Context in Logo

Here’s the translation of the Go code to Java, with explanations in Markdown format suitable for Hugo:

Our example demonstrates the usage of Context for controlling cancellation in an HTTP server. A Context carries deadlines, cancellation signals, and other request-scoped values across API boundaries and threads.

import java.io.IOException;
import java.io.PrintWriter;
import java.util.concurrent.TimeUnit;
import javax.servlet.AsyncContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

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

    @Override
    protected void doGet(HttpServletRequest request, HttpServletResponse response) 
            throws ServletException, IOException {
        
        final AsyncContext asyncContext = request.startAsync();
        asyncContext.setTimeout(15000); // 15 seconds timeout

        System.out.println("server: hello handler started");

        new Thread(() -> {
            try {
                TimeUnit.SECONDS.sleep(10);
                if (asyncContext.getRequest().isAsyncStarted()) {
                    PrintWriter out = asyncContext.getResponse().getWriter();
                    out.println("hello");
                    asyncContext.complete();
                }
            } catch (InterruptedException e) {
                System.out.println("server: " + e.getMessage());
            } catch (IOException e) {
                e.printStackTrace();
            } finally {
                System.out.println("server: hello handler ended");
            }
        }).start();

        asyncContext.addListener(new AsyncListener() {
            @Override
            public void onComplete(AsyncEvent event) throws IOException {
                // Handle completion
            }

            @Override
            public void onTimeout(AsyncEvent event) throws IOException {
                System.out.println("server: request timed out");
                asyncContext.getResponse().setStatus(HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
                asyncContext.complete();
            }

            @Override
            public void onError(AsyncEvent event) throws IOException {
                // Handle error
            }

            @Override
            public void onStartAsync(AsyncEvent event) throws IOException {
                // Handle the start of async processing
            }
        });
    }
}

In this Java servlet:

We use AsyncContext to handle long-running operations asynchronously, which is similar to the concept of context in the original example.
The servlet is annotated with @WebServlet and asyncSupported = true to enable asynchronous processing.
In the doGet method, we start asynchronous processing with request.startAsync().
We simulate work by sleeping for 10 seconds in a new thread.
If the async context is still active after 10 seconds, we write the response.
We add an AsyncListener to handle timeout scenarios, which is analogous to watching the ctx.Done() channel in the original example.
If a timeout occurs, we set an internal server error status, similar to the original example.

To run this servlet, you would need to deploy it to a servlet container like Tomcat or Jetty. The exact deployment process depends on your chosen server and build tools.

This Java implementation provides similar functionality to the original example, demonstrating how to handle long-running operations and cancellation in an HTTP server context.

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