8.A] Explain how to handle HTTP request and response with an example
Answer:
In Java servlets, handling HTTP requests and responses involves overriding methods from the HttpServlet class. The most common methods are doGet() and doPost(), which correspond to HTTP GET and POST requests, respectively. Here’s a breakdown of how to handle these requests and responses with examples.
Common HTTP Methods
- GET Method
- Purpose: Retrieves data from the server.
- Usage: Often used for requesting data or resources.
- Characteristics: Parameters are sent in the URL.
- Example URL:
http://example.com/servlet?param1=value1¶m2=value2
2. POST Method
- Purpose: Submits data to be processed by the server.
- Usage: Often used for form submissions and data modifications.
- Characteristics: Parameters are sent in the body of the request, not in the URL.
Example: Handling HTTP Requests and Responses
1. HTML Form for GET and POST Requests
<!DOCTYPE html>
<html>
<head>
<title>Form Example</title>
</head>
<body>
<!-- Form to handle GET requests -->
<h2>GET Request</h2>
<form method="get" action="getServlet">
Name: <input type="text" name="name">
<input type="submit" value="Submit">
</form>
<!-- Form to handle POST requests -->
<h2>POST Request</h2>
<form method="post" action="postServlet">
Name: <input type="text" name="name">
<input type="submit" value="Submit">
</form>
</body>
</html>
2. Handling GET Requests in a Servlet
import javax.servlet.*;
import javax.servlet.http.*;
import java.io.IOException;
import java.io.PrintWriter;
public class GetServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// Set content type
response.setContentType("text/html");
// Get the PrintWriter to write the response
PrintWriter out = response.getWriter();
// Retrieve parameters from the request
String name = request.getParameter("name");
// Generate response
out.println("<html><body>");
out.println("<h2>GET Request</h2>");
out.println("<p>Hello, " + name + "!</p>");
out.println("</body></html>");
// Close the PrintWriter
out.close();
}
}
3. Handling POST Requests in a Servlet
import javax.servlet.*;
import javax.servlet.http.*;
import java.io.IOException;
import java.io.PrintWriter;
public class PostServlet extends HttpServlet {
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// Set content type
response.setContentType("text/html");
// Get the PrintWriter to write the response
PrintWriter out = response.getWriter();
// Retrieve parameters from the request
String name = request.getParameter("name");
// Generate response
out.println("<html><body>");
out.println("<h2>POST Request</h2>");
out.println("<p>Hello, " + name + "!</p>");
out.println("</body></html>");
// Close the PrintWriter
out.close();
}
}
Explanation
- HTML Form:
- GET Form: Submits data using the GET method, appending parameters to the URL.
- POST Form: Submits data using the POST method, including parameters in the request body.
2. Servlets:
doGet()Method: Handles GET requests. Retrieves parameters from the URL and generates a response.doPost()Method: Handles POST requests. Retrieves parameters from the request body and generates a response.
Differences Between GET and POST Requests:
| Feature | GET Request | POST Request |
|---|---|---|
| Data Visibility | Data is visible in the URL query string. Suitable for non-sensitive data. | Data is included in the request body. Suitable for sensitive data and larger amounts of data. |
| Data Length | Limited by URL length restrictions (typically around 2048 characters). | No practical limits on data size. |
| Idempotency | Idempotent; multiple identical GET requests should have the same effect as a single request. | Not necessarily idempotent; each request can have a different effect. |
| Caching | Requests can be cached by browsers and servers. | Requests are generally not cached. |