使用 Retrofit 2.0.x 进行 HTTP 缓存

Question

我正在尝试使用 Retrofit 2.0 在我的应用中缓存一些响应，但我遗漏了一些东西。

我安装了一个缓存文件如下：

private static File httpCacheDir;
private static Cache cache;
try {
    httpCacheDir = new File(getApplicationContext().getCacheDir(), "http");
    httpCacheDir.setReadable(true);
    long httpCacheSize = 10 * 1024 * 1024; // 10 MiB
    HttpResponseCache.install(httpCacheDir, httpCacheSize);
    cache = new Cache(httpCacheDir, httpCacheSize);
    Log.i("HTTP Caching", "HTTP response cache installation success");
} catch (IOException e) {
    Log.i("HTTP Caching", "HTTP response cache installation failed:" + e);
}

public static Cache getCache() {
        return cache;
    }

在/data/user/0/<PackageNmae>/cache/http 中创建一个文件 ，然后准备一个网络拦截器如下：

public class CachingControlInterceptor implements Interceptor {
    @Override
    public Response intercept(Chain chain) throws IOException {
        Request request = chain.request();

        // Add Cache Control only for GET methods
        if (request.method().equals("GET")) {
            if (ConnectivityUtil.checkConnectivity(getContext())) {
                // 1 day
                request.newBuilder()
                    .header("Cache-Control", "only-if-cached")
                    .build();
            } else {
                // 4 weeks stale
                request.newBuilder()
                    .header("Cache-Control", "public, max-stale=2419200")
                    .build();
            }
        }

        Response originalResponse = chain.proceed(chain.request());
        return originalResponse.newBuilder()
            .header("Cache-Control", "max-age=86400")
            .build();
    }
}

我的Retrofit 和OkHttpClient 实例：

OkHttpClient client = new OkHttpClient();
client.setCache(getCache());
client.interceptors().add(new MainInterceptor());
client.interceptors().add(new LoggingInceptor());
client.networkInterceptors().add(new CachingControlInterceptor());
Retrofit restAdapter = new Retrofit.Builder()
        .client(client)
        .baseUrl(Constants.BASE_URL)
        .addConverterFactory(GsonConverterFactory.create(gson))
        .build();

productsService = restAdapter.create(ProductsService.class);

其中ProductsService.class 包含：

@Headers("Cache-Control: max-age=86400")
@GET("categories/")
Call<PagedResponse<Category>> listCategories();

和

Call<PagedResponse<Category>> call = getRestClient().getProductsService().listCategories();
call.enqueue(new GenericCallback<PagedResponse<Category>>() {
      // whatever 
      // GenericCallback<T> implements Callback<T>
   }
});

这里的问题是：如何让它在设备离线时访问缓存的响应？

后端响应的标头是：

Allow → GET, HEAD, OPTIONS
Cache-Control → max-age=86400, must-revalidate
Connection → keep-alive
Content-Encoding → gzip
Content-Language → en
Content-Type → application/json; charset=utf-8
Date → Thu, 17 Dec 2015 09:42:49 GMT
Server → nginx
Transfer-Encoding → chunked
Vary → Accept-Encoding, Cookie, Accept-Language
X-Frame-Options → SAMEORIGIN
x-content-type-options → nosniff
x-xss-protection → 1; mode=block

Answer 1

在您的CachingControlInterceptor 中，您创建新请求，但从未实际使用它们。您调用newBuilder 并忽略结果，因此标头修改实际上永远不会发送到任何地方。尝试将这些值分配给request，然后不要在chain.request() 上调用proceed，而是在request 上调用它。

public class CachingControlInterceptor implements Interceptor {
    @Override
    public Response intercept(Chain chain) throws IOException {
        Request request = chain.request();

