import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.*;
import javax.servlet.http.*;
public class AllAboutServlet extends HttpServlet {
private static final String CONTENT_TYPE = "text/html; charset=windows-1252";
public AllAboutServlet() {
System.out.println("CTOR : Servlet constructor can be overriden .. " +
"should not be private , protected , nor default");
System.out.println("CTOR : The ctor will be called by the container ... ");
System.out.println("CTOR : At present its a normal java object .. " +
"doesnt understand ServletContext and ServletConfig ");
System.out.println("CTOR : Servlets are usually instantiated by the servlet " +
"container using the Class.newInstance() method, with no arguments");
}
private AllAboutServlet(int i){
System.out.println("Parameterized ctor value "+i);
System.out.println("It is possible to have a custom constructor for a servlet, " +
"so long as you also add a default constructor with no arguments ?? WHY ??");
System.out.println("the servlet gets instantiated by the container dynamically");
System.out.println("java does not allow to call parametrized constuctor for dynamically " +
"loaded clases");
}
public static void static_method(){
System.out.println("Can have Static method in servlet .. who can call it ??");
System.out.println("Probably no one is stopping other classes to use servlet to" +
"instantiate amnd use it as a normal object ");
System.out.println("Other classes may even call init() service() and then destroy() " +
"that wont make it servlet.. unless container call");
System.out.println("Only container can use servlet class as a servlet ");
}
public void init(ServletConfig config) throws ServletException {
System.out.println("INIT : Servlet init called .. now java object turns servlet .. " +
"understands ServletContext and ServletConfig");
System.out.println("INIT : perform one-time expensive operations, such as acquiring " +
"thread-safe resource acquisition mechanisms ");
// One effective use of the Servlet init method is the creation and caching of
// thread-safe resource acquisition mechanisms, such as JDBC DataSources, EJB Homes,
// and Web Services SOAP Mapping Registry. use this for caching data ...
super.init(config);
// COMPULSORY the abstract superclass implementation of the method in GenericServlet
// stores the servlet configuration object.
// If an exception is thrown in your init(ServletConfig) method, it may be appropriate
// to use the destroy() method to help handle the case. If so, you should still throw
// a ServletException to ensure the servlet is not put into service in this state.
}
public void doGet(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException {response.setContentType(CONTENT_TYPE);
PrintWriter out = response.getWriter();
out.println("<html>");
out.println("<head><title>AllAboutServlet</title></head>");
out.println("<body>");
out.println("<p>The servlet has received a GET. This is the reply.</p>");
out.println("</body></html>");
out.close();
System.out.println("DOGET : doGet called ");
System.out.println("DOGET : one may call delete() from inside service() ... It will do whatever logic you have in destroy() (cleanup, remove attributes, etc.) but it won't \"unload\" the servlet instance itself");
System.out.println("");
}
public void doPost(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException {response.setContentType(CONTENT_TYPE);
PrintWriter out = response.getWriter();
out.println("<html>");
out.println("<head><title>AllAboutServlet</title></head>");
out.println("<body>");
out.println("<p>The servlet has received a POST. This is the reply.</p>");
out.println("</body></html>");
out.close();
}
public void doPut(HttpServletRequest request,
HttpServletResponse response) throws ServletException,
IOException {
}
public void doDelete(HttpServletRequest request,
HttpServletResponse response) throws ServletException,
IOException {
}
public void destroy(){
System.out.println("DESTROY : destroy called by contianer .. when is it called ??" +
"When your application is stopped or Servlet Container shuts down ");
System.out.println("DESTROY : Not when embedded oc4j stopped ");
System.out.println("DESTROY : destroy() does not imply garbage collection");
System.out.println("DESTROY : write the destroy() method and destroy your servlet" +
"because if many servlets running on the same webserver are not destroyed explicitly," +
"then the performance of the web server falls down");
System.out.println("DESTROY : destroy() is not guaranteed to be called... but if it is, " +
"you should make sure it works right");
}
public void destroy(int i){
System.out.println("may overload .. its syntactically ok ... container wont call this...");
}
public void point1() {
System.out.println("Is it possible that the servlet container will call destroy()" +
"while the servlet is still processing a request inside service() on a different thread ?");
System.out.println("yes, but it's a degenerate case. The servlet container is required" +
"to wait a reasonable amount of time for current requests to finish processing. So if your" +
"request is not totally lagging, it should work out fine. If you're spending more than" +
"a few seconds processing a request, that's a UI problem that you should try to work out first.");
}
public void point2() {
// GenericServlet has methods ... init() destroy() log() getInitParameter() getInitParameterNames()
// getServletContext() getServletConfig() getServletInfo() getServletName()
}
public void point3() {
// HttpServlet is declared abstract because the default implementations of the main service methods
// do nothing and must be overridden
}
public void point4() {
// The HttpServletRequestWrapper and HttpServletResponseWrapper classes are designed to make it
// easy for developers to create custom implementations of the servlet request and response types.
// The classes are constructed with the standard HttpServletRequest and HttpServletResponse instances
// respectively and their default behaviour is to pass all method calls directly to the underlying
// objects.
}
}
Tuesday, May 13, 2008
All About Servlets : Run The Servlet
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2 comments:
hey lavnish .
nice post..
do you have any idea how we call servlets and pass request/response to them from flex??
sorry man never tried that out
I havent been able to devote much time to flex ...
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