public void doGet(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
//some code here
}
public void doPost(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
//performTask(req, resp);
//some code here
}
private void insertRequestTemplate() {
HttpSession session = req.getSession();
responsePage = req.getParameter("ResponsePage");
ServletContext ctx = getServletConfig().getServletContext();
ctx.getRequestDispatcher(responsePage).forward(req,resp);
readMessage();
public void readMessage()
{
System.out.println("calling MessageTrigger_ABean");
MessageTrigger_ABean msg = new MessageTrigger_ABean();
msg.read();
}
msg.read() has the code to read messages from MQ. Inside insertRequestTemplate method, I am calling readMessage method after ctx.getRequestDispatcher(responsePage).forward(req,resp);is this the correct way of calling this?
But inside insertRequestTemplate method, the page is not getting forwarded to the next page untill readMessage() is executed because of which the page keeps on loading for a long time until message is read from MQ. Could you please help me on this.
Most examples I have seen of a servlet forwarding the request to another servlet have the dispatcher forward invocation at the end of the method. ie. there is no more code, other than closing braces at the end of the method.
I am guessing that the forwarding doesn't happen until the invoking method completes. So where you have your msg.read() will stop the insertRequestTemplate method from completing. This will more than likely be because the code inside msg.read is being performed synchronously. Leading to http timeouts on the http request.
How you solve this will depend on what you want to do with the messages you obtain from msg.read().
Related
Can someone explain and provide code snippet for passing request body (maybe it can accept value Object) as part of apache sling doPost method -
request :
{ "XDPCont" : "XDP sample string"}
Response :
I have tried with below code but it did't work.
#Override
protected void doPost(final SlingHttpServletRequest req,
final SlingHttpServletResponse resp) throws ServletException, IOException {
final Resource resource = req.getResource();
resp.getOutputStream().println(resource.toString());
resp.getOutputStream().println(
"This content is generated by the HelloServlet POST"+req.getRequestParameter("XDPCont"));
}
Can you please explain with an working code.
I have looked around and previously asked this question but did not get a full answer. When you explicity return from doGet() or doPost() does a response get sent regardless of if you have encoded anything or not. If so what is the default code ? Is it enough to simply response.setStatus() and return ? If not: so I have always manually send back a response ? What is the default way to just respond not using forward or redirect ?
If you do nothing, just return (or not even return) from a servlet, it will send back a status code 200(OK) empty response. Tested it in both tomcat and glassfish servers, using the servlet below:
#WebServlet("/a")
public class a extends HttpServlet {
#Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
return;
}
#Override
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
return;
}
}
Using the network profiler tool of Chrome you can see what I said:
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
homePageController = (HomePageControllerV2) BeanLoader.getBean("homePageControllerV2");
}
}
whenever i hit to servlet from multiple machine. i still get the same instance of homePageController. is there any way can get diffrent instance of object homePageControllerper servlet request.
i have tired with changing the scope of bean to prototype. but still faced the same issue.
What should be done to manually stop Servlet as calling destroy doesn't help unless all threads exited from service.
Say, If I have n number of Servlets and I want to stop only one of them.
That behavior is very important when dealing with Servlets. Instances can be created after the multi-thread model and are thus not thread-safe.
The container does not allow a thread to invoke the service method after destroy has been called.
This gives you the means to close all resources that your Servlet is using (db, file, memory, etc).
#WebServlet
public class OncePerApplicationServlet extends HttpServlet {
private Connection connection;
#Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
if(req.getParameter("closeServlet").equals("true"))
this.destroy();
else
this.service(req, resp); // normal flow
}
// this method will never be called by the container after the destroy method has been invoked
#Override
protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
// 1.
try {
connection = DriverManager.getConnection("someDbUrl");
Statement stm = connection.createStatement();
stm.execute("select * from someTable");
} catch (SQLException e) {
e.printStackTrace();
}
}
#Override
public void destroy() {
// the point is that when this method is called you should be able to
// clean up and close all resources, you can rest assured that there are no "loose"
// threads that need the connection-instance
try {
connection.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
Here is a quote from the API-docs:
This interface defines methods to initialize a servlet, to service
requests, and to remove a servlet from the server. These are known as
life-cycle methods and are called in the following sequence:
The servlet is constructed, then initialized with the init method. Any
calls from clients to the service method are handled. The servlet is
taken out of service, then destroyed with the destroy method, then
garbage collected and finalized.
|
Link to the documentation
Good luck!
I am just beginning with Servlets and managed to have some servlets that act as individual URLs for populating a database for some dummy testing. Something of the form:
public class Populate_ServletName extends HttpServlet {
public void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException {
resp.setContentType("text/plain");
//Insert records
//Print confirmation
}
}
I have about 6 such servlets which I want to execute in a sequence. I was thinking of using setLocation to set the next page to be redirected but was not sure if this is the right approach because the redirects should happen after the records have been inserted. Specifically, I am looking for something like this:
public class Populate_ALL extends HttpServlet {
public void doGet(HttpServletRequest req, HttpServletResponse resp) throws IOException {
resp.setContentType("text/plain");
//Call Populate_1
//Call Populate_2
//Call Populate_3
//...
}
}
Any suggestions?
Use RequestDispatcher#include() on an URL matching the url-pattern of the Servlet.
public class Populate_ALL extends HttpServlet {
public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
response.setContentType("text/plain");
request.getRequestDispatcher("/populateServlet1").include(request, response);
request.getRequestDispatcher("/populateServlet2").include(request, response);
request.getRequestDispatcher("/populateServlet3").include(request, response);
//...
}
}
Note: if those servlets cannot be used independently, then this is the wrong approach and you should be using standalone Java classes for this which does not extend HttpServlet. In your specific case, I think the Builder Pattern may be of interest.
The RequestDispatcher#forward() is not suitable here since it throws IllegalStateException when the response headers are already committed. This will be undoubtely the case when you pass the request/response through multiple servlets which each writes to the response.
The HttpServletResponse#sendRedirect() is absolutely not suitable here since it implicitly creates a brand new request and response, hereby trashing the original ones.
See also:
How do I call a second JSP servlet while in the first JSP servlet?
RequestDispatcher.forward() vs HttpServletResponse.sendRedirect()
communication between remote servlets
It looks like what you may need is a service that each of the servlets can use to perform some work. Then the servlets are not depending one and another, but rather all using the service.
However, here is an explanation of forwarding or redirecting requests.