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OkHttp 使用完全教程(下)

安卓开发精选  · 公众号  · android  · 2016-11-28 21:42

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来源:伯乐在线专栏作者 - 望天

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接上文


4.3 Post方式提交文件


以文件作为请求体是十分简单的。


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());

}


4.4 Post方式提交表单


使用FormEncodingBuilder来构建和HTML

标签相同效果的请求体. 键值对将使用一种HTML兼容形式的URL编码来进行编码.


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());

  }


4.5 Post方式提交分块请求


MultipartBody.Builder可以构建复杂的请求体, 与HTML文件上传形式兼容. 多块请求体中每块请求都是一个请求体, 可以定义自己的请求头. 这些请求头可以用来描述这块请求, 例如它的Content-Disposition. 如果Content-Length和Content-Type可用的话, 他们会被自动添加到请求头中.


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());

  }


5. 其他用法


5.1 提取响应头


典型的HTTP头像是一个Map : 每个字段都有一个或没有值. 但是一些头允许多个值, 像Guava的Multimap.


例如: HTTP响应里面提供的Vary响应头, 就是多值的. OkHttp的api试图让这些情况都适用.


当写请求头的时候, 使用header(name, value)可以设置唯一的name、value. 如果已经有值, 旧的将被移除, 然后添加新的. 使用addHeader(name, value)可以添加多值(添加, 不移除已有的).


当读取响应头时, 使用header(name)返回最后出现的name、value. 通常情况这也是唯一的name、value. 如果没有值, 那么header(name)将返回null. 如果想读取字段对应的所有值, 使用headers(name)会返回一个list.

为了获取所有的Header, Headers类支持按index访问.


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"));

}


5.2 使用Gson来解析JSON响应


Gson是一个在JSON和Java对象之间转换非常方便的api库. 这里我们用Gson来解析Github API的JSON响应.

注意: ResponseBody.charStream()使用响应头Content-Type指定的字符集来解析响应体. 默认是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.EntryString, GistFile> entry : gist.files.entrySet()) {

      System.out.println(entry.getKey());

      System.out.println(entry.getValue().content);

    }

  }

 

  static class Gist {

    MapString, GistFile> files;

  }

 

  static class GistFile {

    String content;

  }


5.3 响应缓存


为了缓存响应, 你需要一个你可以读写的缓存目录, 和缓存大小的限制. 这个缓存目录应该是私有的, 不信任的程序应不能读取缓存内容.


一个缓存目录同时拥有多个缓存访问是错误的. 大多数程序只需要调用一次new OkHttp(), 在第一次调用时配置好缓存, 然后其他地方只需要调用这个实例就可以了. 否则两个缓存示例互相干扰, 破坏响应缓存, 而且有可能会导致程序崩溃.

响应缓存使用HTTP头作为配置. 你可以在请求头中添加Cache-Control: max-stale=3600 , OkHttp缓存会支持. 你的服务通过响应头确定响应缓存多长时间, 例如使用Cache-Control: max-age=9600.


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));

}


如果需要阻值response使用缓存, 使用CacheControl.FORCE_NETWORK. 如果需要阻值response使用网络, 使用CacheControl.FORCE_CACHE.

警告: 如果你使用FORCE_CACHE, 但是response要求使用网络, OkHttp将会返回一个504 Unsatisfiable Request响应.


5.3.1 Force a Network Response


有些时候, 比如用户刚刚点击刷新按钮, 这时必须跳过缓存, 直接从服务器抓取数据. 为了强制全面刷新, 我们需要添加no-cache指令:


connection.addRequestProperty("Cache-Control", "no-cache");


这样就可以强制每次请求直接发送给源服务器, 而不经过本地缓存版本的校验, 常用于需要确认认证的应用和严格要求使用最新数据的应用.


5.3.2 Force a Cache Response


有时你会想立即显示资源. 这样即使在后台正下载着最新资源, 你的客户端仍然可以先显示原有资源, 毕竟有个东西显示比没有东西显示要好.

