Question

我真的坚持这个问题。

我希望在设备离线时缓存服务器响应一段时间以使用数据。所以我为我的OkHttpClient设置了一个缓存。我还设置了Cache-Contlol标题。

这是我的代码：

    public class MainActivity extends AppCompatActivity {

    Retrofit retrofit;
    RecyclerView recyclerView;
    RandomUserAdapter mAdapter;
    Cache cache;
    Button button;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        initViews();

        GsonBuilder gsonBuilder = new GsonBuilder();
        Gson gson = gsonBuilder.create();

        cache = provideOkHttpCache();

        Timber.plant(new Timber.DebugTree());

        button.setOnClickListener(new View.OnClickListener() {
            public void onClick(View v) {
                populateUsers();
            }
        });

        Interceptor cacheInterceptor = new Interceptor() {
            @Override
            public okhttp3.Response intercept(Interceptor.Chain chain) throws IOException {
                okhttp3.Response originalResponse = chain.proceed(chain.request());
                okhttp3.Response modifyedResponse = originalResponse;

                if (true) {
                    modifyedResponse = originalResponse.newBuilder()
                            .header("Cache-Control", "max-age=86400")
                            .build();
                }

                return modifyedResponse;
            }
        };

        HttpLoggingInterceptor httpLoggingInterceptor = new
                HttpLoggingInterceptor(new HttpLoggingInterceptor.Logger() {
            @Override
            public void log(@NonNull String message) {
                Timber.i(message);
            }
        });

        httpLoggingInterceptor.setLevel(HttpLoggingInterceptor.Level.BODY);

        OkHttpClient okHttpClient = new OkHttpClient()
                .newBuilder()
                .addInterceptor(httpLoggingInterceptor)
                .addInterceptor(cacheInterceptor)
                .cache(cache)
                .build();

        retrofit = new Retrofit.Builder()
                .client(okHttpClient)
                .baseUrl("https://randomuser.me/")
                .addConverterFactory(GsonConverterFactory.create(gson))
                .build();

        populateUsers();

    }

    private void initViews() {
        recyclerView = findViewById(R.id.recyclerView);
        recyclerView.setLayoutManager(new LinearLayoutManager(this));
        button = findViewById(R.id.button);
    }

    private void populateUsers() {
        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()) {
                    Log.v("cache-control", "using cache = " + isFromCache(response));
                    mAdapter = new RandomUserAdapter();
                    mAdapter.setItems(response.body().getResults());
                    recyclerView.setAdapter(mAdapter);
                }
            }

            @Override
            public void onFailure(Call<RandomUsers> call, Throwable t) {
                Timber.i(t.getMessage());
                Log.v("cache-control", "response failure");
            }
        });
    }

    public RandomUsersApi getRandomUserService() {
        return retrofit.create(RandomUsersApi.class);
    }

    Cache provideOkHttpCache() {
        int cacheSize = 10 * 1024 * 1024; // 100 MiB
        File cacheDir = new File("cachedirectory");
        Cache cache = new Cache(cacheDir, cacheSize);
        return cache;
    }

    public boolean isFromCache(Response response) {
        return response.raw().cacheResponse() != null;
    }
}

看起来一切都会好起来的。然后我这样做：

运行应用
查看OkHttp日志并在屏幕上确保我们已成功收到数据
关闭应用
打开设备上的飞行模式（关闭所有网络）
运行应用

此时我希望应用程序将使用缓存数据。但事实并非如此。我的logcat中只有空白屏幕和HTTP FAILED: java.net.UnknownHostException: Unable to resolve host "randomuser.me": No address associated with hostname。

Answer 1

好吧，我找到了解决方案。我不确定它为什么会起作用，但确实如此。首先，我们需要修改def load_table_as_array(filename): f = open(filename,'r') # Parsing the first line containing column headers header_line = f.readline() header_line = header_line.strip(',\n') column_names = header_line.split(',’) #Parsing the rest of the file mat = [] row_names = [] for line in f: tokens = line.rstrip().split(',') row_names.append(tokens[0]) #Add first token to row header list values = [float(n) for n in tokens[1:]] # Convert to float mat.append(values) # Append the current row to the matrix f.close() row_names = np.array(row_names) column_names = np.array(column_names) data = np.array(mat) return data, column_names, row_names：

的创建

cacheInterceptor

然后我们需要使用Interceptor cacheInterceptor = 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 = 60; // read from cache return originalResponse.newBuilder() .header("Cache-Control", "public, max-age=" + maxAge) .build(); } else { int maxStale = 60 * 60 * 24 * 28; // tolerate 4-weeks stale return originalResponse.newBuilder() .header("Cache-Control", "public, only-if-cached, max-stale=" + maxStale) .build(); } } };代替addNetworkInterceptor(Interceptor interceptor)：

addInterceptor(Interceptor interceptor)

原始答案：Caching with Retrofit 2.0 and okhttp3

OkHttp 3响应缓存（java.net.UnknownHostException）

1 个答案: