You can initialize servlet parameters in a Java Servlet by using the ServletConfig object. The ServletConfig object contains initialization parameters and configuration data for a specific servlet. These parameters are specified in the web application’s deployment descriptor (web.xml file).

Here’s a step-by-step guide to using ServletConfig for initializing servlet parameters:

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1. Define Initialization Parameters in web.xml

Define the initialization parameters for the servlet in the web.xml deployment descriptor using the <init-param> element inside the <servlet> element.

<web-app xmlns="https://jakarta.ee/xml/ns/jakartaee" version="10">
    <servlet>
        <servlet-name>MyServlet</servlet-name>
        <servlet-class>org.kodejava.servlet.MyServlet</servlet-class>
        <init-param>
            <param-name>param1</param-name>
            <param-value>value1</param-value>
        </init-param>
        <init-param>
            <param-name>param2</param-name>
            <param-value>value2</param-value>
        </init-param>
    </servlet>
    <servlet-mapping>
        <servlet-name>MyServlet</servlet-name>
        <url-pattern>/myServlet</url-pattern>
    </servlet-mapping>
</web-app>

2. Implement the Servlet and Use ServletConfig

The servlet can retrieve these initialization parameters using the ServletConfig object. Typically, you retrieve ServletConfig in the init() method of the servlet.

Here’s an example:

package org.kodejava.servlet;

import jakarta.servlet.ServletConfig;
import jakarta.servlet.ServletException;
import jakarta.servlet.http.HttpServlet;
import jakarta.servlet.http.HttpServletRequest;
import jakarta.servlet.http.HttpServletResponse;

import java.io.IOException;

public class MyServletConfig extends HttpServlet {

    private String param1;
    private String param2;

    @Override
    public void init(ServletConfig config) throws ServletException {
        super.init(config);

        // Retrieve initialization parameters from ServletConfig
        param1 = config.getInitParameter("param1");
        param2 = config.getInitParameter("param2");

        // Log values (optional)
        System.out.println("Parameter 1: " + param1);
        System.out.println("Parameter 2: " + param2);
    }

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // Use the initialized parameters
        resp.setContentType("text/plain");
        resp.getWriter().write("Param1: " + param1 + "\nParam2: " + param2);
    }
}

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3. Access Parameters from ServletConfig

• ServletConfig.getInitParameter(String name): Retrieves a single initialization parameter by its name.
• ServletConfig.getInitParameterNames(): Returns an Enumeration of all defined parameter names.

For example:

Enumeration<String> parameterNames = config.getInitParameterNames();
while (parameterNames.hasMoreElements()) {
    String paramName = parameterNames.nextElement();
    System.out.println("Parameter Name: " + paramName + ", Value: " + config.getInitParameter(paramName));
}

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Output

When you access the servlet (/myServlet), the servlet will use the parameters specified in the web.xml file and display:

Param1: value1
Param2: value2

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This is how you can initialize servlet parameters using ServletConfig. It allows you to externalize configuration values, making them easier to modify without changing the servlet code.

Maven dependencies

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