某些API应该是服务器设置了限制，使得手机端okhttp作为 http客户端时，获取数据，服务器返回HTTP 403禁止访问。

本篇文章用修改okhttp的头部Header字段模拟手机浏览器访问服务器，从而可以通过被限制的服务器。

如果是未修改前，也就是默认时会出现

W/System.err: retrofit2.adapter.rxjava2.HttpException: HTTP 403 Forbidden
服务器禁止访问了，因为okhttp并不是真正的原生的http请求，它在header中并没有真正的User-Agent，而是“okhttp/版本号”。
Request request = new Request.Builder().url(url)
                             .removeHeader("User-Agent")
                             .addHeader("User-Agent", WebSettings.getDefaultUserAgent(App.getINSTANCE()))
                              .build();
            httpClient.newCall(request).enqueue(handler);
如果是okHttp+Retrofit，就要用构造器添加Interceptor
import android.webkit.WebSettings;
import com.minminaya.myapplication.App;
import com.minminaya.myapplication.api.MusicApi;
import java.io.IOException;
import okhttp3.Interceptor;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.Response;
import retrofit2.CallAdapter;
import retrofit2.Converter;
import retrofit2.Retrofit;
import retrofit2.adapter.rxjava2.RxJava2CallAdapterFactory;
import retrofit2.converter.gson.GsonConverterFactory;
 * 初始化网络Retrofit等服务
 * Created by Niwa on 2017/6/24.
public class NetWork {
    private static MusicApi musicApi;
    private static Converter.Factory gsonConverterFactory = GsonConverterFactory.create();
    private static CallAdapter.Factory rxJavaCallAdapterFactory = RxJava2CallAdapterFactory.create();
    public static MusicApi getMusicApi() {
        if (musicApi == null) {
            Retrofit retrofit = new Retrofit.Builder()
                    .client(getOkHttpClient())//获取后的okhttp头部
                    .baseUrl("http://tingapi.ting.baidu.com/v1/restserver/")
                    .addConverterFactory(gsonConverterFactory)
                    .addCallAdapterFactory(rxJavaCallAdapterFactory)
                    .build();
            musicApi = retrofit.create(MusicApi.class);
        return musicApi;
     *  构造okhttp头部
    private static OkHttpClient getOkHttpClient() {
        OkHttpClient httpClient = new OkHttpClient.Builder()
                .addInterceptor(new Interceptor() {
                    @Override
                    public Response intercept(Chain chain) throws IOException {
                        Request request = chain.request()
                                .newBuilder()
                                .removeHeader("User-Agent")//移除旧的
                                .addHeader("User-Agent", WebSettings.getDefaultUserAgent(App.getINSTANCE()))//添加真正的头部
                                .build();
                        return chain.proceed(request);
                }).build();
        return httpClient;