Create an AWS Lambda using Java...

Here's a quick walk through for creating an AWS lambda using Java. I happen to use IntelliJ with maven, but you can use whatever IDE and package management you prefer to use. You can find a similar walk-through in the online AWS documentation or in the AWS Lambda In Action book.

1. Create an IAM role for the Lambda to use:

• Click the "Create new role" button.
• In the "Select role type" section, Click the "Select" button for "AWS Lambda" from the "AWS Service Role" section.
• Enter the policy name of "AmazonS3FullAccess", click the check box, and click the "Next step" button.
• Enter a name in the "Role name" text box (for this example, use "hello-lambda-role"), and enter a fitting description in the "Role description" text box. Click the "Create role" button.

2. Create an S3 bucket.

3. Create a Java project for your AWS Lambda code:

• Using IntelliJ, create a maven project using maven-archetype-quickstart.
• Add the aws lambda core dependency to the project's pom file:

<dependency>
  <groupId>com.amazonaws</groupId>
  <artifactId>aws-lambda-java-core</artifactId>
  <version>1.1.0</version>
</dependency>

• Create a class called HelloWorldLambda that implements RequestHandler<String, String>:

public class HelloWorldLambda implements RequestHandler<String, String> {
@Override
public String handleRequest(String input, Context context) {
    String output = "Hello, " + input + "!";
    return output;
}
}

• Build the project so that the jar is created setting the output jar name to be HelloLambda.jar.

4. Create the lambda in the AWS console:

• Click on the "Get Started Now" button.
• Click on the "Blank Function" item.

• On the "Configure triggers" page, click in the grey dashed square and then select "S3".

• Select the bucket that you created in step 2.
• Select the event type "Object Created (All)".
• Click "Enable trigger".

• Click the "Next" button. 
• Enter a name for the lambda like "hello-lambda"
• Select "Java 8" for the Runtime

• Click on the "Upload" button and select your HelloLambda.jar.

• In the "Lambda function handler and role", enter the full package path to your HelloWorldLambda class.
• Select "Choose an existing role" for the Role section.
• Select the "hello-lambda-role" that you created in step 1.

• In the "Tags" section, enter the value "Name" for the key, and "hello-lambda" for the value.

• In the "Advanced settings", increase the memory to 512 MB. Leave the timeout at 15 seconds.

• Click the "Create function" button.

5. Test the lambda!

* Go to "Functions" section of the AWS console's Lambda page.

* Select the "hello-lambda" function by clicking the option button.

* Click on the "Actions" drop down, and click on "Test function". The "Input test event" dialg will appear.

* Enter the text "testing", and then click the "Save and test" button.

This will trigger the lambda function, and you'll see the output in the "Execution result" section.

6. Test the lambda with an S3 creation event:

Uploading a text file with a single line of text to your S3 bucket that you created in step 2 will trigger your lambda, and you can see that the lambda is invoked by using the following steps.

• Go to the AWS Lambda console page, and select the "Functions" section.
• Click on the "hello-lambda" function. This should take you to the details for your lambda.  
• Click on the "Monitoring" tab. 

You'll see that you have invocations for both the test run, and the S3 upload. My image shows invocations for multiple file uploads, and multiple tests.

Learn more about AWS Lambdas through AWS Lambda In Action.