Java虚拟线程深度解析：Project Loom带来的并发编程革命 | Java技术前沿

1. 虚拟线程的核心概念

随着Java 19的发布，Project Loom引入了虚拟线程（Virtual Threads）这一革命性特性。虚拟线程是轻量级线程，由JVM管理而非操作系统，可以显著提升高并发应用的性能。

1.1 平台线程 vs 虚拟线程

传统平台线程与操作系统线程1:1对应，创建和上下文切换成本高。虚拟线程则是与平台线程多对一关系，在阻塞操作时自动挂起，释放底层线程资源。

// 传统平台线程创建
Thread platformThread = new Thread(() -> {
    System.out.println("平台线程执行中");
});
platformThread.start();

// 虚拟线程创建（Java 19+）
Thread virtualThread = Thread.ofVirtual()
    .name("virtual-thread-", 0)
    .start(() -> {
        System.out.println("虚拟线程执行中");
    });

2. 构建基于虚拟线程的Web服务器

我们将从零开始构建一个基于虚拟线程的高性能HTTP服务器，展示虚拟线程在实际项目中的应用。

2.1 基础HTTP服务器实现

import com.sun.net.httpserver.HttpServer;
import com.sun.net.httpserver.HttpHandler;
import com.sun.net.httpserver.HttpExchange;
import java.io.IOException;
import java.io.OutputStream;
import java.net.InetSocketAddress;
import java.util.concurrent.Executors;

public class VirtualThreadHttpServer {
    private final HttpServer server;
    private final int port;
    
    public VirtualThreadHttpServer(int port) throws IOException {
        this.port = port;
        this.server = HttpServer.create(new InetSocketAddress(port), 0);
    }
    
    public void start() {
        // 使用虚拟线程执行器
        var virtualThreadExecutor = Executors.newThreadPerTaskExecutor(
            Thread.ofVirtual().factory()
        );
        
        server.setExecutor(virtualThreadExecutor);
        
        // 注册路由处理器
        server.createContext("/api/hello", new HelloHandler());
        server.createContext("/api/users", new UserHandler());
        server.createContext("/api/products", new ProductHandler());
        
        server.start();
        System.out.println("虚拟线程HTTP服务器启动在端口: " + port);
    }
    
    static class HelloHandler implements HttpHandler {
        @Override
        public void handle(HttpExchange exchange) throws IOException {
            try {
                // 模拟业务处理延迟
                Thread.sleep(100);
                
                String response = "{"message": "Hello from virtual thread!", " +
                                 ""thread": "" + Thread.currentThread() + ""}";
                exchange.getResponseHeaders().set("Content-Type", "application/json");
                exchange.sendResponseHeaders(200, response.getBytes().length);
                
                try (OutputStream os = exchange.getResponseBody()) {
                    os.write(response.getBytes());
                }
            } catch (InterruptedException e) {
                Thread.currentThread().interrupt();
            }
        }
    }

3. 数据库连接池与虚拟线程集成

在高并发场景下，数据库连接管理是关键。我们将实现一个虚拟线程友好的连接池。

3.1 虚拟线程感知的连接池

import java.sql.*;
import java.util.concurrent.*;
import java.util.concurrent.atomic.AtomicInteger;

public class VirtualThreadConnectionPool {
    private final BlockingQueue connectionPool;
    private final AtomicInteger activeConnections = new AtomicInteger(0);
    private final int maxPoolSize;
    private final String url;
    private final String username;
    private final String password;
    
    public VirtualThreadConnectionPool(String url, String username, 
                                     String password, int maxPoolSize) {
        this.url = url;
        this.username = username;
        this.password = password;
        this.maxPoolSize = maxPoolSize;
        this.connectionPool = new LinkedBlockingQueue(maxPoolSize);
        initializePool();
    }
    
    private void initializePool() {
        for (int i = 0; i < Math.min(5, maxPoolSize); i++) {
            connectionPool.add(createNewConnection());
        }
    }
    
    public Connection getConnection() throws InterruptedException {
        Connection conn = connectionPool.poll();
        if (conn != null) {
            return new PooledConnection(conn);
        }
        
        if (activeConnections.get() < maxPoolSize) {
            return new PooledConnection(createNewConnection());
        }
        
        // 在虚拟线程中等待不会阻塞平台线程
        return new PooledConnection(connectionPool.take());
    }
    
    private Connection createNewConnection() {
        try {
            activeConnections.incrementAndGet();
            return DriverManager.getConnection(url, username, password);
        } catch (SQLException e) {
            activeConnections.decrementAndGet();
            throw new RuntimeException("创建数据库连接失败", e);
        }
    }
    
    private class PooledConnection implements Connection {
        private final Connection delegate;
        private volatile boolean closed = false;
        
        PooledConnection(Connection delegate) {
            this.delegate = delegate;
        }
        
        @Override
        public void close() throws SQLException {
            if (!closed && connectionPool.offer(delegate)) {
                closed = true;
            } else {
                activeConnections.decrementAndGet();
                delegate.close();
            }
        }
        
        // 委托其他Connection方法到delegate
        @Override
        public Statement createStatement() throws SQLException {
            return delegate.createStatement();
        }
        
        // 其他Connection接口方法的实现...
    }
}

4. 高性能数据处理流水线

利用虚拟线程构建数据处理流水线，实现高吞吐量的数据转换和处理。

4.1 异步数据处理框架

import java.util.concurrent.*;
import java.util.function.*;

public class VirtualThreadPipeline {
    private final ExecutorService virtualThreadExecutor;
    
    public VirtualThreadPipeline() {
        this.virtualThreadExecutor = Executors.newThreadPerTaskExecutor(
            Thread.ofVirtual().factory()
        );
    }
    
    public  CompletableFuture processAsync(T input, 
                                               Function processor) {
        return CompletableFuture.supplyAsync(() -> processor.apply(input), 
                                           virtualThreadExecutor);
    }
    
    public  PipelineStage createStage(Function transformer) {
        return new PipelineStage(this, transformer);
    }
    
    public static class PipelineStage {
        private final VirtualThreadPipeline pipeline;
        private final Function transformer;
        
        PipelineStage(VirtualThreadPipeline pipeline, Function transformer) {
            this.pipeline = pipeline;
            this.transformer = transformer;
        }
        
        public  PipelineStage then(Function nextTransformer) {
            return new PipelineStage(pipeline, 
                input -> nextTransformer.apply(transformer.apply(input)));
        }
        
        public CompletableFuture executeAsync(T input) {
            return pipeline.processAsync(input, transformer);
        }
    }
    
    // 使用示例
    public static void main(String[] args) {
        VirtualThreadPipeline pipeline = new VirtualThreadPipeline();
        
        var processingStage = pipeline.createStage(String::toUpperCase)
            .then(str -> str + " - PROCESSED")
            .then(str -> str + " - " + System.currentTimeMillis());
        
        // 并发处理多个数据项
        var futures = java.util.stream.IntStream.range(0, 1000)
            .mapToObj(i -> "item-" + i)
            .map(processingStage::executeAsync)
            .toArray(CompletableFuture[]::new);
        
        CompletableFuture.allOf(futures).join();
        System.out.println("所有处理任务完成");
    }
}