一、前言
此前了解过OKHTTP的缓存的使用，并对缓存的使用进行了初步的总结https://blog.csdn.net/polo2044/article/details/80650856。缓存主要是为了在没有网络的情况下，或者资源不需要实时去后端进行更新时，可以直接从缓存中获取资源信息。一方面是能够在断网的情况下仍然给用户良好的界面展示，另一个方面是避免频繁的请求网络给后端带来压力。目前网络上介绍的在OKHTTP中实现客户端的缓存机制，都是在自定义的Intercept中设置max-age和max-stale的参数值来完成。
但是在查阅网络上的方法后，依旧存在如下疑问：
1. max-age和max-stale在request和response中都可以进行设置，两种设置的效果是否一样。
2.在本人公司的URL测试中发现，max-age和max-stale没有起作用。
为了解决这些疑问，因此有必要在实际代码中对这两个参数进行实际的验证和研究。
二、max-age和max-stale参数的意义
max-age:告知缓存多长时间，在没有超过缓存时间的情况下，请求会返回缓存内的数据，在超出max-age的情况下向服务端发起新的请求，请求失败的情况下返回缓存数据（测试中已验证），否则向服务端重新发起请求。
max-stale:指示客户机可以接收超出max-age时间的响应消息，max-stale在请求设置中有效，在响应设置中无效（测试中已验证，且参见博客https://www.jianshu.com/p/db197279f053）。
因此max-age和max-stale在请求中同时使用的情况下，缓存的时间可以为max-age和max-stale的和。
三、测试验证
在测试中需要构造一个OKHTTP，然后在拦截器中定义不同的max-age和max-stale来进行测试，在Activity中定义一个定时器，每隔3s进行一次网络请求。
Activity中的网络请求如下：
|
@Override
public void onClick(View view) {
if (view.getId() == R.id.button) {
Observable.interval(3, TimeUnit.SECONDS).subscribe(
new Action1<Long>() {
@Override
public void call(Long aLong) {
getRecomandComic();
}
}
);
}
}
private void getRecomandComic() {
RetrofitResearch.getInstance(this)
.getTopRecommendList()
.subscribeOn(Schedulers.computation())
.observeOn(AndroidSchedulers.mainThread())
.subscribe(new Action1<ComicBeanNoCountResult>() {
@Override
public void call(ComicBeanNoCountResult comicBeanNoCountResult) {
}
},
new Action1<Throwable>() {
@Override
public void call(Throwable throwable) {
}
});
}
|
OKHTTP的构造代码如下：
|
public class OkHttpCallFactory {
private static int DEFAULT_TIMEOUT = 30;
private static final int CONST_10 = 10;
private static final int CONST_1024 = 1024;
private static final Logger logger = Logger.getLogger("yansm");
private OkHttpCallFactory() {
}
private static Call.Factory factory;
private static int time =60;
public static Call.Factory getOkHttpFactory(Context context) {
if (factory == null) {
synchronized (OkHttpCallFactory.class) {
if (factory == null) {
OkHttpClient.Builder builder = new OkHttpClient.Builder();
builder.cache(new Cache(context.getCacheDir(),
CONST_10 * CONST_1024 * CONST_1024)); //设置缓存
builder.connectTimeout(DEFAULT_TIMEOUT, TimeUnit.SECONDS);
builder.writeTimeout(DEFAULT_TIMEOUT, TimeUnit.SECONDS);
builder.readTimeout(DEFAULT_TIMEOUT, TimeUnit.SECONDS);
Interceptor interceptor = new NetCacheInterceptor();
builder.addInterceptor(interceptor);
builder.addNetworkInterceptor(interceptor);
builder.addInterceptor(new LoggingInterceptor());
factory = builder.build();
}
}
}
return factory;
}
//日志输出的拦截器
private static class LoggingInterceptor implements Interceptor {
@Override public Response intercept(Chain chain) throws IOException {
long t1 = System.nanoTime();
Request request = chain.request();
logger.info(String.format("Sending request %s on %s%n%s",
request.url(), chain.connection(), request.headers()));
Response response = chain.proceed(request);
long t2 = System.nanoTime();
logger.info(String.format("Received response for %s in %.1fms%n%s",
request.url(), (t2 - t1) / 1e6d, response.headers()));
