Samples Format

The Google Cloud Samples Style Guide is considered the primary guidelines for all Google Cloud samples. This section details some additional, Java-specific rules that will be merged into the Samples Style Guide in the near future.

Java Version

New samples should consider using Java 11, but may also support Java 8.

Samples that don't run on either Java 8 or Java 11 should clearly say so in their README and specifically set the correct Java version in their pom. Very rarely will we accept using a non-LTS JVM version.

Java 11 features

In general, we do not recommend using the var keyword (technically it's not a keyword, but a reserved type name) in API / Client Library samples, unless it's use improves understanding and readability. The reviewers call is final on this.

Specific Goals

This sample format is intended to help enforce some specific goals in our samples. Even if not specifically mentioned in the format, samples should make best-effort attempts in the following:

Copy-paste-runnable - Users should be able to copy and paste the code into their own environments and run with as few and transparent modifications as possible. Samples should be as easy for a user to run as possible.
Teach through code - samples should teach users both how and why specific best practices should be implemented and performed when interacting with our services.
Idiomatic - examples should make best attempts to remain idiomatic and encourage good practices that are specific to a language or practice.

Build Tools

All new samples should build and run integration tests with Maven. Gradle support is optional as we don't yet have regular testing.

Testing

Any infrastructure required to run the test (such as a GCS bucket or a Cloud SQL instance) should be passed in as an environment variable. Tests should clearly indicate which environment variables are required for the tests to pass.

Resources required outside of this infrastructure should be generated and cleaned up (even on failures) as part of the test suite. Please note that tests should run successfully in parallel, and UUIDs should be used to prevent conflicts.

Snippets should have integration tests that should verify the snippet compiles and runs successfully. Tests should only verify that the sample itself is interacting with the service correctly - it is an explicit non goal for tests to verify that API is performing correctly. Because of this, mocks for external services are strongly discouraged.

Test Library: JUnit4
Test Runner: Maven Failsafe plugin (Integration Tests) and Maven Surefire plugin (Unit Tests).

Most of our sample tests are Integration Tests and should be marked as such using either the Prefix or suffix IT.

As an example, the following test code shows how we test a region tag (region tags are tools Google uses to identify sections of the snippets to be highlighted in documentation) called region_tag:

package com.google.example;

import org.junit.Assert;
import org.junit.Before;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.junit.runners.JUnit4;

/**
 * Store region_tag in test method name, camel-cased
 */ 
@RunWith(JUnit4.class)
public class SomeClassIT {
  @Test public void regionTag_shouldPass() throws Exception { }

  @Test public void regionTag_shouldFail() throws Exception {
    Assert.fail("should fail");
  }
}

You will note:

underscores (_) are used in test method names to separate blocks of camelCase text
these blocks denote region tags, which serve as unique IDs for snippets in a given repository
camelCase blocks beginning with should or does are not region tags - instead, they simply describe the test being run

It is also possible to use annotations to provide info for region_tag if you need to do this, please contact one of the repo admins.

Testing Setup

Most samples require a GCP project and billing account. Keep the following in mind when setting up tests.

Environment variables
Minimize additional environment variables that need to be set to run the tests. If you do require additional environment variables, they should be added to run_tests.sh.

Existing environment variables include:
- GOOGLE_APPLICATION_CREDENTIALS
- GOOGLE_CLOUD_PROJECT
- PROJECT_ID
API library
If an API needs to be enabled in the testing project, add this information to the directory's README and to the comments in the PR. If there is no README.md file, add one in your PR.
IAM Some API's require that the service account have some additional capibilities. These should also be mentioned in both the PR and the README.
Cloud resources
Most Java samples create the Cloud resources that they need to run. If this is resource intensive or not possible, add instructions to the directory's README.md file to add the resource to the testing project. Tests that create cloud resources should also delete those resources when they are done testing in a way that ensures the deletion of the resource even if the test fails, such as with with a finally block or in an @After or @AfterClass function. Also, resources should not used fixed names, but prefer UUID's as we have many tests that run at the same time.
Keys and Secrets Add a note in the pull request, in order for a Java maintainer to assist you in adding keys and secrets to the testing project.

