OkHttp Wiki翻译（四）使用说明

来源：互联网发布：淘宝卫浴好店编辑：程序博客网时间：2024/06/04 23:22

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

下面是翻译：

说明

我们写了一些说明，用于演示如何解决OkHttp的常见问题。（你应该）阅读他们，以了解整个过程是如何协同工作的。自由剪切并粘贴这些例子; 这就是他们的目的。

同步Get

下载一个文件，打印其响应头，并以字符串的形式打印其响应正文。

响应体上的string()方法对于小文档来说既方便又高效。但是如果响应体很大（大于1 MiB），则应该避免使用string()方法，因为它会将整个文档都加载到内存中。在这种情况下，更应该以流的方式来处理响应体。

private final OkHttpClientclient = new OkHttpClient();

public void run() throwsException

{

Request request = new Request.Builder()

.url("http://publicobject.com/helloworld.txt")

.build();

Response response =client.newCall(request).execute();

if (!response.isSuccessful()) throw newIOException("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

在工作线程上下载文件，并在响应可读时调用。在响应头准备就绪后进行回调。阅读响应体还可能会导致阻塞。 OkHttp当前还不提供部分接收响应主体的异步API。

private final OkHttpClientclient = new OkHttpClient();

public void run() throwsException

{

Request request = new Request.Builder()

.url("http://publicobject.com/helloworld.txt")

.build();

client.newCall(request).enqueue(newCallback()

{

@Override public void onFailure(Callcall, IOException e)

{

e.printStackTrace();

}

@Override public void onResponse(Callcall, Response response) throws IOException

{

if (!response.isSuccessful()) thrownew 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());

}

});

}

访问响应头

通常情况下，HTTP header的工作方式类似于Map <String，String>：每个字段都有一个值或为空。但是有些header允许多个值，如Guava的Multimap。例如，HTTP响应提供多个Vary header是合法和通用的。 OkHttp的API尝试使这两种情况的使用都很舒适。

当在写请求头时，应使用 “请求头（名称，值）”来设置值的唯一的名称。如果已经存在现有的值，则应该在添加新值之前将它们删除。使用 addHeader（name，value）来添加请求头，这种方式不会删除已经存在的请求头。

当读取响应头时，使用header（name）返回最后一次出现的命名值。通常这也是唯一的出现！如果没有值，header（name）将会返回null。要读取所有字段的值来作为一个列表，请使用 headers（name）。

要访问所有的header，请使用支持通过索引访问的Headers类。

private final OkHttpClientclient = new OkHttpClient();

public void run() throwsException

{

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 newIOException("Unexpected code " + response);

System.out.println("Server: " +response.header("Server"));

System.out.println("Date: " +response.header("Date"));

System.out.println("Vary: " +response.headers("Vary"));

}

提交字符串

使用HTTP POST将请求体发送到服务。此示例将一个markdown文档post到以HTML格式呈现为markdown的Web服务。因为整个请求体同时在内存中，所以避免使用这个API发布大的（大于1个MiB）文档。

public static final MediaTypeMEDIA_TYPE_MARKDOWN

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

private final OkHttpClientclient = new OkHttpClient();

public void run() throwsException

{

String postBody = ""

+ "Releases\n"

+ "--------\n"

+ "\n"

+ " * _1.0_ May 6,2013\n"

+ " * _1.1_ June 15,2013\n"

+ " * _1.2_ August11, 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 newIOException("Unexpected code " + response);

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

}

提交数据流

这里我们以流的方式发送一个请求体。请求体的内容会在流写入的同时生成。此示例中的流会直接进入Okio缓冲接收器。您的程序可能更适合使用OutputStream，您可以从BufferedSink.outputStream()获取。

public static final MediaTypeMEDIA_TYPE_MARKDOWN

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

private final OkHttpClientclient = new OkHttpClient();

public void run() throwsException

{

RequestBody requestBody = new RequestBody()

{

@Override public MediaTypecontentType()

{

return MEDIA_TYPE_MARKDOWN;

}

@Override public voidwriteTo(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) returnfactor(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 newIOException("Unexpected code " + response);

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

}

提交文件

将文件用作请求体很容易。

public static final MediaTypeMEDIA_TYPE_MARKDOWN

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

private final OkHttpClientclient = new OkHttpClient();

public void run() throwsException

{

File file = newFile("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 newIOException("Unexpected code " + response);