return response;
}
}
}
|
3.1 在拦截器的response中设置max-age = 60和max-stale = 120
|
public class NetCacheInterceptor implements Interceptor {
@Override
public Response intercept(Chain chain) throws IOException {
Request request = chain.request();
CacheControl cacheControl = new CacheControl.Builder()
.maxAge(60, TimeUnit.SECONDS)
.maxStale(120, TimeUnit.SECONDS).build();
Response response = chain.proceed(request);
return response.newBuilder()
.removeHeader("Pragma")
.removeHeader("Cache-Control")
.header("Cache-Control", cacheControl.toString())
.build();
}
}
|
测试日志结果如下，每隔三秒发送一次请求：
|
第一次网络请求
06-22 13:59:51.816 32336-469/com.example.moxie.cacheresearch I/yansm: Sending request http://lbs.sougu.net.cn/app.php?m=souguapp&c=appusers&a=network on null
06-22 13:59:52.200 32336-469/com.example.moxie.cacheresearch I/yansm: Received response for http://lbs.sougu.net.cn/app.php?m=souguapp&c=appusers&a=network in 381.9ms
Server: Tengine
Content-Type: text/json;charset=UTF-8
Content-Length: 1492
Date: Fri, 22 Jun 2018 05:59:51 GMT
Expires: Thu, 19 Nov 1981 08:52:00 GMT
X-Powered-By: PHP/7.0.1
Set-Cookie: PHPSESSID=pef8qomvm3kjg90bs94ojpugf1; path=/
Set-Cookie: SERVERID=37f80876073565188d4968aa47392891|1529647191|1529647191;Path=/
Via: cache14.l2eu6-1[103,200-0,M], cache4.l2eu6-1[103,0], cache8.cn785[155,200-0,M], cache7.cn785[159,0]
X-Cache: MISS TCP_MISS dirn:-2:-2 mlen:-1
X-Swift-SaveTime: Fri, 22 Jun 2018 05:59:51 GMT
X-Swift-CacheTime: 0
Timing-Allow-Origin: *
EagleId: 3d9bde1b15296471912141111e
Connection: keep-alive
Cache-Control: max-age=60, max-stale=120
第二次网络请求
06-22 13:59:54.733 32336-469/com.example.moxie.cacheresearch I/yansm: Sending request http://lbs.sougu.net.cn/app.php?m=souguapp&c=appusers&a=network on null
06-22 13:59:54.759 32336-469/com.example.moxie.cacheresearch I/yansm: Received response for http://lbs.sougu.net.cn/app.php?m=souguapp&c=appusers&a=network in 25.1ms
Server: Tengine
Content-Type: text/json;charset=UTF-8
Content-Length: 1492
Date: Fri, 22 Jun 2018 05:59:51 GMT
Expires: Thu, 19 Nov 1981 08:52:00 GMT
X-Powered-By: PHP/7.0.1
Set-Cookie: PHPSESSID=pef8qomvm3kjg90bs94ojpugf1; path=/
Set-Cookie: SERVERID=37f80876073565188d4968aa47392891|1529647191|1529647191;Path=/
Via: cache14.l2eu6-1[103,200-0,M], cache4.l2eu6-1[103,0], cache8.cn785[155,200-0,M], cache7.cn785[159,0]
X-Cache: MISS TCP_MISS dirn:-2:-2 mlen:-1
X-Swift-SaveTime: Fri, 22 Jun 2018 05:59:51 GMT
X-Swift-CacheTime: 0
Timing-Allow-Origin: *
EagleId: 3d9bde1b15296471912141111e
Connection: keep-alive
Cache-Control: max-age=60, max-stale=120
第三次网络请求
06-22 13:59:57.733 32336-469/com.example.moxie.cacheresearch I/yansm: Sending request http://lbs.sougu.net.cn/app.php?m=souguapp&c=appusers&a=network on null
06-22 13:59:57.749 32336-469/com.example.moxie.cacheresearch I/yansm: Received response for http://lbs.sougu.net.cn/app.php?m=souguapp&c=appusers&a=network in 14.9ms
Server: Tengine
Content-Type: text/json;charset=UTF-8
Content-Length: 1492
Date: Fri, 22 Jun 2018 05:59:51 GMT
