This is a sample template for AWS - Below is a brief explanation of what we have generated for you:

├── README.md                                   <-- This instructions file
├── HelloWorldFunction                          <-- Source for HelloWorldFunction Lambda Function
│   ├── pom.xml                                 <-- Java dependencies
│   └── src
│       ├── main
│       │   └── java
│       │       └── helloworld
│       │           ├── App.java                <-- Lambda function code
│       │           └── GatewayResponse.java    <-- POJO for API Gateway Responses object 
│       └── test                                <-- Unit tests
│           └── java
│               └── helloworld
│                   └── AppTest.java
└── template.yaml

• AWS CLI already configured with Administrator permission
• Java SE Development Kit 8 installed
• Docker installed
• Maven

sam build

You can also build on a Lambda like environment by using

sam build --use-container

Invoking function locally through local API Gateway

sam local start-api

If the previous command ran successfully you should now be able to hit the following local endpoint to invoke your function http://localhost:3000/hello

SAM CLI is used to emulate both Lambda and API Gateway locally and uses our template.yaml to understand how to bootstrap this environment (runtime, where the source code is, etc.) - The following excerpt is what the CLI will read in order to initialize an API and its routes:

...
Events:
    HelloWorld:
        Type: Api # More info about API Event Source: https://github.com/awslabs/serverless-application-model/blob/master/versions/2016-10-31.md#api
        Properties:
            Path: /hello
            Method: get

AWS Lambda Java runtime accepts either a zip file or a standalone JAR file - We use the latter in this example. SAM will use CodeUri property to know where to look up for both application and dependencies:

...
    HelloWorldFunction:
        Type: AWS::Serverless::Function
        Properties:
            CodeUri: target/HelloWorld-1.0.jar
            Handler: helloworld.App::handleRequest

Firstly, we need a S3 bucket where we can upload our Lambda functions packaged as ZIP before we deploy anything - If you don't have a S3 bucket to store code artifacts then this is a good time to create one:

aws s3 mb s3://BUCKET_NAME

Next, run the following command to package our Lambda function to S3:

sam package \
    --output-template-file packaged.yaml \
    --s3-bucket REPLACE_THIS_WITH_YOUR_S3_BUCKET_NAME

Next, the following command will create a Cloudformation Stack and deploy your SAM resources.

sam deploy \
    --template-file packaged.yaml \
    --stack-name aws \
    --capabilities CAPABILITY_IAM

See Serverless Application Model (SAM) HOWTO Guide for more details in how to get started.

After deployment is complete you can run the following command to retrieve the API Gateway Endpoint URL:

aws cloudformation describe-stacks \
    --stack-name aws \
    --query 'Stacks[].Outputs'

We use JUnit for testing our code and you can simply run the following command to run our tests:

cd HelloWorldFunction
mvn test

AWS CLI commands to package, deploy and describe outputs defined within the cloudformation stack:

sam package \
    --template-file template.yaml \
    --output-template-file packaged.yaml \
    --s3-bucket REPLACE_THIS_WITH_YOUR_S3_BUCKET_NAME

sam deploy \
    --template-file packaged.yaml \
    --stack-name aws \
    --capabilities CAPABILITY_IAM \
    --parameter-overrides MyParameterSample=MySampleValue

aws cloudformation describe-stacks \
    --stack-name aws --query 'Stacks[].Outputs'

Here are a few ideas that you can use to get more acquainted as to how this overall process works:

• Create an additional API resource (e.g. /hello/{proxy+}) and return the name requested through this new path
• Update unit test to capture that
• Package & Deploy

Next, you can use the following resources to know more about beyond hello world samples and how others structure their Serverless applications:

• AWS Serverless Application Repository