写一个httpclient处理高并发的工具类

好的，以下是一个简单的Java Http Client的高并发工具类，使用了线程池来实现：

import java.io.IOException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.config.RequestConfig;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.util.EntityUtils;

public class HttpClientUtil {

    private static final CloseableHttpClient HTTP_CLIENT = HttpClients.createDefault();

    private static final ExecutorService THREAD_POOL = Executors.newFixedThreadPool(100);

    private static final RequestConfig REQUEST_CONFIG = RequestConfig.custom()
        .setConnectTimeout(5000)
        .setConnectionRequestTimeout(1000)
        .setSocketTimeout(5000)
        .build();

    public static String executeHttpGet(String url) throws IOException {
        HttpGet httpget = new HttpGet(url);
        httpget.setConfig(REQUEST_CONFIG);
        HttpResponse response = HTTP_CLIENT.execute(httpget);
        HttpEntity entity = response.getEntity();
        return EntityUtils.toString(entity, "UTF-8");
    }

    public static void executeHttpGetAsync(String url, HttpCallback callback) {
        THREAD_POOL.execute(new Runnable() {
            @Override
            public void run() {
                try {
                    String result = executeHttpGet(url);
                    callback.onSuccess(result);
                } catch (IOException e) {
                    callback.onFailure(e);
                }
            }
        });
    }

    public static void shutdown() {
        try {
            HTTP_CLIENT.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
        THREAD_POOL.shutdown();
        try {
            if (!THREAD_POOL.awaitTermination(60, TimeUnit.SECONDS)) {
                THREAD_POOL.shutdownNow();
            }
        } catch (InterruptedException e) {
            THREAD_POOL.shutdownNow();
        }
    }

    public interface HttpCallback {
        void onSuccess(String result);

        void onFailure(Exception e);
    }
}

这个工具类中包含了一个同步的HTTP GET请求方法和一个异步的HTTP GET请求方法。异步方法使用了回调函数，在请求完成之后通过回调函数返回结果或异常。注意需要确保线程池和HttpClient被正确释放。