In the last tutorial, you learned how to access all REST-Endpoints provided by the ApiOmat. But sometimes you have to use REST-Endpoints provided by other servers. As an example, we will use the free pokémon-Api at http://pokeapi.co/ . The page provides a REST-Endpoint for querying pokémon data, like data about pokémon, items, regions etc. For example, if you want to have informations about the item "poké-ball", you can adress the "poké-ball"-resource via the URL http://pokeapi.co/api/v2/item/poke-ball . The information about the poké-ball is then returned as a JSON.

Let's suppose the following use-case, keeping in mind the shopping list we have been building in this toturial. Every-time someone enters the a product with the name "poké-ball", the Module should automatically connect to the poké-api to request the price of the poké-ball.

1. First, change the "name"-attribute of groceries to "mandatory" so that the user is forced to enter a name when a new grocery is created. You can do that easily via the dashboard.
   

   

2. Your module-code should already be downloaded and integrated into eclipse. Go to the "GroceryHooksNonTransient"-class .
   

   

3. Inside the class, enter the following method:

   
   Code

   public String downloadJson( String urlString ) throws IOException

   {

   URL url = new URL( urlString );

    

   HttpURLConnection con = ( HttpURLConnection ) url.openConnection( );

   con.addRequestProperty( "User-Agent", "Cheese" );

   System.out.println( con.getResponseMessage( ) );

    

   if ( con.getResponseCode( ) == HttpURLConnection.HTTP_OK )

   {

   BufferedReader reader = new BufferedReader( new InputStreamReader( con.getInputStream( ) ) );

    

   // transform the response into a single string

   String line;

   String content = "";

   while ( ( line = reader.readLine( ) ) != null )

   {

   content += line;

   }

    

   // extract attributes

   return content;

   }

   return null;

   }

   
   

   This method can be used to download the data inside the body of a html-response.

4. Now, alter the "beforePost"-Hook, so that everytime a new grocery with the name "poké-ball" is created, the resource "http://pokeapi.co/api/v2/item/poke-ball" should be requested in order to access the price of the poké-ball.
   
   Code

   @Override

   public void beforePost( Grocery obj, Request r )

   {

   // enter default price (from previous tutorial)

   Object defaultPrice = TutorialModule.APP_CONFIG_PROXY.getConfigValue( TutorialModule.DEFAULT_PRICE,

   r.getApplicationName( ), r.getSystem( ) );

   obj.setPrice( Double.valueOf( String.valueOf( defaultPrice ) ) );

    

   //if the name of the newly created grocery is "poke-ball", download the information about the poke-ball from the poke-api.

   if ( obj.getName( ).equals( "poke-ball" ) )

   {

   try

   {

   String pokeBallJson = downloadJson( "http://pokeapi.co/api/v2/item/poke-ball" );

   }

   catch ( IOException e )

   {

   e.printStackTrace( );

   }

   catch ( ParseException e )

   }

   }

5. If you enter " http://pokeapi.co/api/v2/item/poke-ball " into your browser, you access the very JSON that will now be contained inside the pokeBallJson- String. The price of the poké-ball can be accessed through the "cost" attribute. To parse the JSON with java, you need an external library, like the JSON.simple - library. You can download the jar right here: json-simple-1.1.1.jar
   
   

6. Copy this jar into the lib-folder of your Module. Then right click on it, and choose [ build-path > add to build path ].
   
   

   

   
   
   

7. Now, you can access the methods provided by the JSON.simple-library to parse the JSON provided by the api.
   
   Code

   @Override

   public void beforePost( Grocery obj, Request r )

   {

   // enter default price (from previous tutorial)

   Object defaultPrice = TutorialModule.APP_CONFIG_PROXY.getConfigValue( TutorialModule.DEFAULT_PRICE,

   r.getApplicationName( ), r.getSystem( ) );

    

   obj.setPrice( Double.valueOf( String.valueOf( defaultPrice ) ) );

    

   //if the name of the newly created grocery is "poke-ball", download the information about the poke-ball from the poke-api.

   if ( obj.getName( ).equals( "poke-ball" ) )

   {

   try

   {

   String pokeBallJson = downloadJson( "http://pokeapi.co/api/v2/item/poke-ball" );

   //parse the JSON-String, extract the cost and enter the value into the price of the grocery

   JSONParser parser = new JSONParser( );

   JSONObject pokeObject = ( JSONObject ) parser.parse( pokeBallJson );

   Long cost = ( Long ) pokeObject.get( "cost" );

   obj.setPrice( cost.doubleValue() );

   }

   catch ( IOException e )

   {

   e.printStackTrace( );

   }

   catch ( ParseException e )

   {

   e.printStackTrace( );

   }

   }

    

   }

8. You're almost finished! Upload the module-code. And try it out! Now, when you enter a new item with the name "poké-ball", the price should autmatically be set by the price provided by the external API, which is 200!