与java.net类和实际浏览器相比，这与wire协议的工作方式有关。浏览器将比您使用的简单java.netapi复杂得多。
如果您想在java中获得等效的响应值，那么需要使用更丰富的httpapi。
此代码将给您与浏览器相同的响应；但是，您需要下载apachehttpjar组件
代码：

import java.io.BufferedReader;
import java.io.DataOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.URL;
import javax.net.ssl.HttpsURLConnection;

import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.client.methods.HttpUriRequest;
import org.apache.http.impl.client.HttpClients;

public class TestDriver
{

public static void main(String[] args)
{
    try
    {
        String url = "http://us.mc-api.net/v3/uuid/193nonaxishsl/csv";

        HttpGet httpGet = new HttpGet(url);
        getResponseFromHTTPReq(httpGet, url);
    }
    catch (Throwable e)
    {
        e.printStackTrace();
    }
}

private static String getResponseFromHTTPReq(HttpUriRequest httpReq, String url)
{
    HttpClient httpclient = HttpClients.createDefault();

    // Execute and get the response.
    HttpResponse response = null;
    HttpEntity entity = null;
    try
    {
        response = httpclient.execute(httpReq);
        entity = response.getEntity();
    }
    catch (IOException ioe)
    {
        throw new RuntimeException(ioe);
    }

    if (entity == null)
    {
        String errMsg = "No response entity back from " + url;
        throw new RuntimeException(errMsg);
    }

    String returnRes = null;
    InputStream is = null;
    BufferedReader buf = null;
    try
    {
        is = entity.getContent();
        buf = new BufferedReader(new InputStreamReader(is, "UTF-8"));

        System.out.println("Response Code : " + response.getStatusLine().getStatusCode());

        StringBuilder sb = new StringBuilder();
        String s = null;
        while (true)
        {
            s = buf.readLine();
            if (s == null || s.length() == 0)
            {
                break;
            }
            sb.append(s);
        }

        returnRes = sb.toString();

        System.out.println("Response: [" + returnRes + "]");
    }
    catch (UnsupportedOperationException | IOException e)
    {
        throw new RuntimeException(e);
    }
    finally
    {
        if (buf != null)
        {
            try
            {
                buf.close();
            }
            catch (IOException e)
            {
            }
        }
        if (is != null)
        {
            try
            {
                is.close();
            }
            catch (IOException e)
            {
            }
        }
    }
    return returnRes;
}

}

输出：
响应代码：404
响应：[错误，未知用户名]

url返回状态码404，因此没有创建输入流（这里是轻度猜测），因此为空。对状态码进行排序，您应该没事。
用这个csv运行，结果很好：其他csv
如果错误代码对您很重要，则可以使用httpurlconnection：

HttpURLConnection conn = (HttpURLConnection) url.openConnection();
    System.out.println("code:"+conn.getResponseCode());

这样，您就可以在进行快速if-then-else检查之前处理响应代码。

我在apachehttp库中尝试过。api端点似乎返回404的状态码，因此出现了错误。我使用的代码如下。

public static void main(String[] args) throws URISyntaxException, ClientProtocolException, IOException {
    HttpClient httpclient = HttpClients.createDefault();
    URIBuilder builder = new URIBuilder("http://us.mc-api.net/v3/uuid/193nonaxishsl/csv/");
    URI uri = builder.build();
    HttpGet request = new HttpGet(uri);
    HttpResponse response = httpclient.execute(request);
    System.out.println(response.getStatusLine().getStatusCode());   // 404
}

关闭 http://us.mc-api.net/v3/uuid/193nonaxishsl/csv/ 与 www.example.com 或者返回200的状态码，这进一步证明了api端点的错误。您可以在这里查看[ApacheHTTP组件]库。