Generate a Java Class From JSON

Generate a Java Class From JSON

The ability to generate a Java class from JSON is an incredibly useful tool for any Java programmer. In this tutorial, you will learn how to generate a Java class from a JSON string or document. By the end of this tutorial, you should be able to create your own Java classes from JSON input.

What Is JSON?

JSON (JavaScript Object Notation) is an open-standard format that uses human-readable text to transmit data objects consisting of attribute–value pairs. It is the most common data format used for data interchange on the web, and is a lightweight alternative to XML.

How To Generate a Java Class From JSON

To generate a Java class from JSON, you need a JSON parser library. There are several popular libraries available, such as Jackson,Gson, and JSonSchema2Pojo. Each of these libraries works differently, but the basic concept remains the same. You will give the library the JSON string or file, and it will generate a corresponding Java class for you.

Here's an example of generating a class with Jackson:

ObjectMapper objectMapper = new ObjectMapper(); 
Class<?> clazz = objectMapper.getTypeFactory().constructFrom(json);

If you have a schema file, you can use JSonSchema2Pojo to generate the class instead of using the ObjectMapper. This is much faster, as the schema file is less verbose than the JSON string. Here's an example of how to use JSonSchema2Pojo to generate the class:

JCodeModel codeModel = new JCodeModel();
FileReader reader = new FileReader("schema.json"); 
JSonSchema2Pojo.generate(codeModel, "MyClass", "com.example.classes", reader);
codeModel.build(new File("output"));

Now you have generated a Java class from your JSON document! You can customize the generated class to fit your needs. For example, you can replace the generic getters and setters with methods that parse the JSON values into types that make more sense in your application.

Conclusion

In this tutorial, you learned how to generate a Java class from a JSON string or document. By using one of the popular JSON parsing libraries, you can easily transform a JSON document into a Java class. If you have a schema file, you can use JSonSchema2Pojo to generate the class much faster. Now you can customize the generated class to fit your specific application needs.