A simple framework for developing java based AWS Lambda functions. Built on Guice for easy dependency injection and module composition, this framework makes it wildly easy to build usable Lambda functions.
Functions are composed on two main components:
- Wrapper (extending LambdaBaseWrapper)
- Handler
The wrapper is a light layer around the the handler function. It's necessary so we can provide a concrete input and output event classes, as well specifying the Guice modules and loader. The parent LambdaBaseWrapper handles instantiating the handler and keeping a handle to the instance as long as the JVM is active (cutting down subsequent invocation time).
The handler provides the 'meat'of the function implementation. It takes an input message and returns an output message.
Properties can be loaded with the PropertiesModule, easily mapping configuration values to @Named injectable values. By leveraging a standard Java Properties file you can easily configure your functions at build time without forcing static values into your code.
| Module | Description |
|---|---|
| DefaultCredentialsModule | Load AWS credentials from the default credentials chain |
| SingleInstanceModule | Bind a class to a single instance |
| InstanceToNamed | map a @Named tag to a class instance. Helps automatically injecting types |
| NullableNamedInstanceModule | like InstanceToNamed, but also supporting a null instance |
| UtcClockModule | inject a Java 8 Clock, useful for testing and enforcing timestamps |
Starting out developing Lambda functions, people often just return the error to the user. However, as function implementations become more complex and when leveraging the Lambda function with AWS API Gateway, you will want to start returning standard errors.
The ExternalFacingRequestHandler supports a variety of error handling utilities, including the
ability to throw coherent, REST-style 400 errors and automatically translating unexpected
exceptions into 500 errors.
By default, AWS Lambda functions use log4j and eventually end up generating simple system.out log statements. However, many existing code bases use SLF4J. We include an Slf4jLogFactory to seamlessly support the existing code and minimize the number of additional dependencies you need to include.
This module makes it easier to develop lambda functions that interact with DynamoDB. Specifically, it provides Guice modules to configure and load DynamoDB components. It also provides Junit rules for spinning up a local DynamoDB instance.
When using the DynamoDB test rule, you will need to run
$ mvn install
first to copy the necessary DynamoDB-local jars to the runtime dependencies folder.
Helpful module for generating a maven archetype to use when generating a new maven-based Lambda function. Install the archetype with:
$ mvn install
Then you can use it to generate a maven project suitable to creating a deployable lambda function:
$ mvn archetype:generate -DarchetypeGroupId=io.fineo.lambda -DarchetypeArtifactId=lambda-archetype -DarchetypeVersion=1.0-SNAPSHOT -DgroupId=io.fineo.YOUR_PROJECT -DartifactId=YOUR_ARTIFACT -Dversion=1.0-SNAPSHOT