OKHTTP(四) Recipes(使用方法)

Recipes

我们已经编写了一些使用方法，演示如何使用OkHttp解决常见问题。
仔细阅读它们，了解一切如何协同工作。自由剪切和粘贴这些例子;

Synchronous Get

下载文件，打印其标题，并将其响应正文打印为字符串。
响应体上的string（）方法对于小文档来说非常方便有效。
但是如果响应体很大（大于1 MiB），请避免使用string（），因为它会将整个文档加载到内存中。在这种情况下，更喜欢将消息体作为流来处理。

private final OkHttpClient client = new OkHttpClient();

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

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

     Headers responseHeaders = response.headers();
     for (int i = 0; i < responseHeaders.size(); i++) {
       System.out.println(responseHeaders.name(i) + ": " + responseHeaders.value(i));
     }

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

Asynchronous Get

在工作线程上下载文件，并在响应可读时回调。
回调是在响应头准备好之后进行的。
阅读响应正文可能仍会阻止。
OkHttp目前不提供异步API来接收部分响应主体。

private final OkHttpClient client = new OkHttpClient();

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

    client.newCall(request).enqueue(new Callback() {
      @Override 
      public void onFailure(Call call, IOException e) {
        e.printStackTrace();
      }

      @Override 
      public void onResponse(Call call, Response response) throws IOException {
        try (ResponseBody responseBody = response.body()) {
          if (!response.isSuccessful()) throw new IOException("Unexpected code " + response);

          Headers responseHeaders = response.headers();
          for (int i = 0, size = responseHeaders.size(); i < size; i++) {
            System.out.println(responseHeaders.name(i) + ": " + responseHeaders.value(i));
          }

          System.out.println(responseBody.string());
        }
      }
    });
  }

Accessing Headers(访问标题)

通常，HTTP标头的工作方式类似于Map <String，String>：每个字段都有一个值或没有。
但是一些标题允许多个值，例如Guava的Multimap。
例如，HTTP响应提供多个Vary标头是合法且常见的。
OkHttp的API试图使两种情况都很舒适。

在编写请求标头时，使用标头（名称，值）将name的唯一出现设置为value。
如果存在现有值，则在添加新值之前将删除它们。
使用addHeader（name，value）添加标头而不删除已存在的标头。

读取响应标头时，使用标头（名称）返回最后一次出现的命名值。
通常这也是唯一的发生！
如果没有值，则header（name）将返回null。
要将所有字段的值作为列表读取，请使用标题（名称）。

要访问所有标头，请使用支持索引访问的Headers类。

private final OkHttpClient client = new OkHttpClient();

  public void run() throws Exception {
    Request request = new Request.Builder()
        .url("https://api.github.com/repos/square/okhttp/issues")
        .header("User-Agent", "OkHttp Headers.java")
        .addHeader("Accept", "application/json; q=0.5")
        .addHeader("Accept", "application/vnd.github.v3+json")
        .build();

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

      System.out.println("Server: " + response.header("Server"));
      System.out.println("Date: " + response.header("Date"));
      System.out.println("Vary: " + response.headers("Vary"));
    }
  }

Posting a String

使用HTTP POST将请求正文发送到服务。
此示例将markdown文档发布到将markdown呈现为HTML的Web服务。
由于整个请求主体同时在内存中，因此请避免使用此API发布大型（大于1 MiB）文档。

public static final MediaType MEDIA_TYPE_MARKDOWN
      = MediaType.parse("text/x-markdown; charset=utf-8");

  private final OkHttpClient client = new OkHttpClient();

  public void run() throws Exception {
    String postBody = ""
        + "Releases\n"
        + "--------\n"
        + "\n"
        + " * _1.0_ May 6, 2013\n"
        + " * _1.1_ June 15, 2013\n"
        + " * _1.2_ August 11, 2013\n";

    Request request = new Request.Builder()
        .url("https://api.github.com/markdown/raw")
        .post(RequestBody.create(MEDIA_TYPE_MARKDOWN, postBody))
        .build();

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

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

Post a file

public static final MediaType MEDIA_TYPE_MARKDOWN
      = MediaType.parse("text/x-markdown; charset=utf-8");

  private final OkHttpClient client = new OkHttpClient();

  public void run() throws Exception {
    File file = new File("README.md");

