请问Android 我的HttpUrlConnection返回的数据为什么不是Gzip格式的？

我的请求总是返回content-length，而且是错误的，Volley的没有返回这个头，这是什么原因导致的呢？

 12-25 09:26:25.335: E/zouguibao(3555): Connection keep-alive
 12-25 09:26:25.335: E/zouguibao(3555): Content-Length 272
 12-25 09:26:25.345: E/zouguibao(3555): Content-Type text/plain;charset=UTF-8
 12-25 09:26:25.345: E/zouguibao(3555): Date Fri, 25 Dec 2015 14:27:21 GMT
 12-25 09:26:25.345: E/zouguibao(3555): Server Apache/2.2.21
 12-25 09:26:25.345: E/zouguibao(3555): Set-Cookie BIGipServerpool_N0_IP47.161_P80=3204489482.20480.0000; path=/
 12-25 09:26:25.345: E/zouguibao(3555): X-Android-Received-Millis 1451053585345
 12-25 09:26:25.345: E/zouguibao(3555): X-Android-Response-Source NETWORK 200
 12-25 09:26:25.345: E/zouguibao(3555): X-Android-Selected-Transport http/1.1
 12-25 09:26:25.345: E/zouguibao(3555): X-Android-Sent-Millis 1451053585249

12-25 09:28:35.047: E/zouguibao(3615): Connection keep-alive
 12-25 09:28:35.047: E/zouguibao(3615): Content-Type text/plain;charset=UTF-8
 12-25 09:28:35.047: E/zouguibao(3615): Date Fri, 25 Dec 2015 14:29:31 GMT
 12-25 09:28:35.047: E/zouguibao(3615): Server Apache/2.2.21
 12-25 09:28:35.047: E/zouguibao(3615): Set-Cookie BIGipServerpool_N0_IP47.161_P80=3204489482.20480.0000; path=/
 12-25 09:28:35.047: E/zouguibao(3615): Transfer-Encoding chunked
 12-25 09:28:35.047: E/zouguibao(3615): Vary Accept-Encoding
 12-25 09:28:35.047: E/zouguibao(3615): X-Android-Received-Millis 1451053715058
 12-25 09:28:35.047: E/zouguibao(3615): X-Android-Response-Source NETWORK 200
 12-25 09:28:35.047: E/zouguibao(3615): X-Android-Selected-Transport http/1.1
 12-25 09:28:35.047: E/zouguibao(3615): X-Android-Sent-Millis 1451053714859