How Can I Enable Concurrency for Multiple Browser Requests in a Servlet?

How can I enable concurrency for multiple browser requests in a Servlet?

import javax.servlet.*; 
import javax.servlet.http.*; 
import java.io.*; 

public class MyServlet extends HttpServlet { 
    @Override 
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 
        PrintWriter out = response.getWriter(); 
        // Simulating a long-running process 
        try { 
            Thread.sleep(5000); 
        } catch (InterruptedException e) { 
            e.printStackTrace(); 
        } 
        out.println("Response to: " + request.getParameter("name")); 
    } 
}

Servlets are inherently designed to handle multiple requests concurrently, but the handling mechanism depends on proper configuration and coding practices. Therefore, to ensure your Servlet can manage concurrent browser requests effectively, certain steps and coding practices are crucial.

<async-supported>true</async-supported>
public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { 
    AsyncContext asyncContext = request.startAsync(); 
    asyncContext.setTimeout(0); // No timeout 
    asyncContext.start(() -> { 
        try { 
            // Simulate long running process 
            Thread.sleep(5000); 
            PrintWriter out = asyncContext.getResponse().getWriter(); 
            out.println("Task completed!"); 
        } catch (InterruptedException | IOException e) { 
            e.printStackTrace(); 
        } finally { 
            asyncContext.complete(); 
        } 
    }); 
}

Causes

• Servlet synchronization issues can arise if methods within the Servlet are defined as synchronized, which prevents concurrent access.
• Long-running processes or blocking I/O operations in the Servlet can cause the threads to wait for completion before serving additional requests.
• Using shared resources improperly can lead to thread contention, thereby impacting performance.

Solutions

• Avoid marking the Servlet's service methods (like doGet or doPost) as synchronized. Instead, let the Servlet container manage thread safety.
• Use asynchronous processing capabilities introduced in Servlet 3.0 for long-running tasks. Implement the use of AsyncContext to handle requests asynchronously.
• Implement resource locks (like ReentrantLock) judiciously if you must use shared resources, ensuring minimal contention.

Mistake: Using synchronized methods in a Servlet.

Solution: Avoid using synchronized methods as it limits concurrency and hinders performance.

Mistake: Not configuring the web.xml for asynchronous support.

Solution: Ensure to set <async-supported>true</async-supported> in your web.xml to allow async processing.

Mistake: Neglecting to manage resources properly, leading to resource leaks.

Solution: Use try-with-resources statements to manage resource closure automatically.