OkHttp3 详解及开发实例—官方原版（二）

 

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二、方法

Posting a multipart request

MultipartBody.Builder 可以构建与HTML文件上传表单兼容的复杂请求主体。多部分请求正文的每个部分本身都是请求正文，并且可以定义自己的标头。如果存在，这些标头应该描述部件主体，例如其内容处置。内容长度和内容类型标头将自动添加（如果可用）。

/**
   * The imgur client ID for OkHttp recipes. If you're using imgur for anything other than running
   * these examples, please request your own client ID! https://api.imgur.com/oauth2
   */
  private static final String IMGUR_CLIENT_ID = "...";
  private static final MediaType MEDIA_TYPE_PNG = MediaType.parse("image/png");

  private final OkHttpClient client = new OkHttpClient();

  public void run() throws Exception {
    // Use the imgur image upload API as documented at https://api.imgur.com/endpoints/image
    RequestBody requestBody = new MultipartBody.Builder()
        .setType(MultipartBody.FORM)
        .addFormDataPart("title", "Square Logo")
        .addFormDataPart("image", "logo-square.png",
            RequestBody.create(MEDIA_TYPE_PNG, new File("website/static/logo-square.png")))
        .build();

    Request request = new Request.Builder()
        .header("Authorization", "Client-ID " + IMGUR_CLIENT_ID)
        .url("https://api.imgur.com/3/image")
        .post(requestBody)
        .build();

    try (Response response = client.newCall(request).execute()) {
      if (!response.isSuccessful()) throw new IOException("Unexpected code " + response);

      System.out.println(response.body().string());
    }
  }

Parse a JSON Response With Moshi 

Moshi是一个方便的API，用于在JSON和Java对象之间进行转换。这里，我们使用它来解码来自GitHub API的JSON响应。

请注意，ResponseBody.charStream（）使用Content-Type响应标头来选择解码响应正文时要使用的字符集。如果未指定字符集，则默认为UTF-8。

private final OkHttpClient client = new OkHttpClient();
  private final Moshi moshi = new Moshi.Builder().build();
  private final JsonAdapter<Gist> gistJsonAdapter = moshi.adapter(Gist.class);

  public void run() throws Exception {
    Request request = new Request.Builder()
        .url("https://api.github.com/gists/c2a7c39532239ff261be")
        .build();
    try (Response response = client.newCall(request).execute()) {
      if (!response.isSuccessful()) throw new IOException("Unexpected code " + response);

      Gist gist = gistJsonAdapter.fromJson(response.body().source());

      for (Map.Entry<String, GistFile> entry : gist.files.entrySet()) {
        System.out.println(entry.getKey());
        System.out.println(entry.getValue().content);
      }
    }
  }

  static class Gist {
    Map<String, GistFile> files;
  }

  static class GistFile {
    String content;
  }

Response Caching 

要缓存响应，您需要一个可以读取和写入的缓存目录，以及对缓存大小的限制。缓存目录应该是私有的，不受信任的应用程序应该无法读取其内容！

让多个缓存同时访问同一缓存目录是错误的。大多数应用程序应该只调用一次新的OkHttpClient（），用它们的缓存配置它，并在任何地方使用相同的实例。否则，两个缓存实例将相互踩踏，损坏响应缓存，并可能使程序崩溃。

响应缓存对所有配置使用HTTP标头。您可以添加请求标头，如Cache-Control:max-state=3600，OkHttp的缓存将支持它们。Web服务器使用自己的响应标头配置响应的缓存时间，如Cache-Control:max-age=9600。有缓存标头来强制缓存响应、强制网络响应或强制使用条件GET验证网络响应。

private final OkHttpClient client;

  public CacheResponse(File cacheDirectory) throws Exception {
    int cacheSize = 10 * 1024 * 1024; // 10 MiB
    Cache cache = new Cache(cacheDirectory, cacheSize);

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

  public void run() throws Exception {
    Request request = new Request.Builder()
        .url("http://publicobject.com/helloworld.txt")
        .build();

    String response1Body;
    try (Response response1 = client.newCall(request).execute()) {
      if (!response1.isSuccessful()) throw new IOException("Unexpected code " + response1);

      response1Body = response1.body().string();
      System.out.println("Response 1 response:          " + response1);
      System.out.println("Response 1 cache response:    " + response1.cacheResponse());
      System.out.println("Response 1 network response:  " + response1.networkResponse());
    }

    String response2Body;
    try (Response response2 = client.newCall(request).execute()) {
      if (!response2.isSuccessful()) throw new IOException("Unexpected code " + response2);

      response2Body = response2.body().string();
      System.out.println("Response 2 response:          " + response2);
      System.out.println("Response 2 cache response:    " + response2.cacheResponse());
      System.out.println("Response 2 network response:  " + response2.networkResponse());
    }

    System.out.println("Response 2 equals Response 1? " + response1Body.equals(response2Body));
  }

要防止响应使用缓存，请使用CacheControl。FORCE_NETWORK.要防止它使用网络，请使用CacheControl。强制捕获。请注意：如果使用FORCE_CACHE，并且响应需要网络，OkHttp将返回504 Unsatisfailable Request响应。
 

