Triggering Cloud Functions With Cloud Storage in Java

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Google Cloud Functions is a serverless execution environment for building and connecting cloud services. With Cloud Functions, you write simple, single-purpose functions that are attached to events emitted from your cloud infrastructure and services. Your function is triggered when an event being watched is fired. Your code executes in a fully managed environment. There is no need to provision any infrastructure or worry about managing any servers.

  • Serverless execution environment for building and connecting cloud services
  • Write simple, single-purpose functions that are attached to events emitted from your cloud services
  • These functions execute code in response to events based on triggers

Key Terms used in Cloud Functions


Events are the things that happen in the cloud environment. These can be:

  • changes to data in a database
  • files added to a storage system
  • a new virtual machine instance being created


Declaration of interest in an event. We bind a function to a trigger and when the trigger is set, the function is executed.

Triggers available in Cloud Function

Triggers are associated with available resources such as Cloud storage, Cloud pub-sub, HTTP, Firebase Analytics, Firebase Authentication and Firebase real-time database.


Cloud Functions supports multiple language runtimes:

Multiple language runtimes for Cloud Functions

Triggering Cloud Storage with Cloud Functions

The idea is when an object is put in Google Cloud Storage, the cloud function must be triggered and it will be logged likewise.

Step 1.) Create a Cloud Storage Bucket

Go to Navigation — Cloud Storage Give a unique bucket name

When the GCS bucket is created, it looks like this.

Step 2.) Create a Cloud Function

Go to Navigation —> Cloud Functions —> Create Function

Step 3.) Selecting the Trigger and Event Type

After clicking Create Function, you must give a proper name of the Cloud Function and select the Trigger as Cloud Storage and Event type as Finalise/Create (this determines when an object is put into the bucket, it will trigger cloud function).

Select Cloud Storage as the Trigger

Step 4.) Select the Google Cloud Storage bucket you want to trigger.

Selecting cloud-function-gcsbucket in the Browse-able Bucket field

Step 5.) Selecting the Runtime for running the Cloud Function

The Java programming language recently turned 25 years old, and it’s still one of the top-used languages powering today’s enterprise application customers. Google brought Java 11 to Google Cloud Functions in Q1 2020. That means you can now write Cloud Functions using your favourite JVM languages (JavaKotlinGroovyScala, etc) with our Functions Framework for Java, and also with Spring Cloud Functions and Micronaut!

With Cloud Functions for Java 11, now in beta, you can use Java to build business-critical applications and integration layers, and deploy the function in a fully managed environment, complete with access to resources in a private VPC network. Java functions will scale automatically based on your load. You can write HTTP functions to respond to HTTP events, and background functions to process events sourced from the various cloud and GCP services, such as Pub/Sub, Cloud Storage, Firestore, and more.

So, you have to select Java 11 in the Runtime drop-down.


<?xml version="1.0" encoding="UTF-8"?>
<project xmlns=""


  <!-- Required for Java 11 functions in the inline editor -->


package com.example;

import com.example.Example.GCSEvent;
import java.util.logging.Logger;

public class Example implements BackgroundFunction<GCSEvent> {
  private static final Logger logger = Logger.getLogger(Example.class.getName());

  public void accept(GCSEvent event, Context context) {"Processing file: " +;
    throw new UnsupportedOperationException("Not supported yet.");

  public static class GCSEvent {
    String bucket;
    String name;
    String metageneration;

Step 6.) Click the Create button for creating Cloud Function

Step 7.) Check and confirm that the Cloud Function is successfully created.

Step. 8) Check the View logs under Actions —> 3-horizontal-dots

When the function is created, you can view the logs to see that the function has been created.

Logs updated after triggerGCSEvent function is created

Step 9.) Upload a file in the GCS bucket to trigger Cloud Functions

Uploaded an image, Sitting.jpeg in the GCS bucket

Step 10.) Check the logs after uploading the file in the GCS bucket

Cloud Function got triggered when the file is uploaded in the GCS object


Cloud Functions are a great fit for serverless application backends for integrating with third-party services and APIs, or for mobile or IoT backends. You can also use functions for real-time data processing systems, like processing files as they are uploaded to Cloud Storage, or handling real-time streams of events from Pub/Sub. Last but not least, functions can serve intelligent applications like virtual assistants and chatbots, or video, image and sentiment analysis.

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