使用OKHttp进行改造可以在离线时使用缓存数据-Java 学习之路

138

我正在尝试使用Retrofit和OKHttp来缓存HTTP响应 . 我跟着this gist，最后得到了这段代码：

File httpCacheDirectory = new File(context.getCacheDir(), "responses");

HttpResponseCache httpResponseCache = null;
try {
     httpResponseCache = new HttpResponseCache(httpCacheDirectory, 10 * 1024 * 1024);
} catch (IOException e) {
     Log.e("Retrofit", "Could not create http cache", e);
}

OkHttpClient okHttpClient = new OkHttpClient();
okHttpClient.setResponseCache(httpResponseCache);

api = new RestAdapter.Builder()
          .setEndpoint(API_URL)
          .setLogLevel(RestAdapter.LogLevel.FULL)
          .setClient(new OkClient(okHttpClient))
          .build()
          .create(MyApi.class);

这是带有Cache-Control标头的MyApi

public interface MyApi {
   @Headers("Cache-Control: public, max-age=640000, s-maxage=640000 , max-stale=2419200")
   @GET("/api/v1/person/1/")
   void requestPerson(
           Callback<Person> callback
   );

首先，我在线请求并检查缓存文件 . 有正确的JSON响应和 Headers . 但是当我尝试离线请求时，我总是得到 RetrofitError UnknownHostException . 我还有什么办法让Retrofit从缓存中读取响应吗？

EDIT: 由于OKHttp 2.0.x HttpResponseCache 是 Cache ， setResponseCache 是 setCache

6 回答

173

编辑改造2.x：

OkHttp Interceptor是离线时访问缓存的正确方法：

1）创建拦截器：

private static final Interceptor REWRITE_CACHE_CONTROL_INTERCEPTOR = new Interceptor() {
    @Override public Response intercept(Chain chain) throws IOException {
        Response originalResponse = chain.proceed(chain.request());
        if (Utils.isNetworkAvailable(context)) {
            int maxAge = 60; // read from cache for 1 minute
            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();
        }
    }

2）设置客户端：

OkHttpClient client = new OkHttpClient();
client.networkInterceptors().add(REWRITE_CACHE_CONTROL_INTERCEPTOR);

//setup cache
File httpCacheDirectory = new File(context.getCacheDir(), "responses");
int cacheSize = 10 * 1024 * 1024; // 10 MiB
Cache cache = new Cache(httpCacheDirectory, cacheSize);

//add cache to the client
client.setCache(cache);

3）添加客户端进行改造

Retrofit retrofit = new Retrofit.Builder()
        .baseUrl(BASE_URL)
        .client(client)
        .addConverterFactory(GsonConverterFactory.create())
        .build();

另请查看 @kosiara - Bartosz Kosarzycki 的answer . 您可能需要从响应中删除一些标头 .

OKHttp 2.0.x（查看原始答案）：

由于OKHttp 2.0.x HttpResponseCache 是 Cache ， setResponseCache 是 setCache . 所以你应该 setCache 这样：

File httpCacheDirectory = new File(context.getCacheDir(), "responses");

        Cache cache = null;
        try {
            cache = new Cache(httpCacheDirectory, 10 * 1024 * 1024);
        } catch (IOException e) {
            Log.e("OKHttp", "Could not create http cache", e);
        }

        OkHttpClient okHttpClient = new OkHttpClient();
        if (cache != null) {
            okHttpClient.setCache(cache);
        }
        String hostURL = context.getString(R.string.host_url);

        api = new RestAdapter.Builder()
                .setEndpoint(hostURL)
                .setClient(new OkClient(okHttpClient))
                .setRequestInterceptor(/*rest of the answer here */)
                .build()
                .create(MyApi.class);

原文答案：

事实证明，服务器响应必须 Cache-Control: public 才能使 OkClient 从缓存中读取 .