Canceling a Call

使用Call.cancel（）立即停止正在进行的呼叫。如果线程当前正在写入请求或读取响应，则它将接收IOException。当不再需要通话时，使用此选项可保留网络；例如，当用户离开应用程序时。同步和异步调用都可以取消。

 private final ScheduledExecutorService executor = Executors.newScheduledThreadPool(1);
  private final OkHttpClient client = new OkHttpClient();

  public void run() throws Exception {
    Request request = new Request.Builder()
        .url("http://httpbin.org/delay/2") // This URL is served with a 2 second delay.
        .build();

    final long startNanos = System.nanoTime();
    final Call call = client.newCall(request);

    // Schedule a job to cancel the call in 1 second.
    executor.schedule(new Runnable() {
      @Override public void run() {
        System.out.printf("%.2f Canceling call.%n", (System.nanoTime() - startNanos) / 1e9f);
        call.cancel();
        System.out.printf("%.2f Canceled call.%n", (System.nanoTime() - startNanos) / 1e9f);
      }
    }, 1, TimeUnit.SECONDS);

    System.out.printf("%.2f Executing call.%n", (System.nanoTime() - startNanos) / 1e9f);
    try (Response response = call.execute()) {
      System.out.printf("%.2f Call was expected to fail, but completed: %s%n",
          (System.nanoTime() - startNanos) / 1e9f, response);
    } catch (IOException e) {
      System.out.printf("%.2f Call failed as expected: %s%n",
          (System.nanoTime() - startNanos) / 1e9f, e);
    }
  }

Timeouts 

当对等方不可访问时，使用超时使呼叫失败。网络分区可能是由于客户端连接问题、服务器可用性问题或两者之间的任何问题造成的。OkHttp支持连接、写入、读取和完全调用超时。

 private final OkHttpClient client;

  public ConfigureTimeouts() throws Exception {
    client = new OkHttpClient.Builder()
        .connectTimeout(10, TimeUnit.SECONDS)
        .writeTimeout(10, TimeUnit.SECONDS)
        .readTimeout(30, TimeUnit.SECONDS)
        .build();
  }

  public void run() throws Exception {
    Request request = new Request.Builder()
        .url("http://httpbin.org/delay/2") // This URL is served with a 2 second delay.
        .build();

    try (Response response = client.newCall(request).execute()) {
      System.out.println("Response completed: " + response);
    }
  }

Per-call Configuration

所有HTTP客户端配置都存在于OkHttpClient中，包括代理设置、超时和缓存。当您需要更改单个调用的配置时，请调用OkHttpClient.newBuilder（）。这将返回一个与原始客户端共享相同连接池、分派器和配置的构建器。在下面的示例中，我们发出一个超时500毫秒的请求，另一个超时3000毫秒。
 

private final OkHttpClient client = new OkHttpClient();

  public void run() throws Exception {
    Request request = new Request.Builder()
        .url("http://httpbin.org/delay/1") // This URL is served with a 1 second delay.
        .build();

    // Copy to customize OkHttp for this request.
    OkHttpClient client1 = client.newBuilder()
        .readTimeout(500, TimeUnit.MILLISECONDS)
        .build();
    try (Response response = client1.newCall(request).execute()) {
      System.out.println("Response 1 succeeded: " + response);
    } catch (IOException e) {
      System.out.println("Response 1 failed: " + e);
    }

    // Copy to customize OkHttp for this request.
    OkHttpClient client2 = client.newBuilder()
        .readTimeout(3000, TimeUnit.MILLISECONDS)
        .build();
    try (Response response = client2.newCall(request).execute()) {
      System.out.println("Response 2 succeeded: " + response);
    } catch (IOException e) {
      System.out.println("Response 2 failed: " + e);
    }
  }

Handling authentication

OkHttp可以自动重试未经身份验证的请求。当响应为401未授权时，将要求验证者提供凭据。实现应构建包含缺少的凭据的新请求。如果没有可用的凭据，则返回null以跳过重试。

使用Response.challenges（）获取任何身份验证挑战的方案和领域。在完成基本质询时，使用Credentials.Basic（用户名、密码）对请求头进行编码。
 

private final OkHttpClient client;

  public Authenticate() {
    client = new OkHttpClient.Builder()
        .authenticator(new Authenticator() {
          @Override public Request authenticate(Route route, Response response) throws IOException {
            if (response.request().header("Authorization") != null) {
              return null; // Give up, we've already attempted to authenticate.
            }

            System.out.println("Authenticating for response: " + response);
            System.out.println("Challenges: " + response.challenges());
            String credential = Credentials.basic("jesse", "password1");
            return response.request().newBuilder()
                .header("Authorization", credential)
                .build();
          }
        })
        .build();
  }

  public void run() throws Exception {
    Request request = new Request.Builder()
        .url("http://publicobject.com/secrets/hellosecret.txt")
        .build();

    try (Response response = client.newCall(request).execute()) {
      if (!response.isSuccessful()) throw new IOException("Unexpected code " + response);

      System.out.println(response.body().string());
    }
  }

为了避免在身份验证不工作时进行多次重试，可以返回null放弃。例如，当已经尝试了这些确切的凭据时，您可能希望跳过重试：
 

 if (credential.equals(response.request().header("Authorization"))) {
    return null; // If we already failed with these credentials, don't retry.
   }

当达到应用程序定义的尝试限制时，也可以跳过重试：

  if (responseCount(response) >= 3) {
    return null; // If we've failed 3 times, give up.
  }

上述代码依赖于此responseCount（）方法：

  private int responseCount(Response response) {
    int result = 1;
    while ((response = response.priorResponse()) != null) {
      result++;
    }
    return result;
  }