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https://github.com/codepath/android-rest-client-template-kotlin

Template Creating an Android OAuth REST Client (Kotlin)
https://github.com/codepath/android-rest-client-template-kotlin

Last synced: 4 months ago
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Template Creating an Android OAuth REST Client (Kotlin)

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README 

        
# RestClientTemplate



## Overview



RestClientTemplate is a skeleton Android project that makes writing Android apps sourced from OAuth JSON REST APIs as easy as possible. This skeleton project

combines the best libraries and structure to enable quick development of rich API clients. The following things are supported out of the box:



 * Authenticating with any OAuth 1.0a or OAuth 2 API

 * Sending requests for and parsing JSON API data using a defined client

 * Persisting data to a local SQLite store through an ORM layer

 * Displaying and caching remote image data into views



The following libraries are used to make this possible:



 * [scribe-java](https://github.com/fernandezpablo85/scribe-java) - Simple OAuth library for handling the authentication flow.

 * [Android Async HTTP](https://github.com/codepath/AsyncHttpClient) - Simple asynchronous HTTP requests with JSON parsing

 * [codepath-oauth](https://github.com/thecodepath/android-oauth-handler) - Custom-built library for managing OAuth authentication and signing of requests

 * [Glide](https://github.com/bumptech/glide) - Used for async image loading and caching them in memory and on disk.

 * [Room](https://developer.android.com/training/data-storage/room/index.html) - Simple ORM for persisting a local SQLite database on the Android device



## Usage



### 1. Configure the REST client



Open `src/com.codepath.apps.restclienttemplate/RestClient.java`. Configure the `REST_API_INSTANCE` and`REST_URL`.



For example if I wanted to connect to Twitter:



```kotlin

// RestClient.kt

class RestClient(context: Context) : OAuthBaseClient {

    companion object {

        val REST_API_INSTANCE = TwitterApi.instance()



        const val REST_URL = "https://api.twitter.com/1.1"



        const val REST_CONSUMER_KEY =

            BuildConfig.CONSUMER_KEY // Change this inside apikey.properties



        const val REST_CONSUMER_SECRET =

            BuildConfig.CONSUMER_SECRET // Change this inside apikey.properties



        // ...constructor and endpoints

    }



}

```



Rename the `apikey.properties.example` file to `apikey.properties`.   Replace the `CONSUMER_KEY` and `CONSUMER_SECRET` to the values specified in the Twitter console:



CONSUMER_KEY="adsflfajsdlfdsajlafdsjl"

CONSUMER_SECRET="afdsljkasdflkjsd"



Next, change the `intent_scheme` and `intent_host` in `strings.xml` to a unique name that is special for this application.

This is used for the OAuth authentication flow for launching the app through web pages through an [Android intent](https://developer.chrome.com/multidevice/android/intents).



```xml

oauth

codepathtweets

```



Next, you want to define the endpoints which you want to retrieve data from or send data to within your client:



```kotlin

// RestClient.jt

fun getHomeTimeline(page: Int, handler: JsonHttpResponseHandler) {

  val apiUrl = getApiUrl("statuses/home_timeline.json")

  val params = RequestParams()

  params.put("page", String.valueOf(page))

  client.get(apiUrl, params, handler)

}

```



Note we are using `getApiUrl` to get the full URL from the relative fragment and `RequestParams` to control the request parameters.

