Java EE多线程实战：从线程池到异步编排

Java EE初阶启程记09：多线程案例（2）

线程池优化任务调度

线程池是多线程编程中的核心组件，能够有效管理线程生命周期和资源分配。通过ExecutorService接口及其实现类（如ThreadPoolExecutor），可以避免频繁创建销毁线程的开销。以下是一个固定大小线程池的典型用法：

ExecutorService executor = Executors.newFixedThreadPool(4);
for (int i = 0; i < 10; i++) {
    executor.submit(() -> {
        System.out.println("Task executed by " + Thread.currentThread().getName());
    });
}
executor.shutdown();

关键参数包括核心线程数、最大线程数、空闲存活时间和工作队列类型。SynchronousQueue适合短任务，LinkedBlockingQueue适合长任务。

生产者-消费者模式实战

使用BlockingQueue实现线程安全的生产者-消费者模型，无需显式同步：

BlockingQueue<Integer> queue = new ArrayBlockingQueue<>(10);

// 生产者
new Thread(() -> {
    try {
        queue.put(1); // 阻塞直到空间可用
    } catch (InterruptedException e) {
        Thread.currentThread().interrupt();
    }
}).start();

// 消费者
new Thread(() -> {
    try {
        Integer item = queue.take(); // 阻塞直到元素可用
    } catch (InterruptedException e) {
        Thread.currentThread().interrupt();
    }
}).start();

CompletableFuture异步编排

Java 8引入的CompletableFuture支持链式异步操作：

CompletableFuture.supplyAsync(() -> fetchDataFromDB())
    .thenApply(data -> processData(data))
    .thenAccept(result -> saveResult(result))
    .exceptionally(ex -> {
        System.err.println("Error: " + ex.getMessage());
        return null;
    });

该方法支持任务组合（thenCombine）、并行执行（allOf）和回调处理，显著简化异步编程复杂度。

线程安全集合应用

针对高并发场景，优先选择并发集合类：

• ConcurrentHashMap替代HashMap
• CopyOnWriteArrayList替代ArrayList
• ConcurrentLinkedQueue实现无锁队列

示例代码展示ConcurrentHashMap的原子操作：

ConcurrentHashMap<String, Integer> map = new ConcurrentHashMap<>();
map.computeIfAbsent("key", k -> calculateValue(k));

性能监控与调优

通过工具定位多线程问题：

1. 使用jstack获取线程转储分析死锁
2. JVisualVM监控线程状态和CPU占用
3. 日志中添加Thread.currentThread().getName()追踪执行流

典型优化策略包括调整线程池大小、减少锁粒度、使用读写锁（ReentrantReadWriteLock）替代独占锁。

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