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

}

从表单参数发送Post请求

使用FormBody.Builder构建一个像HTML <form>标签一样的请求体。名称和值将会以HTML兼容的表单URL编码形式进行编码。

private final OkHttpClientclient = new OkHttpClient();

public void run() throwsException

{

RequestBody formBody = newFormBody.Builder()

.add("search", "JurassicPark")

.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 newIOException("Unexpected code " + response);

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

}

提交多个请求

MultipartBody.Builder可以构建与HTML文件上传表单兼容的复杂请求体。多部分请求体的每个部分本身就是一个请求体，并且这个请求体可以定义自己的请求头。如果已经存在，这些头部信息应该描述请求体，例如其内容位置（Content-Disposition）。如果内容长度和内容类型可用，那么这些都会自动添加。

private static final StringIMGUR_CLIENT_ID = "...";

private static finalMediaType MEDIA_TYPE_PNG = MediaType.parse("image/png");

private final OkHttpClientclient = new OkHttpClient();

public void run() throwsException

{

// Use the imgur image upload API asdocumented at https://api.imgur.com/endpoints/image

RequestBody requestBody = newMultipartBody.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 newIOException("Unexpected code " + response);

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

}

用Gson解析JSON数据

Gson是用于在JSON和Java对象之间进行转换的方便的API。这里我们使用它来对来自GitHub返回的JSON进行进行解析。

请注意，ResponseBody.charStream()使用Content-Type响应头来选择在解析响应体时要使用的字符集。如果未指定字符集，则默认为UTF-8。

private final OkHttpClientclient = new OkHttpClient();

private final Gson gson = newGson();

public void run() throwsException

{

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，您需要一个可以读取和写入的缓存目录，并对缓存的大小进行限制。缓存目录应该是私有的，不受信任的应用程序不能读取其内容！

让多个缓存同时访问同一个缓存目录是一个错误。大多数应用程序应该调用新的OkHttpClient()一次，配置它们的缓存，并在任何地方使用相同的实例。否则两个缓存实例将彼此冲突，损坏响应缓存，并可能会导致程序崩溃。

响应缓存使用HTTP头进行所有配置。您可以添加类似于这样的缓存控制的请求头：max-stale = 3600，OkHttp的缓存将会使其符合要求。您的网络服务器可以配置缓存响应的时间长短与其自己的响应头，如Cache-Control：max-age = 9600。缓存和头部信息会在网络请求响应时强制去返回，后者强制网络以get的形式去返回可用的响应。

private final OkHttpClientclient;

public CacheResponse(FilecacheDirectory) 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() throwsException

{

Request request = new Request.Builder()

.url("http://publicobject.com/helloworld.txt")

.build();

Response response1 =client.newCall(request).execute();

if (!response1.isSuccessful()) throw newIOException("Unexpected code " + response1);

String response1Body =response1.body().string();

System.out.println("Response 1response: " + response1);

System.out.println("Response 1 cacheresponse: " +response1.cacheResponse());

System.out.println("Response 1 networkresponse: " +response1.networkResponse());

Response response2 =client.newCall(request).execute();

if (!response2.isSuccessful()) throw newIOException("Unexpected code " + response2);

String response2Body = response2.body().string();

System.out.println("Response 2response: " + response2);

System.out.println("Response 2 cacheresponse: " +response2.cacheResponse());

System.out.println("Response 2 networkresponse: " +response2.networkResponse());

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

}

要防止响应使用缓存，请使用CacheControl.FORCE_NETWORK。要防止它使用网络，请使用CacheControl.FORCE_CACHE。警告：如果您使用FORCE_CACHE并且响应需要网络，OkHttp将返回504请求失败的响应。

取消请求

使用Call.cancel()可以立即停止正在进行的请求。如果线程当前正在写请求或读取响应数据，它将收到一个IOException。当不再需要请求时，应使用它来节省网络资源；例如，当您的用户在使用应用程序结束导航时。同步和异步呼叫都可以取消。

private finalScheduledExecutorService executor = Executors.newScheduledThreadPool(1);

private final OkHttpClientclient = new OkHttpClient();

public void run() throwsException

{

Request request = new Request.Builder()

.url("http://httpbin.org/delay/2") // This URL is served witha 2 second delay.

