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AWS Lambda Context Object in Java

When Lambda runs your function, it passes a context object to the handler. This object provides methods and properties that provide information about the invocation, function, and execution environment.

Context Methods

  • getRemainingTimeInMillis() – Returns the number of milliseconds left before the execution times out.
  • getFunctionName() – Returns the name of the Lambda function.
  • getFunctionVersion() – Returns the version of the function.
  • getInvokedFunctionArn() – Returns the Amazon Resource Name (ARN) used to invoke the function. Indicates if the invoker specified a version number or alias.
  • getMemoryLimitInMB() – Returns the amount of memory configured on the function.
  • getAwsRequestId() – Returns the identifier of the invocation request.
  • getLogGroupName() – Returns the log group for the function.
  • getLogStreamName() – Returns the log stream for the function instance.
  • getIdentity() – (mobile apps) Returns information about the Amazon Cognito identity that authorized the request.
  • getClientContext() – (mobile apps) Returns the client context provided to the Lambda invoker by the client application.
  • getLogger() – Returns the logger object for the function.

The following example shows a handler function that logs context information.

Example ContextLogger.java

package example;
import java.io.InputStream;
import java.io.OutputStream;
import com.amazonaws.services.lambda.runtime.Context;

public class ContextLogger {
    public static void myHandler(InputStream inputStream, OutputStream outputStream, Context context) {
        int letter;
        try {
            while((letter = inputStream.read()) != -1)
            {
                outputStream.write(Character.toUpperCase(letter));
            }
            Thread.sleep(3000); // Intentional delay for testing the getRemainingTimeInMillis() result.
        }
        catch (Exception e)
        {
            e.printStackTrace();
        }
        // Print info from the context object
        System.out.println("Function name: " + context.getFunctionName());
        System.out.println("Max mem allocated: " + context.getMemoryLimitInMB());
        System.out.println("Time remaining in milliseconds: " + context.getRemainingTimeInMillis());
        System.out.println("CloudWatch log stream name: " + context.getLogStreamName());
        System.out.println("CloudWatch log group name: " + context.getLogGroupName());
    }
}

Dependencies

  • aws-lambda-java-core

Build the code with the Lambda library dependencies to create a deployment package. For instructions, see AWS Lambda Deployment Package in Java.