Serverless Java container

The aws-serverless-java-container is collection of interfaces and their implementations that let you run Java application written with frameworks such as Jersey or Spark in AWS Lambda.

The library contains a core artifact called aws-serverless-java-container-core that defines the interfaces and base classes required as well as default implementation of the Java servlet HttpServletRequest and HttpServletResponse. The library also includes two initial implementations of the interfaces to support Jersey apps (aws-serverless-java-container-jersey) and Spark (aws-serverless-java-container-spark).

To include the library in your Maven project, add the desired implementation to your pom.xml file, for example:

<dependency>
    <groupId>com.amazonaws.serverless</groupId>
    <artifactId>aws-serverless-java-container-jersey</artifactId>
    <version>0.2</version>
</dependency>

Integrating with Lambda

The simplest way to run your application serverlessly is to configure API Gateway to use the AWS_PROXY integration type and configure your desired LambdaContainerHandler implementation to use AwsProxyRequest/AwsProxyResponse readers and writers. Both Spark and Jersey implementations provide static helper methods that pre-configure this for you.

Jersey support

The library expects to receive a valid JAX-RS application object. For the Jersey implementation this is the ResourceConfig object.

public class LambdaHandler implements RequestHandler<AwsProxyRequest, AwsProxyResponse> {
    private ResourceConfig jerseyApplication = new ResourceConfig().packages("my.jersey.app.package");
    private JerseyLambdaContainerHandler<AwsProxyRequest, AwsProxyResponse> handler
        = JerseyLambdaContainerHandler.getAwsProxyHandler(jerseyApplication);

    public AwsProxyResponse handleRequest(AwsProxyRequest awsProxyRequest, Context context) {
        return handler.proxy(awsProxyRequest, context);
    }
}

Spring support

The library supports Spring applications that are configured using annotations (in code) rather than in an XML file. The simplest possible configuration uses the @ComponentScan annotation to load all controller classes from a package. For example, our unit test application has the following configuuration class.

@Configuration
@ComponentScan("com.amazonaws.serverless.proxy.spring.echoapp")
public class EchoSpringAppConfig {
}

Once you have declared a configuration class, you can initialize the library with the class name:

public class LambdaHandler implements RequestHandler<AwsProxyRequest, AwsProxyResponse> {
    SpringLambdaContainerHandler<AwsProxyRequest, AwsProxyResponse> handler = 
        SpringLambdaContainerHandler.getAwsProxyHandler(EchoSpringAppConfig.class);
    
    public AwsProxyResponse handleRequest(AwsProxyRequest awsProxyRequest, Context context) {
        return handler.proxy(awsProxyRequest, context);
    }
}

Spark support

The library also supports applications written with the Spark framework. When using the library with Spark, it's important to initialize the SparkLambdaContainerHandler before defining routes.

public class LambdaHandler implements RequestHandler<AwsProxyRequest, AwsProxyResponse> {
    private SparkLambdaContainerHandler<AwsProxyRequest, AwsProxyResponse> handler = 
            SparkLambdaContainerHandler.getAwsProxyHandler();
    private boolean initialized = false;
    
    public AwsProxyResponse handleRequest(AwsProxyRequest awsProxyRequest, Context context) {
        if (!initialized) {
            defineRoutes();
            initialized = true;
        }
        return handler.proxy(awsProxyRequest, context);
    }
    
    private void defineRoutes() {
        get("/hello", (req, res) -> "Hello World");
    }
}

Security context

The aws-serverless-java-container-core contains a default implementation of the SecurityContextWriter that supports API Gateway's proxy integration. The generated security context uses the API Gateway $context object to establish the request security context. The context looks for the following values in order and returns the first matched type:

1. Cognito My User Pools
2. Custom authorizers
3. IAM auth.

The String values for these are exposed as static variables in the AwsProxySecurityContext object.

1. AUTH_SCHEME_COGNITO_POOL
2. AUTH_SCHEME_CUSTOM
3. AUTH_SCHEME_IAM

Supporting other event types

The RequestReader and ResponseWriter interfaces in the core package can be used to support event types and generate different responses. For example, ff you have configured mapping templates in API Gateway to create a custom event body or response you can create your own implementation of the RequestReader and ResponseWriter to handle these.

The LambdaContainerHandler also requires a SecurityContextWriter and an ExceptionHandler. You can also create custom implementations of these interfaces.

The RequestReader, ResponseWriter, SecurityContextWriter, and ExceptionHandler objects are passed to the constructor of the LambdaContainerHandler implementation:

JerseyLambdaContainerHandler<AwsProxyRequest, AwsProxyResponse> handler =
    new JerseyLambdaContainerHandler<>(new MyCustomRequestReader(),
                                       new MyCustomResponseWriter(),
                                       new MyCustomSecurityContextWriter(),
                                       new MyCustomExceptionHandler(),
                                       jaxRsApplication);

Jersey Servlet request

The aws-serverless-java-container-jersey includes a Jersey factory class to produce HttpServletRequest objects for your methods. First, you will need to register the factory with your Jersey application.

ResourceConfig app = new ResourceConfig()
    .packages("com.amazonaws.serverless.proxy.test.jersey")
    .register(new AbstractBinder() {
        @Override
        protected void configure() {
            bindFactory(JerseyAwsProxyServletRequestFactory.class)
                .to(HttpServletRequest.class)
                .in(RequestScoped.class);
        }
    });

Once the factory is registered, you can receive HttpServletRequest objects in your methods.

@Path("/my-servlet") @GET
public String echoServletHeaders(@Context HttpServletRequest context) {
    Enumeration<String> headerNames = context.getHeaderNames();
    while (headerNames.hasMoreElements()) {
        String headerName = headerNames.nextElement();
    }
    return "servlet";
}