方式一、直接在參數里寫 每次訪問的時候都要傳入一下

@GET("weatherservice/citylist") 
Observable<WeatherRestBean> request(@Header("apikey") String apikey,@Query("cityname") String cityname);

方式二、寫到注解里這樣就少了個參數，但是每定義個接口都要寫一次也是比較麻煩

@Headers("apikey:ac7c302dc489a69082cbee6a89e3646c") 
@GET("weatherservice/cityid") request<WeatherEntity> query(@Query("cityid")String cityid); 

方式三、在創建Retrofit的時候添加，最方便的方式

OkHttpClient client = new OkHttpClient.Builder()
 .addInterceptor(new Interceptor() { 
@Override 
public Response intercept(Chain chain) throws IOException { 
Request request = chain.request(); 
Request.Builder builder1 = request.newBuilder(); 
Request build = builder1.addHeader("apikey", "ac7c302dc489a69082cbee6********").build(); 
return chain.proceed(build); } })
.retryOnConnectionFailure(true)
 .build();
 mRetrofit = new Retrofit.Builder()
 .client(client)
 .baseUrl(ConstantApi.url) 
.addCallAdapterFactory(...

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