Configure the Advanced I/O Function

Let’s begin coding the Alien City application by configuring the function component.

The Java function directory ( functions/AlienCityAIO ) contains the following files:

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

You will be adding code in the AlienCityAIO.java main function file.

The two APIs in the Advanced I/O function that handle the routing between the server and the Data Store are:

• GET /alien: To check whether aliens are present in a city
• POST /alien: To report an alien presence in a city
  

Let’s now add the code in the function file.

Copy the code given below and paste it in AlienCityAIO.java in the functions/AlienCityAIO directory of your project, and save the file. You can use any IDE of your choice to work with the application’s files.

    

        
AlienCityAIO.java
        

            
copy
            

                

            
        
    
    

    

         import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.logging.Level;
import java.util.logging.Logger;
import com.zc.common.ZCProject;

import javax.servlet.ServletInputStream;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.catalyst.advanced.CatalystAdvancedIOHandler;
import com.zc.component.object.ZCObject;
import com.zc.component.object.ZCRowObject;
import com.zc.component.zcql.ZCQL;

import org.json.simple.JSONObject;
import org.json.simple.parser.JSONParser;


public class AlienCityAIO implements CatalystAdvancedIOHandler {
private static final Logger LOGGER = Logger.getLogger(AlienCityAIO.class.getName());

    private static String TABLENAME = "AlienCity";
    private static String COLUMNNAME = "CityName";
    JSONObject responseData = new JSONObject();
    static String GET = "GET";
    static String POST = "POST";

    @Override
    @SuppressWarnings("unchecked")
    public void runner(HttpServletRequest request, HttpServletResponse response) throws Exception {
    	try {
			ZCProject.initProject();
    		//Fetches the endpoint and method to which the call was made
    		String url = request.getRequestURI();
    		String method = request.getMethod();

    		//The GET API that checks the table for an alien encounter in that city
    		if ((url.equals("/alien")) && method.equals(GET)) {
    			String cityName = request.getParameter("city_name");

    			//Queries the Catalyst Data Store table and checks whether a row is present for the given city
    			int length = getAlienCountFromCatalystDataStore(cityName);
    			if (length > 0) {
    				responseData.put("message", "Uh oh! Looks like there are aliens in this city!");
    				responseData.put("signal", "positive");
    			} else {
    				responseData.put("message", "Hurray! No alien encounters in this city yet!");
    				responseData.put("signal", "negative");
    			}
    		}
    		//The POST API that reports the alien encounter for a particular city
    		else if ((url.equals("/alien")) && method.equals(POST)) {
    			//Gets the request body and parses it
    			ServletInputStream requestBody = request.getInputStream();
    			JSONParser jsonParser = new JSONParser();
    			JSONObject jsonObject = (JSONObject) jsonParser.parse(new InputStreamReader(requestBody, "UTF-8"));

    			String cityName = (String) jsonObject.get("city_name");

    			//Queries the Catalyst Data Store table and checks whether a row is present for the given city
    			int length = getAlienCountFromCatalystDataStore(cityName);
    			if (length > 0) {
    				responseData.put("message",
    					"Looks like you are not the first person to encounter aliens in this city! Someone has already reported an alien encounter here!");
    			}

    			//If the row is not present, then a new row is inserted
    			else {
    				ZCRowObject row = ZCRowObject.getInstance();
    				row.set("CityName", cityName);
    				ZCObject.getInstance().getTableInstance(TABLENAME).insertRow(row);
    				responseData.put("message", "Thanks for reporting!");
    			}
    		} else {
    			//The actions are logged. You can check the logs from Catalyst Logs.
    			LOGGER.log(Level.SEVERE, "Error. Invalid Request");
    			responseData.put("error", "Request Endpoint not found");
    			response.setStatus(404);
    		}

    		//Sends the response back to the Client
    		response.setContentType("application/json");
    		response.getWriter().write(responseData.toString());
    		response.setStatus(200);
    	} catch (Exception e) {
    		//The actions are logged. You can check the logs from Catalyst Logs.
    		LOGGER.log(Level.SEVERE, "Exception in AlienCityAIO", e);
    		responseData.put("error", "Internal server error occurred. Please try again in some time.");
    		response.getWriter().write(responseData.toString());
    		response.setStatus(500);
    	}
    }

    /**
     * Checks whether an alien encounter is already reported for the given city by
     * querying the Data Store table
     *
     * @param {*} catalystApp
     * @param {*} cityName
     */
    private int getAlienCountFromCatalystDataStore(String cityName) throws Exception {

    	String query = "select * from " + TABLENAME + " where " + COLUMNNAME + " = " + cityName;

    	//Gets the ZCQL instance and executes query using the query string
    	ArrayList rowList = ZCQL.getInstance().executeQuery(query);
    	return rowList.size();
    }

}

         
View more
    

The functions directory is now configured. We will discuss the architecture of the function and the client in the next section.