.build();

finallong startNanos = System.nanoTime();

final Call call = client.newCall(request);

// Schedule a job to cancel the call in 1second.

executor.schedule(new Runnable()

{

@Override public void run()

{

System.out.printf("%.2fCanceling call.%n", (System.nanoTime() - startNanos) / 1e9f);

call.cancel();

System.out.printf("%.2fCanceled call.%n", (System.nanoTime() - startNanos) / 1e9f);

}

}, 1, TimeUnit.SECONDS);

try

{

System.out.printf("%.2f Executingcall.%n", (System.nanoTime() - startNanos) / 1e9f);

Response response = call.execute();

System.out.printf("%.2f Call wasexpected to fail, but completed: %s%n",

(System.nanoTime() -startNanos) / 1e9f, response);

}

catch (IOException e)

{

System.out.printf("%.2f Callfailed as expected: %s%n",

(System.nanoTime() -startNanos) / 1e9f, e);

}

超时

当访问不可到达时，就会发生超时。网络中断可能是由于客户端连接问题，服务器可用性问题或这两者之间。 OkHttp支持连接，读取和写入的超时动作。

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() throwsException

{

Request request = new Request.Builder()

.url("http://httpbin.org/delay/2") // This URL is served witha 2 second delay.

.build();

Response response =client.newCall(request).execute();

System.out.println("Responsecompleted: " + response);

}

每一请求的配置

所有HTTP客户端配置都建立在OkHttpClient的基础上，包括代理的设置，超时和高速缓存。当您需要更改单个调用的配置时，请调用OkHttpClient.newBuilder()方法。这将返回与原始客户端共享相同连接池，调度程序和配置的构建器。在下面的示例中，我们发出一个超时500 ms的请求，另一个请求超时3000 ms。

private final OkHttpClientclient = new OkHttpClient();

public void run() throwsException

{

Request request = new Request.Builder()

.url("http://httpbin.org/delay/1") // This URL is served witha 1 second delay.

.build();

try

{

// Copy to customize OkHttp for thisrequest.

OkHttpClient copy = client.newBuilder()

.readTimeout(500,TimeUnit.MILLISECONDS)

.build();

Response response =copy.newCall(request).execute();

System.out.println("Response 1succeeded: " + response);

}

catch (IOException e)

{

System.out.println("Response 1failed: " + 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 2succeeded: " + response);

}

catch (IOException e)

{

System.out.println("Response 2failed: " + e);

}

处理认证（证书）

OkHttp可以自动重试未经身份验证的请求。当答复为401未授权时，将要求验证者提供凭证。实现应该构建一个新的请求，其中应包含缺少的凭据。如果没有可用的凭据，返回null以跳过重试。

使用Response.challenges()方法来获取约束和任何证书认证。当通过基本认证之后，请使用Credentials.basic(用户名,密码)对请求请求头进行编码。

private final OkHttpClient client;

public Authenticate()

{

client = new OkHttpClient.Builder()

.authenticator(new Authenticator()

{

@Override public Requestauthenticate(Route route, Response response) throws IOException

{

System.out.println("Authenticatingfor response: " + response);

System.out.println("Challenges: " + response.challenges());

String credential =Credentials.basic("jesse", "password1");

returnresponse.request().newBuilder()

.header("Authorization",credential)

.build();

}

})

.build();

}

public void run() throwsException

{

Request request = new Request.Builder()

.url("http://publicobject.com/secrets/hellosecret.txt")

.build();

Response response =client.newCall(request).execute();

if (!response.isSuccessful()) throw newIOException("Unexpected code " + response);

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

}

为了避免在身份验证失效时的多次重试，您可以返回null来放弃。例如，您可能希望在尝试过这些证书认证之后放弃时跳过重试。

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

{

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

}

当您遇到应用定义的尝试限制时，您也可以跳过重试：

if (responseCount(response)>= 3)

{

return null; // If we've failed 3 times,give up.

}

上面的代码依赖于这个响应Count（）方法：

private intresponseCount(Response response)

{

int result = 1;

while ((response =response.priorResponse()) != null)

{

result++;

}

return result;

}

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