如果需要限制让请求优先使用本地缓存资源, 需要增加only-if-cached指令:


try {

     connection.addRequestProperty("Cache-Control", "only-if-cached");

     InputStream cached = connection.getInputStream();

     // the resource was cached! show it

  catch (FileNotFoundException e) {

     // the resource was not cached

}

}


5.4 取消一个Call


使用Call.cancel()可以立即停止掉一个正在执行的call. 如果一个线程正在写请求或者读响应, 将会引发IOException. 当call没有必要的时候, 使用这个api可以节约网络资源. 例如当用户离开一个应用时, 不管同步还是异步的call都可以取消.

你可以通过tags来同时取消多个请求. 当你构建一请求时, 使用RequestBuilder.tag(tag)来分配一个标签, 之后你就可以用OkHttpClient.cancel(tag)来取消所有带有这个tag的call.


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);

    }

  }


5.5 超时


没有响应时使用超时结束call. 没有响应的原因可能是客户点链接问题、服务器可用性问题或者这之间的其他东西. OkHttp支持连接超时, 读取超时和写入超时.


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);

  }


5.6 每个call的配置


使用OkHttpClient, 所有的HTTP Client配置包括代理设置、超时设置、缓存设置. 当你需要为单个call改变配置的时候, 调用OkHttpClient.newBuilder(). 这个api将会返回一个builder, 这个builder和原始的client共享相同的连接池, 分发器和配置.


下面的例子中,我们让一个请求是500ms的超时、另一个是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);

    }

  }


5.7 处理验证


这部分和HTTP AUTH有关.


5.7.1 HTTP AUTH


使用HTTP AUTH需要在server端配置http auth信息, 其过程如下:

– 客户端发送http请求

– 服务器发现配置了http auth, 于是检查request里面有没有”Authorization”的http header

– 如果有, 则判断Authorization里面的内容是否在用户列表里面, Authorization header的典型数据为”Authorization: Basic jdhaHY0=”, 其中Basic表示基础认证, jdhaHY0=是base64编码的”user:passwd”字符串. 如果没有,或者用户密码不对,则返回http code 401页面给客户端.

– 标准的http浏览器在收到401页面之后, 应该弹出一个对话框让用户输入帐号密码; 并在用户点确认的时候再次发出请求, 这次请求里面将带上Authorization header.


一次典型的访问场景是:


  • 浏览器发送http请求(没有Authorization header)

  • 服务器端返回401页面

  • 浏览器弹出认证对话框

  • 用户输入帐号密码,并点确认

  • 浏览器再次发出http请求(带着Authorization header)

  • 服务器端认证通过,并返回页面

  • 浏览器显示页面


5.7.2 OkHttp认证


OkHttp会自动重试未验证的请求. 当响应是401 Not Authorized时,Authenticator会被要求提供证书. Authenticator的实现中需要建立一个新的包含证书的请求. 如果没有证书可用, 返回null来跳过尝试.

使用Response.challenges()来获得任何authentication challenges的 schemes 和 realms. 当完成一个Basic challenge, 使用Credentials.basic(username, password)来解码请求头.


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());

  }


当认证无法工作时, 为了避免多次重试, 你可以返回空来放弃认证. 例如, 当exact credentials已经尝试过, 你可能会直接想跳过认证, 可以这样做:


if (credential.equals(response.request().header("Authorization"))) {

    return null; // If we already failed with these credentials, don't retry.

   }


当重试次数超过定义的次数, 你若想跳过认证, 可以这样做:


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;

  }


这样, 对OkHttp的使用我们就讲完了, 下一节会讲OkHttp内部实现.


谢谢下列文章:


http://www.blogjava.net/yongboy/archive/2015/03/18/423570.html

http://www.jcodecraeer.com/a/anzhuokaifa/androidkaifa/2015/0106/2275.html

http://www.jianshu.com/p/aad5aacd79bf

https://imququ.com/post/protocol-negotiation-in-http2.html

http://blog.csdn.net/wwwsq/article/details/7255062


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