dcsimg

How do I pass a variable into a thread that can be accessed from the run() method?

Created May 4, 2012

Alex Chaffee

Create a subclass of Thread with a custom instance variable and initialize it in the constructor. (This is basic object-oriented programming design, BTW.)

For instance, to pass in a PrintWriter from the doGet method of a Servlet: 


public MyThread extends Thread {
 private PrintWriter myWriter;
 public MyThread(PrintWriter writer)
 {
    myWriter = writer;
 }
 public void run() 
 {
   ...
   myWriter.print(...);
   ...
 }
}

public void doGet(...)
{
 ...
 MyThread mt = new MyThread(response.getWriter());
 mt.start();
 mt.join();
 ...
}
This is a very dangerous technique, however, since the doGet() method may return before the thread finishes. So watch out. That's why you need the join() call -- it waits until the thread is finished.