java并发编程学习书中遇到不解1

/**

• @author weip 书中讲到计数器count是线程安全(毋庸置疑,AtomicLong是命令级的线程安全),

•     而计数器的状态就是servlet的状态,这是为何？
  

  *
  */
  @ThreadSafe
  public class CountingFactorizer extends GenericServlet implements Servlet {
  private final AtomicLong count = new AtomicLong(0);

  public long getCount() {
  return count.get();
  }

  public void service(ServletRequest req, ServletResponse resp) {
  BigInteger i = extractFromRequest(req);
  BigInteger[] factors = factor(i);
  count.incrementAndGet();
  encodeIntoResponse(resp, factors);
  }

  void encodeIntoResponse(ServletResponse res, BigInteger[] factors) {
  }

  BigInteger extractFromRequest(ServletRequest req) {
  return null;
  }

  BigInteger[] factor(BigInteger i) {
  return null;
  }
  }

http://blog.csdn.net/column/details/concurrency.html