Question

我已经阅读了很多关于我的问题的问题和答案，但我无法理解如何解决它。

我需要从服务器获取响应并将其存储在缓存中。在此之后，当设备处于脱机状态时，我想使用缓存响应。当设备在线时，我想从服务器获取响应。

看起来并不那么复杂。

以下是我尝试这样做的方式（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Interceptor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和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）进行网络呼叫的方法

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进入第2页中的脱机代码块。如果max-age仍然是合法的，则使用缓存响应进行改造。如果反应在前一段时间被缓存，并且max-age不合法，则有两种情况：

1）设备在线：Retrofit向服务器发出新请求（一切正常）

2）设备离线：调用onFailure内的回调方法networkCall()（第4页代码示例）

我的代码有什么问题？我真的不明白为什么应用程序无法使用脱机控制的离线情况。

抱歉文字过多。谢谢！

Answer 1

解决。

诀窍是合并Interceptor和NetworkInterceptor。

步骤：

1）为两个拦截器分别使用REWRITE_CACHE_CONTROL_INTERCEPTOR，一个用于在线工作，另一个用于离线工作：

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）将拦截器添加到okHttpClient

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

Link to original article

改进离线请求和响应

1 个答案: