Add more context to Exception or Error in Groovy - exception

Question

When I want just to add more context to any exception that has happened (including parsing errors and even out of memory) I write code as follows
try {
new JsonSlurper().parseText(response)
} catch (any) {
throw new IllegalStateException("Cannot parse response:\n$response", any)
}
This works fine, but I may end up with OutOfMemoryError being wrapped in IllegalStateException which doesn't sound right, as further there could be dedicated exception handling mechanism just for Error throwables.
Is there any way to just add more context to exception and still preserve its original type or category? I.e. when I get OOME, I want to rethrow Error, when I get some parsing exception, I want to rethrow some unchecked exception etc. And of course I don't want to do it manually for each category, as OOME is pretty unlikely and I don't want to produce special code for corner cases (while still I want to be technically correct).

Answer 1

You can definitely do this in groovy by using its metaprogramming features. In particular, for your case metaclasses provides everything you need. Using them you can dynamically add/attach a contextData object to the exception you want it to carry around:
private static void throwsEnhancedException() throws IOException {
try {
throwsBasicException()
} catch (IOException e) {
e.metaClass.contextData = "My context data"
throw e;
}
}
Then to retrieve this contextData in other parts of the code, just inspect the exception object like this:
private static void doSomethingWithContextData(Closure contextDataHandler) throws IOException {
try {
throwsEnhancedException();
} catch (IOException e) {
// RETRIEVE `contextData` FROM `e` OR NULL IF THE PROPERTY DO NOT EXIST
def contextData = e.hasProperty('contextData')?.getProperty(e)
// DO SOMETHING WITH `contextData`
contextDataHandler(contextData)
}
}
There I am using the argument contextDataHandler as a groovy Closure to handle contextData in a flexible manner.
The following is a full working demo of this:
import java.time.LocalDateTime
class ExceptionEnhancer {
static void main(String[] args) {
def logger = { println "${LocalDateTime.now()} - Context Data = [$it]" }
doSomethingWithContextData logger
}
private static void doSomethingWithContextData(Closure contextDataHandler) throws IOException {
try {
throwsEnhancedException();
} catch (IOException e) {
// RETRIEVE `contextData` FROM `e` OR NULL IF THE PROPERTY DO NOT EXIST
def contextData = e.hasProperty('contextData')?.getProperty(e)
// DO SOMETHING WITH `contextData`
contextDataHandler(contextData)
}
}
private static void throwsEnhancedException() throws IOException {
try {
throwsBasicException()
} catch (IOException e) {
e.metaClass.contextData = "My context data"
throw e;
}
}
public static void throwsBasicException() throws IOException {
throw new IOException();
}
}
Complete code on GitHub
Hope this helps.