why do we use servletconfig interface and servletcontext interface [closed]

Question

Hi all I am new in servlet and jsp I am not clear with servletconfig interface and servletcontext interface I started jsp again I encounter the term PageContext. So any body explain me these term with the nice example.

servletconfig interface and servletcontext interface and PageContext in jsp

Answer 1

ServletConfig

ServletConfig object is created by web container for each servlet to pass information to a servlet during initialization.This object can be used to get configuration information from web.xml file.

when to use : if any specific content is modified from time to time. you can manage the Web application easily without modifing servlet through editing the value in web.xml

Your web.xml look like :

 <web-app>  
      <servlet>  
        ......     
        <init-param>  
        <!--here we specify the parameter name and value -->
          <param-name>paramName</param-name>  
          <param-value>paramValue</param-value>  
        </init-param> 
        ......  
      </servlet>  
    </web-app>

This way you can get value in servlet :

public void doGet(HttpServletRequest request, HttpServletResponse response)  
    throws ServletException, IOException {  
     //getting paramValue
    ServletConfig config=getServletConfig();  
    String driver=config.getInitParameter("paramName"); 
    } 

---

ServletContext

web container create one ServletContext object per web Application. This object is used to get information from web.xml

when to use : If you want to share information to all sevlet, it a better way to make it available for all servlet.

web.xml look like :

<web-app>  
 ......  

  <context-param>  
    <param-name>paramName</param-name>  
    <param-value>paramValue</param-value>  
  </context-param>  
 ......  
</web-app>  

This way you can get value in servlet :

public void doGet(HttpServletRequest request,HttpServletResponse response)  
throws ServletException,IOException  
{  
 //creating ServletContext object  
ServletContext context=getServletContext();  

//Getting the value of the initialization parameter and printing it  
String paramName=context.getInitParameter("paramName");   
}  

---

PageContext

Is class in jsp, its implicit object pageContext is used to set , get or remove attribute from following scope:

1.page

2.request

3.session

4.application

Answer 2

ServletConfig is implemented by GenericServlet (which is a superclass of HttpServlet). It allows the application deployer to pass parameters to the servlet (in the web.xml global config file), and servlet to retrieve those parameters during its initialization.

For example, your web.xml could look like :

<servlet>
    <servlet-name>MyServlet</servlet-name>
    <servlet-class>com.company.(...).MyServlet</servlet-class>
    <init-param>
        <param-name>someParam</param-name>
        <param-value>paramValue</param-value>
    </init-param>
</servlet>

In you servlet, the "someParam" param can then be retrieved like this :

public class MyServlet extends GenericServlet {
    protected String myParam = null;

    public void init(ServletConfig config) throws ServletException {
        String someParamValue = config.getInitParameter("someParam");
    }
}

ServletContext is a bit different. It is quite badly named, and you'd better think of it as "Application scope".

It is an application-wide scope (think "map") that you can use to store data that is not specific to any user, but rather belongs to the application itself. It is commonly used to store reference data, like the application's configuration.

You can define servlet-context parameters in web.xml :

<context-param>
        <param-name>admin-email</param-name>
        <param-value>[email protected]</param-value>
</context-param>

And retrieve them in your code like this in your servlet :

public void doGet(HttpServletRequest req, HttpServletResponse res) throws IOException {
    String adminEmail = getServletContext().getInitParameter("admin-email")); 
}