I want to excute a servlet to get server name,server port and ContextPath from request.
But I don't want to invoke servlet by user interacting. I want excute this servlet by Java code.
I'm not sure it's possible.
Please give me recommendation.
Why not just simply make use of URL to request the servlet.
For more sophisticated use try HttpClient.
If you mean you just want to execute some code to extract information from the request, why are you trying to invoke a servlet? Just write a method somewhere, and call it.
You could also use a Servlet Filter to extract this info on every request, add the results to the HttpServletRequest object as an attribute, so that any other servlets that process the request can find it and use it.
If you mean you want to make the servlet load at startup, you can add this within the web.xml configuration:
<servlet>
...
<load-on-startup>1</load-on-startup>
</servlet>
If your servlet is doing something like calling a service every x minutes without a user interaction then you probably want to do something different.
You can use a ServletContextListener to listen to when the web context is started and to then start whatever code you want.
http://java.sun.com/javaee/5/docs/api/javax/servlet/ServletContextListener.html
Thanks for your answers
Actually, my problem is : I have an web application and a WebService (on diferent server).
I want web application invoke webservice (after specific duration) to send data (domain, port,context path..) to webservice so that I can know where my web application is deployed.
To solve this problem I have created a servlet to call WebService and by using this servlet I have HttpServletRequest object and I can get domain, port, context path.Then I can send data to webservice.
But I don't know how to execute this servlet(after specific duration) without user interaction
Related
Imagine the following situation:
A webapplication gets deployed to a tomcat server. A jersey servlet is started that serves requests at http://localhost/myServlet
Now, when somebody is requesting
http://localhost/myServlet/this/path/shall/be/handled, the myServlet should feel responsible for this request and handle it appropiately.
Edit: To be more specific: I do NOT know the path the user is requesting. Think about this like a virtual file system where the user requests myServlet/path/to/file. MyServlet shall be responsible for this GET request. As you can see mapping those URLs to Annotations is not possible. I'd like to annotate like myServlet/*, if that is more understandable.
Could anybody point me to the right direction? I feel a bit lost, but I am quite sure this is possible!
Jersey Servlet (com.sun.jersey.spi.spring.container.servlet.SpringServlet) is the end point for REST API (if we are using Jersey REST) Call. So, When ever the servlet get any request , The same request is been processed by its Handler.
When the application get a request with myServlet with the appropriate url-pattern then Its corresponding Handler will activate and process the request for the appropriate response.
To make a poll form using an applet, i wanted to know how can my applet communicate with a servlet . That servlet is meant to write the result to the text file on the server. I have no idea how can i do this.
You could use java.net.URLConnection for this.
Assuming that your servlet is mapped on an URL pattern of /myservlet and your applet is been served from the context root, then this should do:
InputStream servletResponse = new URL(getCodeBase(), "myservlet").openStream();
// ...
That's all. The getCodeBase() is inherited from Applet class and dynamically returns the applet's code base URL (from where the applet was been downloaded). The servletResponse will contain whatever you wrote to response.getOutputStream() or response.getWriter() in the servlet. For example just an "ok" string or an easily parseable format like XML or JSON. You could pass request parameters as a query string in the GET request URL, or in the POST request body.
See also:
Using java.net.URLConnection to fire and handle HTTP requests
https://stackoverflow.com/questions/9361399/how-to-send-list-of-objects-from-servlet-to-applet
The applet and the servlet is separate. There is no easy way you can use magic to make this easier.
A servlet is a snippet inside a web server which gets executed when a HTTP request is being made to the correct URL on the web server. Hence you need to make a HTTP request to the correct URL on the web server where your servlet is running.
This is done in the same way you do any other HTTP request from an applet, which is done in the same way that you do a HTTP request from a self-standing application.
Well you have several options for the applet/servlet communication....
http requests. (This may be the easiest). For this you can use Apache HTTP Components
Remote Method Invocation RMI. This may be more complicated than http requests but it depends on what you want to achieve.
Sockets. (I think http requests is flexible enough for your use case but just in case)
javascript. You can call a javascript function from your applet and let the javascript function submit the information to the servlet through ajax, websockets, etc.
Of course there are many other options but these are some ideas and remember that you may need to sign your applet.
