. . .

Integrating external APIs

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.

images/download/attachments/23364323/pokeApi.png

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.

    images/download/attachments/23364323/mandatory.png
  2. Your module-code should already be downloaded and integrated into eclipse. Go to the "GroceryHooksNonTransient"-class .

    images/download/attachments/23364323/HooksNonTransient.png
  3. Inside the class, enter the following mehthod:

    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.

    @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:

    images/inline/08f4bed02a42917b19a8fbd63875e8285ca4c92d.png
  6. Copy this jar into the lib-folder of your Module. Then right click on it, and choose [ build-path > add to build path ].

    images/download/attachments/23364323/addJsonLib.png
  7. Now, you can access the methods provided by the JSON.simple-library to parse the JSON provided by the api.

    @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!

    images/download/attachments/23364323/newCreatedPokeBall.png
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