ASYNCHRONOUS - Java EE Design Patterns - page 122

LISTING 9-3: (continued)

@Override
public void onStartAsync(AsyncEvent event) throws IOException {
// Code not shown for brevity
}
});

new Thread() {
@Override
public void run() {
asyncContext.complete();
}
}.start();

res.getWriter().write("Results:");
//Read data from database
data = "Queried data…";
//sleep thread for some time…
}
}

This servlet prints Results: and later prints retrieved data from the database, which is a simple string
in this scenario. You need to initialize a separate thread. AsyncListener's onComplete method is
executed only when the execution completes. Several other life cycle methods exist in the AsyncListener:

onStartAsync —executes when the asynchronous context starts

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onTimeOut —executes only if a timeout occurs

onError —executes only if an error is received

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The Servlet 3.1 specii cation provided an easier way to implement asynchronous servlets by
using managed thread pools and the executor service. The example in Listing 9‐4 uses a
ManagedThreadFactory to create a new thread.

LISTING 9‐4: An example that uses ManagedThreadFactory

package com.devchronicles.asynchronous;

import java.io.*;
import javax.servlet.*;
import javax.servlet.annotation.*;
import javax.servlet.http.*;

@WebServlet(urlPatterns="/async", asyncSupported=true)
public class AsyncServlet extends HttpServlet {

@Resource
private ManagedThreadFactory factory;

@Override