What are the best practices for handling concurrency and synchronization in Java web services?

1 Use thread pools

One of the best practices for handling concurrency in Java web services is to use thread pools, which are collections of pre-created threads that can execute tasks in parallel. Thread pools reduce the overhead of creating and destroying threads, and allow the web service to handle multiple requests efficiently. The Java platform provides several classes and interfaces for creating and managing thread pools, such as Executor, ExecutorService, ThreadPoolExecutor, and ScheduledExecutorService. You can also use the @Async annotation in Spring or the @Asynchronous annotation in Jakarta EE to mark methods that should run in a separate thread pool.

2 Use synchronization mechanisms

Another best practice for handling concurrency and synchronization in Java web services is to use synchronization mechanisms, which are techniques that prevent multiple threads from accessing or modifying shared data at the same time. Synchronization mechanisms ensure the thread safety and consistency of the web service state, and prevent errors such as data corruption, lost updates, or stale reads. The Java platform provides several synchronization mechanisms, such as synchronized blocks, synchronized methods, volatile variables, atomic variables, locks, and concurrent collections. You can also use the @Lock annotation in Jakarta EE to specify the locking strategy for a web service class or method.

3 Use concurrent utilities

A third best practice for handling concurrency and synchronization in Java web services is to use concurrent utilities, which are classes and interfaces that provide high-level abstractions and functionality for concurrent programming. Concurrent utilities simplify the development and testing of complex concurrent tasks, such as coordination, communication, caching, scheduling, or result aggregation. The Java platform provides several concurrent utilities, such as CompletableFuture, CountDownLatch, CyclicBarrier, Semaphore, Exchanger, Future, Callable, and ForkJoinPool. You can also use the @Cacheable annotation in Spring or the @CacheResult annotation in Jakarta EE to cache the results of web service methods.

4 Use reactive programming

A fourth best practice for handling concurrency and synchronization in Java web services is to use reactive programming, which is a paradigm that deals with asynchronous and event-driven data streams. Reactive programming enables the web service to handle non-blocking and back-pressured requests, and to compose and transform data streams declaratively. Reactive programming also improves the scalability and responsiveness of the web service, as it reduces the number of threads and resources needed. The Java platform provides several libraries and frameworks for reactive programming, such as Reactor, RxJava, Vert.x, Akka, and Spring WebFlux.

5 Use testing tools

A fifth best practice for handling concurrency and synchronization in Java web services is to use testing tools, which are tools that help you verify the correctness and performance of your concurrent code. Testing tools can help you detect and fix concurrency bugs, such as deadlocks, race conditions, memory leaks, or performance bottlenecks. The Java platform provides several testing tools, such as JUnit, TestNG, Mockito, JMeter, Gatling, and ThreadSafe. You can also use the @Test annotation in Spring or the @ConcurrentTest annotation in Jakarta EE to mark methods that should run concurrently during testing.

6 Use best practices guidelines

A sixth and final best practice for handling concurrency and synchronization in Java web services is to use best practices guidelines. These general principles and recommendations can help you write better concurrent code, avoid common pitfalls and mistakes, and follow the standards and conventions of the Java platform and frameworks. For instance, you should use immutable objects and stateless web services whenever possible, as they are inherently thread-safe and easy to reason about. Additionally, you should use the least restrictive synchronization mechanism that suits your needs, as excessive synchronization can reduce performance and cause deadlocks. Moreover, you should use the appropriate concurrent utility for your use case, as it can simplify your code and improve its readability and maintainability. Reactive programming is also recommended when dealing with asynchronous and event-driven data streams, as it can enhance the scalability and responsiveness of your web service. Furthermore, you should use testing tools to verify the correctness and performance of your concurrent code, as concurrency bugs can be hard to detect and fix. Ultimately, best practices guidelines can help you write better concurrent code.

7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?