HttpServlet doGet() Method Example

Author:
In Java web applications, handling HTTP requests is a common requirement. The doPost method in a servlet is designed to handle HTTP POST requests, typically used for submitting form data, while the doGet method handles HTTP GET requests, often used to retrieve data. In this tutorial, we'll create a simple application that collects student form data using the doPost method, stores it in memory, and retrieves it using the doGet method.

Prerequisites

Before starting, ensure you have:

  • Basic understanding of Java Servlets and JSP.
  • Java web application development environment set up (e.g., Apache Tomcat).
  • Maven for managing project dependencies.

Project Structure

Here's what our project structure will look like:

student-form/
├── src/
│   ├── main/
│   │   ├── java/
│   │   │   └── com/
│   │   │       └── example/
│   │   │           └── servlet/
│   │   │               └── StudentServlet.java
│   │   ├── resources/
│   │   └── webapp/
│   │       ├── index.jsp
│   │       └── studentDetails.jsp
└── pom.xml

Dependencies

Add the necessary dependencies to your pom.xml file for the latest versions of JSP and servlet APIs:

<dependency>
    <groupId>jakarta.servlet</groupId>
    <artifactId>jakarta.servlet-api</artifactId>
    <version>6.1.0</version>
    <scope>provided</scope>
</dependency>
<dependency>
    <groupId>jakarta.servlet.jsp.jstl</groupId>
    <artifactId>jakarta.servlet.jsp.jstl-api</artifactId>
    <version>3.0.0</version>
</dependency>

Creating the JSP Form Page

First, let's create a JSP page index.jsp that will collect student data:

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<!DOCTYPE html>
<html>
<head>
    <title>Student Registration Form</title>
</head>
<body>
    <h2>Student Registration Form</h2>
    <form action="student" method="post">
        <label for="firstName">First Name:</label>
        <input type="text" id="firstName" name="firstName" required><br><br>
        <label for="lastName">Last Name:</label>
        <input type="text" id="lastName" name="lastName" required><br><br>
        <label for="email">Email:</label>
        <input type="email" id="email" name="email" required><br><br>
        <label for="password">Password:</label>
        <input type="password" id="password" name="password" required><br><br>
        <input type="submit" value="Submit">
    </form>
    
    <h2>Retrieve Student Data</h2>
    <form action="student" method="get">
        <label for="retrieveEmail">Email:</label>
        <input type="email" id="retrieveEmail" name="email" required><br><br>
        <input type="submit" value="Retrieve">
    </form>
</body>
</html>

Creating the Servlet to Handle Requests

Next, we'll create a servlet named StudentServlet.java to handle the POST and GET requests. We'll use an in-memory data structure to store the student data:

package com.example.servlet;

import jakarta.servlet.ServletException;
import jakarta.servlet.annotation.WebServlet;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

import java.io.IOException;
import java.util.HashMap;
import java.util.Map;

@WebServlet("/student")
public class StudentServlet extends HttpServlet {
    private Map<String, Student> studentDatabase = new HashMap<>();

    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // Retrieve form data from the request
        String firstName = request.getParameter("firstName");
        String lastName = request.getParameter("lastName");
        String email = request.getParameter("email");
        String password = request.getParameter("password");

        // Store data in memory
        Student student = new Student(firstName, lastName, email, password);
        studentDatabase.put(email, student);

        // Set attributes to request object
        request.setAttribute("message", "Student data has been saved successfully!");

        // Forward to JSP page to display the details
        request.getRequestDispatcher("index.jsp").forward(request, response);
    }

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // Retrieve email from request parameters
        String email = request.getParameter("email");

        // Get student data from memory
        Student student = studentDatabase.get(email);

        // Set attributes to request object
        if (student != null) {
            request.setAttribute("firstName", student.getFirstName());
            request.setAttribute("lastName", student.getLastName());
            request.setAttribute("email", student.getEmail());
            request.setAttribute("password", student.getPassword());
        } else {
            request.setAttribute("message", "No student found with the provided email.");
        }

        // Forward to JSP page to display the details
        request.getRequestDispatcher("studentDetails.jsp").forward(request, response);
    }
}

Creating the JSP Page to Display Details

Create another JSP page studentDetails.jsp to display the student details:

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<!DOCTYPE html>
<html>
<head>
    <title>Student Details</title>
</head>
<body>
    <h2>Student Details</h2>
    <c:if test="${not empty message}">
        <p>${message}</p>
    </c:if>
    <c:if test="${not empty firstName}">
        <p>First Name: ${firstName}</p>
        <p>Last Name: ${lastName}</p>
        <p>Email: ${email}</p>
        <p>Password: ${password}</p>
    </c:if>
</body>
</html>

Explanation of the doPost and doGet Methods

  1. Handling POST Requests (doPost method):

    • The doPost method retrieves form data using the HttpServletRequest object's getParameter method.
    • It stores the data in an in-memory HashMap.
    • Attributes are set to the request object to be forwarded to the JSP page for display.
    @Override
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    // Retrieve form data from the request
    String firstName = request.getParameter("firstName");
    String lastName = request.getParameter("lastName");
    String email = request.getParameter("email");
    String password = request.getParameter("password");

    // Store data in memory
    Student student = new Student(firstName, lastName, email, password);
    studentDatabase.put(email, student);

    // Set attributes to request object
    request.setAttribute("message", "Student data has been saved successfully!");

    // Forward to JSP page to display the details
    request.getRequestDispatcher("index.jsp").forward(request, response);
}

  2. Handling GET Requests (doGet method):

    • The doGet method retrieves the student data from the in-memory HashMap based on the email parameter.
    • Attributes are set to the request object to be forwarded to the JSP page for display.
    @Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    // Retrieve email from request parameters
    String email = request.getParameter("email");

    // Get student data from memory
    Student student = studentDatabase.get(email);

    // Set attributes to request object
    if (student != null) {
        request.setAttribute("firstName", student.getFirstName());
        request.setAttribute("lastName", student.getLastName());
        request.setAttribute("email", student.getEmail());
        request.setAttribute("password", student.getPassword());
    } else {
        request.setAttribute("message", "No student found with the provided email.");
    }

    // Forward to JSP page to display the details
    request.getRequestDispatcher("studentDetails.jsp").forward(request, response);
}

Conclusion

In this tutorial, we learned how to handle form data using Java Servlets. We used the doPost method to collect and store data, and the doGet method to retrieve and display the data. This example demonstrates the basic concepts of handling HTTP requests in a Java web application.

Related Servlet Posts

Comments

Post a Comment

Leave Comment