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 document shows how to create a simple HTTP function and build it using either Maven or Gradle.

Guide structure

  1. Creating a GCP project using Cloud SDK
  2. Creating a function
  3. Specifying dependencies
  4. Building and testing locally
  5. Deploying the function
  6. Testing the deployed function
  7. Viewing logs

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 and Cloud Build APIs.

    Enable the APIs

  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

This section describes how to create a function.

Maven

  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 the source directory and source file.

    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!"

Gradle

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

    Linux or Mac OS X:

     mkdir ~/helloworld-gradle
     cd ~/helloworld-gradle
    

    Windows:

     mkdir %HOMEPATH%\helloworld-gradle
     cd %HOMEPATH%\helloworld-gradle
    
  2. Create the project structure to contain the source directory and source file.

     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

The next step is to set up dependencies:

Maven

Change directory to the helloworld directory you created above, and create a pom.xml file:

 cd ~/helloworld
 touch pom.xml

To manage dependencies using Maven, specify 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.

<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>1.0.2</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>0.9.5</version>
        <configuration>
          <functionTarget>functions.HelloWorld</functionTarget>
        </configuration>
      </plugin>
    </plugins>
  </build>
</project>

See helloworld for a complete sample based on Maven.

Gradle

Change directory to the helloworld-gradle directory you created above, and create a build.gradle file:

 cd ~/helloworld-gradle
 touch build.gradle

To manage dependencies using Gradle, specify the dependencies in the build.gradle file of your project. For this exercise, copy the following contents into your build.gradle file. Note that this build.gradle file includes a custom task to help you run functions locally.

apply plugin: 'java'

repositories {
  jcenter()
  mavenCentral()
}
configurations {
    invoker
}

dependencies {
  // Every function needs this dependency to get the Functions Framework API.
  compileOnly 'com.google.cloud.functions:functions-framework-api:1.0.1'

  // To run function locally using Functions Framework's local invoker
  invoker 'com.google.cloud.functions.invoker:java-function-invoker:1.0.0-alpha-2-rc5'

  // These dependencies are only used by the tests.
  testImplementation 'com.google.cloud.functions:functions-framework-api:1.0.1'
  testImplementation 'junit:junit:4.12'
  testImplementation 'com.google.truth:truth:1.0.1'
  testImplementation 'org.mockito:mockito-core:3.4.0'

}

// Register a "runFunction" task to run the function locally
tasks.register("runFunction", JavaExec) {
  main = 'com.google.cloud.functions.invoker.runner.Invoker'
  classpath(configurations.invoker)
  inputs.files(configurations.runtimeClasspath, sourceSets.main.output)
  args(
    '--target', project.findProperty('runFunction.target') ?: '',
    '--port', project.findProperty('runFunction.port') ?: 8080
  )
  doFirst {
    args('--classpath', files(configurations.runtimeClasspath, sourceSets.main.output).asPath)
  }
}

See helloworld-gradle for a complete sample based on Gradle.

Building and testing locally

Before deploying the function, you can build and test it locally:

Maven

Run the following command to confirm that your function builds:

mvn compile

Another option is to use the mvn package command to compile your Java code, run any tests, and package the code up in a JAR file within the target directory. You can learn more about the Maven build lifecycle here.

To test the function, run the following command:

mvn function:run

Gradle

Run the following command to confirm that your function builds:

gradle build

To test the function, run the following command:

gradle runFunction -PrunFunction.target=functions.HelloWorld

If testing 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

Maven

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).

Gradle

To deploy the function with an HTTP trigger, run the following command in the helloworld-gradle 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      my-first-function  k2bqgroszo4u  2020-07-24 18:18:01.791  Function execution started
D      my-first-function  k2bqgroszo4u  2020-07-24 18:18:01.958  Function execution took 168 ms, finished with status code: 200
...

Using the Logging dashboard

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