when i am compiling the program first time it was successfully compiling.but from the second time i got the errors like InsertServlet.java:3: package javax.servlet does not exist import javax.servlet.*; ^ InsertServlet.java:4: package javax.servlet.http does not exist import javax.servlet.http.*; ^ InsertServlet.java:6: cannot find symbol symbol: class HttpServlet public class InsertServlet extends HttpServlet{ ^ InsertServlet.java:7: cannot find symbol symbol : class HttpServletRequest location: class InsertServlet public void doPost(HttpServletRequest req,HttpServletResponse res) throws Se rvletException,IOException { ^ InsertServlet.java:7: cannot find symbol symbol : class HttpServletResponse location: class InsertServlet public void doPost(HttpServletRequest req,HttpServletResponse res) throws Se rvletException,IOException { ^ InsertServlet.java:7: cannot find symbol symbol : class ServletException location: class InsertServlet public void doPost(HttpServletRequest req,HttpServletResponse res) throws Se rvletException,IOException { ^