Android retrofit 2 load image

Upload file in Android Java with retrofit 2

Nov 13, 2019 · 4 min read

In this article, we will implement a function upload file with Retrofit2 for android. Retrofit2 is one of the most popular network request libraries for android.

Retrofit

Annotations on the interface methods and its parameters indicate how a request will be handled. Request Method Every…

1. Add retrofit 2 to gradle file (app level).

We also add Gson package which is used to parse JSON to Object when we get JSON return from API and of course we can convert a java object to JSON when we send post to the server.

2. Create Retrofit Instance

As you can see we just declare one base API endpoint at the top of the class.

in this case, I get value from the grade file config, but you can change with your API endpoint. Then we create a retrofit instance, I also added a connection timeout is 60 s because the default of Retrofit time out is 10 second so when you upload a large size, time out can occur.

3. Create an interface to upload file

In this code, we will define a request which is needed to map with API, what type if request POST, GET or PUT. What is the parameter and API endpoint.

As you can see, we just declare these parameter

Please make sure that you are using HTTPS if you are using HTTP Retrofit2 will throw the error.

in this interface, we are using POST method to send a file to the server

Luckily, Retrofit2 is supported to send a cookie to the server site. As you know almost API nowadays use token to validate user in some case, we can use a cookie. In my case, I have used cookies so I add cookies here.
You can create a cookie as String and just add to header.

4. Post Parameters, upload the file and handle the response

This is the most important things, we need to send a file to the server. In this case, we are uploading files so we will `MultipartBody`

And next is the body, you can send the body as JSON or text.

4. Upload the file

This is the way we create a request network from our main controller.

As the top line, we just initiated service with a retrofit client

Next, creating parameters and pass these values to interface

Finally, catch the callback response from the server, in this callback. If return success we will handle at the function `onResponse` else failed we will handle at `onFailure`

Bonus:

It is very important for debugging some cases when we must to know what is the api response. In some cases, the response can be not a json format instead of it is an HTML page, how we know what is the response? Fortunately, we can use the library interceptor

add interceptor to gradle app file, I got some issue when building the project, maybe you need to clean project and rebuild again.

Add log to Retrofit client

we can use ‘ ProgressDialog’ to let the user know that the upload is processing. In order to user ProgressDialog, just declare a process dialog before call API and dismiss it when finishing upload file

Then just dismiss the dialog after done calling.

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Learn2Crack

Android Upload Image using Retrofit #2

Creating Node.js Server

For the first part of the tutorial to create Node.js server to upload Images.

In this second part of the tutorial, we will create an Android app with Retrofit to upload an image to the Node.js server we created before.

Here I have created an Android Studio project with package com.learn2crack.imageupload also Activity as MainActivity and layout as activity_main.

We need to add dependencies for Retrofit and Retrofit GSON converter library. Also, make sure you have Design Support library and Constraint Layout library in your build.gradle. Latest versions of Android Studio adds these libraries on creating new project.

Adding Permissions Required

We need to add Internet permission in our AndroidManifest.xml

Our main layout has a content layout included which has two buttons to upload and view image. It also has a progress bar.

Creating Model class

We are creating a Model Response.java class with message and path fields.

Creating Retrofit Interface

We have defined a Retrofit interface with Multipart as the type to upload the image.

In our MainActivity when the image select button is pressed we start a Intent to pick image. On Result, we will get the Uri of the image. From that Uri, we will open an InputStream and read the image contents as a byte array. From Android Nougat there were some changes which do not allow us to get the Real file path of the image. So we are using this alternate method. With the byte array, we will create an okhttp RequestBody object. From that, we can create a MultipartBody.Part object which can be used with the Retrofit interface to upload the image. We display the message in a Snackbar when the image is uploaded, or any error message is returned.

When the image is uploaded successfully, we will get the path of the uploaded image. We will use this path of the image to construct the URL and launch an external browser to view the image.

Complete Project Files

You can download the complete project as zip or fork from our Github repository.

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Retrofit 2 — How to Download Files from Server

Moonshoot

Moonshoot is a
Student Feature.