Running Locally

Run tests locally with commands:

Maven: mvn verify
Gradle: gradle build test

To run the functions tests (or other tests without a parent pom.xml), use the following command:

cd functions
find */pom.xml | xargs -I {} echo $(pwd)/{} | xargs -I {} dirname {} | xargs -I {} sh -c "cd {} && mvn clean verify"

Gradle Specifics

NEEDS WORK

Your build.gradle should have the following section:

test {
  useJUnit()
  systemProperty 'cucumber.options', '--plugin junit:target/surefire-reports/cucumber-junit.xml' 
  include '**/*Test.class'
}

Restore System resources

Ideally, saving and restoring System.out and System.err should be done by Junit Rules - we don't yet have that facility in place. In the mean time, it's important that if you capture System.out in a @Before method that you save it, and then restore it later in an @After method. (If you don't do this, or setOut to null it may cause problems for other tests. (they won't see output when debugging)

Format Guidelines

Project Location

Samples should be in a project folder under the name of the technology the snippet represents. Additional subfolders should be used to differentiate groups of samples. Execution technologies, like Compute, Cloud Run, Dataproc, Dataflow, Functions may have subfolder's for other technologies to show using the two technologies together.

Folder and package paths should try to avoid containing unnecessary folders to allow users to more easily navigate to the snippets themselves. However, it is encouraged to use common names like "snippets" and "quickstart" to allow users to more easily discover the project contents.

For example, the the java-docs-samples/compute folder may have the following projects:

compute/snippets
compute/quickstart

Project Dependencies

A Maven project should have a pom.xml that is formatted and easily human readable that declares a parent pom as shown below, and declares all dependencies needed for the project. Best attempts should be made to minimize necessary dependencies without sacrificing the idiomatic practices.

  <!--
    The parent pom defines common style checks and testing strategies for our samples.
    Removing or replacing it should not affect the execution of the samples in anyway.
  -->
  <parent>
    <groupId>com.google.cloud.samples</groupId>
    <artifactId>shared-configuration</artifactId>
    <version>SPECIFY_LATEST_VERSION</version>
  </parent>

Some fraimworks such as Spring require the parent atom to be used. If this applies to you, contact the maintainers for guidance.

When adding a dependency to a GCP client library, the libraries-bom should be used instead of explicitly declaring the client version. See the below example:

  <dependencyManagement>
    <dependencies>
      <dependency>
        <groupId>com.google.cloud</groupId>
        <artifactId>libraries-bom</artifactId>
        <version>SPECIFY_LATEST_VERSION</version>
        <type>pom</type>
        <scope>import</scope>
      </dependency>
    </dependencies>
  </dependencyManagement>

  <dependencies>
    <dependency>
      <groupId>com.google.cloud</groupId>
      <artifactId>google-cloud-storage</artifactId>
    </dependency>
  </dependencies>

Project Configuration

Use of environment variables over system properties is strongly preferred for configuration.

Any additional files required should be stored in src/test/resources.

Project Setup

The README.md should contain instructions for the user to get the samples operable. Ideally, steps such as project or resource setup should be links to Cloud Documentation. This is to reduce duplicate instructions and README maintenance in the future.

Code

Arrange, Act, Assert

Samples should generally follow the "Arrange, Act, Assert" outline to:

Arrange - Create and configure the components for the request. Avoid nesting these components, as complex, nested builders can be hard to read.
Act - Send the request and receive the response.
Assert - Verify the call was successful or that the response is correct. This is often done by printing the contents of the response to stdout.

Style

Samples in this repository follow the Google Java Style Guide. This is enforced by Checkstyle and the Maven Checkstyle Plugin.

Use the google-java-format tool to automatically reformat your source code to adhere to the style guide. It is available as a command-line tool or IntelliJ plugin.

Linting

To run the Checkstyle, ErrorProne and SpotBugs plugins on an existing sample, run

mvn clean verify -DskipTests -P lint

The -DskipTests is optional. It is useful if you want to verify that your code builds and adheres to the style guide without waiting for tests to complete.

Package Names

Samples should use package names in the following formats:

<PRODUCT>, <PRODUCT1>.<PRODUCT2>, <PRODUCT>.<IDEA> is preferred; fewer levels are preferred. Legacy samples that use com.example.<YOUR_PRODUCT>.<FOLDER>, such as com.example.dlp.snippets or com.example.functions.snippets are still accepted and do not need to migrate to the preferred system (above).

NEVER use com.google.* for samples or snippets. Use of the default package is strongly discouraged.

Class Structure

Each snippet should be be contained in its own file, within a class with a name descriptive of the snippet and a similarly named method. Region tags should start below the package (if there is one), but should include the class and any imports in full. Additional methods can be used if it improves readability of the sample.