If your question is about how to write to a file there are many tutorials. Here is a good one
I would like to call a servlet from another servlet doing two things:
setting the content type to "multipart/form-data"
setting the method to "POST".
This is very easy to do from a form, but I need to do it from another servlet. Any ideas how?
You can use java.net.HttpUrlConnection or maybe Apache HTTP client to send a POST/GET request to the other servlet. You will basically be invoking the other servlet the same way a browser would.
It sounds like request forwarding or include is what you're looking for. What you actually do will depend on what you intend to do with the output of the target servlet. Are you going to display it somehow? Or are you simply discarding it? You may in some cases, need to be a bit more "creative" in how you invoke those methods (e.g., either creating your own request/response instances, or wrapping the current request/response so that state changes are isolated).
Alternatively, to keep things simple you may want to just open a network connection to your target servlet's mapped URL as Jeff suggested.
It sounds like you want to send an HTTP POST with java. I would recommend using apache HttpClient. Check out this question Add parameters to Apache HttpPost
You can also do this with pure java with (HttpUrlConnection)[ http://download.oracle.com/javase/6/docs/api/java/net/HttpURLConnection.html].
I need to call a servlets POST method from another servlet and pass a blob in the servlets parameters. Is this posible, if so how can it be done. PS: I cant use Apache HttpClient
You need to create and send a HTTP request yourself. You cannot make use of forward/redirect/include because you want to change the method from GET to POST and you want to send a multipart/form-data request.
As HttpClient (and other 3rd party library?) is apparently not an option, your best bet is to use the standard Java SE API provided java.net.URLConnection. Long story short: Using java.net.URLConnection to fire and handle HTTP requests At the bottom you can find a multipart/form-data example.
Please note that this problem is not specific to servlets. In other words, you must be able to execute this code in a plain vanilla Java application with a main() method. This allows for easier testing and finetuning. Once you get it to work, just let the servlet execute the same piece of code.
Unrelated to the problem, I have the impression that there's a major design failure somewhere, certainly if the both servlets runs in the same webapplication context. The other servlet where you want to send the POST request to is apparently too tight coupled and should be refactored.
You can get a dispatcher to another servlet in your application and forward it or include it as #Ryan suggests. The code should be something like this inside your first servlet:
ServletContext context = this.getServletContext();
RequestDispatcher dispatcher = context.getRequestDispatcher("/otherurltoservlet");
// change your request and response accordingly
dispatcher.forward(request, response);
Do you mean call from your application to another web service? If so, then something like HttpClient is what you want. If you mean you want to programmatically invoke another servlet in your app, then you're looking to either forward to it or include it.
I'm developing a servlet that gets a name of a web service and could be forward the request to an external web service, for example: http://www.webservice.com/...
I have build a response wrapper that intercept response output but I can't forward request to an external web service, it works only if I redirect the request to a servlet that is on same server.
Example:
request.getRequestDispatcher("aMyServlet").forward(request, response) // WORKS
request.getRequestDispatcher("http://www.webservice.com/...").forward(request, response)
Doesn't because Tomcat searches http://www.webservice.com/... on the server as a local resource.
How can I do external request?
Thanks
forward method that you are using is used for communicating between server resources, (eg: servlet to servlet as you have found out) If you want to redirect to another location, you can use the HttpServletResponse's sendRedirect method.
Better option is to
Perform your own HTTP request and stream the results back to the
browser. This sounds harder than it is. Basically you create a
java.net.HttpURLConnection with the URL of the web site you want to
"redirect" to. This can actually contain the query parameters (as long as
they're not too large) since it will never be sent to the user's browser
either and will not appear in the browser URL bar. Open the connection, get
the content and write it to the Servlet's OutputStream.
To make any request to an outside service, you'll have to explicitly make a new HTTP request and handle its response. Take a look at the HttpUrlConnection class.
You don't mention what kind of service you want to invoke, but either way, your servlet is functioning as a service client, so you should be looking at service client technologies.
For invoking REST style services, java.net.URL or Apache Commons HttpClient can be used to send a request for a URL and fetch the reponse.
For invoking SOAP services, you can use Apache Axis, or Java WSIT.