        // Add Cache Control only for GET methods
        if (request.method().equals("GET")) {
            if (ConnectivityUtil.checkConnectivity(getContext())) {
                // 1 day
                request = request.newBuilder()
                    .header("Cache-Control", "only-if-cached")
                    .build();
            } else {
                // 4 weeks stale
                request = request.newBuilder()
                    .header("Cache-Control", "public, max-stale=2419200")
                    .build();
            }
        }

        Response originalResponse = chain.proceed(request);
        return originalResponse.newBuilder()
            .header("Cache-Control", "max-age=600")
            .build();
    }
}

Answer 2

我终于得到了答案。

网络拦截器应该如下：

public class CachingControlInterceptor implements Interceptor {
    @Override
    public Response intercept(Chain chain) throws IOException {
        Request request = chain.request();

        // Add Cache Control only for GET methods
        if (request.method().equals("GET")) {
            if (ConnectivityUtil.checkConnectivity(YaootaApplication.getContext())) {
                // 1 day
               request = request.newBuilder()
                        .header("Cache-Control", "only-if-cached")
                        .build();
            } else {
                // 4 weeks stale
               request = request.newBuilder()
                        .header("Cache-Control", "public, max-stale=2419200")
                        .build();
            }
        }

        Response originalResponse = chain.proceed(request);
        return originalResponse.newBuilder()
            .header("Cache-Control", "max-age=600")
            .build();
    }
}

那么安装缓存文件就这么简单

long SIZE_OF_CACHE = 10 * 1024 * 1024; // 10 MiB
Cache cache = new Cache(new File(context.getCacheDir(), "http"), SIZE_OF_CACHE);
OkHttpClient client = new OkHttpClient();
client.cache(cache);
client.networkInterceptors().add(new CachingControlInterceptor());

Answer 3

    OkHttpClient client = new OkHttpClient.Builder().cache(cache).build();

Answer 4

你也可以试试：

public class CachingInterceptor implements Interceptor {
    @Override
    public okhttp3.Response intercept(Chain chain) throws IOException {
        Request request = chain.request();

        request = new Request.Builder()
                .cacheControl(new CacheControl.Builder()
                        .maxAge(1, TimeUnit.DAYS)
                        .minFresh(4, TimeUnit.HOURS)
                        .maxStale(8, TimeUnit.HOURS)
                        .build())
                .url(request.url())
                .build();


        return chain.proceed(request);
    }
}

Answer 5

我终于在 Retrofit 2.x 和 OkHttp 3.x 中找到了适合我的解决方案

我必须实现两个拦截器，其中一个负责重写请求标头，另一个负责重写响应标头。

1. 首先，确保删除所有旧缓存。 （根资源管理器 /data/data/com.yourapp/cache

2. 实例化客户端生成器：

   OkHttpClient.Builder okHttpClientBuilder = new OkHttpClient.Builder()
       .cache(cache)
       .addInterceptor(new RewriteRequestInterceptor())
       .addNetworkInterceptor(new RewriteResponseCacheControlInterceptor())
   

3. 创建 RewriteRequestInterceptor

   public class RewriteRequestInterceptor implements Interceptor {
       @Override
       public Response intercept(Chain chain) throws IOException {
           int maxStale = 60 * 60 * 24 * 5;
           Request request;
           if (NetworkUtils.isNetworkAvailable()) {
               request = chain.request();
           } else {
               request = chain.request().newBuilder().header("Cache-Control", "max-stale=" + maxStale).build();
           }
           return chain.proceed(request);
       }
   }
   

4. 创建 RewriteResponseCacheControlInterceptor

   public class RewriteResponseCacheControlInterceptor implements Interceptor {
       @Override
       public Response intercept(Chain chain) throws IOException {
           int maxStale = 60 * 60 * 24 * 5;
           Response originalResponse = chain.proceed(chain.request());
           return originalResponse.newBuilder().header("Cache-Control", "public, max-age=120, max-stale=" + maxStale).build();
       }
   }
   

务必确保将 ResponseCacheControlInterceptor 添加为网络拦截器，并将 RewriteRequestInterceptor 添加为拦截器（就像我在第二步中所做的那样）。