---
title: "Configure the Basic I/O function"
url: https://docs.catalyst.zoho.com/en/tutorials/hosted-login-app/java/configure-function/
description: "Create a simple Basic or React application using the features of Catalyst Hosted Authentication that provides user sign-up, application login, password reset, and implements sign-in using prevalent federated identity providers."
last_updated: 2025-11-19T15:07:41Z
service: All Services
type: tutorial
related_links:
  - name: "Basic I/O Functions"
    url: /en/serverless/help/functions/basic-io/
  - name: "Functions Directory Structure"
    url: /en/cli/v1/project-directory-structure/functions-directory
---

# Configure the Function

Now, we will begin coding the authorization portal application by configuring the function component.

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

* The `Custom_User_Validation_Java.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 `Custom_User_Validation_Java.java` file.

The Basic I/O function contains the following functionalities:

* The end-user's details will provided as a JSON input to the *Custom User Validation* function.
* The function is coded to implement a custom logic based upon which the end-user will either be authenticated or denied.

> **Note:** For the purpose of this tutorial, we have coded a logic for the Custom User Validation function where if the user's email provider is anyone other than Zylker Technology (`@zylker.com`) the end-user will not be able to sign up to the application. You can either use the same or code a logic of your preference.

Now, let’s begin coding the Basic I/O function.

Copy the code given below and paste it in the `Custom_User_Validation_Java.java` file in the `functions/authorization_portal_function` 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.

**Custom_User_Validation_Java.java**

```java
import com.catalyst.Context;
import com.catalyst.basic.BasicIO;
import com.catalyst.basic.ZCFunction;
import com.fasterxml.jackson.databind.ObjectMapper;
import java.util.logging.Logger;
import java.util.logging.Level;
import com.zc.api.APIConstants.ZCSignupValidationStatus;
import com.zc.common.ZCProject;
import com.zc.component.auth.ZCSignupResponseUserDetails;
import com.zc.component.auth.ZCSignupUserValidationRequest;
import com.zc.component.auth.ZCSignupUserValidationResponse;
import com.zc.component.users.ZCSignupUserService;
public class Custom_User_Validation_Java implements ZCFunction {
private static final Logger LOGGER = Logger.getLogger(Custom_User_Validation_Java.class.getName());
@Override
public void runner(Context context, BasicIO basicIO) throws Exception {
try {
ZCProject.initProject();
ZCSignupUserValidationRequest requestDetails = ZCSignupUserService.getSignupValidationRequest(basicIO);
if(requestDetails != null) {
ZCSignupUserValidationResponse validationResponse = ZCSignupUserValidationResponse.getInstance();
if(requestDetails.getUserDetails().getEmailId().contains("@zylker.com")) {
validationResponse.setStatus(ZCSignupValidationStatus.FAILURE); // The user has failed authentication
}
else { 
// The actions that occur in the event of a successful authentication can be customized
validationResponse.setStatus(ZCSignupValidationStatus.SUCCESS); 
ZCSignupResponseUserDetails respUserDetails = ZCSignupResponseUserDetails.getInstance();
respUserDetails.setRoleIdentifier("App User"); // If you want to override the default role, you can specify the role id/name here.
validationResponse.setUserDetails(respUserDetails);
}
basicIO.setStatus(200);
basicIO.write(new ObjectMapper().writeValueAsString(validationResponse));
}
}
catch(Exception e) {
LOGGER.log(Level.SEVERE,"Exception in Custom_User_Validation_Java",e);
basicIO.setStatus(500);
basicIO.write("An error has occured. Please try again after sometime.");
}   
}
}

```

> **Note:** You can also use this [SDK](https://docs.catalyst.zoho.com/en/sdk/java/v1/cloud-scale/authentication/custom-user-validation/) to code your own custom logic instead of the one implemented above.

The function directory is now configured. We can now proceed to configuring the client directory.