Retrofit添加通用Header

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

这里拦截到request，Request的newBuilder方法会将自己的属性添加到一个新的Builder中，借助这个Builder我们可以重新添加Header

client.interceptors().add(new Interceptor() {
            @Override
            public Response intercept(Chain chain) throws IOException {
                Request request = chain.request();
                Request.Builder newBuilder = request.newBuilder().addHeader("test" , "test");
                return chain.proceed(newBuilder.build());
            }
        });

Retrofit retrofit = new Retrofit.Builder()
            .baseUrl(url)
            //增加返回值为String的支持
            .addConverterFactory(ScalarsConverterFactory.create())
            .client(client)
                .addConverterFactory(GsonConverterFactory.create())
            .build();