Read CSV Files in Java Using Scanner 📄

Discover how to efficiently read CSV files in Java using the `Scanner` class, handling missing data, and improve your code with practical examples.
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This video is based on the question https://stackoverflow.com/q/66490381/ asked by the user 'gretta' ( https://stackoverflow.com/u/14819996/ ) and on the answer https://stackoverflow.com/a/66490474/ provided by the user 'ahll' ( https://stackoverflow.com/u/3114566/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Read CSV Files Using Scanner in Java: A Step-by-Step Guide

Reading CSV files is a common requirement in software development, especially for data processing and analysis. Java provides several ways to handle CSV files, and one of the methods is using the Scanner class. In this guide, we’ll dive into how you can efficiently read a CSV file in Java and manage potential issues along the way.

Understanding the Problem

Suppose you're tasked with reading data from a CSV file structured like this:

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The goal is to load this data into a list that can hold four fields:

Date (of type DateTime)

Europe Cases (of type int)

Asia Cases (of type int)

Africa Cases (of type int)

However, there are a few challenges to consider. First, you want to skip the header row, and second, you need to handle any missing data gracefully to prevent runtime errors.

Solution to the Problem

Step 1: Clearing the Existing List

Before you start reading new records, it’s good practice to clear any existing data from your list. You can do this by invoking the clear() method on your list that holds the records.

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Step 2: Setting Up the Scanner

The core of reading a CSV file in Java involves using the Scanner class to parse each line of the file. Here’s how you can initialize the Scanner:

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Step 3: Reading and Processing Each Line

In a loop, read each line after the header, split the line by commas, and then check for data integrity. You can use a simple check to ensure that no fields are missing:

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Step 4: Parsing Data and Creating Records

Once you ensure that the data is clean, you can parse the values and create CaseRecord objects. Here’s how:

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Summary

To summarize, reading a CSV file using the Scanner class in Java involves:

Clearing the existing records list.

Setting up a scanner to read the file and skipping the header line.

Processing each line by validating data integrity.

Creating objects from the data and adding them to the list.

Alternative Approach with Lambda Expressions

If you're looking for a modern approach, consider using Java Streams to read the CSV file. By using lambda expressions, the code can be more succinct:

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Using Streams can make your code cleaner and enhance readability, especially when dealing with larger datasets.

Conclusion

Whether you choose the traditional method with Scanner or the modern approach with Java Streams, you now have the tools to efficiently read CSV files in Java while gracefully handling potential issues. Happy coding!