In this blog post of our Retrofit launch sequence we’ll show you one of the most requested topics: how to download files. We’ll give you all the insight and snippets you need to use Retrofit to download everything, from tiny .png ‘s to large .zip files.

If this is your first Retrofit post on futurestud.io, feel free to browse our other Retrofit posts:

Retrofit Series Overview

Getting Started and Creating an Android Client

Basics of API Description

Creating a Sustainable Android Client

URL Handling, Resolution and Parsing

How to Change API Base Url at Runtime

Multiple Server Environments (Develop, Staging, Production)

Share OkHttp Client and Converters between Retrofit Instances

Upgrade Guide from 1.9

Beyond Android: Retrofit for Java Projects

How to use OkHttp 3 with Retrofit 1

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

Synchronous and Asynchronous Requests

Send Objects in Request Body

Add Custom Request Header

Manage Request Headers in OkHttp Interceptor

Dynamic Request Headers with @HeaderMap

Multiple Query Parameters of Same Name

Optional Query Parameters

Send Data Form-Urlencoded

Send Data Form-Urlencoded Using FieldMap

How to Add Query Parameters to Every Request

Add Multiple Query Parameter With QueryMap

How to Use Dynamic Urls for Requests

Constant, Default and Logic Values for POST and PUT Requests

Reuse and Analyze Requests

Optional Path Parameters

How to Send Plain Text Request Body

Customize Network Timeouts

How to Trust Unsafe SSL certificates (Self-signed, Expired)

Dynamic Endpoint-Dependent Interceptor Actions

How to Update Objects on the Server (PUT vs. PATCH)

How to Delete Objects on the Server

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

Ignore Response Payload with Call

Receive Plain-String Responses

Crawl HTML Responses with jspoon (Wikipedia Example)

Loading Data into RecyclerView and CardView

1. Ignore Response Payload with Call
2. Receive Plain-String Responses
3. Crawl HTML Responses with jspoon (Wikipedia Example)
4. Loading Data into RecyclerView and CardView

Introduction to (Multiple) Converters

Adding & Customizing the Gson Converter

Implementing Custom Converters

How to Integrate XML Converter

Access Mapped Objects and Raw Response Payload

Supporting JSON and XML Responses Concurrently

Handling of Empty Server Responses with Custom Converter

Send JSON Requests and Receive XML Responses (or vice versa)

Unwrapping Envelope Responses with Custom Converter

Wrapping Requests in Envelope with Custom Converter

Define a Custom Response Converter

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

Simple Error Handling

Error Handling for Synchronous Requests

Catch Server Errors Globally with Response Interceptor

How to Detect Network and Conversion Errors in onFailure

Log Requests and Responses

Enable Logging for Development Builds Only

Log Network Traffic with Stetho and Chrome Developer Tools

Using the Log Level to Debug Requests

Analyze Network Traffic with Android Studio Profiler

Debug and Compare Requests with RequestBin

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

Introduction to Call Adapters

Custom Call Adapter to Separate OnResponse Callback

How to Integrate RxJava 1.x Call Adapter

How to Integrate RxJava 2.x Call Adapter

How to Integrate Guava Call Adapter

Custom Call Adapter to Separate Network and Gson Errors

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

Pagination Using Query Parameter

Pagination Using Link Header and Dynamic Urls (Like GitHub)

Pagination Using Range Header Fields (Like Heroku)

1. Pagination Using Query Parameter
2. Pagination Using Link Header and Dynamic Urls (Like GitHub)
3. Pagination Using Range Header Fields (Like Heroku)

How to Upload Files to Server

How to Upload Multiple Files to Server

How to Upload a Dynamic Amount of Files to Server

Upload Files with Progress

Passing Multiple Parts Along a File with @PartMap

How to Download Files from Server

Download Files with Progress Updates

How to Upload Files to Server

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 How to Download Files from Server
6. Download Files with Progress Updates
7. How to Upload Files to Server

Basic Authentication on Android

Token Authentication on Android

OAuth on Android

Hawk Authentication on Android

How to Refresh an Access Token

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

Activate Response Caching (Etag, Last-Modified)

