okhttp3与okhttp的区别

OkHttpClient创建方式不同，
okhttp直接newOkHttpClient，而okhttp3中提供了Builder，很好的使用了创建者设计模式

cookie的设置方式不同：
okhttp调用OkHttpClient的setCookieHandler方法，CookieHandler是Android SDK提供的标注的cookie管理，CookieHandler 的之类CookieManager实现了cookie的具体
管理方法，构建CookieManager需要实现CookieStore接口，系统提供了一个默认的实现CookieStoreImpl，只负责把cookie存储在内存中。
okhttp3中已经没有setCookieHandler方法了，而改成了cookieJar，新增了Builder，用Builder构建okhttp,设置cookie在Builder的cookieJar方法中设置

post消息体构建方式不同
okhttp使用MultipartBuilder，FormEncodingBuilder构建post消息体，最终构建出来的都是RequestBody，而okhttp3增加了RequestBody的子类，构造器放到了RequestBody的子类中，MultipartBody.Builder既可以添加表单数据，也可以添加文件等二进制数据

Call和Callback不同

okhttp的callback方法是  void onFailure(Request request, IOException e);void onResponse(Response response) throws IOException;  okhttp3 的Callback方法有void onFailure(Call call, IOException e);void onResponse(Call call, Response response) throws IOException;okhttp3对Call做了更简洁的封装，okhttp3 Call是个接口，okhttp的call是个普通class，一定要注意，无论哪个版本，call都不能执行多次，多次执行需要重新创建。

对https支持的不同
okhttp默认调用了getDefaultSSLSocketFactory方法，该方法提供了默认的SSLSocketFactory，就算不设置SSLSocketFactory也可以支持https,setSslSocketFactory没有做非空判断，如果设置为空，则使用默认的SSLSocketFactory。okhttp3设置https的方法sslSocketFactory，对SSLSocketFactory做了非空判断，为空会抛出异常。如果不主动设置SSLSocketFactory，okhttp3也提供了默认的http3支持
if (builder.sslSocketFactory != null || !isTLS) {
    this.sslSocketFactory = builder.sslSocketFactory;
  } else {
     try {
      SSLContext sslContext = SSLContext.getInstance("TLS");
       sslContext.init(null, null, null);
       this.sslSocketFactory = sslContext.getSocketFactory();
    } catch (GeneralSecurityException e) {
       throw new AssertionError(); // The system has no TLS. Just give up.
    }
}

OkHttp的基本使用

HTTP GET
OkHttpClient client = new OkHttpClient();
String doGet(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 { 
    return ""; //根据自己的需要做异常数据处理
  }
}
Request是OkHttp中访问的请求，Builder是辅助类。Response即OkHttp中的响应。
Response类：
public boolean isSuccessful()
Returns true if the code is in [200..300), which means the request was successfully received, understood, and accepted.
response.body()返回ResponseBody类

可以方便的获取string
public final String string() throws IOException
Returns the response as a string decoded with the charset of the Content-Type header. If that header is either absent or lacks a charset, this will attempt to decode the response body as UTF-8.
Throws:
IOException
当然也能获取到流的形式：
public final InputStream byteStream()

HTTP POST
POST提交Json数据
public static final MediaType JSON = MediaType.parse("application/json; charset=utf-8");
OkHttpClient client = new OkHttpClient();
String post(String url, String jsonstr) throws IOException {
        RequestBody body = RequestBody.create(JSON, jsonstr);

   Request request = new Request.Builder()
    .url(url)
    .post(body)
    .build();
        Response response = client.newCall(request).execute();
  f (response.isSuccessful()) {
    return response.body().string();
  } else {
    return ""; //根据自己的需要做异常数据处理
  }
}

使用Request的post方法来提交请求体RequestBody
POST提交键值对
很多时候我们会需要通过POST方式把键值对数据传送到服务器。 OkHttp提供了很方便的方式来做这件事情。

OkHttpClient client = new OkHttpClient();
String post(String url, String json) throws IOException {
        RequestBody formBody = new FormEncodingBuilder()
  .add("platform", "android")
  .add("name", "robert")
  .add("info", "abcdefg")
  .build();
        Request request = new Request.Builder()
      .url(url)
      .post(body)
      .build();
        Response response = client.newCall(request).execute();
  if (response.isSuccessful()) {
      return response.body().string();
  } else {
      return ""; //根据自己的需要做异常数据处理

  }

}