Expires: Thu, 19 Nov 1981 08:52:00 GMT
X-Powered-By: PHP/7.0.1
Set-Cookie: PHPSESSID=pef8qomvm3kjg90bs94ojpugf1; path=/
Set-Cookie: SERVERID=37f80876073565188d4968aa47392891|1529647191|1529647191;Path=/
Via: cache14.l2eu6-1[103,200-0,M], cache4.l2eu6-1[103,0], cache8.cn785[155,200-0,M], cache7.cn785[159,0]
X-Cache: MISS TCP_MISS dirn:-2:-2 mlen:-1
X-Swift-SaveTime: Fri, 22 Jun 2018 05:59:51 GMT
X-Swift-CacheTime: 0
Timing-Allow-Origin: *
EagleId: 3d9bde1b15296471912141111e
Connection: keep-alive
Cache-Control: max-age=60, max-stale=120
|
charles抓包结果
测试结果分析：在实验中，对response的max-age和max-stale进行了设置，分别为60秒和120秒，在日志的输出中可以看到这一点。但是通过实际的抓包结果能够看到max-age时效起作用了，max-stale没有起时效，客户端在60s内没有向服务端发送请求，但是在60s后向服务端发送了请求。
3.2 在拦截器的request中设置max-age=120和max-stale=60
参考代码如下
|
@Override
public Response intercept(Chain chain) throws IOException {
Request request = chain.request();
CacheControl cacheControl = new CacheControl.Builder().maxAge(120, TimeUnit.SECONDS)
.maxStale(60, TimeUnit.SECONDS).build();
request = request.newBuilder()
.cacheControl(cacheControl)
.build();
return chain.proceed(request);
}
|
测试日志结果如下：
|
第一次网络请求
06-22 13:33:28.131 29674-30389/com.example.moxie.cacheresearch I/yansm: Sending request http://lbs.sougu.net.cn/app.php?m=souguapp&c=appusers&a=network on null
Cache-Control: max-age=120, max-stale=60
06-22 13:33:28.700 29674-30389/com.example.moxie.cacheresearch I/yansm: Received response for http://lbs.sougu.net.cn/app.php?m=souguapp&c=appusers&a=network in 567.5ms
Server: Tengine
Content-Type: text/json;charset=UTF-8
Content-Length: 1492
Date: Fri, 22 Jun 2018 05:33:27 GMT
Expires: Thu, 19 Nov 1981 08:52:00 GMT
X-Powered-By: PHP/7.0.1
Set-Cookie: PHPSESSID=t6j4tnss1nkpbm0tddqdr0o2j1; path=/
Set-Cookie: SERVERID=37f80876073565188d4968aa47392891|1529645607|1529645607;Path=/
Via: cache14.l2eu6-1[102,200-0,M], cache21.l2eu6-1[106,0], cache10.cn883[190,200-0,M], cache1.cn883[214,0]
X-Cache: MISS TCP_MISS dirn:-2:-2 mlen:-1
X-Swift-SaveTime: Fri, 22 Jun 2018 05:33:27 GMT
X-Swift-CacheTime: 0
Timing-Allow-Origin: *
EagleId: af06f99515296456075954226e
Connection: keep-alive
Cache-Control: public, max-age=6000
第N次网络请求
06-22 13:35:25.057 29674-30389/com.example.moxie.cacheresearch I/yansm: Received response for http://lbs.sougu.net.cn/app.php?m=souguapp&c=appusers&a=network in 9.6ms
Server: Tengine
Content-Type: text/json;charset=UTF-8
Content-Length: 1492
Date: Fri, 22 Jun 2018 05:33:27 GMT
Expires: Thu, 19 Nov 1981 08:52:00 GMT
X-Powered-By: PHP/7.0.1
Set-Cookie: PHPSESSID=t6j4tnss1nkpbm0tddqdr0o2j1; path=/
Set-Cookie: SERVERID=37f80876073565188d4968aa47392891|1529645607|1529645607;Path=/
Via: cache14.l2eu6-1[102,200-0,M], cache21.l2eu6-1[106,0], cache10.cn883[190,200-0,M], cache1.cn883[214,0]
X-Cache: MISS TCP_MISS dirn:-2:-2 mlen:-1
X-Swift-SaveTime: Fri, 22 Jun 2018 05:33:27 GMT
X-Swift-CacheTime: 0
Timing-Allow-Origin: *
EagleId: af06f99515296456075954226e
Connection: keep-alive
Cache-Control: public, max-age=6000
第N+1次网络请求
