Скачать или смотреть How to Select Data from a Text File and Print into Different Text Files in Java

A step-by-step guide to efficiently filter and save data from a text file into multiple text files using Java. Learn how to correct common mistakes in file handling and improve your code.
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This video is based on the question https://stackoverflow.com/q/71424257/ asked by the user 'Shawzz' ( https://stackoverflow.com/u/17695051/ ) and on the answer https://stackoverflow.com/a/71425605/ provided by the user 'Ernesto López' ( https://stackoverflow.com/u/18356893/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Filtering and Saving Employee Data in Java

In this post, we’ll explore how to select data from a text file and save it into different text files based on specific criteria. This technique is particularly useful for organizing data and managing employee records.

The Problem

Imagine you have an employees.txt file with the following structure:

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

You need to filter employees based on their IDs:

Lines starting with 18 should go to employees18.txt

Lines starting with 19 should go to employees19.txt

Lines starting with 20 should go to employees20.txt

However, if you only see the last entry being written to the respective text files when running your code, then there's an issue with how file writing is handled.

Understanding the Error

The main issue in your current approach is that for every line being processed, you are creating a new BufferedWriter instance. This results in every new write operation overwriting the previous content of the file. Instead, you need to open the files once, write to them during the loop, and close them after processing all lines.

The Solution

Step 1: Open Files Before Iterating

First, we should create and open our BufferedWriter instances before entering the loop where we read the employees.txt file. Here’s how to do it:

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

Step 2: Iterate and Write to Files

Next, we will loop through the lines in the employees.txt file and write the lines to the corresponding files as per their prefixes:

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

Step 3: Close the Files

Once all lines have been processed, it is essential to close the files to ensure that all data is properly flushed and saved:

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

Complete Code Example

Here’s the complete and improved version of your original code:

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

Conclusion

By adopting the practices mentioned, you should be able to successfully filter data from a text file into multiple files without overwriting previous entries. Proper file handling not only dictates functionality but also improves efficiency and reliability in data management.

Now you can run your Java program, and it should work perfectly, filling employees18.txt, employees19.txt, and employees20.txt with the correct entries as expected.

Happy coding!