Скачать или смотреть How to Use JsonPath to Filter Nested Arrays in Java

Learn how to effectively filter nested arrays using `JsonPath` in Java to extract specific values from complex JSON structures.
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Mastering JsonPath: Filtering Nested Arrays in Java

JSON data structures can be complex, especially when they contain nested arrays and objects. When you need to extract specific values from these intricate structures, libraries like JsonPath come in handy. In this post, we will tackle a common problem when filtering nested arrays in JSON using JsonPath, and provide a clear solution.

The Challenge

Imagine you have a JSON object that contains nested arrays. In a particular case, you want to retrieve the value of case_identifier__c where source__c contains the value nci__c from the following JSON structure:

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

However, when you try the following JsonPath expression, it returns an empty value:

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

This can be frustrating! So, what’s the problem here?

Understanding the Problem

Why the Expression Fails

The issue with the initial JsonPath expression lies in the way the in operator is utilized:

Left Side: Represents the array source__c.

Right Side: Represents an array of values being checked for inclusion.

The in operator expects the left side to be a single value (a single source from the source__c array), rather than the entire array itself.

The Correct Approach

To correctly filter and retrieve the desired value, a slight adjustment to your JsonPath expression is necessary. Instead of checking if the array contains the value directly, you should use the correct syntax to evaluate the filter condition using the in operator correctly.

The Solution

Updated JsonPath Expression

Here is the corrected JsonPath expression:

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

Explanation of the Expression

$..case_version__v.case_number__vr.none2b_references__cr: Starts from the root and navigates through the JSON hierarchy to reach the desired array.

[?('nci__c' in -.source__c)]: This is the filter condition, which checks if 'nci__c' is found in the source__c array. Here, -.source__c refers to the current context where the filter is applied.

.case_identifier__c: Finally, it selects the case_identifier__c field from the filtered elements that satisfy the condition.

Expected Result

Using this corrected expression, the desired value THIS-IS-MINE will be correctly retrieved from the JSON structure.

Conclusion

Filtering nested arrays can be intricate, but with the right understanding and adjustments to JsonPath syntax, you can efficiently extract the information you need. By ensuring the use of the in operator is appropriate, you'll avoid common pitfalls and achieve the desired results seamlessly.

Feel free to experiment with your JSON data and JsonPath expressions for various filtering scenarios. Happy coding!