okhttp的簡單使用，主要包含：
一般的get請求
一般的post請求
基於Http的檔案上傳
檔案下載
載入圖片
支援請求回撥，直接返回物件、物件集合
支援session的保持

//新增依賴

    implementation 'com.squareup.okhttp3:okhttp:3.11.0'
    implementation 'com.squareup.okhttp3:logging-interceptor:3.11.0'  //攔截日誌

import android.util.Log;

import java.io.IOException;
import java.util.concurrent.TimeUnit;

import okhttp3.Call;
import okhttp3.Callback;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.Response;
import okhttp3.logging.HttpLoggingInterceptor;

/**
 * date:2018/11/16
 * author:QMY(QMY)
 * function:
 */
public class OkHttpUtils{
    public void requestData(String s) {
//日誌攔截
        HttpLoggingInterceptor logging = new HttpLoggingInterceptor(new HttpLoggingInterceptor.Logger() {
            @Override
            public void log(String message) {
                Log.e("msg", "++++++++" + message);
            }
        });
        logging.setLevel(HttpLoggingInterceptor.Level.BODY);

        //建立okhttp物件
        OkHttpClient okHttpClient = new OkHttpClient.Builder()
                .readTimeout(10, TimeUnit.SECONDS)
                .connectTimeout(10, TimeUnit.SECONDS)
                .addInterceptor(logging)
                .build();

        //建立request
        final Request request = new Request.Builder()
                .url(s)
                .build();
        //建立call
        okHttpClient.newCall(request).enqueue(new Callback() {
            @Override
            public void onFailure(Call call, IOException e) {

            }

            @Override
            public void onResponse(Call call, Response response) throws IOException {
                String string = response.body().string();

              
            }
        });
    }

//單例模式
    public class Singleton {//懶漢式
        private volatile Singleton singleton;
        private Singleton() {}
        public  Singleton getInstance() {
            if (singleton == null) {
                synchronized (Singleton.class) {
                    if (singleton == null) {
                        singleton = new Singleton();
                    }
                }
            }
            return singleton;
        }
    }
  
}