How to invoke an aws lambda function from another aws lambda in Java?

Question

I have a code in java that returns an integer value. for example:

public class Hello {

    public int myHandler(Object name, Context context) {

        int count = 5;
        return count;
    }
}

I have uploaded this code on AWS with the handler name as example.Hello::myHandler and function name as AWSLAMBDA under the us-east-2 region.

Now I want to write another code in Java which invokes the output value (count) of the earlier code. Note that count is an integer. Since I am a novice in both java and aws. Kindly help me with this and please provide a simple explanation if possible.

Does this answer your question? AWS Lambda chaining best practice — Stephan
– Stephan, Commented Oct 29, 2019 at 18:33

amittn · Accepted Answer · 2019-10-30 04:32:36Z

1

This is the code snippet example aws sdk
To invoke a function asynchronously, set InvocationType to Event
To invoke a function synchronously, set InvocationType to RequestResponse (which is the default value).
The calling lambda should have a role with attached policy having lambda:InvokeFunction action.

import com.amazonaws.regions.Regions;
import com.amazonaws.services.lambda.AWSLambda;
import com.amazonaws.services.lambda.AWSLambdaClientBuilder;
import com.amazonaws.services.lambda.model.InvokeRequest;
import com.amazonaws.services.lambda.model.InvokeResult;

AWSLambda client = AWSLambdaClientBuilder.standard().build();
InvokeRequest request = new InvokeRequest().withFunctionName("MyFunction").withInvocationType("RequestResponse").withLogType("Tail").withClientContext("MyApp")
        .withPayload(ByteBuffer.wrap("fileb://file-path/input.json".getBytes())).withQualifier("1");
InvokeResult response = client.invoke(request);

edited Oct 30, 2019 at 4:32

answered Oct 29, 2019 at 20:58

amittn

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4 Comments

Vikram Over a year ago

Thanks for answering. It is throwing an error in java stating that method invoke is undefined for the type AWSLambda. The error is in this line of the code. InvokeResult response = client.invoke(request);

amittn Over a year ago

I have updated the answer with few of the imports that you need, check that

amittn Over a year ago

Vikram if it has helped you can you please accept the answer. So that it can help others as well.

Big Pumpkin Over a year ago

Make sure your Maven or Gradle pulls in dependency com.amazonaws:aws-java-sdk-lambda.

splieth · Accepted Answer · 2019-10-29 21:03:37Z

0

Besides the Java code you also need to make sure that the policy attached to your Lambda function is actually able to invoke the second Lambda function. Otherwise, the Java snippet will fail since the invoking Lambda misses the permission to invoke other functions

answered Oct 29, 2019 at 21:03

splieth

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