Difference between ServletConfig and ServletContext in Java Servlet

ServletConfig and ServletContext are important interfaces in Java Servlets used for configuration and communication. ServletConfig is used to store servlet-specific initialization parameters, while ServletContext is used to share data across the entire application. Together, they help manage configuration and enable communication between servlets.

• Servlet Config holds configuration data specific to a single servlet and is initialized once.
• Servlet Context stores application-wide data and is shared among all servlets.

ServletConfig

ServletConfig is an object that contains initialization parameters for a specific servlet. It is created by the servlet container and passed to the servlet during initialization.

• Defined inside <servlet> in web.xml
• Each servlet has its own ServletConfig object
• Accessed using getServletConfig()

Syntax

ServletConfig config = getServletConfig();
String value = config.getInitParameter("param-name");

Example: The following example demonstrates how ServletConfig is used to provide servlet-specific initialization parameters that are accessible only to a single servlet.

web.xml

<servlet>
    <servlet-name>RecruiterServlet</servlet-name>
    <servlet-class>RecruiterServlet</servlet-class>

    <init-param>
        <param-name>Email</param-name>
        <param-value>recruiter@jobportal.com</param-value>
    </init-param>
</servlet>

RecruiterServlet.java

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

public class RecruiterServlet extends HttpServlet {

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

        ServletConfig config = getServletConfig();
        String email = config.getInitParameter("Email");

        PrintWriter out = response.getWriter();
        out.println("Recruiter Contact Email: " + email);
    }
}

Output:

Recruiter Contact Email: recruiter@jobportal.com

Explanation:

• ServletConfig object is created per servlet
• The parameter Email is available only to RecruiterServlet
• Another servlet can have the same parameter name with a different value

ServletContext

ServletContext is an object that holds application-wide configuration information. It is shared among all servlets in the web application.

• Application-wide configuration
• Defined using <context-param> in web.xml
• Only one ServletContext object per application
• Accessed using getServletContext()

Syntax

ServletContext context = getServletContext();
String value = context.getInitParameter("param-name");

Example: The example demonstrates how ServletContext is used to share application-wide configuration data that can be accessed by all servlets.

web.xml

<context-param>
    <param-name>WebsiteName</param-name>
    <param-value>NewWebsite.tg</param-value>
</context-param>

AnyServlet.java

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

public class AnyServlet extends HttpServlet {

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

        ServletContext context = getServletContext();
        String website = context.getInitParameter("WebsiteName");

        PrintWriter out = response.getWriter();
        out.println("Website Name: " + website);
    }
}

Output:

Website Name: NewWebsite.tg

Explanation:

• ServletContext object is shared across the entire application
• The parameter WebsiteName is accessible by all servlets
• Defined once in web.xml, avoids duplication

ServletConfig Vs ServletContext