此外，如果要在可用时从网络请求，则应添加 Cache-Control: max-age=0 请求标头 . This answer显示了如何进行参数化 . 这就是我使用它的方式：

RestAdapter.Builder builder= new RestAdapter.Builder()
   .setRequestInterceptor(new RequestInterceptor() {
        @Override
        public void intercept(RequestFacade request) {
            request.addHeader("Accept", "application/json;versions=1");
            if (MyApplicationUtils.isNetworkAvailable(context)) {
                int maxAge = 60; // read from cache for 1 minute
                request.addHeader("Cache-Control", "public, max-age=" + maxAge);
            } else {
                int maxStale = 60 * 60 * 24 * 28; // tolerate 4-weeks stale
                request.addHeader("Cache-Control", 
                    "public, only-if-cached, max-stale=" + maxStale);
            }
        }
});

回复于 2024-04-28T06:04:00+08:00

以上所有的东西都不适合我 . 我试图在 retrofit 2.0.0-beta2 中实现离线缓存 . 我使用 okHttpClient.networkInterceptors() 方法添加了一个拦截器，但是当我尝试脱机使用缓存时收到 java.net.UnknownHostException . 事实证明我也必须添加 okHttpClient.interceptors() .

问题是缓存没有写入闪存存储，因为服务器返回了 Pragma:no-cache ，这阻止了OkHttp存储响应 . 即使在修改请求标头值后，脱机缓存也不起作用 . 经过一些试验和错误后，我通过从响应中删除pragma而不是请求来使缓存工作而不修改后端端 - response.newBuilder().removeHeader("Pragma");

改造： 2.0.0-beta2 ; OkHttp： 2.5.0

OkHttpClient okHttpClient = createCachedClient(context);
Retrofit retrofit = new Retrofit.Builder()
        .client(okHttpClient)
        .baseUrl(API_URL)
        .addConverterFactory(GsonConverterFactory.create())
        .build();
service = retrofit.create(RestDataResource.class);

...

private OkHttpClient createCachedClient(final Context context) {
    File httpCacheDirectory = new File(context.getCacheDir(), "cache_file");

    Cache cache = new Cache(httpCacheDirectory, 20 * 1024 * 1024);
    OkHttpClient okHttpClient = new OkHttpClient();
    okHttpClient.setCache(cache);
    okHttpClient.interceptors().add(
            new Interceptor() {
                @Override
                public Response intercept(Chain chain) throws IOException {
                    Request originalRequest = chain.request();
                    String cacheHeaderValue = isOnline(context) 
                        ? "public, max-age=2419200" 
                        : "public, only-if-cached, max-stale=2419200" ;
                    Request request = originalRequest.newBuilder().build();
                    Response response = chain.proceed(request);
                    return response.newBuilder()
                        .removeHeader("Pragma")
                        .removeHeader("Cache-Control")
                        .header("Cache-Control", cacheHeaderValue)
                        .build();
                }
            }
    );
    okHttpClient.networkInterceptors().add(
            new Interceptor() {
                @Override
                public Response intercept(Chain chain) throws IOException {
                    Request originalRequest = chain.request();
                    String cacheHeaderValue = isOnline(context) 
                        ? "public, max-age=2419200" 
                        : "public, only-if-cached, max-stale=2419200" ;
                    Request request = originalRequest.newBuilder().build();
                    Response response = chain.proceed(request);
                    return response.newBuilder()
                        .removeHeader("Pragma")
                        .removeHeader("Cache-Control")
                        .header("Cache-Control", cacheHeaderValue)
                        .build();
                }
            }
    );
    return okHttpClient;
}

...

public interface RestDataResource {

    @GET("rest-data") 
    Call<List<RestItem>> getRestData();

}

回复于 2024-04-28T06:04:00+08:00

我的解决方案

private BackendService() {

    httpCacheDirectory = new File(context.getCacheDir(),  "responses");
    int cacheSize = 10 * 1024 * 1024; // 10 MiB
    Cache cache = new Cache(httpCacheDirectory, cacheSize);

    httpClient = new OkHttpClient.Builder()
            .addNetworkInterceptor(REWRITE_RESPONSE_INTERCEPTOR)
            .addInterceptor(OFFLINE_INTERCEPTOR)
            .cache(cache)
            .build();

