Validate resource model if type mismatch

[wbingli]

Issue #, if available: #273

Description of changes:

This targets to solve the problem #273, which the Java plugin will fail sadly if the resource model type mismatch.e.g. needs a String but giving a List. Customer will see Internal Failure for such issue, it's pretty bad experience to debug such error, which needs cloudformation service support.

The whole fix is not trying to refactor the way we are doing validation now, but try to solve this specified problem. Therefore, the change and risk is minimal but result is what we expected.

Why change branch coverage to 0.80
The build failed due to branch coverage. But this change covers the code change, it's due to the whole all branch increase but other classes has low branch coverage.

Testing

Tested with LogGroup with an invalid property:

The RetentionInDays should an number not a list.

  LogGroup:
    Type: 'AWS::Logs::LogGroup'
    Properties:
      RetentionInDays:
        - 1

Got expected validation message:

2020-06-08 01:37:42 | AWS::Logs::LogGroup | LogGroup |   | CREATE_FAILED | Model validation failed (#/RetentionInDays: #: only 0 subschema matches out of 2 #/RetentionInDays: expected type: Number, found: JSONArray #/RetentionInDays: failed validation constraint for keyword [enum]) |

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[rjlohan]

What happens to exceptions thrown here, if the JSON payload is completely malformed and doesn't contain the fields you're expecting?

[wbingli]

1. The JSON payload completely malformed only if it invoked not by CloudFormation, which this case is really unlikely, or someone debug with local sam.

2. The above this.serializer.deserialize(input, typeReference) will throw different exception if the payload is malformed, it won't be catched by MismatchedInputException. We have unit test to cover the malformed input (0 bytes or invalid json), those passed as expected.

3. The only case I can think that rawInput.getJSONObject("requestData").getJSONObject("resourceProperties"); is null or malformed requestData, the whole payload HandlerRequest has MismatchedInputException in other fields. However, I don't think it's case we need to worry about.