我已经读过很多关于我的问题的问题和答案,但是我一直不知道如何解决.

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.

看起来没那么复杂.

这是我尝试执行此操作的方式(代码示例)：

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头

 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并进行改造

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)拨打网络电话的方法

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中的离线代码块.
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：

1)设备在线：翻新对服务器的新请求(一切正常)

2)设备离线：调用networkCall()内部的onFailure回调方法(代码示例的第4页)

我的代码有什么问题？我真的不明白为什么该应用程序不能使用脱机情况下的缓存控制.

抱歉,文本过多.
谢谢！

解决方法:

解决了.

诀窍在于结合拦截器和网络拦截器.

脚步：

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：

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)添加拦截器到okHttpClient

        OkHttpClient okHttpClient = new OkHttpClient.Builder()
            .addInterceptor(httpLoggingInterceptor)
            //.addNetworkInterceptor(REWRITE_CACHE_CONTROL_INTERCEPTOR)
            .addInterceptor(OFFLINE_INTERCEPTOR)
            .addNetworkInterceptor(ONLINE_INTERCEPTOR)
            .cache(provideOkHttpCache())
            .build();

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