Your First Function: Java

This guide takes you through the process of writing a Cloud Function using the Java runtime. There are two types of Cloud Functions:

  • An HTTP function, which you invoke from standard HTTP requests.
  • A background function, which you use to handle events from your Cloud infrastructure, such as messages on a Cloud Pub/Sub topic, or changes in a Cloud Storage bucket.

The sample shows how to create a simple HTTP function.

Guide structure

  1. Creating a GCP project using Cloud SDK
  2. Creating a function
  3. Specifying dependencies
  4. Deploying your function
  5. Testing your function

Creating a GCP project using Cloud SDK

  1. Sign in to your Google Account.

    If you don't already have one, sign up for a new account.

  2. In the Cloud Console, on the project selector page, select or create a Cloud project.

    Go to the project selector page

  3. Make sure that billing is enabled for your Google Cloud project. Learn how to confirm billing is enabled for your project.

  4. Enable the Cloud Functions API.

    Enable the API

  5. Install and initialize the Cloud SDK.
  6. Update and install gcloud components:
    gcloud components update
  7. Need a command prompt? You can use the Google Cloud Shell. The Google Cloud Shell is a command line environment that already includes the Google Cloud SDK, so you don't need to install it. The Google Cloud SDK also comes preinstalled on Google Compute Engine Virtual Machines.

  8. Prepare your development environment.

    Go to the Java setup guide

Creating a function

  1. Create a directory on your local system for the function code:

    Linux or Mac OS X

    mkdir ~/helloworld
    cd ~/helloworld
    

    Windows

    mkdir %HOMEPATH%\helloworld
    cd %HOMEPATH%\helloworld
    
  2. Create the project structure, to contain a pom.xml file,the source directory, and source file.

    touch pom.xml
    mkdir -p src/main/java/functions
    touch src/main/java/functions/HelloWorld.java
    
  3. Add the following contents to the HelloWorld.java file:

    
    package functions;
    
    import com.google.cloud.functions.HttpFunction;
    import com.google.cloud.functions.HttpRequest;
    import com.google.cloud.functions.HttpResponse;
    import java.io.BufferedWriter;
    import java.io.IOException;
    
    public class HelloWorld implements HttpFunction {
      // Simple function to return "Hello World"
      @Override
      public void service(HttpRequest request, HttpResponse response)
          throws IOException {
        BufferedWriter writer = response.getWriter();
        writer.write("Hello World!");
      }
    }

    This example function outputs the greeting "Hello World!"

Specifying dependencies

To manage dependencies using Maven, you need to specifying the dependencies in the <dependencies> section inside the pom.xml file of your project. For this exercise, copy the following contents into your pom.xml file, which should be in the helloworld directory you created at the beginning of this exercise.

<project xmlns="http://maven.apache.org/POM/4.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>

  <groupId>com.example.cloud.functions</groupId>
  <artifactId>functions-hello-world</artifactId>
  <version>1.0.0-SNAPSHOT</version>
  <properties>
    <maven.compiler.target>11</maven.compiler.target>
    <maven.compiler.source>11</maven.compiler.source>
  </properties>

  <dependencies>
    <!-- Required for Function primitives -->
    <dependency>
      <groupId>com.google.cloud.functions</groupId>
      <artifactId>functions-framework-api</artifactId>
      <version>1.0.1</version>
      <scope>provided</scope>
    </dependency>
  </dependencies>
  <build>
    <plugins>
      <plugin>
        <!--
          Google Cloud Functions Framework Maven plugin

          This plugin allows you to run Cloud Functions Java code
          locally. Use the following terminal command to run a
          given function locally:

          mvn function:run -Drun.functionTarget=your.package.yourFunction
        -->
        <groupId>com.google.cloud.functions</groupId>
        <artifactId>function-maven-plugin</artifactId>
        <version>0.9.3</version>
        <configuration>
          <functionTarget>functions.HelloWorld</functionTarget>
        </configuration>
      </plugin>
    </plugins>
  </build>
</project>

Building and testing locally

Before deploying the function, you can test it locally with the following command to confirm that it builds:

mvn compile

To test the function, run the following command:

mvn function:run

If this completes successfully, it displays the URL you can visit in your web browser to see the function in action: http://localhost:8080/. You should see a Hello World! message.

Alternatively, you can send requests to this function using curl from another terminal window:

curl localhost:8080
# Output: Hello, World

Deploying the function

To deploy the function with an HTTP trigger, run the following command in the helloworld directory:

gcloud functions deploy my-first-function --entry-point functions.HelloWorld --runtime java11 --trigger-http --memory 512MB --allow-unauthenticated

where my-first-function is the registered name by which your function will be identified in the Cloud Console, and --entry-point specifies your function's fully qualified class name (FQN).

Testing the deployed function

  1. When the function finishes deploying, take note of the httpsTrigger.url property or find it using the following command:

    gcloud functions describe my-first-function
    

    It should look like this:

    https://GCP_REGION-PROJECT_ID.cloudfunctions.net/my-first-function
  2. Visit this URL in your browser. You should see a Hello World! message.

Viewing logs

Using the command-line tool

Logs for Cloud Functions are viewable in the Stackdriver Logging UI, and via the gcloud command-line tool.

To view logs for your function with the gcloud tool, use the logs read command, followed by the name of the function:

gcloud functions logs read my-first-function

The output should resemble the following:

LEVEL  NAME       EXECUTION_ID  TIME_UTC                 LOG
D      HelloWorld  30yj7zllsznl  2020-05-06 20:56:41.531  Function execution started
D      HelloWorld  30yj7zllsznl  2020-05-06 20:56:41.663  Function execution took 132 ms, finished with status code: 200

Using the Logging dashboard

You can also view logs for Cloud Functions from the Cloud Console.