what is the ? on groovy variables?

I saw in some groovy code this:

trip.id?.encodeAsH开发者_如何学PythonTML()

What is the difference between using or not using "id?."?

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It checks if the object is null or not. Using it, you can prevent nullpointer exception.

If you use it, you should use it for the whole object (eg: trip.id?.otherstuff?.morestuff?.encodeAsHTML()

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It's called the "null-safe dereferencing operator". The difference is that if trip.id is null, instead of throwing a NullPointerException, it will return null as the result of the method call.

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It's the Groovy null-safe operator. It performs a null check before dereferencing the object. See more on Groovy Operators here.