Best Way To Test For Correct JSON Serialization

I use the Jackson library with Java to serialize POJOs to JSON and vice versa. Let's say that I am running some tests where I am serializing an object and I know that the expected JSON string is {"firstName":"John", "lastName":"Doe"}. What is the best way to validate that my object serialized to the above string? Or better yet, what is the best way to validate that each of the fields is what I expect?

I have tried simply hard coding that string in and doing a comparison, but I have had cases where I serialize to JSON -> deserialize to POJO -> then serialize the deserialized POJO back to JSON again, and the fields are out of order. Then the string comparison fails even though all of the fields are correct.

Is there are better/different way to verify that my JSON string has the expected fields in it when testing?