ServletContext Interface

• An object of ServletContext is created by the web container at time of deploying the project.
• This object can be used to get configuration information from web.xml file.
• There is only one ServletContext object per web application.
• If any information is shared to many servlet, it is better to provide it from the web.xml file using the <context-param> element.
• If the information is changed in web.xml, we don't need to modify the servlet.
• The ServletContext object can be used to set, get or remove attribute from the web.xml file.
  The ServletContext object can be used to provide inter-application communication.

 Commonly used methods of ServletContext interface

1. public String getInitParameter(String name):Returns the parameter value for the specified parameter name.
2. public Enumeration getInitParameterNames():Returns the names of the context's initialization parameters as an Enumeration of String objects..
3. public void setAttribute(String name,Object object):sets the given object in the application scope.
4. public Object getAttribute(String name):Returns the attribute for the specified name.
5. public void removeAttribute(String name):Removes the attribute with the given name from the servlet context.

Syntax to call the methods of ServletContext interface


    //We can get the ServletContext object from ServletConfig object 
    ServletContext application=getServletConfig().getServletContext(); 
     
    //Another convenient way to get the ServletContext object 
    ServletContext application=getServletContext();

Syntax to provide the initialization parameter in Context scope

<web-app> 
 ...... 
     
  <context-param> 
    <param-name>parametername</param-name> 
    <param-value>parametervalue</param-value> 
  </context-param> 
 ...... 
</web-app>

Example of ServletContext to get the initialization parameter

In this example, we are getting the initialization parameter from the web.xml file and printing the value of the initialization parameter. Notice that the object of ServletContext represents the application scope. So if we change the value of the parameter from the web.xml file, all the servlet classes will get the changed value. So we don't need to modify the servlet. So it is better to have the common information for most of the servlets in the web.xml file by context-param element.

DemoServlet.java

    import java.io.*; 
    import javax.servlet.*; 
    import javax.servlet.http.*; 
     
     
    public class DemoServlet extends HttpServlet{ 
    public void doGet(HttpServletRequest req,HttpServletResponse res) 
    throws ServletException,IOException 
    { 
    res.setContentType("text/html"); 
    PrintWriter pw=res.getWriter(); 
     
    //creating ServletContext object 
    ServletContext context=getServletContext(); 
     
    //Getting the value of the initialization parameter and printing it 
    String driverName=context.getInitParameter("drivername"); 
    pw.println("driver name is="+driverName); 
     
    pw.close(); 
     
    }}

web.xml

    <web-app> 
     
    <servlet> 
    <servlet-name>DemoServlet</servlet-name> 
    <servlet-class>DemoServlet</servlet-class> 
    </servlet> 
     
    <context-param> 
    <param-name>drivername</param-name> 
    <param-value>sun.jdbc.odbc.JdbcOdbcDriver</param-value> 
    </context-param> 
     
    <servlet-mapping> 
    <servlet-name>DemoServlet</servlet-name> 
    <url-pattern>/context</url-pattern> 
    </servlet-mapping> 
     
    </web-app> 

Example of ServletContext to get all the initialization parameters

In this example, we are getting all the initialization parameter from the web.xml file. For getting all the parameters, we have used the getInitParameterNames() method in the servlet class. 

DemoServlet.java

    import java.io.*; 
    import javax.servlet.*; 
    import javax.servlet.http.*; 
     
     
    public class DemoServlet extends HttpServlet{ 
    public void doGet(HttpServletRequest req,HttpServletResponse res) 
    throws ServletException,IOException 
    { 
    res.setContentType("text/html"); 
    PrintWriter out=res.getWriter(); 
     
    ServletContext context=getServletContext(); 
    Enumeration<String> e=context.getInitParameterNames(); 
         
    String str=""; 
    while(e.hasMoreElements()){ 
        str=e.nextElement(); 
        out.print("<br> "+context.getInitParameter(str)); 
    } 
    }}

web.xml

    <web-app> 
     
    <servlet> 
    <servlet-name>DemoServlet</servlet-name> 
    <servlet-class>DemoServlet</servlet-class> 
    </servlet> 
     
    <context-param> 
    <param-name>dname</param-name> 
    <param-value>sun.jdbc.odbc.JdbcOdbcDriver</param-value> 
    </context-param> 
     
    <context-param> 
    <param-name>username</param-name> 
    <param-value>system</param-value> 
    </context-param> 
     
    <context-param> 
    <param-name>password</param-name> 
    <param-value>oracle</param-value> 
    </context-param> 
     
    <servlet-mapping> 
    <servlet-name>DemoServlet</servlet-name> 
    <url-pattern>/context</url-pattern> 
    </servlet-mapping> 
     
    </web-app>