Starting an AWS Step Functions State Machine from Java

Just over two years ago, I wrote a quick post to document how to invoke an AWS Lambda function from Java. I recently was asked how to start execution of an AWS Step Function state machine and also found a working example challenging to dig up … so I put together a quick example:

import com.amazonaws.regions.Regions;
import com.amazonaws.services.stepfunctions.AWSStepFunctions;
import com.amazonaws.services.stepfunctions.AWSStepFunctionsClientBuilder;
import com.amazonaws.services.stepfunctions.model.StartExecutionRequest;
import com.amazonaws.services.stepfunctions.model.StartExecutionResult;
import org.json.JSONObject;

// ...

// (1) Define the AWS Region in which the function is to be invoked.
Regions region = Regions.fromName(System.getenv("AWS_REGION"));

// (2) Instantiate AWSStepFunctionsClientBuilder to build the client
AWSStepFunctionsClientBuilder builder = AWSStepFunctionsClientBuilder.standard()
                                          .withRegion(region);

// (3) Build the client, which will ultimately do the work
AWSStepFunctions client = builder.build();

// (4) Construct the JSON input to the state machine
JSONObject sfnInput = new JSONObject();
sfnInput.put("key1", "hello");
sfnInput.put("key2", "world");

// (5) Create a request to start execution with needed parameters
StartExecutionRequest request = new StartExecutionRequest()
                                      .withStateMachineArn("MY_STATE_MACHINE_ARN")
                                      .withInput(sfnInput.toString());

// (6) Start the state machine and capture response
StartExecutionResult result = client.startExecution(request);

// (7) Handle the result, this includes the execution ID

The example above makes use of the DefaultAWSCredentialsProviderChain to pull credentials from environment variables, instance profile, etc. You can use BasicAWSCredentials if you need to hardcode keys, but this is a much less desirable option.