Cannot pass string to AWS Lambda using InvokeRequest.withPayload() method - json

Question

I have a lambda function that accepts a String as an input parameter. When running the lambda function I get the following error:
Can not deserialize instance of java.lang.String out of START_OBJECT token\n
This is what my code too call it looks like:
InvokeRequest request = new InvokeRequest();
final String payload = "";
request.withFunctionName(FUNCTION_NAME).withPayload((String) null);
InvokeResult invokeResult = lambdaClient.invoke(request);
Assert.assertEquals(new String (invokeResult.getPayload().array(), "UTF-8"), "Success");
And this is what my handler looks like:
public String handleRequest(String s, Context context) {}
Now the contents of the string don't matter, it could be null it could be anything. I don't use the input. The obvious solution is to remove it, but because of an annotation generator i'm using I can't do that. I've tried a ByteBuffer input, String, empty String, JSON String {\"s\":\"s\"} but nothing seems to work. I believe I need to pass in a string (i.e no {}). But since I'm using InvokeRequest I don't believe I can do that. Any suggestions would be greatly appreciated.

Answer 1

It works by passing a JSON valid String.
String payload = "{ \"subject\" : \"content\"}";
request.withFunctionName(functionName)
.withPayload(payload);
At the receiving end you have to map it from Object to String again if that's what you want. Here I used Jackson ObjectMapper for this.
ObjectMapper objectMapper = new ObjectMapper();
try {
String payload = objectMapper.writeValueAsString(input);
} catch (JsonProcessingException e) {
e.printStackTrace();
}