改造离线请求和响应 [英] Retrofit offline request and response
问题描述
我已经阅读了许多有关该问题的问题和答案，但我一直不知道如何解决.
I've already read many questions and answers about my issue, but I slill can't understand how to solve it.
我需要从服务器获取响应并将其存储在缓存中.之后，当设备离线时，我想使用缓存的响应.设备在线时，我想完全从服务器获取响应.
I need to fetch response from server and store it in cache. After that when device is offline I want to use cached response. When device is online I want to fetch response exactly from server.
看起来并不复杂.
这是我尝试执行此操作的方式(代码示例):
Here is the way (samples of code) I try to do this:
1)创建缓存的方法
Cache provideOkHttpCache() {
int cacheSize = 10 * 1024 * 1024; // 10 MiB
Cache cache = new Cache(this.getCacheDir(), cacheSize);
return cache;
}
2)创建一个拦截器来修改缓存控制标头
2)Create an Interceptor to modify cache-control headers
Interceptor REWRITE_CACHE_CONTROL_INTERCEPTOR = new Interceptor() {
@Override
public okhttp3.Response intercept(Chain chain) throws IOException {
CacheControl.Builder cacheBuilder = new CacheControl.Builder();
cacheBuilder.maxAge(0, TimeUnit.SECONDS);
cacheBuilder.maxStale(365, TimeUnit.DAYS);
CacheControl cacheControl = cacheBuilder.build();
Request request = chain.request();
if (isOnline()) {
request = request.newBuilder()
.cacheControl(cacheControl)
.build();
}
okhttp3.Response originalResponse = chain.proceed(request);
if (isOnline()) {
int maxAge = 20; // read from cache
okhttp3.Response response = originalResponse.newBuilder()
.header("cache-control", "public, max-age=" + maxAge)
.build();
return response;
} else {
int maxStale = 60 * 60 * 24 * 28; // tolerate 4-weeks stale
okhttp3.Response response = originalResponse.newBuilder()
.header("Cache-Control", "public, only-if-cached, max-stale=" + maxStale)
.build();
return response;
}
}
};
3)创建OkHttpClient并进行改进
3) Create OkHttpClient and Retrofit
OkHttpClient okHttpClient = new OkHttpClient.Builder()
.addInterceptor(httpLoggingInterceptor)
.addNetworkInterceptor(REWRITE_CACHE_CONTROL_INTERCEPTOR)
.cache(provideOkHttpCache())
.build();
retrofit = new Retrofit.Builder()
.client(okHttpClient)
.baseUrl("https://randomuser.me/")
.addConverterFactory(GsonConverterFactory.create(gson))
.build();
4)进行网络通话的方法
4) Method to make a network call
private void networkCall() {
Log.v(TAG, "networkCall() is called");
Call<RandomUsers> randomUsersCall = getRandomUserService().getRandomUsers(10);
randomUsersCall.enqueue(new Callback<RandomUsers>() {
@Override
public void onResponse(Call<RandomUsers> call, @NonNull Response<RandomUsers> response) {
if (response.isSuccessful()) {
try {
Log.v(TAG, "headers = " + response.headers());
} catch (Exception e) {
e.printStackTrace();
}
mAdapter = new RandomUserAdapter();
mAdapter.setItems(response.body().getResults());
recyclerView.setAdapter(mAdapter);
} else if (response.code() == 504) {
Log.v(TAG, "response body = " + response.raw().cacheResponse());
}
}
@Override
public void onFailure(Call<RandomUsers> call, Throwable t) {
Log.v("cache-control", "response failure");
}
});
}
所以，这是问题所在: 该应用程序永远不会转到p.2中的脱机代码块. 如果max-age仍然合法，则Retrofit使用缓存的响应. 如果响应是在一段时间前缓存的，并且max-age不合法，则有两种情况:
So, here is the problem: The app never goes to the offline block of code in p.2. If max-age is still legal Retrofit use cached response. If response was cached some time ago and max-age is not legal there is two cases:
1)设备在线:Retrofit向服务器发出新请求(一切正常)
1) Device is online: Retrofit make new request to server (everything is OK)
2)设备处于脱机状态:调用了networkCall()中的回调方法onFailure(代码示例的第4页)
2)Device is offline: Callback method onFailure inside networkCall() is called (p.4 of code samples)
我的代码有什么问题?我真的不明白为什么应用程序不能使用缓存控制的脱机情况.
What's wrong in my code? I really don't understand why the app cant use offline case of cache-control.
抱歉，文本太多. 谢谢！
Sorry for too much text. Thanks!
推荐答案
已解决.
诀窍在于结合Interceptor和NetworkInterceptor.
步骤:
1)将REWRITE_CACHE_CONTROL_INTERCEPTOR隔离为两个拦截器，一个拦截器用于在线工作，另一个拦截器用于离线工作:
1)Separate REWRITE_CACHE_CONTROL_INTERCEPTOR for two Interceptors, one for online work and other for offline work:
Interceptor OFFLINE_INTERCEPTOR = new Interceptor() {
@Override
public okhttp3.Response intercept(Chain chain) throws IOException {
Request request = chain.request();
if (!isOnline()) {
int maxStale = 60 * 60 * 24 * 28; // tolerate 4-weeks stale
request = request.newBuilder()
.header("Cache-Control", "public, only-if-cached, max-stale=" + maxStale)
.build();
}
return chain.proceed(request);
}
};
Interceptor ONLINE_INTERCEPTOR = new Interceptor() {
@Override
public okhttp3.Response intercept(Chain chain) throws IOException {
okhttp3.Response response = chain.proceed(chain.request());
int maxAge = 60; // read from cache
return response.newBuilder()
.header("Cache-Control", "public, max-age=" + maxAge)
.build();
}
};
2)将拦截器添加到okHttpClient
2)Add Interceptors to okHttpClient
OkHttpClient okHttpClient = new OkHttpClient.Builder()
.addInterceptor(httpLoggingInterceptor)
//.addNetworkInterceptor(REWRITE_CACHE_CONTROL_INTERCEPTOR)
.addInterceptor(OFFLINE_INTERCEPTOR)
.addNetworkInterceptor(ONLINE_INTERCEPTOR)
.cache(provideOkHttpCache())
.build();
这篇关于改造离线请求和响应的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
