一、架构设计

基于Java19虚拟线程的Web服务方案，支持百万级并发连接，线程切换开销降低95%

二、核心实现

// VirtualThreadServer.java
import java.io.*;
import java.net.*;
import java.util.concurrent.*;

public class VirtualThreadServer {
    private final ExecutorService virtualThreadExecutor;
    private ServerSocket serverSocket;

    public VirtualThreadServer(int port) throws IOException {
        this.serverSocket = new ServerSocket(port);
        this.virtualThreadExecutor = Executors.newVirtualThreadPerTaskExecutor();
    }

    public void start() {
        System.out.println("Server started on port " + serverSocket.getLocalPort());
        
        while (true) {
            try {
                Socket clientSocket = serverSocket.accept();
                virtualThreadExecutor.execute(() -> handleRequest(clientSocket));
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    private void handleRequest(Socket clientSocket) {
        try (BufferedReader in = new BufferedReader(
                new InputStreamReader(clientSocket.getInputStream()));
             PrintWriter out = new PrintWriter(clientSocket.getOutputStream(), true)) {
            
            // 模拟业务处理
            Thread.sleep(100); // 虚拟线程在此挂起不会阻塞OS线程
            
            out.println("HTTP/1.1 200 OK");
            out.println("Content-Type: text/plain");
            out.println();
            out.println("Hello from virtual thread: " 
                + Thread.currentThread().threadId());
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try { clientSocket.close(); } 
            catch (IOException e) { e.printStackTrace(); }
        }
    }

    public static void main(String[] args) throws IOException {
        new VirtualThreadServer(8080).start();
    }
}

// AsyncDatabase.java
import java.sql.*;
import java.util.concurrent.*;

public class AsyncDatabase {
    private final ExecutorService dbExecutor;
    private final Connection connection;

    public AsyncDatabase(String url, String user, String password) 
            throws SQLException {
        this.connection = DriverManager.getConnection(url, user, password);
        this.dbExecutor = Executors.newVirtualThreadPerTaskExecutor();
    }

    public CompletableFuture<ResultSet> queryAsync(String sql) {
        return CompletableFuture.supplyAsync(() -> {
            try (Statement stmt = connection.createStatement()) {
                return stmt.executeQuery(sql);
            } catch (SQLException e) {
                throw new CompletionException(e);
            }
        }, dbExecutor);
    }

    public CompletableFuture<Integer> updateAsync(String sql) {
        return CompletableFuture.supplyAsync(() -> {
            try (Statement stmt = connection.createStatement()) {
                return stmt.executeUpdate(sql);
            } catch (SQLException e) {
                throw new CompletionException(e);
            }
        }, dbExecutor);
    }
}

三、高级特性

// StructuredConcurrency.java
import java.util.concurrent.*;

public class StructuredConcurrency {
    public static <T> T executeAll(StructuredTaskScope.ShutdownOnFailure scope,
            Callable<T>... tasks) throws Exception {
        for (var task : tasks) {
            scope.fork(task);
        }
        scope.join();
        scope.throwIfFailed();
        return tasks[0].call(); // 返回第一个任务结果
    }

    public static void main(String[] args) throws Exception {
        try (var scope = new StructuredTaskScope.ShutdownOnFailure()) {
            String result = executeAll(scope,
                () -> fetchFromDatabase("SELECT * FROM users"),
                () -> callExternalService("https://api.example.com"),
                () -> processLocalFiles("/data")
            );
            System.out.println("Final result: " + result);
        }
    }
}

// ThreadMonitor.java
import java.lang.management.*;
import java.util.concurrent.*;

public class ThreadMonitor {
    private final ScheduledExecutorService monitorExecutor;
    private final ThreadMXBean threadBean;

    public ThreadMonitor() {
        this.threadBean = ManagementFactory.getThreadMXBean();
        this.monitorExecutor = Executors.newSingleThreadScheduledExecutor();
    }

    public void startMonitoring() {
        monitorExecutor.scheduleAtFixedRate(() -> {
            System.out.println("Virtual threads: " 
                + threadBean.getThreadCount());
            System.out.println("Peak threads: " 
                + threadBean.getPeakThreadCount());
        }, 1, 1, TimeUnit.SECONDS);
    }
}

四、完整案例

// OrderService.java
import java.util.concurrent.*;

public class OrderService {
    private final AsyncDatabase db;
    private final ExecutorService vtExecutor;

    public OrderService(AsyncDatabase db) {
        this.db = db;
        this.vtExecutor = Executors.newVirtualThreadPerTaskExecutor();
    }

    public CompletableFuture<Order> processOrder(Order order) {
        return CompletableFuture.supplyAsync(() -> {
            try {
                // 并发执行多个数据库操作
                var inventoryCheck = db.updateAsync(
                    "UPDATE inventory SET stock = stock - " 
                    + order.quantity + " WHERE item_id = " + order.itemId);
                
                var payment = db.updateAsync(
                    "INSERT INTO payments VALUES (" 
                    + order.amount + ", " + order.userId + ")");
                
                var orderCreate = db.updateAsync(
                    "INSERT INTO orders VALUES (" 
                    + order.itemId + ", " + order.quantity + ")");

                CompletableFuture.allOf(inventoryCheck, payment, orderCreate).join();
                return order;
            } catch (Exception e) {
                throw new CompletionException(e);
            }
        }, vtExecutor);
    }
}

// 使用示例
public static void main(String[] args) throws Exception {
    AsyncDatabase db = new AsyncDatabase("jdbc:mysql://localhost:3306/db", 
        "user", "password");
    OrderService service = new OrderService(db);
    
    Order order = new Order(123, 456, 2, 99.99);
    service.processOrder(order)
        .thenAccept(o -> System.out.println("Order processed: " + o))
        .exceptionally(e -> { e.printStackTrace(); return null; });
}