Discovered something fun while testing my JSON representation and Oracle Java 7

[Glenn McAllister]

I've just started using dropwizard, so this may already be well known to the community; my apologies if I'm repeating common wisdom.

I started testing my json representation using the .asJson(), .fromJson(), and .jsonFixture() methods. Pretty straightforward, but nothing was working. It took me a little while to notice that the generated json was always putting the properties in random order. And that's when I remembered the pain our team just went through recently when we had to fix a bunch of badly written unit tests when we moved from Oracle JRE 1.6 to 1.7, where the test writer assumed that things put into a collection would come out of that collection in the same order, even though the interface does not guarantee that. In JRE 1.7 they really do randomize the iteration order.

The way I got around the problem (there are probably other, better ways, but I'm new to Jackson) was to use @JsonPropertyOrder to explicitly state the order in which I wanted the properties to be written out. This ensured my tests would pass because the normalized strings produced by the JsonHelpers methods now matched the stable order produced by Jackson.

At any rate, I wanted to put this out there in case any other newbie was caught scratching their head for a while like I was.

Glenn McAllister

[Dan Everton]

You can also modify the object mapper to sort properties alphabetically. Something like

    bootstrap.getObjectMapperFactory().enable(MapperFeature.SORT_PROPERTIES_ALPHABETICALLY);

Should result in all JSON output with keys in alphabetical order.

You might also need

    bootstrap.getObjectMapperFactory().enable(SerializationFeature.ORDER_MAP_ENTRIES_BY_KEYS);

To ensure that maps come out ordered as well.

Cheers,

Dan

[Glenn McAllister]

I'll give that a shot and see if that simplifies things, thanks.

Glenn

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