Servlet Form Data

Forms are a fundamental part of the web as they allow us to send data from the client to the server. In a Java Servlet, you can handle form data in your doGet and doPost methods.

1. HTML Form

First, you need an HTML form. This form will send data to the server when the user submits the form. Here's a simple example:

<form action="processForm" method="post">
    <label for="fname">First name:</label><br>
    <input type="text" id="fname" name="fname"><br>
    <label for="lname">Last name:</label><br>
    <input type="text" id="lname" name="lname"><br>
    <input type="submit" value="Submit">
</form>

In this example, when the user submits the form, the browser will send a POST request to the "processForm" URL with the form data.

2. Servlet

Next, you need a Servlet to handle the form data. Here's a simple example:

import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;

public class FormServlet extends HttpServlet {

    protected void doPost(HttpServletRequest request, HttpServletResponse response) 
            throws ServletException, IOException {

        // Get the form data
        String firstName = request.getParameter("fname");
        String lastName = request.getParameter("lname");

        // Use the form data
        PrintWriter out = response.getWriter();
        out.println("Hello, " + firstName + " " + lastName + "!");
    }
}

In this example, request.getParameter("fname") and request.getParameter("lname") are used to get the form data. These methods return the values of the form fields with the given names.

3. Configure the Servlet

Finally, you need to configure your Servlet. This can be done using annotations or by modifying the web.xml deployment descriptor.

Using annotations:

import javax.servlet.annotation.WebServlet;

@WebServlet("/processForm")
public class FormServlet extends HttpServlet {
    //...
}

Using web.xml:

<web-app>
    <servlet>
        <servlet-name>FormServlet</servlet-name>
        <servlet-class>com.example.FormServlet</servlet-class>
    </servlet>

    <servlet-mapping>
        <servlet-name>FormServlet</servlet-name>
        <url-pattern>/processForm</url-pattern>
    </servlet-mapping>
</web-app>

Once your Servlet is running, you should be able to fill out the form in your web browser and see a greeting with your name displayed on the page when you submit the form.

Java Servlet form parameters: Access form parameters in a Servlet using request.getParameter().
```
String username = request.getParameter("username");
```

Handling POST requests in Servlets: Process form data from POST requests in a Servlet.

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    // Servlet code for handling POST requests
}

Accessing form parameters in Servlet: Retrieve form parameters using request.getParameter() method.
```
String username = request.getParameter("username");
```
Servlet form data encoding: Set the character encoding for form data in the Servlet.
```
request.setCharacterEncoding("UTF-8");
```

Parsing form data in Java Servlets: Parse and process form data in a Servlet.

String username = request.getParameter("username");
int age = Integer.parseInt(request.getParameter("age"));

Retrieving form data in Servlet: Retrieve and process form data from the request in a Servlet.

String username = request.getParameter("username");
String password = request.getParameter("password");

Handling checkbox and radio button data in Servlet: Process checkbox and radio button values in a Servlet.
- Use request.getParameterValues() for multiple values.
```
String[] hobbies = request.getParameterValues("hobbies");
```