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Cannot run simple servlet with use of annotations

I am new java programmer. So I do understand the process of running servlet through mapping etc in the web.xml and I also can launch the servlet through annotation, my question is when I use the annotation, and run the project on the server, why do I have to write the serlvet name in the URL after project name for it to launch.
Is there any way without using web.xml file at all, giving an annotation and then when I run project on server that it would automatically launch and run the servlet? Instead of my writing the servlet name and hitting enter for it to launch.
#WebServlet(urlPatterns = {"/GetDate"})
public class GetDate extends HttpServlet{
#Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
Date date =new Date();
resp.setContentType("text/html");//this says we will send back html type
//get a pen to write back
PrintWriter pen=resp.getWriter();
//write back
pen.write(date.toString());
}
}
I would like the above simple servlet to just launch automatically as soon as I select run on server from eclipse.

You can specify load on startup in annotation, then the servlet's init() method is invoked when the web server starts
#WebServlet(urlPatterns = {"/GetDate"}, loadOnStartup=1)
public class GetDate extends HttpServlet{
#Override
public void init() throws ServletException {
// do some init stuff
}

It's all in the #WebServlet notation. If you change your code to be:
#WebServlet(urlPatterns = {"/"})
public class GetDate extends HttpServlet {
#Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
Date date =new Date();
resp.setContentType("text/html");//this says we will send back html type
//get a pen to write back
PrintWriter pen=resp.getWriter();
//write back
pen.write(date.toString());
}
}
Then the servlet is served at the / URL (after your webapplication name)
Be careful doing this. Traditionally you serve HTML resources from the / location. If you take this over with your servlet then you can't serve HTML. Additionally if you have more than one servlet then which one gets the / path - where do the rest go? It can be a bit self documenting to have the URL match the servlet. Note that there is no need to keep it the same name as the servlet - call it /myBigLongURLMapping if you like - the name is up to you.

Instead of #WebServlet(urlPatterns = {"/GetDate"}) write like this #WebServlet("/GetDate")
#WebServlet("/GetDate")
public class GetDate extends HttpServlet{
#Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
Date date =new Date();
resp.setContentType("text/html");//this says we will send back html type
//get a pen to write back
PrintWriter pen=resp.getWriter();
//write back
pen.write(date.toString());
}
}

Whats the difference between ActionContext,ServletContext and ServletActionContext？

In Java EE, we often use ActionContext,ServletContext and ServletActionContext, they have similar name, but I don't know the difference between them.
I only know the ServletActionContext inherit the ActionContext.
Someone can explain them?

There have many difference between them.
ServletContext
From the ServletContext's package(javax.servlet.ServletContext) we can know it is standard JavaEE WebApplication class library.
ServletContext provides the standard Servlet run-time environment. Actually is some methods of servlet communicate with web container.
public interface ServletContext {
// Returns the URL prefix for the ServletContext.
public String getServletContextName();
//Returns the context-path for the web-application.
public String getContextPath();
//Returns the ServletContext for the uri.
public ServletContext getContext(String uri);
//Returns the real file path for the given uri.
public String getRealPath(String uri);
public RequestDispatcher getNamedDispatcher(String servletName);
public RequestDispatcher getRequestDispatcher(String uri);
ServletContext is included in the ServletConfig, and ServletConfig often read from servlet or filter's init() method:
servletConfig.getServletContext()
filterConfig.getServletContext()
ActionContext
Comes from Struts, but at first comes from Struts1 and Struts2 they are different.
From Struts1:
A servlet (servlet org.apache.struts.action.ActionServlet) handle all the *.do action.
From Struts2:
The filter(org.apache.struts2.dispatcher.FilterDispatcher) handle all the request.
Because struts1 belongs to servlet scope. struts1 action's essentially is servlet.
struts2 action is normal Java bean, out of the servlet limitations.
The ActionContext makes up the lost WEB environment after the strtus2 action out of the stand servlet framework.
The ActionContext main function:
Provide the WEB context.
Solve the thread security issue.
Solve the incompatibility problem with other Framework(such as: webLogic))
ServletActionContext
As you say, ServletActionContext is ActionContext's subclass.
Its functions is starting at ActionContext, and encapsulate the methods, make it more simple and intuitive.
We can also study its source code:
public class ServletActionContext extends ActionContext implements StrutsStatics {
//HTTP servlet request
public static void setRequest(HttpServletRequest request) {
ActionContext.getContext().put(HTTP_REQUEST, request);
}
public static HttpServletRequest getRequest() {
return (HttpServletRequest) ActionContext.getContext().get(HTTP_REQUEST);
}
//HTTP servlet response
public static void setResponse(HttpServletResponse response) {
ActionContext.getContext().put(HTTP_RESPONSE, response);
}
public static HttpServletResponse getResponse() {
return (HttpServletResponse) ActionContext.getContext().get(HTTP_RESPONSE);
}
//servlet context.
public static ServletContext getServletContext() {
return (ServletContext) ActionContext.getContext().get(SERVLET_CONTEXT);
}
public static void setServletContext(ServletContext servletContext) {
ActionContext.getContext().put(SERVLET_CONTEXT, servletContext);
}
From above we can know the ServletActionContext extends ActionContext.

