What Happens
1: Override public service(SR,SR)	This method handles ALL request types (GET, POST, etc.) — doXxx() is never called
2: Override both public and protected service	Public service(SR,SR) handles all requests — protected service is bypassed
3: Override protected service() + doGet()	Protected service() handles all requests including GET — doGet() is never called
4: GET request, no doGet() but doPost() exists	HttpServlet doGet() returns 405 GET not supported
5: POST request, no doPost() but doGet() exists	HttpServlet doPost() returns 405 POST not supported
6: Common response for GET and POST	Implement doGet() and have doPost() call doGet(req, resp)

Case 6: Common Response for GET and POST

To provide the same response for both GET and POST requests:

Example08

JCode Cell

1
2	public class FirstSevlet extends HttpServlet
3	{
4	public void doGet(HttpServletRequest req,HttpServletResponse resp) throws ServletException,IOException
5	{
6	PrintWriter out = resp.getWriter();
7	out.println("<h1>This is common response for both GET and Post methods...</h1>");
8	}
9	public void doPost(HttpServletRequest req,HttpServletResponse resp) throws ServletException,IOException
10	{
11	doGet(req,resp);
12	}
13	}
14

Output


<h1>This is common response for both GET and Post methods...</h1>

📝 Key Takeaways

HttpServlet extends GenericServlet
Two service methods: public and protected
Request method determines which doXxx() is called
Exam-style questions at the end

🧠 Test Your Knowledge

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