Скачать или смотреть How to Map CSV to an Object with a List Using CsvMapper in Java

Discover how to efficiently map CSV files to Java objects, including lists of objects, using CsvMapper. Learn effective strategies and alternative solutions for better outcomes.
---
This video is based on the question https://stackoverflow.com/q/68472732/ asked by the user 'kaptan' ( https://stackoverflow.com/u/6286622/ ) and on the answer https://stackoverflow.com/a/68499953/ provided by the user 'kaptan' ( https://stackoverflow.com/u/6286622/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: How to map a CSV to Object with List using CsvMapper?

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Mapping a CSV to an Object with a List in Java

When developing applications with Java, you may often find the need to load data from CSV files into your objects. This can become challenging, especially when your objects contain fields that are lists or complex types, like a list of hobbies. In this guide, we'll explore how to use CsvMapper to map a CSV file to an object, particularly focusing on the situation where you want to store a list of fields in your object. We'll cover both the common approach with CsvMapper as well as an alternative using Apache Commons CSV. Let's get started!

Understanding the Problem

Let's take a look at the CSV file structure you'll be working with. For this example, assume you have a CSV file that looks like this without headers:

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

This file contains the following fields:

Field 1: name

Field 2: gender

Field 3: hobby (comma-separated list)

Field 4: relation

You want to map this CSV content into a User object defined as follows:

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

Attempting to Use CsvMapper

In your attempts to read the CSV file using CsvMapper, you initially constructed a schema that looked like this:

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

You tried reading the CSV file into a Map using a MappingIterator, but faced challenges when trying to map it directly to your User object. This is a common scenario that many developers encounter when dealing with complex object structures in CSV.

Finding a Solution with Apache Commons CSV

Instead of using CsvMapper, there is a more straightforward way to tackle this problem using Apache Commons CSV. This library offers a simple and effective approach to parsing CSV files. Here's how you can implement the desired functionality using this library.

Step-by-Step Implementation

Include the Library: First, make sure to include Apache Commons CSV in your project. You can add the following dependency in your pom.xml if you are using Maven:

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

Reading the CSV File: Use the following code snippet to read the CSV file and map its contents into a list of User objects:

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

Explanation of the Implementation

CSVParser: We create a CSVParser that reads from the CSV file using the specified delimiter (;) for separating the fields. We also set the parser to ignore empty lines.

Iterating Through Records: We go through each CSVRecord parsed from the file, fetching the relevant fields and converting them into appropriate types.

Creating User Objects: For each record, we fetch the data and invoke the User.from() method to create and store the User object in our list.

Conclusion

Using Apache Commons CSV simplifies the process of reading and mapping CSV files compared to CsvMapper, especially when handling complex objects that involve lists. By following the steps outlined above, you can effectively transform CSV data into Java objects with list fields, enhancing your application's data handling capabilities.

If you're facing challenges in mapping CSV to objects or have suggestions for improvements, feel free to share your thoughts in the comments below! Happy coding!