Invoke, list, and delete AWS Lambda functions

This section provides examples of programming with the Lambda service client by using the AWS SDK for Java 2.x.

Invoke a Lambda function

You can invoke a Lambda function by creating a LambdaClient object and invoking its invoke method. Create an InvokeRequest object to specify additional information such as the function name and the payload to pass to the Lambda function. Function names appear as arn:aws:lambda:us-east-1:123456789012:function:HelloFunction. You can retrieve the value by looking at the function in the AWS Management Console.

To pass payload data to a function, create a SdkBytes object that contains information. For example, in the following code example, notice the JSON data passed to the Lambda function.

Imports

import software.amazon.awssdk.services.lambda.LambdaClient;
import software.amazon.awssdk.regions.Region;
import software.amazon.awssdk.services.lambda.model.InvokeRequest;
import software.amazon.awssdk.core.SdkBytes;
import software.amazon.awssdk.services.lambda.model.InvokeResponse;
import software.amazon.awssdk.services.lambda.model.LambdaException;

Code

The following code example demonstrates how to invoke a Lambda function.

    public static void invokeFunction(LambdaClient awsLambda, String functionName) {

         InvokeResponse res = null ;
        try {
            //Need a SdkBytes instance for the payload
            String json = "{\"Hello \":\"Paris\"}";
            SdkBytes payload = SdkBytes.fromUtf8String(json) ;

            //Setup an InvokeRequest
            InvokeRequest request = InvokeRequest.builder()
                    .functionName(functionName)
                    .payload(payload)
                    .build();

            res = awsLambda.invoke(request);
            String value = res.payload().asUtf8String() ;
            System.out.println(value);

        } catch(LambdaException e) {
            System.err.println(e.getMessage());
            System.exit(1);
        }
    }

See the complete example on GitHub.

List Lambda functions

Build a LambdaClient object and invoke its listFunctions method. This method returns a ListFunctionsResponse object. You can invoke this object’s functions method to return a list of FunctionConfiguration objects. You can iterate through the list to retrieve information about the functions. For example, the following Java code example shows how to get each function name.

Imports

import software.amazon.awssdk.regions.Region;
import software.amazon.awssdk.services.lambda.LambdaClient;
import software.amazon.awssdk.services.lambda.model.LambdaException;
import software.amazon.awssdk.services.lambda.model.ListFunctionsResponse;
import software.amazon.awssdk.services.lambda.model.FunctionConfiguration;
import java.util.List;

Code

The following Java code example demonstrates how to retrieve a list of function names.

    public static void listFunctions(LambdaClient awsLambda) {

        try {
            ListFunctionsResponse functionResult = awsLambda.listFunctions();
            List<FunctionConfiguration> list = functionResult.functions();

            for (FunctionConfiguration config: list) {
                System.out.println("The function name is "+config.functionName());
            }

        } catch(LambdaException e) {
            System.err.println(e.getMessage());
            System.exit(1);
        }
    }

See the complete example on GitHub.

Delete a Lambda function

Build a LambdaClient object and invoke its deleteFunction method. Create a DeleteFunctionRequest object and pass it to the deleteFunction method. This object contains information such as the name of the function to delete. Function names appear as arn:aws:lambda:us-east-1:123456789012:function:HelloFunction. You can retrieve the value by looking at the function in the AWS Management Console.

Imports

import software.amazon.awssdk.services.lambda.LambdaClient;
import software.amazon.awssdk.regions.Region;
import software.amazon.awssdk.services.lambda.model.DeleteFunctionRequest;
import software.amazon.awssdk.services.lambda.model.LambdaException;

Code

The following Java code demonstrates how to delete a Lambda function.

    public static void deleteLambdaFunction(LambdaClient awsLambda, String functionName ) {
        try {
            DeleteFunctionRequest request = DeleteFunctionRequest.builder()
                    .functionName(functionName)
                    .build();

            awsLambda.deleteFunction(request);
            System.out.println("The "+functionName +" function was deleted");

        } catch(LambdaException e) {
            System.err.println(e.getMessage());
            System.exit(1);
        }
    }

See the complete example on GitHub.