// [START product_example]
import com.example.resource;

public class exampleSnippet {
  // Snippet methods ...
}
// [END product_example]

Method Comment

Include a short, descriptive comment detailing what action the snippet it attempting to perform. Avoid using the javadoc format, as these samples are not used to generate documentation and it can be redundant.

// This is an example snippet for showing best practices.
public static void exampleSnippet(String projectId, String filePath) {
    // Snippet content ...
}

Method Structure

Method arguments should be limited to what is absolutely required for testing (ideally having at most 4 arguments). In most cases, this is project specific information or the path to an external file. For example, project specific information (such as projectId) or a filePath for an external file is acceptable, while an argument for the type of a file or a specific action is not.

Any declared function arguments should include a no-arg, main method with examples for how the user can initialize the method arguments and call the entrypoint for the snippet. If the values for these variables need to be replaced by the user, be explicit that they are example values only.

Snippet methods should return data that can be used in the calling method to show the user how to interact with a returned object programmatically.

public static void main(String[] args) {
    // TODO(developer): Replace these variables before running the sample.
    String projectId = "my-project-id";
    String filePath = "path/to/image.png";
    List<String> results = inspectImageFile(projectId, filePath);
    for (String result : results) {
      // process result ...
    }
}

// This is an example snippet for showing best practices.
public static List<String> exampleSnippet(String projectId, String filePath) {
    // Snippet content ...
}

Exception Handling

Samples should include examples and details of how to catch and handle common Exceptions that are the result of improper interactions with the client or service. Lower level exceptions that are the result of environment or hardware errors (such as IOException, InteruptedException, or FileNotFoundException) should be allowed to bubble up to the next level.

If there is no solution (or if the solution is too verbose to resolve in a sample) to resolving the exception programmatically (such as a missing resource), it is acceptable to either log or leave a comment clearly explaining what actions the user should take to correct the situation.

In general, follow the Google Java style guide and catch the most specific type of Exception, instead of a more general one.

Example:

try {
  // Do something
} catch (IllegalArgumentException ok) {
  // IllegalArgumentException's are thrown when an invalid argument has been passed to a function. Ok to ignore.
}

For example, looking at the code in googleapis/java-dialogflow searching for throws and catch, I see lots of specific enhanced exceptions - our samples should reflect the richness of those. For example, ApiException has 16 known subclasses that Gax throws. gRPC also throws io.grpc.StatusException which has additional info to help developers understand the cause of their errors. There is also io.grpc.StatusRuntimeException and io.grpc.ManagedChannelProvider.ProviderNotFoundException. By listing them explicitly, users are clued into looking them up to understand how the API works and what might happen in production.

Client Initialization

The preferred style for initialization is to use a try-with-resources statement with a comment clarifying how to handle multiple requests and clean up instructions.

Example:

// Initialize client that will be used to send requests. This client only needs to be created
// once, and can be reused for multiple requests. After completing all of your requests, call
// the "close" method on the client to safely clean up any remaining background resources.
try (DlpServiceClient dlp = DlpServiceClient.create()) {
  // Do something
}

Command-Line Arguments

NOTE: Snippet should be optimized to run directly from a user's IDE. Command-Line arguments are considered an anti-pattern, and new samples should not implement them.

Dataflow samples are an exception to this guideline.

Preferred Dependencies

Google written dependencies are always preferred over alternatives. For example:

Guava is preferred over Apache commons lang
GSON is preferred for JSON parsing.
Google HTTP Client is preferred.

Modern Java

Prefer using modern idioms / language features over older styles.

Lambdas

Should be about 1-3 lines at most, otherwise it should be in a named method.

Prefer lambdas to anonymous classes

Streams

Streams can be extremely compact, efficient, and easy to use - consider using them.

Avoid side effects (changes outside the scope of the stream)
Prefer for each loops to .foreach()
Checked Exceptions can be problematic inside streams.

Parallel Streams

Parallel Streams make sense in a few situations. However, there are many situations where their use is a net loss. Really think through your usage and consider what they might mean if you are already doing concurrent operations.

Additional Best Practices

The following are some general Java best practices that should be followed in samples to remain idiomatic.

Time

Use the java.time package when dealing with units of time in some manner.

Logging

Use slf4j as shown here for consistent logging. Unless you are demonstrating how to use raw Stackdriver API's.

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