OkHttp之示例

作者: DoAndKeep | 来源:发表于2016-08-06 14:48 被阅读611次

我们写了一些方法来示例如果使用OkHttp来解决常见问题。通读它们了解它们是如何一起工作的。随意地进行复制、粘贴，这是它们存在的目的。

同步Get请求

下载一个文件，打印它的头，并将其响应主体以字符串形式打印。

作用在响应主体上的string()方法对于小文档来说是方便和高效的。但是如果响应主体比较大(大于1MB)，避免使用string()，因为它会加载整个文档到内存中。在这种情况下，优先使用stream来处理主体。

  private final OkHttpClient client = new OkHttpClient();

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

    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());
  }

异步Get请求

在一个工作线程下载一个文件，当响应可读时获取回调。这个回调将在响应头准备好时执行。读取响应主体可能仍然阻塞。OkHttp当前没有提供异步API来局部地接收响应主体。

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 {
        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(response.body().string());
      }
    });
  }

访问Header

典型的HTTP头工作起来像一个Map< String, String >，每一个字段有一个值或没有值。但是有一些头允许多个值，像Guava的Multimap。对于一个HTTP响应来应用多个Vary头是合法的并且常见的。OkHttp的API试图兼容这些情况。

当写请求头时，使用header(name, value)的方式来设置唯一出现的键值。如果已有值，会在新值添加前移除已有值。使用addHeader(name, value)来添加一个头而不移除已经存在的头。

当读取一个响应头时，使用header(name)来返回最后一次出现的键值对。通常这是唯一出现的键值对。如果不存在值，header(name)会返回null。使用headers(name)来用一个list读取一个字段的所有值。

使用支持按索引访问的Headers类来访问所有的头。

  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"));
  }

上传字符串

使用HTTP POST来发送请求主体到服务器。这个例子上传了一个markdown文档到一个用HTML渲染markdown的服务器中。因为整个请求主体同时存在内存中，避免使用这个API上传大的文档(大于1MB)。

  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());
  }

上传流

这里以stream的形式上传请求主体。请求主体的内容如它写入的进行生成。这个示例stream直接放入到了Okio缓存sink中。你的程序可能需要一个OutputStream，你可以从BufferedSink.outputStream()中获取。

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());
  }

上传文件

使用文件作为请求主体很容易。

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());
  }

上传表格参数

使用FormBody.Builder来构建一个工作起来像HTML< form >标签的请求主体。键值对会使用一个兼容HTML form的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();

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

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

上传多部分请求

MultipartBody.Builder可以构造复杂的请求主体与HTML文件上传表单兼容。multipart请求主体的每部分本身就是一个请求主体，可以定义它自己的头。如果存在自己的头，那么这些头应该描述部分主体，例如它的Content-Disposition。Content-Length和Content-Type会在其可用时自动添加。

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 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();

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

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

使用Gson解析Json响应

Gson是一个便利API来实现JSON和Java对象之间的转化。这里我们使用它来解码来自GitHub API的JSON响应。

ResponseBody.charStream()使用响应头Content-Type来确定在解码响应主体时使用哪个字符集。如果没有指定字符集，则默认使用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;
  }

响应缓存

要缓存响应，你需要一个进行读取和写入的缓存目录，以及一个缓存大小的限制。缓存目录应该是私有的，且不被信任的应用不能够读取它的内容。

让多个缓存同时访问相同的混存目录是错误的。大多数应用应该只调用一次new OkHttpClient()，配置它们的缓存，并在所有地方使用相同的实例。否则两个缓存实例会相互进行干涉，腐朽响应缓存，有可能造成你的程序崩溃。

响应缓存使用HTTP头进行所有配置。你可以添加像Cache-Control:max-stale=3600这样的请求头并且OkHttp的缓存会尊重它们。你的服务器使用自己的响应头像Cache-Control:max-age=9600来配置响应缓存多久。这里有缓存头来强制一个缓存响应，强制一个网络响应，强制使用一个条件的GET来验证网络响应。

 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();

    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));
  }

使用CacheControl.FORCE_NETWORK来阻止响应使用缓存。使用CacheContril.FORCE_CACHE来阻止使用网络。注意：如果你使用FORCE_CACHE且响应需要网络，OkHttp会返回一个504 Unsatisfiable Request响应。

取消调用

使用Call.cancel()来立即停止一个正在进行的调用。如果一个线程正在写请求或读响应，它会接收到一个IOException。当一个调用不再需要时，使用这个来节省网络，例如当用户从应用离开。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);

    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);
    }
  }

超时

使用超时来使调用在当另一端没有到达时失败。网络部分可能是由于连接问题，服务器可用性问题或者其他。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();

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

单独配置调用

所有HTTP client配置都存在OkHttpClient中，包括代理设置，超时和缓存。当你需要改变一个单独call的配置时，调用OkHttpClient.newBuilder()。这个会返回一个builder，与原始的client共享下共同的连接池，调度器和配置。在下面的例子中，我们让一个请求有500ms的超时而另一个有3000ms的超时。

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);
    }
  }

处理认证

OkHttp会自动重试未认证请求。当一个响应为401 Not Authorized时，会要求Authenticator来应用证书。Authenticator的实现应该构建一个包含缺失证书的新请求。如果没有证书可用，返回null来跳过重试。

使用Response.challenges()来获取所有认证挑战的模式和领域。当完成一个Basic挑战时，使用Credentials.basic(username，password)来编码请求头。

  private final OkHttpClient client;

  public Authenticate() {
    client = new OkHttpClient.Builder()
        .authenticator(new Authenticator() {
          @Override public Request authenticate(Route route, Response response) throws IOException {
            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();

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

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

为了避免当认证无法工作时过多的尝试，你可以返回null来放弃。例如，当这些明确的证书已经尝试过了，你可能想跳过。

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

你可能也想在达到应用定义的尝试限制次数时跳过尝试：

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

上面的代码依赖这个responseCount()方法：

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

原文链接：
https://github.com/square/okhttp/wiki/Recipes

OkHttp官方文档系列文章：

OkHttp之示例

同步Get请求

异步Get请求

访问Header

上传字符串

上传流

上传文件

上传表格参数

上传多部分请求

使用Gson解析Json响应

响应缓存

取消调用

超时

单独配置调用

处理认证

相关文章

网友评论

延伸阅读

深度阅读

栏目导航

热点阅读

OkHttp

Android知识

Android开发经验谈

Android技术知识

Android开发

OkHttp之示例

同步Get请求

异步Get请求

访问Header

上传字符串

上传流

上传文件

上传表格参数

上传多部分请求

使用Gson解析Json响应

响应缓存

取消调用

超时

单独配置调用

处理认证

相关文章

网友评论

延伸阅读

深度阅读

栏目导航

热点阅读

OkHttp

Android知识

Android开发经验谈

Android技术知识

Android开发

OkHttp