Jackson uses a class called ObjectMapper as its main entrypoint. It’s very tempting to mix Jackson code with application logic which can make reading and testing your code hard.Your code that works with Jackson’s tree model objects can be verbose.Jackson can do some implicit and explicit type coercions for you.You will not need to create any extra classes of your own.These objects are called things like JsonNode or JsonArray and are provided by Jackson. Jackson allows you to read JSON into a tree model: Java objects that represent JSON objects, arrays and values. This is common in JSON documents as it avoids precision issues on very small or very large numbers. We also need to be aware that speeds are stored as strings not numbers, eg "kilometers_per_second": "6.076659807". What is the name and speed of the fastest Near Earth Object? Again, we need to loop through but this time the objects are more complex.How many of them are potentially hazardous? We need to loop through each NEO and check the is_potentially_hazardous_asteroid key, which is a boolean value in the JSON.How many are there? This can be found by looking at the element_count key at the root of the JSON object.I’ll be showing how answer the following questions in Java: The NeoWS Feed API request returns a list of all asteroids whose closest approach to Earth is within the next 7 days. This API is maintained by the brilliantly-named SpaceRocks team. To find some example data I read Tilde’s recent post 7 cool APIs you didn’t know you needed, and picked out the Near Earth Object Web Service API from the NASA APIs. You can see the Jackson dependency for the examples here. In this post I will be using Jackson, and there is an equivalent post with Gson code examples here. The most popular Java libraries for working with JSON, as measured by usage in maven central and GitHub stars, are Jackson and Gson. Other Java Libraries for working with JSON I’ll compare three different approaches:Īll the code used in this post is in this repository. In this post I’ll pick a fairly complex JSON document and three queries which I want to make using Jackson. Jackson is one of the most popular Java JSON libraries, and is the one I use most frequently. Despite its shortcomings, JSON is the most common format for APIs on the web so we need a way to work with it in Java. JSON doesn’t have type definitions and is lacking some features which we would like - there’s only strings, numbers, booleans and null, so to store other types (like dates or times) we’re forced to use a string-based convention. If you’re working in a statically-typed language like Java then dealing with JSON can be tricky.
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