OkHttp_Recipes

我們寫了一些例子來演示怎么使用OkHttp解決通用的問題，通過閱讀這些例子來學習怎么組織所有的事情。自由復制粘貼這些例子。

Synchronous Get

下載一個文件，打印響應頭和響應體轉化后的字符串。
對于小的文檔response body的<code>String()</code>方法是方便且高效的。但是如果response body比較到大（>1M）應避免使用<code>String()</code>方法，因為這將把整個文檔導入內存。這種情況下，優(yōu)先吧response body作為流使用。

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());
}

Asynchronous Get

在工作線程下載文件，在response響應時回調。當響應頭準備好時調用回調函數。讀取response body可能阻塞線程。OkHttp目前沒有提供獲取response body 部分內容的API。

private final OkHttpClient client = new OkHttpClient();

public void run() throws Exception {
    Request request = new Request.Builder()
        .url("http://publicobject.com/hellowworld.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 = resonseHeaders.size();  i < size;i++) {
                System.out.println(responseHeaders.name(i) + ":" + responseHeaders.value(i));
            }
            System.out.println(response.body().string());
        }
    });
}

Accessing Headers

一般HTTP頭的就像一個<code>Map<String, String></code>：每個字段對應一個值或空值。但是一些頭允許多個值就像Guava的Multimap。比如一個HTTP的response支持多個<code>Vary</code>頭。OkHttp的API試圖使這些情況的使用更舒服。

當寫請求頭時使用<code>header(name, value)</code>設置唯一的name對應的value。當一個name對應多個value時，新的設置的value會替換原來的value。使用<code>addHeader(name, value)</code>添加的頭不會覆蓋原有的頭。

當讀取response中的一個頭時，使用<code>header(name)</code>將返回最后一個name的值。一般情況也只有一個。如果沒有value對應<code>header(name)</code>將返回null，<code>headers(name)</code>將返回一個當前name對應value的list。

要訪問所有的頭，使用<code>Headers</code>類，這個類支持索引訪問。

private final OkHttpClient client = new OkHttpClient();

public void run() throws Exception {
    Request request = new Request.Builder()
        .url("http://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("Unexcepted code " + response);

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

Posting a String

用HTTP POST 發(fā)送請求體到服務器。 這個例子發(fā)送了一個markdown文件到web服務器把markdown作為HTML展示。當請求體大于1M時應該避免使用這個API因為它會把請求體全部保存到內存中。

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

private final OkHttoClient client = new OkHttpClient();

public void run() throws IOException {
    String postBody = ""
        + "Release\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("http://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

這里我們將請求體作為流提交（POST方式）。請求體的內容在它開始寫的時候生成。這個例子流將直接寫入 Okio 的緩沖槽。你編程時可能更傾向于<code>OutputStream</code>, 你可以通過<code>BufferedSink.outputStream()</code>獲取。

public static final MediaType MEDIA_TYPE_MARKDOWN =
    MediaType.parse("text/x-markdown; cjarset=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) + x +" x " +i; 
                }
                return Integer,toString(n);
            }
        }
    };

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

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

Posting a File

使用文件作為請求體是非常方便的。

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

private final OkHttoClient client = new OkHttpClient();

public void run() throws IOException {
     File file = new File("README.md");
     Request request =  new Request.Builder()
        .url("http://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

用<code>FormBody.Builder</code>創(chuàng)建請求體是可以的就像HTML的<code><form></code>標簽。鍵和值將URL編碼來兼容HTML表單。

private final OkHttoClient client = new OkHttpClient();

public void run() throws IOException {
     RequestBody formBody = new FormBody.Builder()
          .add("search", "Jurassic Park")
          .build();
     Request request =  new Request.Builder()
        .url("http://api.github.com/markdown/raw")
        .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 a multipart request

<code>MultipartBody.Builder</code>用于創(chuàng)建復雜的請求體來兼容HTML文件上傳。復雜請求體的每一部分本事就是一個請求體，能夠定義其本身的頭。目前，這些頭應該描述每一部分的請求體，就像它本身的<code>Content-Disposition</code>。<code>Content-Length</code>和<code>Content-Type</code>頭將在可用時自動添加。

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 document at https://api.imgur.com/endpoints.image
    RequestBody requestBody = new MultipartBody.Bulder()
        .setType(MultiparBody.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("Autorization", "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()); 
}

Parse a JSON Response With Gson

Gson 是一個處理JSON字符串與java對象轉換的好用的API。這里我們使用Gson來解析從GitHub API獲取的JSON。

注意<code>ResponseBody.charStream()</code>方法將使用從響應頭中獲取的<code>Content-Type</code>值作為響應體的解碼格式。在沒有指定的情況下將使用utf-8作為解碼格式。

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.budy.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

