How to dynamically set headers in Retrofit (Android)

Question

I am using an API that uses an authorization scheme that requires a special "X-Authorization" header to be set to authenticate the request. For example, this Retrofit setup works perfectly for the user whose auth token is abc123:

@Headers("X-Authorization: abc123")
@GET("/posts")
Observable<List<Post>> get_posts();

I cache the user's X-Authorization token, so I have access to that, however, I can't just drop it in the @Headers declaration.

@Headers("X-Authorization: " + token)
@GET("/posts")
Observable<List<Post>> get_posts();

I get a compile error here: Error:(41, 34) error: element value must be a constant expression

Any ideas on how I could get around this?

Answer 1

Passing header in parameter would be helpful. Look to the following code;

 @GET("/posts")
Observable<JsonElement> getDataFromService(
        @HeaderMap Map<String, String> headers,
        @QueryMap HashMap<String, Object> queryParams
);

        hashMap1.put("Authorization", token);
    return ApiService.getAPI_test().getDataFromService(hashMap1, url, hashMap)
            .observeOn(AndroidSchedulers.mainThread())
            .subscribeOn(Schedulers.io());

Update:

More better would be

 @GET("/posts")
Observable<JsonElement> getDataFromService(
        @Header("Authorization") token: String = "Bearer " + PreferenceUtils.getToken(),
        @QueryMap HashMap<String, Object> queryParams
);

Answer 2

Dynamic Header In Retrofit 2

I have struggled too much to add Dynamic Header In Retrofit 2.

I have gone through so many blogs and StackOver flow. Everyone has shown example with Interceptor.

And it’s not a wise thing ,just for one API call we need to do that much work.

You just have to add @HeaderMap as argument of fun. I have done in very simple way :-

In Kotlin

    val headers = HashMap<String, String>()
    headers["KEY_AUTHORIZATION"] = "paste AUTHORIZATION value here"
    headers["KEY_TOKEN"] = "paste TOKEN value here"

    val jsonObject= JsonObject()

I am passing here header and other data also
Calling of fun:-

postEvent(headers,jsonObject)

API Declaration 

    @POST("/v1/post_data")
    fun postEvent(@HeaderMap headers: Map<String, String>, @Body jsonObject: JsonObject): Call<JsonObject>

API Declaration with RxAndroid

    @POST("/v1/post_data")
    fun postEvent(@HeaderMap headers: Map<String, String>, @Body jsonObject: JsonObject): Single<JsonObject>

2nd argument here i have JsonObject. You can replace with anything whatever you need to pass or you can remove it also.

In Java

 HashMap<String, String> headers = new HashMap<String, String>();
    headers.put("KEY_AUTHORIZATION","paste AUTHORIZATION value here");
    headers.put("KEY_TOKEN", "paste TOKEN value here");

    JsonObject jsonObject= new JsonObject();

I am passing here header and other data also

Calling of fun:-
postEvent(headers,jsonObject);

    API Declaration 
    @POST("/v1/post_data")
    Call<JsonObject> postEvent(@HeaderMap Map<String, String> headers, @Body JsonObject jsonObject);

API Declaration with RxAndroid

    @POST("/v1/post_data")
    Single<JsonObject> postEvent(@HeaderMap Map<String, String> headers, @Body JsonObject jsonObject);

2nd argument here i have JsonObject. You can replace with anything whatever you need to pass or you can remove it also.

Answer 3

A request Header can be updated dynamically using the @Header annotation. A corresponding parameter must be provided to the @Header. If the value is null, the header will be omitted. Otherwise, toString will be called on the value, and the result used.

@GET("user")
Call<User> getUser(@Header("Authorization") String authorization)

Answer 4

When the last part of this answer How to dynamically set headers in Retrofit (Android) did not work for me (halfway of the project), I improved it:-

public class MyRetrofitInterceptor implements RequestInterceptor {
// volatile variable
public static String token = null; //change at start of app
@Override
public void intercept(RequestFacade req) {
    // change token from outside the class.
    if (token != null) {
        req.addHeader("X-Authorization", token);
    }
}

It worked as soon as the token was updated from the response from the server API.

I think it worked as the string variable 'token' was used as the reference to its value, in global terms (being public static).