Change the Default Mediation Flow of API Requests

The API Gateway has a default mediation flow for the API invocation requests that it receives. You can extend this default mediation flow to do additional custom mediation for the messages in the API Gateway. An extension is provided as a synapse mediation sequence. You design all sequences using a tool such as the WSO2 API Manager Tooling Plug-in and then store the sequence in the Gateway's registry. 

Let's see how to create a custom sequence using the WSO2 API Manager Tooling Plug-in and then deploy and use it in your APIs.

1. Sign in to the API Publisher.

2. Click Add to create an API with the following information and then click Next: Implement >.

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3. The Implement tab opens. Select Managed API, provide the information given in the table below and click Manage.

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4. Click Next: Manage > to go to the Manage tab, provide the following information and click Save & Publish once you are done.

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5. Download and install the WSO2 API Manager Tooling Plug-in by following one of the three possible methods described in Installing the API Manager Tooling Plug-In if you have not done so already. Start Eclipse by double clicking on the Eclipse application, which is inside the downloaded folder. 

6. Navigate to the Window menu, click Perspective, Open Perspective, and Other to open the Eclipse perspective selection window. 

7. On the dialog box that appears, click WSO2 APIManager and click OK.

8. On the APIM perspective, click the Login icon as shown below.

9. On the dialog box that appears, enter the URL, username, and password of the Publisher server.

10. On the tree view that appears, expand the folder structure of the existing API.

11. Right-click on the in sequence folder and click Create to create a new in sequence.
    

    
    This is because you want the custom sequence to be invoked in the In direction or the request path. If you want it to be involved in the Out or Fault paths, select the respective folder under customsequences.

12. Name the sequence YahooWeatherSequence.

13. Your sequence now appears on the Developer Studio console. From under the Mediators section, drag and drop a Property mediator to your sequence and give the following values to the property mediator. 

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14. Similarly, add another property mediator with the following values. This is an HTTP transport property that appends its value to the address endpoint URL. Once you are done, save the sequence.

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15. Navigate to the File menu, and click Save to save the sequence.

16. Right-click on the sequence and click Commit File to push the changes to the Publisher server.

17. Sign in to the API Publisher again, select the API that you created earlier, and click the Edit link right next to its name to go to the edit wizard.

18. Navigate to the API's Implement tab, select the Enable Message Mediation check box and select the sequence that you created for the In flow. Next, click Manage and Save & Publish the API again.

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19. Sign in to the API Store, subscribe to the API that you just published, and generate the access tokens in order to invoke the API.

20. Click the API Console tab of the API.
    It opens the integrated API Console using which you can invoke the API.

21. Give the following values for the parameters and invoke the API. You can also give any other value of your choice.

    
    Note the response that you get as a JSON object from Yahoo.
    { "query": { "count": 1, "created": "2017-05-04T12:49:03Z", "lang": "en-US", "results": { "channel": { "units": { "distance": "mi", "pressure": "in", "speed": "mph", "temperature": "F" }, "title": "Yahoo! Weather - Aromas, CA, US", "link": "http://us.rd.yahoo.com/dailynews/rss/weather/Country__Country/*https://weather.yahoo.com/country/state/city-12797499/", "description": "Yahoo! Weather for Aromas, CA, US", "language": "en-us", "lastBuildDate": "Thu, 04 May 2017 05:49 AM PDT", "ttl": "60", "location": { "city": "Aromas", "country": "United States", "region": " CA" }, "wind": { "chill": "50", "direction": "245", "speed": "4" }, "atmosphere": { "humidity": "98", "pressure": "999.0", "rising": "0", "visibility": "7.5" }, "astronomy": { "sunrise": "6:9 am", "sunset": "7:58 pm" }, "image": { "title": "Yahoo! Weather", "width": "142", "height": "18", "link": "http://weather.yahoo.com", "url": "http://l.yimg.com/a/i/brand/purplelogo//uh/us/news-wea.gif" }, "item": { "title": "Conditions for Aromas, CA, US at 05:00 AM PDT", "lat": "36.878021", "long": "-121.618973", "link": "http://us.rd.yahoo.com/dailynews/rss/weather/Country__Country/*https://weather.yahoo.com/country/state/city-12797499/", "pubDate": "Thu, 04 May 2017 05:00 AM PDT", "condition": { "code": "33", "date": "Thu, 04 May 2017 05:00 AM PDT", "temp": "51", "text": "Mostly Clear" }, "forecast": [ { "code": "30", "date": "04 May 2017", "day": "Thu", "high": "74", "low": "55", "text": "Partly Cloudy" }, { "code": "28", "date": "05 May 2017", "day": "Fri", "high": "71", "low": "53", "text": "Mostly Cloudy" }, { "code": "30", "date": "06 May 2017", "day": "Sat", "high": "65", "low": "47", "text": "Partly Cloudy" }, { "code": "12", "date": "07 May 2017", "day": "Sun", "high": "62", "low": "48", "text": "Rain" }, { "code": "30", "date": "08 May 2017", "day": "Mon", "high": "69", "low": "46", "text": "Partly Cloudy" }, { "code": "30", "date": "09 May 2017", "day": "Tue", "high": "69", "low": "48", "text": "Partly Cloudy" }, { "code": "28", "date": "10 May 2017", "day": "Wed", "high": "70", "low": "52", "text": "Mostly Cloudy" }, { "code": "30", "date": "11 May 2017", "day": "Thu", "high": "72", "low": "52", "text": "Partly Cloudy" }, { "code": "30", "date": "12 May 2017", "day": "Fri", "high": "72", "low": "48", "text": "Partly Cloudy" }, { "code": "34", "date": "13 May 2017", "day": "Sat", "high": "71", "low": "46", "text": "Mostly Sunny" } ], "description": "<![CDATA[<img src=\"http://l.yimg.com/a/i/us/we/52/33.gif\"/>\n<BR />\n<b>Current Conditions:</b>\n<BR />Mostly Clear\n<BR />\n<BR />\n<b>Forecast:</b>\n<BR /> Thu - Partly Cloudy. High: 74Low: 55\n<BR /> Fri - Mostly Cloudy. High: 71Low: 53\n<BR /> Sat - Partly Cloudy. High: 65Low: 47\n<BR /> Sun - Rain. High: 62Low: 48\n<BR /> Mon - Partly Cloudy. High: 69Low: 46\n<BR />\n<BR />\n<a href=\"http://us.rd.yahoo.com/dailynews/rss/weather/Country__Country/*https://weather.yahoo.com/country/state/city-12797499/\">Full Forecast at Yahoo! Weather</a>\n<BR />\n<BR />\n(provided by <a href=\"http://www.weather.com\" >The Weather Channel</a>)\n<BR />\n]]>", "guid": { "isPermaLink": "false" } } } } } }

In this tutorial, you created a sequence to change the default mediation flow of API requests, deployed it in the API Gateway and invoked an API using the custom mediation flow.