You can easily send post requests (or put or delete) using a similar approach:



```kotlin

// RestClient.kt

fun postTweet(body: String, handler: JsonHttpResponseHandler) {

    val apiUrl = getApiUrl("statuses/update.json")

    val params = RequestParams()

    params.put("status", body)

    client.post(apiUrl, params, handler)

}

```



These endpoint methods will automatically execute asynchronous requests signed with the authenticated access token. To use JSON endpoints, simply invoke the method

with a `JsonHttpResponseHandler` handler:



```kotlin

// SomeActivity.kt

val client = RestApplication.getRestClient()

client.getHomeTimeline(object : JsonHttpResponseHandler() {

    override fun onSuccess(statusCode: Int, headers: okhttp3.Headers, json: JSON) {

        Log.i(TAG, "onSuccess!")

        // parse json response here

    }



    override fun onFailure(

        statusCode: Int,

        headers: okhttp3.Headers,

        response: String,

        throwable: Throwable

    ) {

        Log.i(TAG, "onFailure!", throwable)

    }



})

```



Based on the JSON response (array or object), you need to declare the expected type inside the OnSuccess signature i.e

`public void onSuccess(JSONObject json)`. If the endpoint does not return JSON, then you can use the `AsyncHttpResponseHandler`:



```kotlin

val client = RestApplication.getRestClient()

client.getSomething(object : JsonHttpResponseHandler() {

    override fun onSuccess (statusCode: Int, headers: Headers, json: JSON) {

        System.out.println(json)

    }

});

```

Check out [Android Async HTTP Docs](https://github.com/codepath/AsyncHttpClient) for more request creation details.



### 2. Define the Models



In the `src/com.codepath.apps.restclienttemplate.models`, create the models that represent the key data to be parsed and persisted within your application.



For example, if you were connecting to Twitter, you would want a Tweet model as follows:



```kotlin

// models/Tweet.kt

package com.codepath.apps.restclienttemplate.models



import androidx.room.ColumnInfo

import androidx.room.Embedded



import androidx.room.Entity

import androidx.room.PrimaryKey



import org.json.JSONException

import org.json.JSONObject



@Entity

class Tweet {

  // Define database columns and associated fields

  @PrimaryKey

  @ColumnInfo

  var id: Long = 0L



  @ColumnInfo

  var userHandle: String = ""



  @ColumnInfo

  var timestamp: String = ""



  @ColumnInfo

  var body: String = ""



  // Use @Embedded to keep the column entries as part of the same table while still

  // keeping the logical separation between the two objects.

  @Embedded

  @Nullable

  var user: User = null

}

```



Note there is a separate `User` object but it will not actually be declared as a separate table.  By using the `@Embedded` annotation, the fields in this class will be stored as part of the Tweet table.  Room specifically does not load references between two different entities for performance reasons (see https://developer.android.com/training/data-storage/room/referencing-data), so declaring it this way causes the data to be denormalized as one table.



```kotlin

// models/User.java



class User {



    @ColumnInfo

    var name: String + ""



    // normally this field would be annotated @PrimaryKey because this is an embedded object

    // it is not needed

    @ColumnInfo

    var twitter_id: Long = 0L

}

```

Notice here we specify the SQLite table for a resource, the columns for that table, and a constructor for turning the JSON object fetched from the API into this object. For more information on creating a model, check out the [Room guide](https://developer.android.com/training/data-storage/room/).



In addition, we also add functions into the model to support parsing JSON attributes in order to instantiate the model based on API data.  For the User object, the parsing logic would be:



```kotlin

// Parse model from JSON

companion object {

    fun parseJSON(tweetJson: JSONObject) : User {

        val user = User()

        this.twitter_id = tweetJson.getLong("id")

        this.name = tweetJson.getString("name")

        return user

    }

}

```



For the Tweet object, the logic would would be:



```kotlin

// models/Tweet.kt

@Entity

companion object {

    fun fromJson(jsonObject: JSONObject): Tweet {

        val tweet = Tweet()

        tweet.body = jsonObject.getString("text")

        tweet.createdAt = jsonObject.getString("created_at")

        tweet.user = User.fromJson(jsonObject.getJSONObject("user"))

        return tweet

    }



    fun fromJsonArray(jsonArray: JSONArray): List {

        val tweets = ArrayList()

        for (i in 0 until jsonArray.length()) {

            tweets.add(fromJson(jsonArray.getJSONObject(i)))

        }

        return tweets

    }

}

```



Now you have a model that supports proper creation based on JSON. Create models for all the resources necessary for your mobile client.



