Exception type hierarchy in thrift / java

Question

Is there a way of adding type hierarchy information to generated thrift exception types for Java.

I want to define some common set of exceptions, that people can reuse. It often happens that clients instead of handling individual exceptions, want to handle a group of exceptions. For example, lets say a java client wants to catch all bad requests and print the exception message. The client does not want to handle the individual exceptions like TooBigParamException, MissingParamException etc, but instead just wants to catch a parent of these: BadRequestException. Is there a way to to change the generated codes of TooBigParamException, MissingParamException etc to add an extends relationship?

I tried Facebook swift (Java -> Thrift conversion), but it looks like it does not work seamlessly with Apache thrift.

Answer 1

In its current state Apache Thrift does not support inheritance, neither with struct / union nor with exception . My guess would be that this is because there are languages out there where inheritance would be too complex to implement because it is not really part of the language.

One solution that comes to my mind is to convert the exceptions into structs, having only one Thrift exception and union the exception data into that one. The client side catches the "common" exception and re-raises whatever it is in that package.

struct OverflowError {
  1: double operator1
  2: double operator2
  3: string operation
}

struct DivByZeroError {
  1: double numerator
}

union AllTheErrors {
  1: OverflowError  over
  2: DivByZeroError  div0
  // more to come
}

exception MathError {
  1: AllTheErrors  theError
}


service ExceptionalCalculator {
  double Add(1: double arg1, 2: double arg2) throws (1: MathError mex)
  double Subtract(1: double arg1, 2: double arg2) throws (1: MathError mex)
  double Divide(1: double arg1, 2: double arg2) throws (1: MathError mex)
  double PriceOfDowJonesNextThursday() throws (1: MathError mex)
}

Involves quite a bit of work, but could be a solution.

Over there is a related discussion about protobuf , which may be helpful as well.

Answer 2

I found one decent solution. Though I would not say that there are no hacks in that.

When I began, there were only 2 options with me:

1. Write the Java code first, then I can generate the IDL using FB Swift, but the java types written by me, would not be compatible with Thrift as they would not contain the read() and write() methods required by Thrift.
2. Write the idl first, I can generate java classes from it. But they would not contain any type-hierarchy and also, they would be mutable. I do not prefer mutable objects.

I was able to workaround these problems, by combining the above 2. I first wrote the java exceptions and then generated IDL using swift. Then generated another version of java exceptions from idl. I used modelmapper to convert between my original java types and generated java types. My service-core uses the first version of exceptions and my service -thrift layer, converts them to their thrift version using modelmapper.