Dinesh on Java

ServletConfig is implemented by the servlet container to initialize a single servlet using init(). That is, you can pass initialization parameters to the servlet using the web.xml deployment descriptor. For understanding, this is similar to a constructor in a java class.An object of ServletConfig is created by the web container for each servlet. This object can be used to get configuration information from web.xml file.

If the configuration information is modified from the web.xml file, we don’t need to change the servlet. So it is easier to manage the web application if any specific content is modified from time to time.

Advantage of ServletConfig

The core advantage of ServletConfig is that you don’t need to edit the servlet file if information is modified from the web.xml file.

Methods of ServletConfig interface

• public String getInitParameter(String name):Returns the parameter value for the specified parameter name.
• public Enumeration getInitParameterNames():Returns an enumeration of all the initialization parameter names.
• public String getServletName():Returns the name of the servlet.
• public ServletContext getServletContext():Returns an object of ServletContext.

 

How to initialize a servlet inside web.xml

Inside servlet class:

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

Example of ServletConfig to get initialization parameter

In this example, we are getting the one initialization parameter from the web.xml file and printing this information in the servlet.

HelloServlet.java

import java.io.*;  
import javax.servlet.*;  
import javax.servlet.http.*;  
  
public class HelloServlet extends HttpServlet {  
public void doGet(HttpServletRequest request, HttpServletResponse response)  
    throws ServletException, IOException {  
  
    response.setContentType("text/html");  
    PrintWriter out = response.getWriter();  
      
    ServletConfig config=getServletConfig();  
    String email=config.getInitParameter("email");  
    out.print("Email is: "+eamil);  
          
    out.close();  
    }  
  
}  

web.xml

<web-app>  
  
<servlet>  
<servlet-name>HelloServlet</servlet-name>  
<servlet-class>HelloServlet</servlet-class>  
  
<init-param>  
<param-name>email</param-name>  
<param-value>admin@dineshonjava.com</param-value>  
</init-param>  
  
</servlet>  
  
<servlet-mapping>  
<servlet-name>HelloServlet</servlet-name>  
<url-pattern>/servlet1</url-pattern>  
</servlet-mapping>  
  
</web-app>  

Example of ServletConfig to get all the initialization parameters

In this example, we are getting all the initialization parameter from the web.xml file and printing this information in the servlet.

HelloServlet.java

import java.io.IOException;  
import java.io.PrintWriter;  
import java.util.Enumeration;  
  
import javax.servlet.ServletConfig;  
import javax.servlet.ServletException;  
import javax.servlet.http.HttpServlet;  
import javax.servlet.http.HttpServletRequest;  
import javax.servlet.http.HttpServletResponse;  
  
  
public class HelloServlet extends HttpServlet {  
public void doGet(HttpServletRequest request, HttpServletResponse response)  
        throws ServletException, IOException {  
  
    response.setContentType("text/html");  
    PrintWriter out = response.getWriter();  
      
    ServletConfig config=getServletConfig();  
    Enumeration<String> e=config.getInitParameterNames();  
          
    String str="";  
    while(e.hasMoreElements()){  
    str=e.nextElement();  
    out.print("<br>Name: "+str);  
    out.print(" value: "+config.getInitParameter(str));  
    }  
          
    out.close();  
}  
  
}  
  

web.xml

<web-app>  
  
<servlet>  
<servlet-name>HelloServlet</servlet-name>  
<servlet-class>HelloServlet</servlet-class>  
  
<init-param>  
<param-name>name</param-name>  
<param-value>dinesh</param-value>  
</init-param>  
  
<init-param>  
<param-name>email</param-name>  
<param-value>admin@dineshonjava.com</param-value>  
</init-param>  
  
</servlet>  
  
<servlet-mapping>  
<servlet-name>HelloServlet</servlet-name>  
<url-pattern>/servlet1</url-pattern>  
</servlet-mapping>  
  
</web-app>