How to Effectively Use Java 8 Streams to Sum Values from a List of Objects

Learn how to efficiently calculate the total of specific field values using Java 8 Streams with a practical example based on JSON data.
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How to Effectively Use Java 8 Streams to Sum Values from a List of Objects

In modern Java development, particularly with the introduction of Java 8, the Stream API has become a go-to solution for processing collections of data. Whether it's filtering, mapping, or performing calculations, streams provide a powerful, concise way to work with data. Today, we’ll tackle a common problem: how to sum specific field values from a nested JSON-like structure using Java 8 Streams.

The Problem

Imagine you have a JSON request similar to the one shown below, and your goal is to calculate the total of the "cols"."value" field wherever the "cols"."name" is "tran_amt":

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

At first glance, one might think to filter through these records in the first table’s entries to pull the values, but as you might have encountered, a naive approach may only retrieve values from the first object in the collection, leaving out valid entries that should be counted.

The Solution

To solve the problem of summing the specified values correctly, you can use the following approach, which utilizes the Stream API effectively:

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

Breakdown of the Solution

Accessing Tables:

Start with the getTables() method which provides access to the list of tables in the request.

Stream for Each Table:

Use stream() to convert the List of tables into a Stream.

Flatten the Records:

Flatten the Columns:

Filtering for Specific Column Names:

Converting Values to Integer:

Summing the Values:

Finally, sum() aggregates all filtered and converted integer values into a total.

Conclusion

Using Java 8 Streams can streamline data processing tasks such as summing values in complex collections. By carefully chaining stream operations, you can efficiently access and manipulate nested data structures like in our JSON example. This method not only enhances code readability but also boosts performance by leveraging parallel processing when needed.

With these tools and a solid understanding of how to traverse nested data using streams, you'll be well-equipped for any similar challenges in your Java development journey. Happy coding!