    Retrofit retrofit = new Retrofit.Builder()
            .baseUrl("https://api.backend.com")
            .client(httpClient)
            .addConverterFactory(GsonConverterFactory.create())
            .build();

    backendApi = retrofit.create(BackendApi.class);
}

private static final Interceptor REWRITE_RESPONSE_INTERCEPTOR = chain -> {
    Response originalResponse = chain.proceed(chain.request());
    String cacheControl = originalResponse.header("Cache-Control");

    if (cacheControl == null || cacheControl.contains("no-store") || cacheControl.contains("no-cache") ||
            cacheControl.contains("must-revalidate") || cacheControl.contains("max-age=0")) {
        return originalResponse.newBuilder()
                .header("Cache-Control", "public, max-age=" + 10)
                .build();
    } else {
        return originalResponse;
    }
};

private static final Interceptor OFFLINE_INTERCEPTOR = chain -> {
    Request request = chain.request();

    if (!isOnline()) {
        Log.d(TAG, "rewriting request");

        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);
};

public static boolean isOnline() {
    ConnectivityManager cm = (ConnectivityManager) MyApplication.getApplication().getSystemService(Context.CONNECTIVITY_SERVICE);
    NetworkInfo netInfo = cm.getActiveNetworkInfo();
    return netInfo != null && netInfo.isConnectedOrConnecting();
}

回复于 2024-04-28T06:04:00+08:00

28

Build 在@ kosiara-bartosz-kasarzycki的answer上，我创建了一个示例项目，使用改造，okhttp，rxjava和guava从内存 - >磁盘 - >网络正确加载 . https://github.com/digitalbuddha/StoreDemo

回复于 2024-04-28T06:04:00+08:00
1
答案是肯定的，根据上述答案，我开始编写单元测试来验证所有可能的用例：
- Use cache when offline
- 首先使用缓存响应，直到过期，然后使用网络
- 首先使用网络然后缓存某些请求
- 不要在缓存中存储某些响应
我构建了一个小助手lib来轻松配置OKHttp缓存，你可以在Github上看到相关的单元测试：https://github.com/ncornette/OkCacheControl/blob/master/okcache-control/src/test/java/com/ncornette/cache/OkCacheControlTest.java

单元测试，演示离线时使用缓存：
```
@Test
public void test_USE_CACHE_WHEN_OFFLINE() throws Exception {
    //given
    givenResponseInCache("Expired Response in cache", -5, MINUTES);
    given(networkMonitor.isOnline()).willReturn(false);

    //when
    //This response is only used to not block when test fails
    mockWebServer.enqueue(new MockResponse().setResponseCode(404));
    Response response = getResponse();

    //then
    then(response.body().string()).isEqualTo("Expired Response in cache");
    then(cache.hitCount()).isEqualTo(1);
}
```
如您所见，即使缓存已过期，也可以使用缓存 . 希望它会有所帮助 .
回复于 2024-04-28T06:04:00+08:00

使用Retrofit2和OkHTTP3缓存：

OkHttpClient client = new OkHttpClient
  .Builder()
  .cache(new Cache(App.sApp.getCacheDir(), 10 * 1024 * 1024)) // 10 MB
  .addInterceptor(new Interceptor() {
    @Override public Response intercept(Chain chain) throws IOException {
      Request request = chain.request();
      if (NetworkUtils.isNetworkAvailable()) {
        request = request.newBuilder().header("Cache-Control", "public, max-age=" + 60).build();
      } else {
        request = request.newBuilder().header("Cache-Control", "public, only-if-cached, max-stale=" + 60 * 60 * 24 * 7).build();
      }
      return chain.proceed(request);
    }
  })
  .build();

NetworkUtils.isNetworkAvailable（）静态方法：

public static boolean isNetworkAvailable(Context context) {
        ConnectivityManager cm =
                (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);
        NetworkInfo activeNetwork = cm.getActiveNetworkInfo();
        return activeNetwork != null &&
                activeNetwork.isConnectedOrConnecting();
    }

然后只需将客户端添加到改造构建器：

Retrofit retrofit = new Retrofit.Builder()
                    .baseUrl(BASE_URL)
                    .client(client)
                    .addConverterFactory(GsonConverterFactory.create())
                    .build();

原始来源：https://newfivefour.com/android-retrofit2-okhttp3-cache-network-request-offline.html

回复于 2024-04-28T06:04:00+08:00

使用OKHttp进行改造可以在离线时使用缓存数据

6 回答

编辑改造2.x：

OKHttp 2.0.x（查看原始答案）：

原文答案：

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