一、虚拟线程核心概念

Java 19引入的虚拟线程(Virtual Thread)是轻量级线程，由JVM管理：

// 创建虚拟线程 (Java 19+)
Thread virtualThread = Thread.ofVirtual()
    .name("virtual-thread-", 0)
    .start(() -> {
        System.out.println("运行在虚拟线程: " 
            + Thread.currentThread());
    });

// 与传统平台线程对比
Thread platformThread = Thread.ofPlatform()
    .start(() -> {
        System.out.println("运行在平台线程: " 
            + Thread.currentThread());
    });

二、虚拟线程与异步编程对比

CompletableFuture.supplyAsync(() -> {
    // 模拟IO操作
    try { Thread.sleep(1000); } 
    catch (InterruptedException e) {}
    return "结果";
}).thenAccept(result -> {
    System.out.println("获取结果: " + result);
});

Thread.ofVirtual().start(() -> {
    // 同步代码但实际非阻塞
    String result = ioOperation();
    System.out.println("获取结果: " + result);
});

String ioOperation() {
    try { Thread.sleep(1000); }
    catch (InterruptedException e) {}
    return "结果";
}

三、百万级并发实战

虚拟线程轻松支持百万级并发连接：

try (var executor = Executors.newVirtualThreadPerTaskExecutor()) {
    IntStream.range(0, 1_000_000).forEach(i -> {
        executor.submit(() -> {
            String response = handleRequest(i);
            System.out.println(response);
            return null;
        });
    });
}

String handleRequest(int requestId) {
    try {
        // 模拟业务处理
        Thread.sleep(Duration.ofMillis(100));
        return "处理请求-" + requestId;
    } catch (InterruptedException e) {
        throw new RuntimeException(e);
    }
}

四、性能优化技巧

• 线程局部变量：谨慎使用ThreadLocal
• 同步控制：避免在虚拟线程中使用synchronized
• 线程池配置：使用newVirtualThreadPerTaskExecutor()
• 异常处理：虚拟线程异常不会影响其他线程

// 正确使用锁
private final ReentrantLock lock = new ReentrantLock();

void safeMethod() {
    lock.lock();  // 替代synchronized
    try {
        // 临界区代码
    } finally {
        lock.unlock();
    }
}

五、与传统线程性能对比

六、实际应用场景

void handleHttpRequest(Socket socket) {
    Thread.ofVirtual().start(() -> {
        try (var in = new BufferedReader(
                new InputStreamReader(socket.getInputStream()));
             var out = new PrintWriter(socket.getOutputStream())) {
            
            // 处理HTTP请求
            String request = in.readLine();
            String response = processRequest(request);
            
            out.println("HTTP/1.1 200 OK");
            out.println("Content-Length: " + response.length());
            out.println();
            out.println(response);
        } catch (IOException e) {
            e.printStackTrace();
        }
    });
}

Path dir = Path.of("data/");
try (var executor = Executors.newVirtualThreadPerTaskExecutor()) {
    Files.list(dir)
        .forEach(path -> executor.submit(() -> {
            processFile(path);
            return null;
        }));
}

void processFile(Path file) {
    try {
        String content = Files.readString(file);
        // 处理文件内容...
    } catch (IOException e) {
        throw new UncheckedIOException(e);
    }
}