    Request request = new Request.Builder()
        .url("https://api.github.com/markdown/raw")
        .post(RequestBody.create(MEDIA_TYPE_MARKDOWN, file))
        .build();

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

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

Post Streaming

在这里，我们将请求主体作为流发布。
该请求正文的内容正在编写时生成。
此示例直接流入Okio缓冲接收器。
您的程序可能更喜欢OutputStream，您可以从BufferedSink.outputStream（）获取它。

public static final MediaType MEDIA_TYPE_MARKDOWN
      = MediaType.parse("text/x-markdown; charset=utf-8");

  private final OkHttpClient client = new OkHttpClient();

  public void run() throws Exception {
    RequestBody requestBody = new RequestBody() {
      @Override 
      public MediaType contentType() {
        return MEDIA_TYPE_MARKDOWN;
      }

      @Override 
      public void writeTo(BufferedSink sink) throws IOException {
        sink.writeUtf8("Numbers\n");
        sink.writeUtf8("-------\n");
        for (int i = 2; i <= 997; i++) {
          sink.writeUtf8(String.format(" * %s = %s\n", i, factor(i)));
        }
      }

      private String factor(int n) {
        for (int i = 2; i < n; i++) {
          int x = n / i;
          if (x * i == n) return factor(x) + " × " + i;
        }
        return Integer.toString(n);
      }
    };

    Request request = new Request.Builder()
        .url("https://api.github.com/markdown/raw")
        .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());
    }
  }

Posting form parameters

使用FormBody.Builder构建一个像HTML

标记一样工作的请求体。
名称和值将使用HTML兼容的表单URL编码进行编码。

private final OkHttpClient client = new OkHttpClient();

  public void run() throws Exception {
    RequestBody formBody = new FormBody.Builder()
        .add("search", "Jurassic Park")
        .build();
    Request request = new Request.Builder()
        .url("https://en.wikipedia.org/w/index.php")
        .post(formBody)
        .build();

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

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

Posting a multipart request

MultipartBody.Builder可以构建与HTML文件上载表单兼容的复杂请求主体。
多部分请求主体的每个部分本身都是一个请求主体，并且可以定义自己的头部。
如果存在，这些标题应描述零件主体，例如其内容 - 处置。
如果Content-Length和Content-Type标头可用，则会自动添加它们。

/**
   * 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(使用Moshi解析JSON响应)

Moshi是一个方便的API，用于在JSON和Java对象之间进行转换。
在这里，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响应头来选择在解码响应主体时使用哪个charset。
如果未指定charset，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不应该能够读取其内容。

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（），使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，破坏响应缓存，并可能导致程序崩溃。

响应缓存使用HTTP标头进行所有配置。
您可以添加请求标头，如Cache-Control：max-stale = 3600，OkHttp的缓存将遵循它们。
您的Web服务器使用自己的响应标头配置缓存响应的时间，例如Cache-Control：max-age = 9600。
有缓存标头可强制缓存响应，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));
}

要阻止响应使用缓存，请使用CacheControl.FORCE_NETWORK。
要阻止它使用网络，请使用CacheControl.FORCE_CACHE。
警告：如果你使用FORCE_CACHE并且响应需要网络，OkHttp将返回504不满意的请求响应。

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，则它将收到IOException。
当不再需要呼叫时，使用它来保护网络;
例如，当您的用户导航离开应用程序时。
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

当对等方无法访问时，使用超时来使呼叫失败。
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其他任何问题。
OkHttp支持连接，读取和写入超时。

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（）。
这将返回与原始客户端共享相同连接池，调度程序和配置的构建器。
在下面的示例中，我们发出一个请求，其中500毫秒超时，另一个请求超时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(认证处理)

OkHttp可以自动重试未经身份验证的请求。
如果响应为401 Not Authorized，则要求Authenticator提供凭据。
实现应该构建包含缺少凭据的新请求。
如果没有可用的凭据，则返回null以跳过重试。

使用Response.challenges（）来获取任何身份验证挑战的方案和领域。
在完成基本挑战时，使用Credentials.basic（用户名，密码）对请求标头进行编码。

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());
    }
  }

为避免在身份验证不起作用时进行多次重试，您可以返回null以放弃。
例如，您可能希望在尝试这些确切凭据时跳过重试：

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

当您达到应用程序定义的尝试限制时，您也可以跳过重试：

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

上面的代码依赖于这个responseCount（）方法：

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