Android OkHttp经验小结

OkHttp应该是目前最完善，也是相当流行的一个底层网络请求库。Google都在用，所以有必要深入了解一下，刚好最近在重构公司项目的网络层，就顺便梳理一下。
———–12.29————
最近暂时没有时间详细整理了。就简单过了一下官方文档。
以下取自官方文档。

网络请求

同步Get方法

以下样例代码下载一个文件，打印headers，打印字符串形式的 response body

private final OkHttpClient client = new OkHttpClient();

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

    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());
  }

注意： response body中的string()方法对小文件是很方便高效的，但是当response body 大于1M时，避免用string()，因为它会加载整个文件到内存，此时应该把body用stream的形式来处理.

异步Get方法

在工作线程下载一个文件，并且当response准备好了的时候回调Callback。 response headers 准备好了的时候，就走回调。读response body 也会阻塞线程，OkHttp暂时没有提供额外的异步
APIs来获得response body。

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(Request request, IOException throwable) {
        throwable.printStackTrace();
      }

      @Override public void onResponse(Response response) throws IOException {
        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());
      }
    });
  }

Accessing Headers

典型的HTTP请求头，像Map<String, String>那样工作，每个field有一个值或者没有，但是有的headers允许有多个值,就像Guava’s Multimap.比如，一个HTTP response 提供多个多样的headers是合法且普遍的。 OkHttp’s APIs 兼容这两种情况。
注意：当写request headers时，header(name, value) 设置唯一的键值对，这会覆盖已有的值。而用方法 addHeader(name, value) 来添加header时，不会移除已有的header。
相应的header(name)来获取最后的这个name的相应value，通常这也是唯一的，如果没有就返回null 。headers(name)用来read所有的field的值，已list的形式。
想要看所有的headers，使用支持通过索引访问的类Headers

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();

  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

由于这个request body同时要完全加载到内存，所以避免用个API来posting大于1M的文件。

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();

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

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

Post Streaming

一下示例代码使用到了Okio的buffered sink，你可能更喜欢使用OutputStream，你可以通过BufferedSink.outputStream()来获得。

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();

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

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

Posting文件

简单

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();

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

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

Posting form parameters(格式化参数)

用FormEncodingBuilder来构建一个request body，像HTML的

标签一样工作，键值对将以兼容HTML的URL编码方式被组织。

private final OkHttpClient client = new OkHttpClient();

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

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

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

Posting一个multipart request(复合请求)

MultipartBuilder可以构建复杂的request bodies，兼容html文件上传forms。复合请求的每个request body分别可以定义自己的headers，如果存在，这些headers分别描述相应的body，例如Content-Disposition。The Content-Length and Content-Type headers 会自动添加。

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 MultipartBuilder()
      .type(MultipartBuilder.FORM)
      .addPart(
          Headers.of("Content-Disposition", "form-data; name=\"title\""),
          RequestBody.create(null, "Square Logo"))
      .addPart(
          Headers.of("Content-Disposition", "form-data; name=\"image\""),
          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();

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

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

用Gson解析JSON返回结果

Gson是一个便利的API用来转换JSON和java对象。
Note that ResponseBody.charStream() uses the Content-Type response header to select which charset to use when decoding the response body. It defaults to UTF-8 if no charset is specified.
注意ResponseBody.charStream()根据返回头的Content-Type来选择相应的编码方式，来解码response body。如果没有定义charset，默认是用UTF-8。

private final OkHttpClient client = new OkHttpClient();
private final Gson gson = new Gson();

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

  Gist gist = gson.fromJson(response.body().charStream(), Gist.class);
  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

缓存请求结果，你需要一个你可以读写的限制大小的缓存目录，缓存目录应该是私有的，禁止未信任的程序随便读取。
Response caching uses HTTP headers for all configuration. You can add request headers like Cache-Control: max-stale=3600 and OkHttp’s cache will honor them. Your webserver configures how long responses are cached with its own response headers, like Cache-Control: max-age=9600. There are cache headers to force a cached response, force a network response, or force the network response to be validated with a conditional GET.
Response caching完全用HTTP headers来配置，你可以添加像这样的请求头：Cache-Control: max-stale=3600，你的web服务器可以这样的请求头Cache-Control: max-age=9600来配置请求结果缓存时间。可以设置相应的headers来强制缓存response，force a network response, or force the network response to be validated(经过验证的) with a conditional GET.

