从线程中读取数据（在Servlet中）

Question

I'm using the ServletContextListener to create a new thread.

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import java.util.concurrent.*;

    public class Port implements ServletContextListener {
        private ExecutorService executor;

        public void contextDestroyed(ServletContextEvent event) {
            executor.shutdown();

        }

        public void contextInitialized(ServletContextEvent event) { 
            // start task
            executor = Executors.newSingleThreadExecutor();
            executor.submit(new Task()); //task should implement Runnable!

        }
    }

Inside this thread I'm reading data from a serial port (SerialPortEventListener). The task.class should read out information from the serial port during the whole period in which the server is active. I've thrown this inside a thread because there can only be one instance that reads from the serial port; data should then be shared to all clients.

Now I would like to acces the data this thread is reading from the serial port.

Can this be done? And if yes then how?

Answer 1

You could, for example, store the read data in a servlet context attribute. Then, from the other classes, you would get the attribute from the servlet context:

public void contextInitialized(final ServletContextEvent event) { 
        // start task
        executor = Executors.newSingleThreadExecutor();
        executor.submit(new Runnable() {
            @Override
            public void run() {
                String data = readFromPort();
                event.getServletContext().setAttribute("serialPortData", data); 
            }
        });
    }
}

Answer 2

Yes it can be done, and you have few options:

1- Using a shared concurrent.BlockingQueue where inside the thread add new data from the SerialPort and in your servlet read from that queue

2- Have an event listener object inside your servlet and pass it in your task constructor. The listener object should have a callback function that is invoked when SerialEvent occur.

In general, this is a typical producer/consumer pattern

Answer 3

You'll need to share the data in the new Runnable you're going to create. You can add to it a concurrent collection .