To
process a servlet request, Servlet container uses the server thread.
To make Application high available, you must ensures that the threads
handling the request are not sitting idle. Lets take a scenario,
client sending large amounts of data to the server, using Servlet
post request. Due to network delays or some other reasons, client may
not send the data as fast as server can read. In these situations the
thread used to process this request some times sits idle (waiting for
input from client).
There
is a solution with Asynchronous processing. For more information
about Asynchronous processing, follow the below link.
Asynchronous
processing using ReadListener
It
supports non blocking read mechanism for servlet and filters in
asynchronous mode.
| Method | Description |
| onAllDataRead() | This method notified when all the data from the specific request has been read. |
| onDataAvailable() | A ServletInputStream instance calls these methods on its listener when there is data available to read. |
| onError(Throwable t) | This method notified when an error occurs while processing the request. |
<!DOCTYPE html> <html> <head> <title>File Upload</title> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> </head> <body> <form method="POST" action="/servlet/FileUpload" enctype="multipart/form-data" > <table> <tr> File:<input type="file" name="file" id="file" /><br /> </tr> <tr> Destination:<input type="text" name="destination"/><br /> </tr> <tr> <input type="submit" value="Upload" name="upload" id="upload" /> </tr> </table> </form> </body> </html>
import javax.servlet.*; import javax.servlet.http.*; import java.io.*; import javax.servlet.annotation.*; @WebServlet(urlPatterns = {"/FileUpload"}, asyncSupported=true) public class FileUpload extends HttpServlet { @Override public void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException { final AsyncContext acontext = request.startAsync(); final ServletInputStream input = request.getInputStream(); input.setReadListener(new ReadListener() { byte buffer[] = new byte[10000]; StringBuilder sbuilder = new StringBuilder(); @Override public void onDataAvailable() { System.out.println("Data Available"); try { do { int length = input.read(buffer); sbuilder.append(new String(buffer, 0, length)); } while(input.isReady()); } catch (IOException ex) { } } @Override public void onAllDataRead() { System.out.println("All Data Read"); try { acontext.getResponse().getWriter() .write(sbuilder.toString()); } catch (IOException ex) { } acontext.complete(); } @Override public void onError(Throwable t) { } }); System.out.println("Container thread return back"); } }
Upload
a file with some data, and you can observe the messages like below in
server console. 'Container thread return back' message seen
immediately, since the request processed in Asynchronous mode.
Info: Container thread return back Info: Data Available Info: Data Available Info: Data Available Info: Data Available Info: Data Available Info: Data Available Info: All Data Read
No comments:
Post a Comment