Convert JSON String to List of Objects with Gson in Java

Описание: Learn how to easily convert a JSON string into a list of objects in Java using Gson. Understand the process, benefits of DTOs, and practical examples!
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Convert JSON String to List of Objects with Gson in Java

Handling JSON data is a common task in many Java applications, especially when dealing with APIs or data interchange formats. One of the popular libraries for parsing JSON in Java is Gson. In this guide, we'll tackle a specific issue: how to convert a JSON string to a list of objects using Gson, focusing on a practical example.

Understanding the Problem

Suppose you have a JSON string formatted as follows:

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You want to extract the data contained in the result key and convert it into a list of custom objects (of type MyCustomObj). The typical approach might look something like this:

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However, the standard fromJson usage above does not directly allow fetching data from a specific key like result. So how do we handle it? Let’s break down the solution!

Solution Steps

Step 1: Create a Data Transfer Object (DTO)

First, you need to define a DTO that describes the structure of your JSON response. This DTO helps Gson understand how to map the JSON fields to Java objects. In our case, you would create a main response class that encapsulates the result list:

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Here, we have:

A Response class that contains a list of MyCustomObject.

The MyCustomObject class has properties x and y.

Step 2: Parse the JSON Response

With the DTO defined, you can now easily parse the JSON string into the Response object:

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Step 3: Retrieve the List of Objects

Finally, to get your list of MyCustomObject instances, simply invoke the getResult() method on the Response object:

[[See Video to Reveal this Text or Code Snippet]]

Key Benefits of This Approach

Encapsulation: Using DTOs allows you to keep your JSON structure and Java data model in sync. This reduces complexity and the chance of runtime errors.

Maintainability: If the JSON structure changes, you only need to update your DTO, making your code more maintainable.

Clarity: This approach promotes clearer and more readable code by clearly defining how the data maps to your objects.

Conclusion

Converting a JSON string to a list of objects in Java using Gson is straightforward once you set up a proper DTO. By encapsulating your JSON response in a class and accurately defining its structure, you can effortlessly extract the information you need while maintaining clean and understandable code.

With this guide, you should now be able to parse JSON responses effectively in your Java applications. Happy coding!