使用本地緩存response需要提供一個可以讀寫的緩存路徑，和緩存的大小。這個緩存路徑應該是私有的，不可信的應用不可以讀取緩存的內容！

多個本地緩存使用同一個路徑是錯誤的，大部分的應用都應該調用<code>new OkHttpClient()</code>的同時配置緩存，并且保證在任何地方都是使用的同一個。否則兩個緩存會相互影響，污染response緩存，甚至使你的程序崩潰。

response 緩存會從的HTTP頭讀取配置。你可以添加一個像<code>Cache-Control: max-stale=3600</code>的請求頭，OkHttp緩存就會遵守。你的服務器通過response頭配置response的緩存時間（就像<code>Cache-Control:max-age=9600</code>）。有些緩存頭可以控制緩存的response，控制一個網絡緩存，或者通過可選的GET驗證控制一個網絡的response。

private final OkHttpClient client;

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

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

public void run() throws Exception {
    Reques 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 " + response);

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

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

    String response2Body = response2.body().string();
    System.out.println("Response 2 response:          " + response2);
    System.out.println("Response 2 cache response:    " + response1.cahceResponse());
    System.out.println("Response 2 network response:  " + response2.networkResponse());

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

通過使用<code>CacheControl.FORCE_NETWORK</code>可以阻止使用本地緩存，<code>CacheControl.FORCE_CACHE</code>可以阻止網絡緩存。警告：如果你使用了<code>FORCE_CACHE</code>response需要使用網絡，否則OkHttp將返回<code>504 Unsatisfiable Request</code>response。
（*注：關于緩存的內容可以參考這里）

Canceling a Call

<code>Call.cancel()</code>可以立刻取消正在進行的call。如果當前的線程正在寫request或者讀response將導致<code>IOException</code>。通過取消不必要的call可以節(jié)省流量；當你通過導航離開應用時應用的同步或異步call都可以被取消。

private final ScheduleExecutorService 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")
        .build();

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

    // Scheduler a jod 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 Canceling call.%n", (System.nanoTime() - startNanos) / 1e9f);
        }
    }, 1, TimeUnit.SECONDS);

    try {
        System.out.prinf("%.2f Canceling call.%n", (System.nanoTime() - startNanos) / 1e9f);
       Response response = call.execute();
        System.out.prinf("%.2f Canceling call.%S%n", (System.nanoTime() - startNanos) / 1e9f, response);
    } catch(IOException e) {
        System.out.prinf("%.2f Canceling call.%S%n", (System.nanoTime() - startNanos) / 1e9f, e);
    }
}

Timeouts

訪問超時取消的call等同于網絡不能訪問，網絡分區(qū)可能引起客戶端的連接問題，或者服務器的不可用問題。OkHttp支持設置連接，讀，寫的超時。

private final OkHttpClient client;

public ConfigureTimeouts() thows Exception {
    client = new OkHttpCLient.Builder()
        .connectTimeout(10, TimeUnit.SECONDS)
        .writeTimeout(10, TimeUnit.SECONDS)
        .readeTimeout(30, TimeUnit.SECONDS)
        .build();
}

public void run() throws Exception {
    Requets requets = new Request.Builder()
        .url("http://httpbin.org.delay/2")
        .build();

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

Per-call Configuration

所有的HTTP客戶端配置依賴于<code>OkHttpClient</code>，包括代理設置，超時，和緩存。當你需要改變某個call的配置時，調用<code>OkHttpClient.newBuilder()</code>將返回與源客戶端公用pool，dispatcher,和配置的一個構造者。在下一個例子中，我們創(chuàng)建了一個請求分別具有500ms的超時和3000ms的超時。

private final OkHttpClient client = new OkHttpClient();

public void run() throws Exception {
    Request request = new Request.Builder()
        .url("http://httpbin.org/delay/1")
        .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

當一個request的返回碼是<code>401 Not Authorized</code>時OkHttp 可以自動重試未授權的requests。 <code>Authenticator</code>用于提供證書。Authenticator的實現應該構建一個帶有確實認證的request，在沒有認證可用時通過返回null來跳過重試。

<code>Response.challenges()</code>方法可以獲取授權問題的scheme 和 realm，<code>Basic</code> 認證可以使用<code>Credentials.basic(username, password)</code>來編碼請求頭。
(*注：關于認證)

private final OkHttpClient client;

public Authenticate() {
    client = new OkHttpClient.Builder()
        .authenticator(new Autenticator() {
            @Override public Request authenticate(Routr rourte, Response response) throws IOException {
                System.out.println("Authenicating for response: " + response);
                System.out.println("Challenges: " + response.challenges());
                String credential = Credentials.basic("jesse", "password1");
                return response.request().newBuilder()
                    .header("Authorization", crebential)
                    .build();
            }
        })
        .build();
}

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

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

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

通過返回null避免認證失敗時的多次重試。例如在已經重試的情況下結束重試：

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

你也可以設置重試的次數：

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

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