深入解析Apache HttpAsyncClient的非阻塞I/O机制

<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpasyncclient</artifactId>
    <version>4.1.4</version>
</dependency>
<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpcore-nio</artifactId>
    <version>4.4.10</version>
</dependency>

import org.apache.http.HttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.concurrent.FutureCallback;
import org.apache.http.impl.nio.client.CloseableHttpAsyncClient;
import org.apache.http.impl.nio.client.HttpAsyncClients;

import java.util.concurrent.CountDownLatch;

public class AsyncHttpClientTutorial {

    public static void main(String[] args) throws Exception {
        // 1. 创建并启动HttpAsyncClient
        // HttpAsyncClients.createDefault() 会创建一个默认配置的异步客户端
        CloseableHttpAsyncClient httpclient = HttpAsyncClients.createDefault();
        httpclient.start(); // 启动客户端，内部线程开始工作

        try {
            final HttpGet request = new HttpGet("http://www.apache.org/");
            final CountDownLatch latch = new CountDownLatch(1); // 用于等待所有请求完成

            System.out.println("主线程：发送异步请求到: " + request.getURI());

            // 2. 执行异步请求并设置回调函数
            httpclient.execute(request, new FutureCallback<HttpResponse>() {
                @Override
                public void completed(final HttpResponse response) {
                    // 请求成功完成时调用
                    System.out.println("回调线程：请求完成 -> " + request.getRequestLine() + " -> " + response.getStatusLine());
                    latch.countDown(); // 计数器减一，表示一个请求已完成
                }

                @Override
                public void failed(final Exception ex) {
                    // 请求失败时调用
                    System.err.println("回调线程：请求失败 -> " + request.getRequestLine() + " -> " + ex.getMessage());
                    ex.printStackTrace();
                    latch.countDown();
                }

                @Override
                public void cancelled() {
                    // 请求被取消时调用
                    System.out.println("回调线程：请求取消 -> " + request.getRequestLine() + " -> cancelled");
                    latch.countDown();
                }
            });

            System.out.println("主线程：请求已提交，继续执行其他任务...");
            // 主线程可以继续做其他事情，无需等待HTTP响应

            // 为了演示，这里阻塞主线程直到所有异步请求完成
            latch.await();

        } finally {
            // 3. 关闭客户端
            // 在所有请求处理完毕后，关闭客户端以释放资源
            httpclient.close();
            System.out.println("主线程：HttpAsyncClient已关闭。");
        }
    }
}