06-22 13:35:28.046 29674-30389/com.example.moxie.cacheresearch I/yansm: Sending request http://lbs.sougu.net.cn/app.php?m=souguapp&c=appusers&a=network on null
Cache-Control: max-age=120, max-stale=60
06-22 13:35:28.056 29674-30389/com.example.moxie.cacheresearch I/yansm: Received response for http://lbs.sougu.net.cn/app.php?m=souguapp&c=appusers&a=network in 8.9ms
Server: Tengine
Content-Type: text/json;charset=UTF-8
Content-Length: 1492
Date: Fri, 22 Jun 2018 05:33:27 GMT
Expires: Thu, 19 Nov 1981 08:52:00 GMT
X-Powered-By: PHP/7.0.1
Set-Cookie: PHPSESSID=t6j4tnss1nkpbm0tddqdr0o2j1; path=/
Set-Cookie: SERVERID=37f80876073565188d4968aa47392891|1529645607|1529645607;Path=/
Via: cache14.l2eu6-1[102,200-0,M], cache21.l2eu6-1[106,0], cache10.cn883[190,200-0,M], cache1.cn883[214,0]
X-Cache: MISS TCP_MISS dirn:-2:-2 mlen:-1
X-Swift-SaveTime: Fri, 22 Jun 2018 05:33:27 GMT
X-Swift-CacheTime: 0
Timing-Allow-Origin: *
EagleId: af06f99515296456075954226e
Connection: keep-alive
Cache-Control: public, max-age=6000
Warning: 110 HttpURLConnection "Response is stale"
|
charles抓包结果
测试结果分析，从测试结果中可以看出在request请求中设置max-age和max-stale值，缓存时间是以两者值得和，测试中max-age = 120s，max-stale = 60s，恰好为3分钟，抓包请求间隔是3分钟。但是有一点，在请求的时间超过120s后，再次请求时，请求的结果中会多出“Warning: 110 HttpURLConnection "Response is stale"”
3.3 异常测试一
上述测试中max-age和max-stale还算符合预期，但是在用公司的url进行测试时，max-age和max-stale似乎失去了效果。依旧在response中设置max-age =60和max-stale =120进行测试。
测试日志结果如下：
|
第一次网络请求
06-22 17:38:27.094 7756-7780/com.example.moxie.cacheresearch I/yansm: Sending request https://comic.mkzhan.com/recom/app/ on null
06-22 17:38:27.253 7756-7780/com.example.moxie.cacheresearch I/yansm: Received response for https://comic.mkzhan.com/recom/app/ in 158.0ms
Server: Tengine
Content-Type: application/json; charset=utf-8
Content-Length: 625
Date: Fri, 22 Jun 2018 08:51:34 GMT
Access-Control-Allow-Origin: *
Access-Control-Allow-Headers: X-Requested-With,app-id,app-version,device-name,device-resolution,device-udid,platform,system-name,system-version
Access-Control-Allow-Methods: GET,POST,OPTIONS
X-Powered-By: mkzhan-A2
Via: cache9.l2cm10-1[0,200-0,H], cache29.l2cm10-1[1,0], cache1.cn1412[0,200-0,H], cache14.cn1412[1,0]
Age: 2812
X-Cache: HIT TCP_MEM_HIT dirn:12:43491335 mlen:-1
X-Swift-SaveTime: Fri, 22 Jun 2018 09:03:10 GMT
X-Swift-CacheTime: 3600
Timing-Allow-Origin: *
EagleId: 7ce89ea215296603064393222e
Connection: keep-alive
Cache-Control: max-age=60, max-stale=120
第二次网络请求
06-22 17:38:30.091 7756-7780/com.example.moxie.cacheresearch I/yansm: Sending request https://comic.mkzhan.com/recom/app/ on null
06-22 17:38:30.249 7756-7780/com.example.moxie.cacheresearch I/yansm: Received response for https://comic.mkzhan.com/recom/app/ in 156.9ms
Server: Tengine
Content-Type: application/json; charset=utf-8
Content-Length: 625
Date: Fri, 22 Jun 2018 08:51:34 GMT
Access-Control-Allow-Origin: *
Access-Control-Allow-Headers: X-Requested-With,app-id,app-version,device-name,device-resolution,device-udid,platform,system-name,system-version
Access-Control-Allow-Methods: GET,POST,OPTIONS
X-Powered-By: mkzhan-A2