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();
  client.setCache(cache);
}

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

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

  String 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());

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

  String 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));
}

阻止使用缓存的response，使用CacheControl.FORCE_NETWORK。阻止使用网络，使用 CacheControl.FORCE_CACHE。注意，如果你使用FORCE_CACHE而response需要网络支持的话，OkHttp 将返回一个 504 Unsatisfiable Request response.

取消一个call

用Call.cancel()会立刻停止一个进行中的请求，如果一个线程正在writing一个request，或者在reading一个response，将会抛IOException。
如果你的用户操作离开了app，所有的同步异步请求都应该取消。
你可以用tags来同时取消多个请求，用RequestBuilder.tag(tag)在创建请求的时候指定一个tag，用OkHttpClient.cancel(tag)取消所有有这个tag的请求。

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);

  try {
    System.out.printf("%.2f Executing call.%n", (System.nanoTime() - startNanos) / 1e9f);
    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

  private final OkHttpClient client;

public ConfigureTimeouts() throws Exception {
  client = new OkHttpClient();
  client.setConnectTimeout(10, TimeUnit.SECONDS);
  client.setWriteTimeout(10, TimeUnit.SECONDS);
  client.setReadTimeout(30, TimeUnit.SECONDS);
}

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();

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

Per-call Configuration 某个请求特殊配置

所有的HTTP client配置都在OkHttpClient，包括代理，超时，缓存，你想为单个请求改变配置的话，clone the OkHttpClient，这个会返回一个浅(shallow)copy让你来单独定制，如下，你make了一个500ms超时的和3000ms超时的请求。

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();

  try {
    OkHttpClient cloned = client.clone(); // Clone to make a customized OkHttp for this request.
    cloned.setReadTimeout(500, TimeUnit.MILLISECONDS);

    Response response = cloned.newCall(request).execute();
    System.out.println("Response 1 succeeded: " + response);
  } catch (IOException e) {
    System.out.println("Response 1 failed: " + e);
  }

  try {
    OkHttpClient cloned = client.clone(); // Clone to make a customized OkHttp for this request.
    cloned.setReadTimeout(3000, TimeUnit.MILLISECONDS);

    Response response = cloned.newCall(request).execute();
    System.out.println("Response 2 succeeded: " + response);
  } catch (IOException e) {
    System.out.println("Response 2 failed: " + e);
  }
}

新版3.0修改为如下：

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();

  try {
    // Copy to customize OkHttp for this request.
    OkHttpClient copy = client.newBuilder()
        .readTimeout(500, TimeUnit.MILLISECONDS)
        .build();

    Response response = copy.newCall(request).execute();
    System.out.println("Response 1 succeeded: " + response);
  } catch (IOException e) {
    System.out.println("Response 1 failed: " + e);
  }

  try {
    // Copy to customize OkHttp for this request.
    OkHttpClient copy = client.newBuilder()
        .readTimeout(3000, TimeUnit.MILLISECONDS)
        .build();

    Response response = copy.newCall(request).execute();
    System.out.println("Response 2 succeeded: " + response);
  } catch (IOException e) {
    System.out.println("Response 2 failed: " + e);
  }
}

Handling authentication(身份验证)

OkHttp可以自动重操作没有验证通过的请求，当一个response是401 Not Authorized(未授权，未认可)，表示认证者需要你提供相应证书，实现是应该新建一个带有相应缺失证书的请求，如果获取不到证书，返回null跳过retry。
Use Response.challenges() to get the schemes and realms of any authentication challenges.
When fulfilling a Basic challenge, use Credentials.basic(username, password) to encode the request header.

private final OkHttpClient client = new OkHttpClient();

public void run() throws Exception {
  client.setAuthenticator(new Authenticator() {
    @Override public Request authenticate(Proxy proxy, Response response) {
      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();
    }

    @Override public Request authenticateProxy(Proxy proxy, Response response) {
      return null; // Null indicates no attempt to authenticate.
    }
  });

  Request request = new Request.Builder()
      .url("http://publicobject.com/secrets/hellosecret.txt")
      .build();

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

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

身份验证失效的时候就别多次retry了，return null放弃就好。

1
2
3

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

You may also skip the retry when you’ve hit an application-defined attempt limit:

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

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