---
title: "Configure the Advanced I/O Function"
url: https://docs.catalyst.zoho.com/en/tutorials/alien-city/java/configure-advio-function/
description: "Create a single-page serverless web application using Catalyst Advanced I/O Function and Catalyst Data Store that allows you to report or look up alien encounters in a city."
last_updated: 2025-11-19T15:07:41Z
service: All Services
type: tutorial
related_links:
  - name: "Functions"
    url: /en/serverless/help/functions/introduction/
  - name: "Advanced I/O Functions"
    url: /en/serverless/help/functions/advanced-io/
  - name: "Functions Directory Structure"
    url: /en/cli/v1/project-directory-structure/functions-directory/
---

# 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 ](https://docs.catalyst.zoho.com/en/cli/v1/project-directory-structure/functions-directory/)` ) 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.

> **Note:** Please go through the code in this section to make sure you fully understand it. 

**AlienCityAIO.java**

```java
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 AlienCity WHERE CityName = '" + cityName + "'";
			//Gets the ZCQL instance and executes query using the query string
			ArrayList<ZCRowObject> rowList = ZCQL.getInstance().executeQuery(query);
			return rowList.size();
		}
}

```

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