2. Tutorials
  3. Retrofit — Optional Query Parameters

Retrofit — Optional Query Parameters

The previous post guided you through the options to add custom headers to your requests. Today, we’re diving into the topic on how to use Retrofit to make request parameters optional.

Retrofit Series Overview

  1. Getting Started and Creating an Android Client
  2. Basics of API Description
  3. Creating a Sustainable Android Client
  4. URL Handling, Resolution and Parsing
  5. How to Change API Base Url at Runtime
  6. Multiple Server Environments (Develop, Staging, Production)
  7. Share OkHttp Client and Converters between Retrofit Instances
  8. Upgrade Guide from 1.9
  9. Beyond Android: Retrofit for Java Projects
  10. How to use OkHttp 3 with Retrofit 1
  1. Synchronous and Asynchronous Requests
  2. Send Objects in Request Body
  3. Add Custom Request Header
  4. Manage Request Headers in OkHttp Interceptor
  5. Dynamic Request Headers with @HeaderMap
  6. Multiple Query Parameters of Same Name
  7. Optional Query Parameters
  8. Send Data Form-Urlencoded
  9. Send Data Form-Urlencoded Using FieldMap
  10. How to Add Query Parameters to Every Request
  11. Add Multiple Query Parameter With QueryMap
  12. How to Use Dynamic Urls for Requests
  13. Constant, Default and Logic Values for POST and PUT Requests
  14. Cancel Requests
  15. Reuse and Analyze Requests
  16. Optional Path Parameters
  17. How to Send Plain Text Request Body
  18. Customize Network Timeouts
  19. How to Trust Unsafe SSL certificates (Self-signed, Expired)
  20. Dynamic Endpoint-Dependent Interceptor Actions
  21. How to Update Objects on the Server (PUT vs. PATCH)
  22. How to Delete Objects on the Server
  1. Ignore Response Payload with Call<Void>
  2. Receive Plain-String Responses
  3. Crawl HTML Responses with jspoon (Wikipedia Example)
  4. Loading Data into RecyclerView and CardView
  1. Introduction to (Multiple) Converters
  2. Adding & Customizing the Gson Converter
  3. Implementing Custom Converters
  4. How to Integrate XML Converter
  5. Access Mapped Objects and Raw Response Payload
  6. Supporting JSON and XML Responses Concurrently
  7. Handling of Empty Server Responses with Custom Converter
  8. Send JSON Requests and Receive XML Responses (or vice versa)
  9. Unwrapping Envelope Responses with Custom Converter
  10. Wrapping Requests in Envelope with Custom Converter
  11. Define a Custom Response Converter
  1. Simple Error Handling
  2. Error Handling for Synchronous Requests
  3. Catch Server Errors Globally with Response Interceptor
  4. How to Detect Network and Conversion Errors in onFailure
  1. Log Requests and Responses
  2. Enable Logging for Development Builds Only
  3. Log Network Traffic with Stetho and Chrome Developer Tools
  4. Using the Log Level to Debug Requests
  5. Analyze Network Traffic with Android Studio Profiler
  6. Debug and Compare Requests with RequestBin
  1. Introduction to Call Adapters
  2. Custom Call Adapter to Separate OnResponse Callback
  3. How to Integrate RxJava 1.x Call Adapter
  4. How to Integrate RxJava 2.x Call Adapter
  5. How to Integrate Guava Call Adapter
  6. Custom Call Adapter to Separate Network and Gson Errors
  1. Pagination Using Query Parameter
  2. Pagination Using Link Header and Dynamic Urls (Like GitHub)
  3. Pagination Using Range Header Fields (Like Heroku)
  1. How to Upload Files to Server
  2. How to Upload Multiple Files to Server
  3. How to Upload a Dynamic Amount of Files to Server
  4. Upload Files with Progress
  5. Passing Multiple Parts Along a File with @PartMap
  6. How to Download Files from Server
  7. Download Files with Progress Updates
  8. How to Upload Files to Server
  1. Basic Authentication on Android
  2. Token Authentication on Android
  3. OAuth on Android
  4. Hawk Authentication on Android
  5. How to Refresh an Access Token
  1. Activate Response Caching (Etag, Last-Modified)
  2. Check Response Origin (Network, Cache, or Both)
  3. Force Server Cache Support with Response Interceptor
  4. Support App Offline Mode by Accessing Response Caches
  5. Analyze Cache Files
  1. Basics of Mocking Server Responses
  2. Customizing Network Behavior of Mocked Server Responses
  3. Mock APIs with JsonServer
  1. Callbacks
  2. Annotations
  3. Fluent Interface with Builders

Query Parameters with Retrofit

Retrofit uses annotations to define query parameters for requests. The annotation is defined before method parameters and specifies the request parameter name. The desired value for this parameter is passed during method call. Let's face a concrete example. The code below illustrates a request method which has /tasks as API endpoint url and provides the option to pass a sort parameter for desired sorting.

Retrofit 2

public interface TaskService {  
    @GET("/tasks")
    Call<List<Task>> getTasks(@Query("sort") String order);
}

Retrofit 1.9

public interface TaskService {  
    @GET("/tasks")
    List<Task> getTasks(@Query("sort") String order);
}

Assuming that your base url to your API is https://your.api.com, the request using the TaskService from above and calling the getTasks method results in this request url: https://your.api.com/tasks?sort=value-of-order-parameter

Optional Query Parameters

Depending on the API design, the sort parameter might be optional. In case you don’t want to pass it with the request, just pass null as the value for order during method call.

service.getTasks(null);

Retrofit skips null parameters and ignores them while assembling the request. Keep in mind, that you can’t pass null for primitive data types like int, float, long, etc. Instead, use Integer, Float, Long, etc and the compiler won’t be grumpy.

The upcoming example depicts the service definition for the previously mentioned data types.

Retrofit 2

public interface TaskService {  
    @GET("/tasks")
    Call<List<Task>> getTasks(
        @Query("sort") String order,
        @Query("page") Integer page);
}

Retrofit 1.9

public interface TaskService {  
    @GET("/tasks")
    List<Task> getTasks(
        @Query("sort") String order,
        @Query("page") Integer page);
}

Now you can pass null for either of the defined query parameters order and page when calling the getTasks method.

service.getTasks(null, null);

Summary

In this tutorial you've seen how you can use optional query parameters.

Please let us know about any problems you ran into on Twitter @futurestud_io or in the comment section below.

Enjoy coding & make it rock!

Additional Ressources

Marcus Pöhls

Marcus is a fullstack JS developer. He’s passionate about the hapi framework for Node.js and loves to build web apps and APIs. Creator of Futureflix and the “learn hapi” learning path.

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