We will be improving the code we created in the Using AWS SDK, Amazon CloudWatch and AWS CLI with Lambda recipe. Before doing Dependency Injection, you need to refactor your code to follow the principle of programming to interfaces.

Refactor the service class into an interface and its implementation. I will also add lombok's @AllArgsConstructor annotation to generate an all args constructor, which will be used during unit testing to inject the mock object.

1. We will first create an interface IAMService:

/**
 * Interface for IAM operations.
 */
public interface IAMService {

We will define the corresponding implementation as IAMServiceImpl:

/**
 * Implementation of {@link IAMService}.
 */
@AllArgsConstructor
public class IAMServiceImpl implements IAMService {

2. Extract the methods as well, and then replace the usage of the implementation with an interface:

private IAMService service;

public MyLambdaHandler() {
    service = new IAMServiceImpl();
}