Example of ServletContext in Java

ServletContext is one of pre-defined interface available in javax.servlet.*; Object of ServletContext interface is available one per web application. An object of ServletContext is automatically created by the container when the web application is deployed.

Assume there exist a web application with 2 servlet classes, and they need to get some technical values from web.xml, in this case ServletContext concept will works great, i mean all servlets in the current web application can access these context values from the web.xml but its not the case in ServletConfig, there only particular servelet can access the values from the web.xml which were written under <servlet> tag, hope you remember.  Have doubt ? just check Example of ServletConfig

How to Get ServletContext Object into Our Servlet Class

In servlet programming we have 3 approaches for obtaining an object of ServletContext interface

Way 1

ServletConfig conf = getServletConfig();
ServletContext context = conf.getServletContext();

• First obtain an object of ServletConfig interface
• ServletConfig interface contain direct method to get Context object, getServletContext();

Way 2

Direct approach, just call getServletContext() method available in GenericServlet [pre-defined].  In general we are extending our class with HttpServlet, but we know HttpServlet is the sub class of GenericServlet.

public class Java4s extends HttpServlet
{
public void doGet/doPost(-,-)
{
//….
}
ServletContext ctx = getServletContext();
}

Way 3

We can get the object of ServletContext by making use of HttpServletRequest object, we have direct method in HttpServletRequest interface.

public class Java4s extends HttpServlet
{
public void doGet/doPost(HttpServletRequest req,-)
{
ServletContext ctx = req.getServletContext();
}
}

How to Retrieve Data from ServletConfig Interface Object

ServletContext provide these 2 methods, In order to retrieve the data from the web..xml [ In web.xml we have write <context-param>tag to provide the values, and this <context-param> should write outside of <servlet> tag as context should be accessed by all servlet classes ].

In general database related properties will be written in this type of situation, where every servlet should access the same data.

• public String getInitParameter(“param name”);
• public Enumeration getInitParameterNames();

I am not going to explain about these methods, these are similar to ‘Retrieve Client Input Data in Servlet‘ but here we are retrieving values from web.xml that’s it.

Example of ServletContext

Directory Structure

Files Required

• index.html
• OnServletContext.java
• web.xml

index.html

<font face="verdana" size="2px">
    <form action="onContext" method="post">
       Example on ServletContext<br> 
       <input type="submit" value="Click Here">
    </form>
</font>

OnServletContext.java

package java4s;

import java.io.IOException;
import java.io.PrintWriter;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class OnServletContext extends HttpServlet  
{
    protected void doPost(HttpServletRequest req,HttpServletResponse res)throws ServletException,IOException
    {
        PrintWriter pw=res.getWriter();
        res.setContentType("text/html");

        // I am using 2nd way to create Context object
        ServletContext context=getServletContext();  

        String s1=context.getInitParameter("n1");
        String s2=context.getInitParameter("n2");

        pw.println("n1 value is " +s1+ " and n2 is " +s2);

       pw.close();    
    }
}

web.xml

<web-app>

    <context-param>
        <param-name> n1 </param-name>
        <param-value> 100 </param-value>
    </context-param>

    <context-param>
        <param-name> n2  </param-name>
        <param-value> 200 </param-value>
    </context-param>

    <servlet>
        <servlet-name>onServletContext</servlet-name>
        <servlet-class>java4s.OnServletContext</servlet-class>
    </servlet>

    <servlet-mapping>
            <servlet-name>onServletContext</servlet-name>
            <url-pattern>/onContext</url-pattern>
    </servlet-mapping>

   <welcome-file-list>  
        <welcome-file>index.html</welcome-file>  
   </welcome-file-list> 

</web-app>

Output

You Might Also Like

• How to Connect Servlet to the Database with Example
• Difference between ServletConfig and ServletContext in Java
• Example of ServletConfig in Java Servlet
• Understanding ServletConfig and ServletContext
• Example on getParameterValues() method of Servlet Request

::. About the Author .::
		Sivateja Kandula - Java/J2EE Full Stack Developer Founder of Java4s - Get It Yourself, A popular Java/J2EE Programming Blog, Love Java and UI frameworks. You can sign-up for the Email Newsletter for your daily dose of Java tutorials.