Lambda is not recognizing the .jar file inside the .zip folder.

Question

I am trying to create a lambda function via CDK as below. Inside code(Code.fromAsset()) option, if I put "lambda-package.zip" which has the jar file. I am getting an exception class not found exception.(Class not found: com.videostore.amazon.lambdas.S3Handler: java.lang.ClassNotFoundException; java.lang.ClassNotFoundException: com.videostore.amazon.lambdas.S3Handler).

But if I put "target/amazon-0.0.1-SNAPSHOT.jar" in code(Code.fromAsset()), it works fine.

I want to use mediainfo binary file along with the .jar, so I am trying to package the 2 files into a .zip. 
Please help me fix this..

Function s3Handler = Function.Builder.create(this, "VideoStoreCDKAPP-S3Handler")
                .functionName("VideoStoreCDKAPP-S3Handler")
                .runtime(Runtime.JAVA_17)
                .handler("com.videostore.amazon.lambdas.S3Handler::handleRequest")
                .timeout(Duration.seconds(15))
                .memorySize(512)
                .code(Code.fromAsset("lambda-package.zip"))
                .environment(Map.of("TABLE_NAME", table.getTableName(),"REGION", "ap-south-1"))
                .role(lambdaExecutionRole)
                .build();

re:Post Agent · Accepted Answer

The issue you're experiencing is related to how Lambda loads Java classes from deployment packages. When you use a .zip file as your deployment package, Lambda expects a specific structure for Java applications.

When you provide just the JAR file directly (`target/amazon-0.0.1-SNAPSHOT.jar`), Lambda can find your handler class because it knows how to load classes from a JAR file. However, when you package your JAR inside a .zip file, Lambda doesn't automatically know to look inside the JAR for your handler class.

For Java Lambda functions deployed with a .zip file, you need to follow a specific structure:

1. Your compiled Java classes should be at the root of the .zip file, or
2. Your JAR files should be in a `/lib` directory within the .zip file

To fix your issue, you have two options:

Option 1: Extract the contents of your JAR file and place them at the root of your .zip file along with your mediainfo binary.

Option 2: Create a .zip file with the following structure:
```
/lib/amazon-0.0.1-SNAPSHOT.jar  (your JAR file goes here)
/mediainfo  (your binary file)
```

Lambda will automatically load classes from JAR files in the `/lib` directory. This way, you can include both your Java code and the mediainfo binary in the same deployment package.

Make sure the files have the correct permissions (644 for non-executable files and 755 for directories and executable files) before creating the .zip file.  
**Sources**  
[Deploy Java Lambda functions with .zip or JAR file archives - AWS Lambda](https://docs.aws.amazon.com/lambda/latest/dg/java-package.html)  
[unable to upload zip folder from s3 to aws lambda | AWS re:Post](https://repost.aws/questions/QUH3pdeNADTQWfAXbpHWGZHQ/unable-to-upload-zip-folder-from-s3-to-aws-lambda)  
[Unable to open file(s) uploaded as a zip file of a lambda function | AWS re:Post](https://repost.aws/questions/QUqBhJ8KoCQ8K-0G4J4Grjvg/unable-to-open-file-s-uploaded-as-a-zip-file-of-a-lambda-function)

Lambda is not recognizing the .jar file inside the .zip folder.

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