OkHttp_Recipes

作者: 谈小龙 | 来源:发表于2016-06-02 15:15 被阅读75次

我们写了一些例子来演示怎么使用OkHttp解决通用的问题，通过阅读这些例子来学习怎么组织所有的事情。自由复制粘贴这些例子。

Synchronous Get

下载一个文件，打印响应头和响应体转化后的字符串。
对于小的文档response body的<code>String()</code>方法是方便且高效的。但是如果response body比较到大（>1M）应避免使用<code>String()</code>方法，因为这将把整个文档导入内存。这种情况下，优先吧response body作为流使用。

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

在工作线程下载文件，在response响应时回调。当响应头准备好时调用回调函数。读取response body可能阻塞线程。OkHttp目前没有提供获取response body 部分内容的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头的就像一个<code>Map<String, String></code>：每个字段对应一个值或空值。但是一些头允许多个值就像Guava的Multimap。比如一个HTTP的response支持多个<code>Vary</code>头。OkHttp的API试图使这些情况的使用更舒服。

当写请求头时使用<code>header(name, value)</code>设置唯一的name对应的value。当一个name对应多个value时，新的设置的value会替换原来的value。使用<code>addHeader(name, value)</code>添加的头不会覆盖原有的头。

当读取response中的一个头时，使用<code>header(name)</code>将返回最后一个name的值。一般情况也只有一个。如果没有value对应<code>header(name)</code>将返回null，<code>headers(name)</code>将返回一个当前name对应value的list。

要访问所有的头，使用<code>Headers</code>类，这个类支持索引访问。

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 发送请求体到服务器。这个例子发送了一个markdown文件到web服务器把markdown作为HTML展示。当请求体大于1M时应该避免使用这个API因为它会把请求体全部保存到内存中。

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

这里我们将请求体作为流提交（POST方式）。请求体的内容在它开始写的时候生成。这个例子流将直接写入 Okio 的缓冲槽。你编程时可能更倾向于<code>OutputStream</code>, 你可以通过<code>BufferedSink.outputStream()</code>获取。

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

使用文件作为请求体是非常方便的。

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>创建请求体是可以的就像HTML的<code><form></code>标签。键和值将URL编码来兼容HTML表单。

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()); 
}

<code>MultipartBody.Builder</code>用于创建复杂的请求体来兼容HTML文件上传。复杂请求体的每一部分本事就是一个请求体，能够定义其本身的头。目前，这些头应该描述每一部分的请求体，就像它本身的<code>Content-Disposition</code>。<code>Content-Length</code>和<code>Content-Type</code>头将在可用时自动添加。

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 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 是一个处理JSON字符串与java对象转换的好用的API。这里我们使用Gson来解析从GitHub API获取的JSON。

注意<code>ResponseBody.charStream()</code>方法将使用从响应头中获取的<code>Content-Type</code>值作为响应体的解码格式。在没有指定的情况下将使用utf-8作为解码格式。

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

使用本地缓存response需要提供一个可以读写的缓存路径，和缓存的大小。这个缓存路径应该是私有的，不可信的应用不可以读取缓存的内容！

多个本地缓存使用同一个路径是错误的，大部分的应用都应该调用<code>new OkHttpClient()</code>的同时配置缓存，并且保证在任何地方都是使用的同一个。否则两个缓存会相互影响，污染response缓存，甚至使你的程序崩溃。

response 缓存会从的HTTP头读取配置。你可以添加一个像<code>Cache-Control: max-stale=3600</code>的请求头，OkHttp缓存就会遵守。你的服务器通过response头配置response的缓存时间（就像<code>Cache-Control:max-age=9600</code>）。有些缓存头可以控制缓存的response，控制一个网络缓存，或者通过可选的GET验证控制一个网络的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));
}

通过使用<code>CacheControl.FORCE_NETWORK</code>可以阻止使用本地缓存，<code>CacheControl.FORCE_CACHE</code>可以阻止网络缓存。警告：如果你使用了<code>FORCE_CACHE</code>response需要使用网络，否则OkHttp将返回<code>504 Unsatisfiable Request</code>response。
（*注：关于缓存的内容可以参考这里）

Canceling a Call

<code>Call.cancel()</code>可以立刻取消正在进行的call。如果当前的线程正在写request或者读response将导致<code>IOException</code>。通过取消不必要的call可以节省流量；当你通过导航离开应用时应用的同步或异步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

访问超时取消的call等同于网络不能访问，网络分区可能引起客户端的连接问题，或者服务器的不可用问题。OkHttp支持设置连接，读，写的超时。

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客户端配置依赖于<code>OkHttpClient</code>，包括代理设置，超时，和缓存。当你需要改变某个call的配置时，调用<code>OkHttpClient.newBuilder()</code>将返回与源客户端公用pool，dispatcher,和配置的一个构造者。在下一个例子中，我们创建了一个请求分别具有500ms的超时和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")
        .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

当一个request的返回码是<code>401 Not Authorized</code>时OkHttp 可以自动重试未授权的requests。 <code>Authenticator</code>用于提供证书。Authenticator的实现应该构建一个带有确实认证的request，在没有认证可用时通过返回null来跳过重试。

<code>Response.challenges()</code>方法可以获取授权问题的scheme 和 realm，<code>Basic</code> 认证可以使用<code>Credentials.basic(username, password)</code>来编码请求头。
(*注：关于认证)

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());
}

通过返回null避免认证失败时的多次重试。例如在已经重试的情况下结束重试：

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

你也可以设置重试的次数：

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;
}

OkHttp_Recipes

Synchronous Get

Asynchronous Get

Accessing Headers

Posting a String

Post Streaming

Posting a File

Posting form parameters

Posting a multipart request

Parse a JSON Response With Gson

Response Caching

Canceling a Call

Timeouts

Per-call Configuration

Handling authentication

相关文章

网友评论

延伸阅读

深度阅读

栏目导航

热点阅读