How to Avoid java.util.ConcurrentModificationException in Your Hibernate Application

Описание: Learn effective strategies to prevent `java.util.ConcurrentModificationException` when working with Hibernate in Java applications, especially when fetching data to a JTable.
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This video is based on the question https://stackoverflow.com/q/64705189/ asked by the user 'Tufan' ( https://stackoverflow.com/u/14105168/ ) and on the answer https://stackoverflow.com/a/64714880/ provided by the user 'DuncG' ( https://stackoverflow.com/u/4712734/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Avoid java.util.ConcurrentModificationException in Your Hibernate Application

If you're developing with Hibernate and Java, you may encounter a frustrating issue known as java.util.ConcurrentModificationException. This error often arises when you're attempting to manipulate collections while iterating over them. In this guide, we'll dive into the problem that one of our readers faced while using Hibernate, and provide a clear and structured solution to avoid this exception in the future.

The Problem

A developer reached out for help with an issue occurring in their application involving Hibernate and JTable. The program was crashing with a ConcurrentModificationException when they added data to their MySQL table.

Code Overview

Here’s a simplified version of the relevant code snippet from the user's application:

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The issue occurs when the code retrieves a list of books from the database, which may accidentally lead to concurrent modifications of the books collection.

Understanding the Cause of the Exception

The core issue in the provided code is that the books list is reassigned from a result set, and then an attempt is made to add items back into that same books list while it’s still being modified. This leads to ConcurrentModificationException because the structure of the list is altered while it is being iterated over.

Here’s the offending part of the code:

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The Solution

To resolve this error, the key is to avoid modifying the collection while iterating over it. Instead of reassigning the books list, simply add the results directly to it using addAll.

Here's how to refactor the code:

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Key Changes Made:

Appending Results: Instead of replacing the original reference of books, we used addAll() to append results directly to the books list.

Avoid Redundant Looping: The loop that was attempting to iterate and add each book back to the same list was removed.

Conclusion

Encountering a java.util.ConcurrentModificationException can be a headache, but understanding the underlying cause is the first step to fixing it. By restructuring the way you handle list operations in your Java-Hibernate applications, you can sidestep this common pitfall.

By following the outlined steps and ensuring you don’t modify collections during iteration, your application will be more stable and reliable when working with dynamic data from a database.

If you have any further questions or issues regarding this exception or any other Hibernate-related queries, feel free to reach out. Happy coding!