Servlet Context

• Defined in,

  javax.servlet.ServletContext (i/f)

• Instance of ServletContext interface's implementation class is created by the container at the application deployment time.

• Only one instance is created per web application.

• NOTE : The ServletContext object is contained within the ServletConfig object, which the WC provides to the servlet once the servlet is initialized.

• Usages

  • Server side logging.

      //Interface ServletContext
      public void log(String mesg)

  • To create context scoped (Application scoped) attributes.

      public void setAttribute(String name,Object val)

    NOTE : Access them always in thread safe manner. as they are mutable as it is a server side object.

• To access global scoped (application scoped) attributes use,

   //Interface ServletContext
    Object getAttribute(String name)

• To add context scoped attributes

    void setAttribute(String name, Object object)

• web.xml tags to create context parameters, no annotations available

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

• To access these parameters in a Servlet once the Servlet instance has initialized i.e init() method has been called.

1. Get ServletContext

   • API of GenericServlet

  public ServletContext getServletContext() //method inherited from GenericServlet

1. ServletContext API String getInitparameter(String paramName) : returns the parameter value. eg : ctx param name : user_name value : abc In the Servlet : getServletContext().getInitparameter("user_name") ---abc

5.4 Creating request dispatcher H.W