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Change the Default Mediation Flow of API Requests
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Sometimes, the backend implementation of a web service does not exactly match your desired API design. In that case, you do various message transformations and orchestrate multiple backend services to achieve the design you want.
In this tutorial, you create a custom sequence using the WSO2 Tooling Plug-in and use it in your APIs to mediate the incoming API calls.
The API Cloud comes with a powerful mediation engine that can transform and orchestrate API calls on the fly. It is built on WSO2 ESB and supports a variety of mediators that you can use as building blocks for your sequences. See the list of mediators supported in the API Cloud and WSO2 ESB.
You can extend the API Gateway's default mediation flow to do custom mediation by providing an extension as a synapse mediation sequence. You need to design all sequences using a tool like the WSO2 Tooling Plug-in and then store the sequence in the Gateway's registry.
Let's get started. See the video tutorial here or a step-by-step walk-through of the video tutorial below.
Here's a step-by-step walk-though of the video tutorial:
Log in to the API Publisher.
https://api.cloud.wso2.com/publisher/ÂClick Add New API, Design a new API, and Start creating to create an API with the following information and then click Implement.
Field  Sample value Name  YahooWeather Context  /weather Version  1.0 Resources URL pattern current/{country}/{zipcode}  Request types GET method to return the current weather conditions of a ZIP code that belongs to a particular country
The Implement tab opens.Â
Select Managed API, provide the information given in the table below and click Next: Manage >.
Field Sample value Endpoint type HTTP/REST endpoint Production endpoint You can find the Yahoo weather API's endpoint from https://developer.yahoo.com/weather/. Copy the part before the '?' sign to get this URL: https://query.yahooapis.com/v1/public/yql
To verify the URL, click the Test button next to it.
Sandbox endpoint https://query.yahooapis.com/v1/public/yql. To verify the URL, click the Test button next to it.
Provide the following information in the Manage tab and click Save & Publish once you are done.
Field Sample value Tier Availability Gold Keep the default values for the other attributes  
Download and install the WSO2 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.Â
On the Window menu click Perspective, Open Perspective, Other to open the Eclipse perspective selection window. Â
- On the dialog box that appears, click WSO2 API Manager and click OK.
On the APIM perspective, click the Login icon as shown below.
 Enter your cloud username (in the format
<email@company_name>) and password, and click OK in the dialog box that appears.
- On the tree view that appears, expand the folder structure of the existing API.
Right-click on theÂ
in sequence folder and click Create to create a newÂin sequence.
Â
This is because you want the custom sequence to be invoked in theÂIn direction or the request path.
If you want it to be involved in theÂOut orÂFault paths, select the respective folder underÂcustomsequences. Tip : If you prefer not to use the registry to upload the sequence or want to engage a sequence to all APIs in WSO2 API-M at once, you can do so by saving the mediation sequence XML file in the file system. See Adding Mediation Extensions for details.- Name the sequenceÂ
YahooWeatherSequence. 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.
Property Name New Property New Property Name YQL Value Type Expression Value Expression For the XPath expression, we take a part of the query in the Yahoo API's endpoint (https://developer.yahoo.com/weather/) and concatenate the zip code and country to it using the synapse get-property XPath expression:
concat('?q=select%20*%20from%20weather.forecast%20where%20woeid%20in%20(select%20woeid%20from%20geo.places(1)%20where%20text%3D%22',syn:get-property('uri.var.zipcode'),',',syn:get-property('uri.var.country'),'%22)&format=json')
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.Property Name New Property New Property Name REST_URL_POSTFIX Value Type Expression Value Expression get-property('YQL') Property Scope Axis2 
- Navigate to the File menu, and click Save to save the sequence.
- Right-click on the sequence and click Commit File, and thereafter click Yes to push the changes to the Publisher server.
- Sign in to WSO2 API Publisher again, search for the API that you created earlier, and click the Edit link to go to the edit wizard.Â
Click Implement and Manage API. Thereafter, click the Enable Message Mediation checkbox, and select the sequence that you created for the In flow. Next, Save the API.
Tip : It might take a few minutes for the sequence to be uploaded into the API Publisher. If it isn't there, please check again later.
When selecting a mediator, make sure that it is a non-blocking mediator as blocking mediators are not supported in API Gateway custom mediations. For more details, see Adding Mediation Extensions.
- 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.
- Click the API Console tab of the API. It opens the integrated API Console using which you can invoke the API.
Give the following values for the parameters and invoke the API. You can also give any other value of your choice.
country usa
zipcode 95004 
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.