### 4. Define your queries



Next, you will need to define the queries by creating a Data Access Object (DAO) class.   Here is an example of declaring queries to return a Tweet by the post ID, retrieve the most recent tweets, and insert tweets.



```kotlin



import androidx.room.Dao

import androidx.room.Insert

import androidx.room.OnConflictStrategy

import androidx.room.Query



import java.util.List



@Dao

interface TwitterDao {

    // @Query annotation requires knowing SQL syntax

    // See http://www.sqltutorial.org/

    @Query("SELECT * FROM SampleModel WHERE id = :id")

    fun byTweetId(tweetId: Long): Tweet?



    @Query("SELECT * FROM Tweet ORDER BY created_at")

    fun getRecentTweets(): List



    // Replace strategy is needed to ensure an update on the table row.  Otherwise the insertion will

    // fail.

    @Insert(onConflict = OnConflictStrategy.REPLACE)

    fun insertTweet(tweets: List);

}

```



The examples here show how to perform basic queries on the Tweet table.  If you need to declare one-to-many or many-to-many relations, see the guides on using the [@Relation](https://developer.android.com/reference/android/arch/persistence/room/Relation) and [@ForeignKey](https://developer.android.com/reference/android/arch/persistence/room/ForeignKey) annotations.



### 5. Create database



We need to define a database that extends `RoomDatabase` and describe which entities as part of this database. We also need to include what data access objects are to be included.  If the entities are modified or additional ones are included, the version number will need to be changed.  Note that only the `Tweet` class is declared:



```kotlin

// bump version number if your schema changes

@Database(entities={Tweet.class}, version=1)

abstract class MyDatabase : RoomDatabase() {

    abstract fun sampleModelDao(): SampleModelDao?



    companion object {

        // Database name to be used

        const val NAME = "MyDataBase"

    }

}

```



When compiling the code, the schemas will be stored in a `schemas/` directory assuming this statement

has been included your `app/build.gradle` file.  These schemas should be checked into your code based.



```gradle

android {

    defaultConfig {



        javaCompileOptions {

            annotationProcessorOptions {

                arguments = ["room.schemaLocation": "$projectDir/schemas".toString()]

            }

        }

    }



}

```



### 6. Initialize database



Inside your application class, you will need to initialize the database and specify a name for it.



```kotlin

class RestClientApp : Application {



  var myDatabase: MyDatabase = null



  override fun onCreate() {

    // when upgrading versions, kill the original tables by using fallbackToDestructiveMigration()

    myDatabase = Room.databaseBuilder(this, MyDatabase.class, MyDatabase.NAME).fallbackToDestructiveMigration().build()

  }



  fun getMyDatabase(): MyDatabase {

    return myDatabase

  }



}

```



### 7. Setup Your Authenticated Activities



Open `src/com.codepath.apps.restclienttemplate/LoginActivity.kt` and configure the `onLoginSuccess` method

which fires once your app has access to the authenticated API. Launch an activity and begin using your REST client:



```kotlin

// LoginActivity.kt

override fun onLoginSuccess() {

  val intent = Intent(this, TimelineActivity:class.java)

  startActivity(i);

}

```



In your new authenticated activity, you can access your client anywhere with:



```kotlin

val client = RestApplication.getRestClient()

client.getHomeTimeline(object : JsonHttpResponseHandler() {

  fun onSuccess(statusCode: Int, headers: Headers , json: JSON) {

    Log.d("DEBUG", "timeline: " + json.jsonArray.toString())

    // Load json array into model classes

  }

});

```



You can then load the data into your models from a `JSONArray` using:



```kotlin

val tweets = Tweet.fromJSON(jsonArray)

```



or load the data from a single `JSONObject` with:



```kotlin

val tweet = Tweet(json)

// t.body = "foo"

```



To save, you will need to perform the database operation on a separate thread by creating an `AsyncTask` and adding the item:



```kotlin

val task = object: AsyncTask() {

    override fun doInBackground(List tweets) {

      val twitterDao = (getApplicationContext() as RestApplication).getMyDatabase().twitterDao()

      twitterDao.insertModel(tweets)

      return null;

    };

  };

  task.execute(tweets);

```



That's all you need to get started. From here, hook up your activities and their behavior, adjust your models and add more REST endpoints.



