android-async-http 基于httpClient封裝的網(wǎng)絡(luò)庫箫踩，android6.0后httpclient不是系統(tǒng)自帶的爱态，目前已不維護(hù)，盡管Google在大部分安卓版本推薦使用HttpURLConnection境钟，但是這個(gè)類太難用了锦担，而OKhttp是一個(gè)相對(duì)成熟的網(wǎng)絡(luò)庫，在android4.4的源碼中HttpURLConnection已經(jīng)替換成OKHttp實(shí)現(xiàn)了慨削，很多大的第三方庫都支持它（fresco洞渔、retrofit）

api調(diào)用方便

OkHttpClient client = new OkHttpClient();
 
String run(String url) throws IOException {
    Request request = new Request.Builder().url(url).build();
    Response response = client.newCall(request).execute();
    if (response.isSuccessful()) {
        return response.body().string();
    } else {
        throw new IOException("Unexpected code " + response);
    }
}

通過Request的Builder輔助類，創(chuàng)建請(qǐng)求對(duì)象缚态，再傳遞給OkHttpClient執(zhí)行磁椒，Response為返回的內(nèi)容，這樣get請(qǐng)求就完成了玫芦。
如果要是實(shí)現(xiàn)post請(qǐng)求浆熔，則創(chuàng)建一個(gè)RequestBody對(duì)象，賦值給Request桥帆，則完成了post請(qǐng)求

public static final MediaType JSON = MediaType.parse("application/json; charset=utf-8");
OkHttpClient client = new OkHttpClient();
String post(String url, String json) throws IOException {
     RequestBody body = RequestBody.create(JSON, json);
      Request request = new Request.Builder()
      .url(url)
      .post(body)
      .build();
      Response response = client.newCall(request).execute();
    f (response.isSuccessful()) {
        return response.body().string();
    } else {
        throw new IOException("Unexpected code " + response);
    }
}

支持各種形式的post請(qǐng)求

post提交字符串

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();

post提交流

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();

post提交文件

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();

post提交表單

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();

OkHttpClient 的執(zhí)行

調(diào)用execute方法是同步執(zhí)行医增，調(diào)用enqueue時(shí)異步執(zhí)行

響應(yīng)頭

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分塊請(qǐng)求

RequestBody 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();

能夠方便的設(shè)置和獲取響應(yīng)頭。

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"));

支持同步和異步請(qǐng)求

enqueue發(fā)起異步請(qǐng)求老虫，execute發(fā)起同步請(qǐng)求

請(qǐng)求攔截

Okhttp支持定義各種攔截器對(duì)整個(gè)網(wǎng)絡(luò)請(qǐng)求流程進(jìn)行攔截（監(jiān)視调窍、重寫、重試調(diào)用）

class LoggingInterceptor implements Interceptor {
  @Override public Response intercept(Interceptor.Chain chain) throws IOException {
   Request request = chain.request();

   long t1 = System.nanoTime();
   logger.info(String.format("Sending request %s on %s%n%s",
   request.url(), chain.connection(), request.headers()));

   Response response = chain.proceed(request);

   long t2 = System.nanoTime();
    logger.info(String.format("Received response for %s in %.1fms%n%s",
   response.request().url(), (t2 - t1) / 1e6d, response.headers()));

return response;
  }
}

OkHttpClient client = new OkHttpClient.Builder()
     .addInterceptor(new LoggingInterceptor())
     .build();

可以定義多個(gè)攔截器张遭，按順序調(diào)用

緩存

Okhttp已經(jīng)內(nèi)置了緩存邓萨，使用DiskLruCache，使用緩存需要在創(chuàng)建OKhttpClient進(jìn)行配置

int cacheSize = 10 * 1024 * 1024; // 10 MiB
File cacheDirectory = new File("cache");
//出于安全性的考慮菊卷，在Android中我們推薦使用Context.getCacheDir()來作為緩存的存放路徑
if (!cacheDirectory.exists()) {
    cacheDirectory.mkdirs();
}
Cache cache = new Cache(cacheDirectory, cacheSize);
OkHttpClient newClient = okHttpClient.newBuilder()
        .Cache(cache)
        .connectTimeout(20, TimeUnit.SECONDS)
        .readTimeout(20, TimeUnit.SECONDS)
        .build();

如果服務(wù)器支持緩存缔恳，請(qǐng)求返回的Response會(huì)帶有Header:Cache-Control, max-age=xxx，Okhttp會(huì)自動(dòng)執(zhí)行緩存洁闰，如果服務(wù)器不支持歉甚，則要通過攔截Response，給其設(shè)置Cache-Control信息

public class CacheInterceptor implements Interceptor {
    @Override
    public Response intercept(Chain chain) throws IOException {
        Request request = chain.request();
        Response response = chain.proceed(request);
        Response response1 = response.newBuilder()
                .removeHeader("Pragma")
                .removeHeader("Cache-Control")
                //cache for 30 days
            .header("Cache-Control", "max-age=" + 3600 * 24 * 30)
                .build();
        return response1;
    }
}

OkHttpClient okHttpClient = new OkHttpClient();

