Java ConnectionPoolTimeOutException在使用AWS SDK进行S3下载时

我通过完成服务（大小为20的固定线程池）获取S3对象

下面是通过completionService.submit（）触发的代码

但是，问题仍然存在，我仍然得到一个

ConnectionPoolTimeoutException

Caused by: org.apache.http.conn.ConnectionPoolTimeoutException: Timeout waiting for connection from pool
    at org.apache.http.impl.conn.PoolingHttpClientConnectionManager.leaseConnection(PoolingHttpClientConnectionManager.java:314)
    at org.apache.http.impl.conn.PoolingHttpClientConnectionManager$1.get(PoolingHttpClientConnectionManager.java:280)
    at sun.reflect.GeneratedMethodAccessor17.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at com.amazonaws.http.conn.ClientConnectionRequestFactory$Handler.invoke(ClientConnectionRequestFactory.java:70)
    at com.amazonaws.http.conn.$Proxy10.get(Unknown Source)
    at org.apache.http.impl.execchain.MainClientExec.execute(MainClientExec.java:190)
    at org.apache.http.impl.execchain.ProtocolExec.execute(ProtocolExec.java:186)
    at org.apache.http.impl.client.InternalHttpClient.doExecute(InternalHttpClient.java:185)
    at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:83)
    at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:56)
    at com.amazonaws.http.apache.client.impl.SdkHttpClient.execute(SdkHttpClient.java:72)
    at com.amazonaws.http.AmazonHttpClient$RequestExecutor.executeOneRequest(AmazonHttpClient.java:1330)
    at com.amazonaws.http.AmazonHttpClient$RequestExecutor.executeHelper(AmazonHttpClient.java:1145)
    ... 22 more

private static final AmazonS3 s3Client = AmazonS3ClientBuilder.standard().withRegion(Regions.US_EAST_1)
        .withClientConfiguration(new ClientConfiguration().withMaxConnections(100).withSocketTimeout(1000*1000))
        .withForceGlobalBucketAccessEnabled(true).build();

Caused by: org.apache.http.conn.ConnectionPoolTimeoutException: Timeout waiting for connection from pool
    at org.apache.http.impl.conn.PoolingHttpClientConnectionManager.leaseConnection(PoolingHttpClientConnectionManager.java:314)
    at org.apache.http.impl.conn.PoolingHttpClientConnectionManager$1.get(PoolingHttpClientConnectionManager.java:280)
    at sun.reflect.GeneratedMethodAccessor17.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at com.amazonaws.http.conn.ClientConnectionRequestFactory$Handler.invoke(ClientConnectionRequestFactory.java:70)
    at com.amazonaws.http.conn.$Proxy10.get(Unknown Source)
    at org.apache.http.impl.execchain.MainClientExec.execute(MainClientExec.java:190)
    at org.apache.http.impl.execchain.ProtocolExec.execute(ProtocolExec.java:186)
    at org.apache.http.impl.client.InternalHttpClient.doExecute(InternalHttpClient.java:185)
    at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:83)
    at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:56)
    at com.amazonaws.http.apache.client.impl.SdkHttpClient.execute(SdkHttpClient.java:72)
    at com.amazonaws.http.AmazonHttpClient$RequestExecutor.executeOneRequest(AmazonHttpClient.java:1330)
    at com.amazonaws.http.AmazonHttpClient$RequestExecutor.executeHelper(AmazonHttpClient.java:1145)
    ... 22 more