### Extras



#### Loading Images with Glide



If you want to load a remote image url into a particular ImageView, you can use Glide to do that with:



```kotlin

Glide.with(this).load(imageUrl)

     .into(imageView);

```



This will load an image into the specified ImageView and resize the image to fit.



#### Logging Out



You can log out by clearing the access token at any time through the client object:



```kotlin

val client = RestApplication.getRestClient()

client.clearAccessToken()

```



### Viewing SQL table



You can use `chrome://inspect` to view the SQL tables once the app is running on your emulator.  See [this guide](https://guides.codepath.com/android/Debugging-with-Stetho) for more details.



### Adding OAuth2 support



Google uses OAuth2 APIs so make sure to use the `GoogleApi20` instance:



```kotlin

companion object {

  const val REST_API_INSTANCE = GoogleApi20.instance()

}

```



Change `REST_URL` to use the Google API:



```java

public static final String REST_URL = "https://www.googleapis.com/calendar/v3"; // Change this, base API URL

```



The consumer and secret keys should be retrieved via [the credentials section](https://console.developers.google.com/apis/credentials) in the Google developer console  You will need to create an OAuth2 client ID and client secret.



Create a file called `apikey.properties`:



```kotlin

REST_CONSUMER_KEY="XXX-XXX.apps.googleusercontent.com"

REST_CONSUMER_SECRET="XX-XXXXXXX"

```



The OAuth2 scopes should be used according to the ones defined in [the OAuth2 scopes](https://developers.google.com/identity/protocols/googlescopes):



```kotlin

companion object {

  const val OAUTH2_SCOPE = "https://www.googleapis.com/auth/calendar.readonly"

}

```



Make sure to pass this value into the scope parameter:



```kotlin

constructor RestClient(context: Context) {

		this(context, REST_API_INSTANCE,

				REST_URL,

				REST_CONSUMER_KEY,

				REST_CONSUMER_SECRET,

				OAUTH2_SCOPE,  // OAuth2 scope, null for OAuth1

				String.format(REST_CALLBACK_URL_TEMPLATE, context.getString(R.string.intent_host),

						context.getString(R.string.intent_scheme), context.getPackageName(), FALLBACK_URL));

	}

```

Google only accepts `http://` or `https://` domains, so your `REST_CALLBACK_URL_TEMPLATE` will need to be adjusted:



```kotlin

companion object {

  const val REST_CALLBACK_URL_TEMPLATE = "https://localhost"

}

```



Make sure to update the `cprest` and `intent_host` to match this callback URL .



### Troubleshooting



* If you receive the following error `org.scribe.exceptions.OAuthException: Cannot send unauthenticated requests for TwitterApi client. Please attach an access token!` then check the following:

 * Is your intent-filter with `` attached to the `LoginActivity`? If not, make sure that the `LoginActivity` receives the request after OAuth authorization.

 * Is the `onLoginSuccess` method being executed in the `LoginActivity`. On launch of your app, be sure to start the app on the LoginActivity so authentication routines execute on launch and take you to the authenticated activity.

 * If you are plan to test with Android API 24 or above, you will need to use Chrome to launch the OAuth flow.

 * Note that the emulators (both the Google-provided x86 and Genymotion versions) for API 24+ versions can introduce intermittent issues when initiating the OAuth flow for the first time.  For best results, use an device for this project.