Android OkHttp解析

http是现在主流应用使用的网络请求方式, 用来交换数据和内容, 有效的使用HTTP可以使你的APP 变的更快和减少流量的使用

OkHttp 是一个很棒HTTP客户端:

• 支持SPDY, 可以合并多个到同一个主机的请求
•  使用连接池技术减少请求的延迟(如果SPDY是可用的话)
•  使用GZIP压缩减少传输的数据量
•  缓存响应避免重复的网络请求

当你的网络出现拥挤的时候,就是OKHttp 大显身手的时候, 它可以避免常见的网络问题,如果你的服务是部署在不同的IP上面的,如果第一个连接失败, OkHTtp会尝试其他的连接. 这个对现在IPv4+IPv6 中常见的把服务冗余部署在不同的数据中心上.  OkHttp 将使用现在TLS特性(SNI ALPN) 来初始化新的连接. 如果握手失败, 将切换到SLLv3

使用OkHttp很容易,   同时支持 异步阻塞请求和回调.

如果你使用OkHttp ,你不用重写你的代码,   okhttp-urlconnection模块实现了 java.net.HttpURLConnection 中的API,  okhttp-apache模块实现了HttpClient中的API

同步get

下载一个文件，打印他的响应头，以string形式打印响应体。
响应体的 string() 方法对于小文档来说十分方便、高效。但是如果响应体太大（超过1MB），应避免适应 string()方法 ，因为他会将把整个文档加载到内存中。
对于超过1MB的响应body，应使用流的方式来处理body。

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

在一个工作线程中下载文件，当响应可读时回调Callback接口。读取响应时会阻塞当前线程。OkHttp现阶段不提供异步api来接收响应体。

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(Request request, Throwable throwable) {    throwable.printStackTrace();  }  @Override public void onResponse(Response response) throws IOException {    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());  }});}

提取响应头

典型的HTTP头 像是一个 Map<String, String> :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"));}

Post方式提交String

使用HTTP POST提交请求到服务。这个例子提交了一个markdown文档到web服务，以HTML方式渲染markdown。因为整个请求体都在内存中，因此避免使用此api提交大文档（大于1MB）。

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());}

Post方式提交流

以流的方式POST提交请求体。请求体的内容由流写入产生。这个例子是流直接写入Okio的BufferedSink。你的程序可能会使用OutputStream，你可以使用BufferedSink.outputStream()来获取。

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());}

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());}

Post方式提交表单

使用FormEncodingBuilder来构建和HTML<form>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 FormEncodingBuilder()    .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());}

Post方式提交分块请求

MultipartBuilder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，例如他的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/imageRequestBody requestBody = new MultipartBuilder()    .type(MultipartBuilder.FORM)    .addPart(        Headers.of("Content-Disposition", "form-data; name=\"title\""),        RequestBody.create(null, "Square Logo"))    .addPart(        Headers.of("Content-Disposition", "form-data; name=\"image\""),        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。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.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

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。

public CacheResponse(File cacheDirectory) throws Exception {int cacheSize = 10 * 1024 * 1024; // 10 MiBCache 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));}

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);}}

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，读取和写入超时。

private final OkHttpClient client;public ConfigureTimeouts() throws Exception {client = new OkHttpClient();client.setConnectTimeout(10, TimeUnit.SECONDS);client.setWriteTimeout(10, TimeUnit.SECONDS);client.setReadTimeout(30, TimeUnit.SECONDS);}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);}

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，clone 一个 OkHttpClient。这个api将会返回一个浅拷贝（shallow copy），你可以用来单独自定义。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 {  Response response = client.clone() // Clone to make a customized OkHttp for this request.      .setReadTimeout(500, TimeUnit.MILLISECONDS)      .newCall(request)      .execute();  System.out.println("Response 1 succeeded: " + response);} catch (IOException e) {  System.out.println("Response 1 failed: " + e);}try {  Response response = client.clone() // Clone to make a customized OkHttp for this request.      .setReadTimeout(3000, TimeUnit.MILLISECONDS)      .newCall(request)      .execute();  System.out.println("Response 2 succeeded: " + response);} catch (IOException e) {  System.out.println("Response 2 failed: " + e);}}