Configure the Advanced I/O Function

Let's now configure the Advanced I/O function component. If you initialized the Advanced I/O function in Java, its directory (functions/NewsApp_AIO) will contain:

• The DatastoreFetch.java main function file
• The catalyst-config.json configuration file
• Java library files in the lib folder
• .classpath and .project dependency files

If you initialized the Advanced I/O function in Node.js, its directory (functions/news_app_function) will contain:

• The index.js main function file
• The catalyst-config.json configuration file
• Node modules
• package.json and package-lock.json dependency files

You will be adding code in the DatastoreFetch.java or index.js, based on the stack you initialized.

The Advanced I/O function fetches the news item from its source table in the Data Store and forwards it to the client component as a JSON response.

Copy the Java code and paste it in DatastoreFetch.java in the functions/NewsApp_AIO directory, or the Node.js code and paste it in index.js in the functions/news_app_function directory of your project, and save the file. You can use any IDE to work with the application's files.

• View code for DatastoreFetch.java, index.js

  JavaNode.js

  Copied 
  import java.util.logging.Logger;
  import java.util.ArrayList;
  import java.util.logging.Level;
  
  import javax.servlet.http.HttpServletRequest;
  import javax.servlet.http.HttpServletResponse;
  
  import com.catalyst.advanced.CatalystAdvancedIOHandler;
  import com.zc.component.object.ZCRowObject;
  import com.zc.component.zcql.ZCQL;
  
  import org.json.JSONArray;
  import org.json.JSONObject;
  
  public class DatastoreFetch implements CatalystAdvancedIOHandler {
  	private static final Logger LOGGER = Logger.getLogger(DatastoreFetch.class.getName());
  
  	@Override
  	public void runner(HttpServletRequest request, HttpServletResponse response) throws Exception {
  		try {
  			//Fetches the endpoint that the call was made to
  			String url = request.getRequestURI();
  			String method = request.getMethod();
  
  			if (url.equals("/fetchData") && method.equals("GET")) {
  				String tableName = request.getParameter("tablename");
  				//Queries the Data Store to fetch news from a particular table using ZCQL
  				String query = "select title,url from " + tableName;
  				ArrayList<ZCRowObject> rowList = ZCQL.getInstance().executeQuery(query);
  				JSONObject data = new JSONObject();
  				JSONArray content = new JSONArray();
  				
  				//Constructs the data from the Data Store as an JSON response
  				for (int i = 0; i < rowList.size(); i++) {
  					JSONObject rowData = new JSONObject();
  					JSONObject tableData = new JSONObject();
  					String urls = (String) rowList.get(i).get(tableName, "url");
  					Object title = rowList.get(i).get(tableName, "title");
  					rowData.put("title", title);
  					rowData.put("url", urls);
  					tableData.put(tableName, rowData);
  					content.put(tableData);
  				}
  				data.put("content", content);
  
  				//Sends the JSON response back to the client
  				response.setContentType("application/json");
  				response.getWriter().write(data.toString());
  				response.setStatus(200);
  			} else {
  //The errors are logged. You can check them from Catalyst Logs.
  				LOGGER.log(Level.SEVERE, "Error. Invalid Request");
  				response.setStatus(404);
  			}
  		} catch (Exception e) {
  			LOGGER.log(Level.SEVERE, "Exception in DatastoreFetch", e);
  			response.setStatus(500);
  		}
  	}
  }
  

  Copied  
  'use strict';
  var express = require('express');
  var app = express();
  var catalyst = require('zcatalyst-sdk-node');
  app.use(express.json());
  
  //GET API that gets the news from the required table
  app.get('/fetchData', (req, res) => {
  	var tablename = req.query.tablename;
  	console.log("Table Name "+tablename);
  
  	//Initializing Catalyst SDK
  	var catalystApp = catalyst.initialize(req);
  
  	//Queries the Catalyst Data Store table and gets the required news
  	getDataFromCatalystDataStore(catalystApp, tablename).then(newsDetails => {
  			res.send({
  				"content": newsDetails
  			})
  	}).catch(err => {
  		console.log(err);
  		sendErrorResponse(res);
  	})
  });
  /**
   * Executes the Query and fetches the news from the table
   * @param {*} catalystApp 
   * @param {*} tablename 
   */
  function getDataFromCatalystDataStore(catalystApp, tablename) {
  	return new Promise((resolve, reject) => {
  		//Queries the Catalyst Data Store table
  		catalystApp.zcql().executeZCQLQuery("Select title,url from " + tablename).then(queryResponse => {
  			resolve(queryResponse);
  		}).catch(err => {
  			reject(err);
  		})
  	});
  
  }
  
  /**
   * Sends an error response
   * @param {*} res 
   */
  function sendErrorResponse(res) {
  	res.status(500);
  	res.send({
  		"error": "Internal server error occurred. Please try again in some time."
  	});
  }
  module.exports = app;
  

The Advanced I/O function is now configured. We will discuss the application's architecture after you configure the client.