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>
- Java Servlets Overview
- Servlet Life Cycle
- Servlet Example
- Difference between ServletConfig and ServletContext
- Difference between GenericServlet and HttpServlet
- What is web application?
- Advantages of Servlets over CGI
- GenericServlet Example
- RequestDispatcher Example
- ServletConfig
- ServletContext
- Servlet Filter Example
- Database Access Example using Sevlet
- File Uploading Example using Servlet