In a typical Java servlet container, how is concurrency for multiple client requests to the same servlet class usually handled?

Introduction / Context:
Java servlets are server side components that handle HTTP requests in web applications. Because web servers must handle many requests from different clients at the same time, concurrency management is critical. Servlet containers follow a specific model for instantiating servlets and dispatching requests across threads. Understanding this model helps developers write thread safe servlets and avoid race conditions.

Given Data / Assumptions:

• We are using a standard servlet container such as Tomcat or Jetty.
• Servlets implement methods such as service, doGet, and doPost.
• The container may reuse servlet instances and threads for performance.
• The question is about typical behaviour, not custom container implementations.

Concept / Approach:
The standard servlet model specifies that the container normally creates a single instance of each servlet class and maintains a pool of threads. For each incoming request, the container selects a thread and invokes the servlet service method, which then calls doGet or doPost as appropriate, all on the same servlet instance. This means that multiple threads can be executing inside the same servlet object concurrently, one per request. Because of this, servlet instance variables must be treated carefully to avoid thread safety problems.

Step-by-Step Solution:
Step 1: Recall that when a servlet is first requested, the container typically loads the class and creates one instance of that servlet.Step 2: The container maintains a thread pool to handle concurrent incoming HTTP requests.Step 3: For each new request to the servlet, the container assigns a thread that calls the service method on the existing servlet instance.Step 4: The service method dispatches to doGet, doPost, or other methods based on the request type.Step 5: As a result, many threads may be executing inside the same servlet instance at the same time, providing concurrency.

Verification / Alternative check:
This behaviour can be confirmed by reading the servlet specification or by adding logging statements that print the current thread name and the hash code of the servlet instance. Developers observe that the thread names differ for different requests but the servlet instance hash code remains the same, indicating that threads are sharing one instance. Application servers also document this model in their threading and performance guidelines, advising against storing per request data in instance fields.

Why Other Options Are Wrong:
Option B is incorrect because containers do not create a new Java Virtual Machine for each request; that would be extremely inefficient. Option C is wrong because modern web servers are designed to serve many clients concurrently and therefore use multiple threads. Option D is not the standard model; while multiple instances can be created in rare cases for load balancing, the usual design is one instance with many threads, not one instance per request.

Common Pitfalls:
A major pitfall is assuming that each request has its own servlet instance, leading developers to store shared mutable state in instance variables without synchronization. This can cause race conditions and data corruption. Another pitfall is creating application level threads manually inside servlets, which can conflict with the container thread pool. It is better to rely on the container managed threading model and design servlets to be stateless or to restrict mutable state to local variables or properly synchronized structures.

Final Answer:
In the standard servlet model, the container creates a new thread for each incoming request and calls service or doGet or doPost on the same servlet instance concurrently, which is option A.