Retrofit + OkHttp缓存处理的示例代码

作者：袖梨 2022-06-25

通过缓存处理可以有效降低服务器的负荷,加快APP界面加载速度,提升用户体验。Retrofit + OkHttp缓存处理流程是这样的,请求响应之后会在data/data/packageName/cache下建立一个response文件夹，保存缓存数据,后续请求时若无网络,则直接读取缓存内容,若有网络则从网络获取最新数据并缓存。

1.设置缓存路径,大小及添加缓存拦截器 

//设置缓存路径
File httpCacheDirectory = new File(CommonApplication.getInstance().getCacheDir(), "responses");
//设置缓存 10M
Cache cache = new Cache(httpCacheDirectory, 10 * 1024 * 1024);
//创建OkHttpClient，并添加拦截器和缓存代码
OkHttpClient client = new OkHttpClient.Builder()
    .addNetworkInterceptor(new CacheInterceptor(CommonApplication.getInstance()))
    .cache(cache).build();

2.定义缓存拦截器。若网络正常,则缓存有效期1分钟;若网络异常,则缓存有效期6小时 

public class CacheInterceptor implements Interceptor {
  private Context mContext;
  public CacheInterceptor(Context context) {
    mContext = context;
  }
  @Override
  public Response intercept(Chain chain) throws IOException {
    Request request = chain.request();
    if (NetworkUtils.isNetworkAvailable(mContext)) {//没网强制从缓存读取(必须得写，不然断网状态下，退出应用，或者等待一分钟后，就获取不到缓存）
      request = request.newBuilder()
          .cacheControl(CacheControl.FORCE_CACHE)
          .build();
    }
    Response response = chain.proceed(request);
    Response responseLatest;
    if (NetworkUtils.isNetworkAvailable(mContext)) {
      int maxAge = 60; //有网失效一分钟
      responseLatest = response.newBuilder()
          .removeHeader("Pragma")
          .removeHeader("Cache-Control")
          .header("Cache-Control", "public, max-age=" + maxAge)
          .build();
    } else {
      int maxStale = 60 * 60 * 6; // 没网失效6小时
      responseLatest = response.newBuilder()
          .removeHeader("Pragma")
          .removeHeader("Cache-Control")
          .header("Cache-Control", "public, only-if-cached, max-stale=" + maxStale)
          .build();
    }
    return responseLatest;
  }
}

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