Via: cache9.l2cm10-1[0,200-0,H], cache29.l2cm10-1[1,0], cache1.cn1412[0,200-0,H], cache14.cn1412[1,0]
Age: 2815
X-Cache: HIT TCP_MEM_HIT dirn:12:43491335 mlen:-1
X-Swift-SaveTime: Fri, 22 Jun 2018 09:03:10 GMT
X-Swift-CacheTime: 3600
Timing-Allow-Origin: *
EagleId: 7ce89ea215296603094162696e
Connection: keep-alive
Cache-Control: max-age=60, max-stale=120
第三次网络请求
06-22 17:38:33.093 7756-7780/com.example.moxie.cacheresearch I/yansm: Sending request https://comic.mkzhan.com/recom/app/ on null
06-22 17:38:33.198 7756-7780/com.example.moxie.cacheresearch I/yansm: Received response for https://comic.mkzhan.com/recom/app/ in 103.4ms
Server: Tengine
Content-Type: application/json; charset=utf-8
Content-Length: 625
Date: Fri, 22 Jun 2018 08:51:34 GMT
Access-Control-Allow-Origin: *
Access-Control-Allow-Headers: X-Requested-With,app-id,app-version,device-name,device-resolution,device-udid,platform,system-name,system-version
Access-Control-Allow-Methods: GET,POST,OPTIONS
X-Powered-By: mkzhan-A2
Via: cache9.l2cm10-1[0,200-0,H], cache29.l2cm10-1[1,0], cache1.cn1412[0,200-0,H], cache14.cn1412[0,0]
Age: 2818
X-Cache: HIT TCP_MEM_HIT dirn:12:43491335 mlen:-1
X-Swift-SaveTime: Fri, 22 Jun 2018 09:03:10 GMT
X-Swift-CacheTime: 3600
Timing-Allow-Origin: *
EagleId: 7ce89ea215296603123821715e
Connection: keep-alive
Cache-Control: max-age=60, max-stale=120
|
抓包结果如下
问题提出：在response中设置了max-age =60s，根据此前的测试情况，抓包得到的请求应该间隔60s，而不是根据请求每次都是3s。针对这一疑问，检查了日志中的返回字段，发现公司服务器返回的字段比此前测试的字段多了一个Age字段
Age字段的定义：当代理服务器用自己缓存的实体去响应请求时，用该头部表明该实体从产生到现在经过多长时间了（可参见该博客的解释https://blog.csdn.net/xifeijian/article/details/46460631）。
由该字段的定义可以猜到，该字段会影响缓存的时效，如果定义的缓存的比改值要小，则缓存从设置起可能就已经失效了。因此需要定义max-age的时间值超过Age的时间值才能让max-age值生效。
3.4 异常测试二
由于Age的时间值也会会是增加的，将max-age的时间值设置为4000，得到如下测试日志：
|
06-22 09:52:47.578 14683-14855/com.example.moxie.cacheresearch I/yansm: Sending request https://comic.mkzhan.com/recom/app/ on null
06-22 09:52:48.216 14683-14855/com.example.moxie.cacheresearch I/yansm: Received response for https://comic.mkzhan.com/recom/app/ in 637.9ms
Server: Tengine
Content-Type: application/json; charset=utf-8
Content-Length: 624
Date: Fri, 22 Jun 2018 00:51:28 GMT
Access-Control-Allow-Origin: *
Access-Control-Allow-Headers: X-Requested-With,app-id,app-version,device-name,device-resolution,device-udid,platform,system-name,system-version
Access-Control-Allow-Methods: GET,POST,OPTIONS
X-Powered-By: mkzhan-A2
Via: cache9.l2cm10-1[0,200-0,H], cache22.l2cm10-1[1,0], cache10.cn978[0,200-0,H], cache2.cn978[1,0]
Age: 3679
X-Cache: HIT TCP_MEM_HIT dirn:6:301393262 mlen:-1
X-Swift-SaveTime: Fri, 22 Jun 2018 01:08:57 GMT
X-Swift-CacheTime: 3600
Timing-Allow-Origin: *
EagleId: 74d3999615296323674053464e
Connection: keep-alive
Cache-Control: public, max-age=4000
|
测试结果是，缓存生效了，但是生效的时间值只有4000s-3679s = 321s，在Age值超过4000s之后，依旧是按照测试代码中设定的间隔每隔3s钟发送一次。为了能够除去Age造成的影响，在response中调用removeHeader将Age给删除，但是并没有起作用。
四、总结
本次主要是对max-age和max-stale的意义在OKHTTP的使用中进行了实际的验证测试，由于起初用公司的URL进行测试时发现与预期不符，经过排查发现是Age参数值搞的鬼。
参考博客：
https://www.jianshu.com/p/db197279f053（比较详细，值得细细阅读）