---
title: "Configure the functions directory"
url: https://docs.catalyst.zoho.com/en/tutorials/todo-list/java/configure-function/
description: "Build a Basic, React, or Angular to-do list web app using Catalyst Advanced I/O Function and Data Store to note down tasks and delete them when done."
last_updated: 2026-11-04T10:10:44Z
service: All Services
type: tutorial
related_links:
  - 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

Next, we will begin coding the to-do list application by configuring the function component.

The [functions directory](https://docs.catalyst.zoho.com/en/cli/v1/project-directory-structure/functions-directory), `functions/ToDoList` contains:

* The `ToDoList.java` main function file
* The `catalyst-config.json` configuration file
* Java library files in the `lib` directory
* `.classpath` and `.project` dependency files

You will be adding code in the `ToDoList.java` file.

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

* **GET /todo:** To obtain the to-do list items from the _TodoItems_ table in the Data Store
* **POST /todo:** To create and save a new list item in the Data Store
* **DELETE /todo:** To delete a list item from the Data Store

Next, let's add the code in the function file. Copy the Java code and paste it in `ToDoList.java` in the `functions/TodoList` 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 given in this section to ensure you fully understand it. We will discuss the architecture of the function and the client in the next section.

**ToDoList.java**

```java
import java.util.ArrayList;
import java.util.HashMap;
import java.util.logging.Level;
import java.util.logging.Logger;
import java.io.InputStreamReader;
import javax.servlet.ServletInputStream;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.json.simple.JSONObject;
import org.json.simple.parser.JSONParser;
import com.catalyst.advanced.CatalystAdvancedIOHandler;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.zc.component.object.ZCObject;
import com.zc.component.object.ZCRowObject;
import com.zc.component.object.ZCTable;
import com.zc.component.zcql.ZCQL;
public class ToDoList implements CatalystAdvancedIOHandler {
    private static final String GET = "GET";
    private static final String POST = "POST";
    private static final String DELETE = "DELETE";
    private JSONObject responseData = new JSONObject();
    private static final Logger LOGGER = Logger.getLogger(ToDoList.class.getName());
    @SuppressWarnings("unchecked")
    @Override
    public void runner(HttpServletRequest request, HttpServletResponse response) throws Exception {
        try {
            String uri = request.getRequestURI();
            String method = request.getMethod();
            // GET method gets data from the TodoItems table in the Data Store.
            if (method.equals(GET) && uri.equals("/all")) {
                Integer page = Integer.parseInt(request.getParameter("page"));
                Integer perPage = Integer.parseInt(request.getParameter("perPage"));
                ArrayList<ZCRowObject> rowList = ZCQL.getInstance().executeQuery("SELECT COUNT(ROWID) FROM TodoItems");
                Integer totalTodos = Integer.parseInt(new ObjectMapper().writeValueAsString(rowList.get(0).get("TodoItems", "COUNT(ROWID)")));
                Boolean hasMore = totalTodos > page * perPage;
                ArrayList<HashMap<String, String>> todoItems = new ArrayList<>();
                ZCQL.getInstance().executeQuery(String.format("SELECT ROWID, Notes FROM TodoItems LIMIT %d, %d",
                        (page - 1) * perPage, perPage)).forEach(row -> {
                    HashMap<String, String> item = new HashMap<>();
                    item.put("id", row.get("TodoItems", "ROWID").toString());
                    item.put("notes", row.get("TodoItems", "Notes").toString());
                    todoItems.add(item);
                });
                response.setStatus(200);
                responseData.put("status", "success");
                responseData.put("data", new JSONObject() {
                    {
                        put("hasMore", hasMore);
                        put("todoItems", todoItems);
                    }
                });
            // POST method adds a new todo item to the TodoItems table in the Data Store.
            } else if (method.equals(POST) && uri.equals("/add")) {
                JSONParser jsonParser = new JSONParser();
                ServletInputStream requestBody = request.getInputStream();
                JSONObject jsonObject = (JSONObject) jsonParser.parse(new InputStreamReader(requestBody, "UTF-8"));
                String notes = jsonObject.get("notes").toString();
                ZCRowObject row = ZCRowObject.getInstance();
                row.set("Notes", notes);
                ZCRowObject todoItem = ZCObject.getInstance().getTable("TodoItems").insertRow(row);
                response.setStatus(200);
                responseData.put("status", "success");
                responseData.put("data", new JSONObject() {
                    {
                        put("todoItem", new JSONObject() {
                            {
                                put("id", todoItem.get("ROWID").toString());
                                put("notes", todoItem.get("Notes").toString());
                            }
                        });
                    }
                });
            // DELETE method deletes a todo item from the Data Store by its ID.
            } else if (method.equals(DELETE) && uri.matches("/\\d+")) {
                ZCTable table = ZCObject.getInstance().getTable("TodoItems");
                table.deleteRow(Long.parseLong(uri.substring(1)));
                response.setStatus(200);
                responseData.put("status", "success");
                responseData.put("data", new JSONObject() {
                    {
                        put("todoItem", new JSONObject() {
                            {
                                put("id", uri.substring(1));
                            }
                        });
                    }
                });
            } else {
                response.setStatus(404);
                responseData.put("status", "failure");
                responseData.put("message", "Please check if the URL trying to access is a correct one");
            }
        } catch (Exception e) {
            LOGGER.log(Level.SEVERE, "Exception in Main", e);
            responseData.put("status", "failure");
            responseData.put("message", "We're unable to process the request.");
        }
        response.setContentType("application/json");
        response.getWriter().write(responseData.toString());
    }
}

```

The functions directory is now configured.