為什么對我的Java GET請求的響應的標頭少於Curl的相同URL

Question

我正在使用OANDA API。 該文檔指出，對所有成功的GET請求的響應都將包含一個ETag標頭： http : //developer.oanda.com/rest-live/development-guide/#etag

我已經向Curl請求成功時，就是這種情況：

$ curl -i "https://api-sandbox.oanda.com/v1/prices?instruments=EUR_USD"
HTTP/1.1 200 OK
Server: openresty/1.7.0.1
Date: Fri, 26 Dec 2014 17:27:01 GMT
Content-Type: application/json
Content-Length: 139
Connection: keep-alive
ETag: "6a6e222a3f90df8f333ff2a6edfb603e4a354905"

{
        "prices" : [
                {
                        "instrument" : "EUR_USD",
                        "time" : "2014-12-26T17:26:12.336249Z",
                        "bid" : 1.24105,
                        "ask" : 1.24119
                }
        ]
}

但是，當我成功使用HttpClient org.apache.httpcomponents 4.3請求時，不包括Content-Length和ETag標頭。

2014-12-26 17:27:54 INFO  RestClient:91 - Executing request: GET https://api-sandbox.oanda.com/v1/prices?instruments=EUR_USD HTTP/1.1
2014-12-26 17:27:55 INFO  RestClient:103 - Response OK, processing...
2014-12-26 17:27:55 INFO  RestClient:108 - {
    "prices" : [
        {
            "instrument" : "EUR_USD",
            "time" : "2014-12-26T17:28:01.935790Z",
            "bid" : 1.241,
            "ask" : 1.24117
        }
    ]
}
2014-12-26 17:27:55 INFO  RestClient:110 - Headers: [Server: openresty/1.7.0.1, Date: Fri, 26 Dec 2014 17:28:14 GMT, Content-Type: application/json, Transfer-Encoding: chunked, Connection: keep-alive]

當我記錄接收到的所有響應Java GET請求的標頭時，我缺少ETag和Content-Length標頭。

我想在我的Java代碼中使用ETag標頭，所以請您能幫助我理解為什么不返回它的原因。

Answer 1

默認情況下，HttpClient啟用了壓縮，並且啟用壓縮后，OANDA API不支持ETag：

Note: ETags can not be used in conjunction with compressed responses.