CacheInterceptor

public final class CacheInterceptor implements Interceptor {
  @Override public Response intercept(Chain chain) throws IOException {
    CacheStrategy strategy = new CacheStrategy.Factory(now, chain.request(), cacheCandidate).get();
    Request networkRequest = strategy.networkRequest;
    Response cacheResponse = strategy.cacheResponse;

    if (cache != null) {
      /**
       * Track an HTTP response being satisfied with {@code cacheStrategy}.
       * 主要是跟踪networkRequest次数以及对应Cache的hitcount
       */
      cache.trackResponse(strategy);
    }

    if (cacheCandidate != null && cacheResponse == null) {
      closeQuietly(cacheCandidate.body()); // The cache candidate wasn't applicable. Close it.
    }

    // If we're forbidden from using the network and the cache is insufficient, fail.
    if (networkRequest == null && cacheResponse == null) {
      return new Response.Builder()
          .request(chain.request())
          .protocol(Protocol.HTTP_1_1)
          .code(504)
          .message("Unsatisfiable Request (only-if-cached)")
          .body(Util.EMPTY_RESPONSE)
          .sentRequestAtMillis(-1L)
          .receivedResponseAtMillis(System.currentTimeMillis())
          .build();
    }

    // If we don't need the network, we're done.
    if (networkRequest == null) {
      return cacheResponse.newBuilder()
          .cacheResponse(stripBody(cacheResponse))
          .build();
    }

    //在chain.proceed()调用下一个拦截器
    Response networkResponse = null;
    try {
      networkResponse = chain.proceed(networkRequest);
    } finally {
      // If we're crashing on I/O or otherwise, don't leak the cache body.
      if (networkResponse == null && cacheCandidate != null) {
        closeQuietly(cacheCandidate.body());
      }
    }

    //处理response并返回
    ...
    return response;
  }
}

CacheStrategy

OkHttpClient

OkHttpClient托管着所有HTTP调用, 每个Client均拥有自己的连接池和线程池

• 实现抽象类Internal的方法，这是Internel抽象类唯一的实现，方法与CacheInterceptor控制Http的Header.Lenient区域和StreamAlloction从连接池中获取连接有关

  private RealConnection findConnection(int connectTimeout, int readTimeout, int writeTimeout,
      int pingIntervalMillis, boolean connectionRetryEnabled) throws IOException {
    ...
    synchronized (connectionPool) {
      ...
      if (result == null) {
        // Attempt to get a connection from the pool.
        Internal.instance.get(connectionPool, address, this, null);
        if (connection != null) {
          foundPooledConnection = true;
          result = connection;
        } else {
          selectedRoute = route;
        }
      }
    }
    return result;
  }

• RouteDatabase && RouteSeletor