Java Servlet Threads .

What about Servlets and Threads?

• The Servlet will executed new Threads for each request so no data should be saved related to the client (user) that making the request.

How to Make Your Servlets Thread-Safe?

• Use method variables for request-specific data.
• As far as possible, use the member variables of the servlet only for data that does not change.
• When you are using member variables or context attributes that can be changed by a request, you need to synchronize access to that data so that different threads aren’t changing the data simultaneously.
• If your servlet accesses outside resources, consider protecting access to that resource. You must include code that manages synchronized access to this resource.

How Not to Make Your Servlets Thread-Safe?

1. Use SingleThreadModel.
   

   public class MyServlet implements SingleThreadModel
   

   This does not guarantee that your servlet is thread-safe. Remember that static member variables are shared by all instances of a servlet; moreover, external resources, such as files, may be accessed concurrently by request threads.
2. Synchronize service(), doPost(), or doGet(). This attempt at making the servlet thread-safe is even worse than attempting to use SingleThreadModel. If you override service() and make it synchronized at the same time, you have limited your to handling only a single request at a time. As the number of requests increases, your clients are more and more likely to spend their time watching the little progress icon go around and around.