OkHttpClient newClient = okHttpClient.newBuilder()
        .addNetworkInterceptor(new CacheInterceptor())
        .cache(cache)
        .connectTimeout(20, TimeUnit.SECONDS)
        .readTimeout(20, TimeUnit.SECONDS)
        .build();

ssl支持

SSL位于TCP/IP和http協(xié)議之間扑眉，他的作用
1纸泄、認(rèn)證用戶和服務(wù)器赖钞，確保數(shù)據(jù)發(fā)送到正確的客戶機(jī)和服務(wù)器；(驗(yàn)證證書)
2聘裁、加密數(shù)據(jù)以防止數(shù)據(jù)中途被竊妊┯；（加密）
3衡便、維護(hù)數(shù)據(jù)的完整性献起，確保數(shù)據(jù)在傳輸過程中不被改變。（摘要算法）
Okhttp默認(rèn)是可以訪問通過CA認(rèn)證的https鏈接镣陕，如果是自簽名的證書谴餐，則應(yīng)用需要存放對(duì)應(yīng)的證書，并添加到okhttp設(shè)置中呆抑。

mContext = context;
        X509TrustManager trustManager;
        SSLSocketFactory sslSocketFactory;
        final InputStream inputStream;
        try {
            inputStream = mContext.getAssets().open("srca.cer"); // 得到證書的輸入流
            try {

                trustManager = trustManagerForCertificates(inputStream);//以流的方式讀入證書
                SSLContext sslContext = SSLContext.getInstance("TLS");
                sslContext.init(null, new TrustManager[]{trustManager}, null);
                sslSocketFactory = sslContext.getSocketFactory();

            } catch (GeneralSecurityException e) {
                throw new RuntimeException(e);
            }

            client = new OkHttpClient.Builder()
                    .sslSocketFactory(sslSocketFactory, trustManager)
                    .build();
        } catch (IOException e) {
            e.printStackTrace();
        }

dns支持

HTTP DNS通過將域名查詢請(qǐng)求放入http中的一種域名解析方式岂嗓，而不用系統(tǒng)自帶的libc庫去查詢運(yùn)營(yíng)商的DNS服務(wù)器，有更大的自由度鹊碍，https下不會(huì)存在任何問題摄闸，證書校驗(yàn)依然使用域名進(jìn)行校驗(yàn)。目前微信妹萨，qq郵箱、等業(yè)務(wù)均使用了HTTP DNS炫欺。
在OKhttp中乎完，提供DNS接口，實(shí)現(xiàn)DNS類品洛，配置到OKhttp中就行了
主要優(yōu)點(diǎn)：
能夠準(zhǔn)確地將站點(diǎn)解析到離用戶最近的CDN站點(diǎn)树姨，方便進(jìn)行流量調(diào)度
解決部分運(yùn)營(yíng)商DNS無法解析國(guó)外站點(diǎn)的問題
TCP在一定程度可以防止UDP無校驗(yàn)導(dǎo)致的DNS欺詐（比如墻，運(yùn)營(yíng)商廣告桥状，404導(dǎo)航站）帽揪，當(dāng)然基于HTTP的話本質(zhì)還是不安全的。

static Dns HTTP_DNS =  new Dns(){
  @Override public List<InetAddress> lookup(String hostname) throws UnknownHostException {
    //防御代碼
    if (hostname == null) throw new UnknownHostException("hostname == null");
    //dnspod提供的dns服務(wù)
    HttpUrl httpUrl = new HttpUrl.Builder().scheme("http")
        .host("119.29.29.29")
        .addPathSegment("d")
        .addQueryParameter("dn", hostname)
        .build();
    Request dnsRequest = new Request.Builder().url(httpUrl).get().build();
    try {
      String s = getHTTPDnsClient().newCall(dnsRequest).execute().body().string();
      //避免服務(wù)器掛了卻無法查詢DNS
      if (!s.matches("\\b(?:\\d{1,3}\\.){3}\\d{1,3}\\b")) {
        return Dns.SYSTEM.lookup(hostname);
      }
      return Arrays.asList(InetAddress.getAllByName(s));
    } catch (IOException e) {
      return Dns.SYSTEM.lookup(hostname);
    }
  }
};

static public synchronized OkHttpClient getClient() {
  if (client == null) {
    final File cacheDir = GlobalContext.getInstance().getExternalCacheDir();
    client = new OkHttpClient.Builder().addNetworkInterceptor(getLogger())
        .cache(new Cache(new File(cacheDir, "okhttp"), 60 * 1024 * 1024))
        .dispatcher(getDispatcher())
        //配置DNS查詢實(shí)現(xiàn)
        .dns(HTTP_DNS)
        .build();
  }
  return client;
}

支持連接池

Okhttp支持5個(gè)并發(fā)KeepAlive辅斟，默認(rèn)鏈路生命為5分鐘(鏈路空閑后转晰，保持存活的時(shí)間)。
socket連接每次需要3次握手士飒、釋放要2次或4次查邢，當(dāng)訪問復(fù)雜網(wǎng)絡(luò)時(shí)，延時(shí)將成為非常重要的因素酵幕，使用連接池的好處就是優(yōu)化網(wǎng)絡(luò)性能扰藕，對(duì)于延遲降低與速度提升的有非常重要的作用。
KeepAlive缺點(diǎn)則是芳撒，在提高了單個(gè)客戶端性能的同時(shí)邓深，復(fù)用卻阻礙了其他客戶端的鏈路速度未桥。

相關(guān)資料

OkHttp使用教程
Okhttp使用指南與源碼分析
Okhttp-wiki 之 Interceptors 攔截器
OkHttp 3.x 源碼解析之Interceptor 攔截器
OkHttp攔截器的實(shí)現(xiàn)原理
使用okHttp支持https
Android使用OkHttp請(qǐng)求自簽名的https網(wǎng)站
OkHttp3應(yīng)用HTTP DNS的實(shí)現(xiàn)
Android OkHttp實(shí)現(xiàn)HttpDns的最佳實(shí)踐（非攔截器）
Android網(wǎng)絡(luò)編程（七）源碼解析OkHttp前篇請(qǐng)求網(wǎng)絡(luò)
OkHttp3源碼分析復(fù)用連接池