How to Use AWS Lambda with Java: Syntax and Example

To use AWS Lambda with Java, write a handler class implementing RequestHandler or RequestStreamHandler interface. Package your code as a jar file and deploy it to Lambda, specifying the handler class name.

Syntax

The main parts to use Lambda with Java are:

• Handler class: A Java class that implements RequestHandler<InputType, OutputType> or RequestStreamHandler.
• Handler method: The handleRequest method processes input and returns output.
• Deployment package: A jar file containing your compiled code and dependencies.
• Handler name: The full class name used by Lambda to invoke your code.

java

import com.amazonaws.services.lambda.runtime.Context;
import com.amazonaws.services.lambda.runtime.RequestHandler;

public class MyLambdaHandler implements RequestHandler<String, String> {
    @Override
    public String handleRequest(String input, Context context) {
        return "Hello, " + input;
    }
}

Example

This example shows a simple Lambda function in Java that greets the input name.

java

import com.amazonaws.services.lambda.runtime.Context;
import com.amazonaws.services.lambda.runtime.RequestHandler;

public class GreetingLambda implements RequestHandler<String, String> {
    @Override
    public String handleRequest(String name, Context context) {
        return "Hello, " + name + "!";
    }
}

// To deploy:
// 1. Compile and package this class into a jar with dependencies.
// 2. Upload the jar to AWS Lambda.
// 3. Set the handler to 'GreetingLambda::handleRequest'.
// 4. Test with input like "World".

// Expected output: "Hello, World!"

Output

Hello, World!

Common Pitfalls

• Not packaging dependencies in the jar causes runtime errors.
• Incorrect handler name format (should be ClassName::methodName).
• Using unsupported Java versions (AWS Lambda supports Java 8, 11, and 17).
• Ignoring the Context parameter which provides useful info.

text

/* Wrong handler name example */
// Handler set as "GreetingLambda.handleRequest" (dot instead of double colon)

/* Correct handler name example */
// Handler set as "GreetingLambda::handleRequest"

Quick Reference

Concept	Description
Handler Interface	Implement RequestHandler or RequestStreamHandler
Handler Method	handleRequest(Input input, Context context)
Deployment	Package code and dependencies as a jar file
Handler Name	Format: ClassName::methodName
Java Versions Supported	Java 8, Java 11, and Java 17

Key Takeaways

Implement AWS Lambda handler by using RequestHandler interface in Java.

Package your Java code and dependencies into a single jar for deployment.

Set the Lambda handler name correctly as ClassName::methodName.

Use supported Java versions (8, 11, or 17) to avoid runtime issues.

Use the Context parameter to access runtime info if needed.