Check Response Origin (Network, Cache, or Both)

Force Server Cache Support with Response Interceptor

Support App Offline Mode by Accessing Response Caches

Analyze Cache Files

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

Basics of Mocking Server Responses

Customizing Network Behavior of Mocked Server Responses

Mock APIs with JsonServer

1. Basics of Mocking Server Responses
2. Customizing Network Behavior of Mocked Server Responses
3. Mock APIs with JsonServer

Fluent Interface with Builders

How to Specify the Retrofit Request

If you’re reading this and you haven’t written code for any Retrofit requests yet, please check our previous blog posts to get started. For all you Retrofit experts: the request declaration for downloading files looks almost like any other request:

If the file you want to download is a static resource (always at the same spot on the server) and on the server your base URL refers to, you can use option 1. As you can see, it looks like a regular Retrofit 2 request declaration. Please note, that we’re specifying ResponseBody as return type. You should not use anything else here, otherwise Retrofit will try to parse and convert it, which doesn’t make sense when you’re downloading a file.

The second option is new to Retrofit 2. You can now easily pass a dynamic value as full URL to the request call. This can be especially helpful when downloading files, which are dependent of a parameter, user or time. You can build the URL during runtime and request the exact file without any hacks. If you haven’t worked with dynamic URLs yet, feel free to head over to our blog post for that topic: dynamic urls in Retrofit 2

Pick what kind of option is useful to you and move on to the next section.

How to Call the Request

After declaring our request, we need to actually call it:

If you’re confused by the ServiceGenerator.create() , head over to our first blog post to get started. Once we’ve created the service, we’ll make the request just like any other Retrofit call!

There is just one thing left, which currently hides behind the function writeResponseBodyToDisk() : writing the file to the disk!

How to Save the File

The writeResponseBodyToDisk() method takes the ResponseBody object and reads and writes the byte values of it to the disk. The code looks much more difficult than it actually is:

Most of it is just regular Java I/O boilerplate. You might need to adjust the first line on where and with what name your file is being saved. When you have done that, you’re ready to download files with Retrofit!

But we’re not completely ready for all files yet. There is one major issue: by default, Retrofit puts the entire server response into memory before processing the result. This works fine for some JSON or XML responses, but large files can easily cause Out-of-Memory-Errors.

If your app needs to download even slightly larger files, we strongly recommend reading the next section.

Beware with Large Files: Use @Streaming!

If you’re downloading a large file, Retrofit would try to move the entire file into memory. In order to avoid that, we’ve to add a special annotation to the request declaration:

The @Streaming declaration doesn’t mean you’re watching a Netflix file. It means that instead of moving the entire file into memory, it’ll pass along the bytes right away. But be careful, if you’re adding the @Streaming declaration and continue to use the code above, Android will trigger a android.os.NetworkOnMainThreadException .

Thus, the final step is to wrap the call into a separate thread, for example with a lovely ASyncTask:

You can still use the same writeResponseBodyToDisk() method. If you remember the @Streaming declaration and this snippet, you can download even large files with Retrofit efficiently.

Next: Download Files with Progress Updates

If you download files in the foreground and they are not small, you might want to inform the user on your actions. Ideally, you would display progress updates how much you’ve downloaded already. We’ve another tutorial on how to download files with progress updates.

Summary

In this tutorial you’ve seen how to download files with Retrofit efficiently. This is everything you need to know to download files with Retrofit.

If you’ve any questions, let us know in the comments or on twitter.

Still Have Questions? Get Our Retrofit Book!

All modern Android apps need to do network requests. Retrofit offers you an extremely convenient way of creating and managing network requests. From asynchronous execution on a background thread, to automatic conversion of server responses to Java objects, Retrofit does almost everything for you. Once you’ve a deep understanding of Retrofit, writing complex requests (e.g., OAuth authentication) will be done in a few minutes.

Invest time to fully understand Retrofit’s principles. It’ll pay off multiple times in the future! Our book offers you a fast and easy way to get a full overview over Retrofit. You’ll learn how to create effective REST clients on Android in every detail.

Boost your productivity and enjoy working with complex APIs.

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