Servlet path info includes empty string

I have the following servlet:
#WebServlet("/publication/topic/*")
public class ViewTopicPublicationsServlet extends HttpServlet {
protected void doGet(HttpServletRequest request, HttpServletResponse response) {
String[] pathInfo = request.getPathInfo().split("/");
System.out.println(Arrays.toString(pathInfo));
...
}
}
And for example if I have such url:
http://localhost:8080/bulletinboard/publication/topic/SALE
I want to omit empty string. So pathInfo resulted in [SALE] instead of [,SALE]
How this may be achieved ?

You can omit the first character since it's always a slash:
request.getPathInfo().substring(1).split("/")

Static or nonstatic action in mvc?

i want to ask you about mvc. How it works. So, this is simple example(I don't use any frameworks)
in Controller(Servlet):
protected void doGet(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException {
processRequest(request, response);
}
protected void doPost(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException {
processRequest(request, response);
}
private void processRequest(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException {
String page = null;
AbstractCommand action;
action = ActionFactory.getAction(request);// get command from factory
page = action.execute(request, response);
RequestDispatcher dispatcher = getServletContext()
.getRequestDispatcher(page);
dispatcher.forward(request, response);
}
for action we create a common interface(Strategy pattern):
public interface AbstractAction {
public String execute(HttpServletRequest request, HttpServletResponse response);
}
Simple Action(Example):
public class HelloAction implements AbstractAction {
#Override
public String execute(HttpServletRequest request,
HttpServletResponse response) {
//....(some actions to modify request)
String page = "/main.jsp";
return page;
}
}
And now, our factory:
public class ActionFactory {
private enum Actions{
HELLO;
}
public static AbstractAction getAction(HttpServletRequest request){
String action = request.getParameter("action");//take parameter from jsp
Actions actionEnum = Actions.valueOf(action.toUpperCase());
switch (actionEnum) {
case HELLO:
return new HelloAction();
}
}
}
We came to the place where I am in confused. Servlet is initialized only once, and only one for all requests. Just forwards requests to the actions where we modify request or response. But, we create NEW instance of the class for every request. Here can occur memory overflow!? Or not?
Can we make these actions static(static method, one for all request)? If two requests come at the same time what will happen to them?
What do you think about this, please share your experience.
P.S. sorry for bad english.

How about Singleton pattern to get the instance of the Action class ?
Just add some abstact getInstance() method in AbstractAction.
Make every implementation provide its own instance.
In every implementation class, use Singleton pattern so that only one instance exists.
Make sure no action class stores any data related to a specific request.

As i understood the jsp, the whole thing is stateless, if u access the servlet by http request, the servlet will be created in a new instance.
After leaving the servlet by .forward(), it will be released by garbage collection.
2,3,...,n requests = 2,3,...,n servlets.
by forwarding to a jsp, the only way to access the servlet from jsp is a new http request = new servlet. ( will move to the doPost method)

Setting ISO-8859-1 encoding for a single Tapestry 4 page in application that is otherwise totally UTF-8

I have a Tapestry application that is serving its page as UTF-8. That is, server responses have header:
Content-type: text/html;charset=UTF-8
Now within this application there is a single page that should be served with ISO-8859-1 encoding. That is, server response should have this header:
Content-type: text/html;charset=ISO-8859-1
How to do this? I don't want to change default encoding for whole application.
Based on google searching I have tried following:
#Meta({ "org.apache.tapestry.output-encoding=ISO-8859-1",
"org.apache.tapestry.response-encoding=ISO-8859-1",
"org.apache.tapestry.template-encoding=ISO-8859-1",
"tapestry.response-encoding=ISO-8859-1"})
abstract class MyPage extends BasePage {
#Override
protected String getOutputEncoding() {
return "ISO-8859-1";
}
}
But neither setting those values with #Meta annotation or overriding getOutputEncoding method works.
I am using Tapestry 4.0.2.
EDIT: I ended up doing this with a Servlet filter with subclassed HttpServletResposeWrapper. The wrapper overrides setContentType() to force required encoding for the response.

Have you considered a Filter? Maybe not as elegant as something within Tapestry, but using a plain Filter, that registers the url mapping(s) of interest. One of its init parameters would be the encoding your after. Example:
public class EncodingFilter implements Filter {
private String encoding;
private FilterConfig filterConfig;
/**
* #see javax.servlet.Filter#init(javax.servlet.FilterConfig)
*/
public void init(FilterConfig fc) throws ServletException {
this.filterConfig = fc;
this.encoding = filterConfig.getInitParameter("encoding");
}
/**
* #see javax.servlet.Filter#doFilter(javax.servlet.ServletRequest, javax.servlet.ServletResponse, javax.servlet.FilterChain)
*/
public void doFilter(ServletRequest req, ServletResponse resp,
FilterChain chain) throws IOException, ServletException {
req.setCharacterEncoding(encoding);
chain.doFilter(req, resp);
}
/**
* #see javax.servlet.Filter#destroy()
*/
public void destroy() {
}
}

You could have done:
#Override
public ContentType getResponseContentType() {
return new ContentType("text/html;charset=" + someCharEncoding);
}

The filter suggestion is good. You can also mix servlets with Tapestry. For instance, we have servlets for serving displaying XML documents and dynamically generated Excel files. Just make sure that correctly set the mappings in web.xml so that that the servlets do not go through Tapestry.

Tapestry has the concept of filters that can be applied to the request/response pipeline, but with the advantage that you can access the T5 IoC Container & Services.
http://tapestry.apache.org/tapestry5/tapestry-core/guide/request.html