7.B] Explain how to read servlet parameters with an example
Answer:
Note: if difficult to understand, Reading Form Parameters is enough
In a servlet, parameters are often sent from the client (e.g., via an HTML form) and can be accessed using the HttpServletRequest object. Parameters can be accessed in a variety of ways, depending on whether they are query parameters, form parameters, or parameters from a URL.
Here’s a breakdown of how to read servlet parameters:
1. Query Parameters
- Purpose: Parameters included in the URL after the
?(query string). Example URL:http://example.com/servlet?param1=value1¶m2=value2. - Method to Use:
getParameter(String name) - Example Code:
import javax.servlet.*;
import javax.servlet.http.*;
import java.io.IOException;
public class QueryParamServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException {
// Retrieve query parameters
String param1 = req.getParameter("param1");
String param2 = req.getParameter("param2");
// Set content type and write response
res.setContentType("text/html");
PrintWriter out = res.getWriter();
out.println("<html><body>");
out.println("<h1>Query Parameters</h1>");
out.println("<p>param1: " + param1 + "</p>");
out.println("<p>param2: " + param2 + "</p>");
out.println("</body></html>");
}
}
2. Form Parameters
- Purpose: Parameters sent via an HTML form using either the GET or POST method.
- Method to Use:
getParameter(String name) - Example HTML Form:
<form action="formServlet" method="post">
<label for="name">Name:</label>
<input type="text" id="name" name="name">
<label for="age">Age:</label>
<input type="text" id="age" name="age">
<input type="submit" value="Submit">
</form>
- Example Servlet Code:
import javax.servlet.*;
import javax.servlet.http.*;
import java.io.IOException;
public class FormParamServlet extends HttpServlet {
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException {
// Retrieve form parameters
String name = req.getParameter("name");
String age = req.getParameter("age");
// Set content type and write response
res.setContentType("text/html");
PrintWriter out = res.getWriter();
out.println("<html><body>");
out.println("<h1>Form Parameters</h1>");
out.println("<p>Name: " + name + "</p>");
out.println("<p>Age: " + age + "</p>");
out.println("</body></html>");
}
}
3. URL Path Parameters
- Purpose: Parameters included in the URL path, typically used with URL rewriting or RESTful web services.
- Method to Use:
getPathInfo(),getServletPath() - Example URL:
http://example.com/servlet/path/to/resource - Example Servlet Code:
import javax.servlet.*;
import javax.servlet.http.*;
import java.io.IOException;
public class PathParamServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException {
// Retrieve path info
String pathInfo = req.getPathInfo();
// Set content type and write response
res.setContentType("text/html");
PrintWriter out = res.getWriter();
out.println("<html><body>");
out.println("<h1>Path Parameters</h1>");
out.println("<p>Path Info: " + pathInfo + "</p>");
out.println("</body></html>");
}
}
Summary
- Query Parameters:
- Accessed using
req.getParameter("paramName"). - Sent as part of the URL after the
?.
2. Form Parameters:
- Accessed using
req.getParameter("paramName"). - Sent via an HTML form with
method="post"ormethod="get".
3. URL Path Parameters:
- Accessed using
req.getPathInfo()orreq.getServletPath(). - Included in the URL path, often used in RESTful services.