24. Can we call destroy() method on servlets from service method?
destroy() is a servlet life-cycle method called by servlet container to kill the instance of the servlet. "Yes". You can call destroy() from within the service(). It will do whatever logic you have in destroy() (cleanup, remove attributes, etc.) but it won't "unload" the servlet instance itself. That can only be done by the container
25. What is the use of ServletConfig and ServletContext?
An interface that describes the configuration parameters for a servlet. This is passed to the servlet when the web server calls its init() method. Note that the servlet should save the reference to the ServletConfig object, and define a getServletConfig() method to return it when asked. This interface defines how to get the initialization parameters for the servlet and the context under which the servlet is running.
An interface that describes how a servlet can get information about the server in which it is running. It can be retrieved via the getServletContext() method of the ServletConfig object.
26. What is difference between forward() and sendRedirect()? Which one is faster than other and which
works on server?
Forward( ) : javax.Servlet.RequestDispatcher interface.
-RequestDispatcher.forward( ) works on the Server.
-The forward( ) works inside the WebContainer.
-The forward( ) restricts you to redirect only to a resource in the same web-Application.
-After executing the forward( ), the control will return back to the same method from where the forward method was called.
-the forward( ) will redirect in the application server itself, it does’n come back to the client.
- The forward( ) is faster than Sendredirect( ) .
To use the forward( ) of the requestDispatcher interface, the first thing to do is to obtain RequestDispatcher Object. The Servlet technology provides in three ways.
1. By using the getRequestDispatcher( ) of the javax.Servlet.ServletContext interface , passing a String containing the path of the other resources, path is relative to the root of the ServletContext.
RequestDispatcher rd=request.getRequestDispatcher(“secondServlet”);
Rd.forward(request, response);
2.getRequestDispatcher( ) of the javax.Servlet.Request interface, the path is relative to current HtpRequest.
RequestDispatcher rd=getServletContext( ).getRequestDispatcher(“servlet/secondServlet”);
Rd.forward(request, response);
3. By using the getNameDispatcher( ) of the javax.Servlet.ServletContext interface.
RequestDispatcher rd=getServletContext( ).getNameDispatcher(“secondServlet”);
Rd.forward(request, response);
Sendredirect( ) : javax.Servlet.Http.HttpServletResponce interface
-RequestDispatcher.SendRedirect( ) works on the browser.
-The SendRedirect( ) allows you to redirect trip to the Client.
-The SendRedirect( ) allows you to redirect to any URL.
-After executing the SendRedirect( ) the control will not return back to same method.
-The Client receives the Http response code 302 indicating that temporarly the client is being redirected to the specified location , if the specified location is relative , this method converts it into an absolute URL before redirecting.
-The SendRedirect( ) will come to the Client and go back,.. ie URL appending will happen.
Response. SendRedirect( “absolute path”);
Absolutepath – other than application , relative path - same application.
When you invoke a forward request, the request is sent to another resource on the server, without the client being informed that a different resource is going to process the request. This process occurs completely within the web container. When a sendRedirtect method is invoked, it causes the web container to return to the browser indicating that a new URL should be requested. Because the browser issues a completely new request any object that are stored as request attributes before the redirect occurs will be lost. This extra round trip a redirect is slower than forward.
destroy() is a servlet life-cycle method called by servlet container to kill the instance of the servlet. "Yes". You can call destroy() from within the service(). It will do whatever logic you have in destroy() (cleanup, remove attributes, etc.) but it won't "unload" the servlet instance itself. That can only be done by the container
25. What is the use of ServletConfig and ServletContext?
An interface that describes the configuration parameters for a servlet. This is passed to the servlet when the web server calls its init() method. Note that the servlet should save the reference to the ServletConfig object, and define a getServletConfig() method to return it when asked. This interface defines how to get the initialization parameters for the servlet and the context under which the servlet is running.
An interface that describes how a servlet can get information about the server in which it is running. It can be retrieved via the getServletContext() method of the ServletConfig object.
26. What is difference between forward() and sendRedirect()? Which one is faster than other and which
works on server?
Forward( ) : javax.Servlet.RequestDispatcher interface.
-RequestDispatcher.forward( ) works on the Server.
-The forward( ) works inside the WebContainer.
-The forward( ) restricts you to redirect only to a resource in the same web-Application.
-After executing the forward( ), the control will return back to the same method from where the forward method was called.
-the forward( ) will redirect in the application server itself, it does’n come back to the client.
- The forward( ) is faster than Sendredirect( ) .
To use the forward( ) of the requestDispatcher interface, the first thing to do is to obtain RequestDispatcher Object. The Servlet technology provides in three ways.
1. By using the getRequestDispatcher( ) of the javax.Servlet.ServletContext interface , passing a String containing the path of the other resources, path is relative to the root of the ServletContext.
RequestDispatcher rd=request.getRequestDispatcher(“secondServlet”);
Rd.forward(request, response);
2.getRequestDispatcher( ) of the javax.Servlet.Request interface, the path is relative to current HtpRequest.
RequestDispatcher rd=getServletContext( ).getRequestDispatcher(“servlet/secondServlet”);
Rd.forward(request, response);
3. By using the getNameDispatcher( ) of the javax.Servlet.ServletContext interface.
RequestDispatcher rd=getServletContext( ).getNameDispatcher(“secondServlet”);
Rd.forward(request, response);
Sendredirect( ) : javax.Servlet.Http.HttpServletResponce interface
-RequestDispatcher.SendRedirect( ) works on the browser.
-The SendRedirect( ) allows you to redirect trip to the Client.
-The SendRedirect( ) allows you to redirect to any URL.
-After executing the SendRedirect( ) the control will not return back to same method.
-The Client receives the Http response code 302 indicating that temporarly the client is being redirected to the specified location , if the specified location is relative , this method converts it into an absolute URL before redirecting.
-The SendRedirect( ) will come to the Client and go back,.. ie URL appending will happen.
Response. SendRedirect( “absolute path”);
Absolutepath – other than application , relative path - same application.
When you invoke a forward request, the request is sent to another resource on the server, without the client being informed that a different resource is going to process the request. This process occurs completely within the web container. When a sendRedirtect method is invoked, it causes the web container to return to the browser indicating that a new URL should be requested. Because the browser issues a completely new request any object that are stored as request attributes before the redirect occurs will be lost. This extra round trip a redirect is slower than forward.
