Скачать или смотреть Resolving Connection has already been closed Error in PostgreSQL JDBC Connection

A guide to fixing the connection issues with PostgreSQL DB using JDBC, including best practices for managing resources and exception handling.
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This video is based on the question https://stackoverflow.com/q/64649507/ asked by the user 'GrigoryKrasovsky' ( https://stackoverflow.com/u/14565141/ ) and on the answer https://stackoverflow.com/a/64649653/ provided by the user 'rzwitserloot' ( https://stackoverflow.com/u/768644/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Resolving Connection has already been closed Error in PostgreSQL JDBC Connection

Connecting to a PostgreSQL database using Java’s JDBC can sometimes come with its own set of challenges. One common issue developers encounter is the dreaded Connection has already been closed error. In this guide, we'll explore the reasons behind this error and provide a structured solution to resolve it effectively. Let's break down the problem and the steps you can take to fix it.

Understanding the Issue

In the code provided, a connection is established to the PostgreSQL database. However, when attempting to execute multiple SQL commands in succession, an error arises indicating that the connection has already been closed. This typically occurs because the connection is being prematurely closed after the first command is executed, rendering the connection unusable for subsequent commands.

Example Code Breakdown

Here's the key part of the provided code that demonstrates the issue:

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By closing the connection within the executeSQL method, any subsequent attempts to use that connection result in a failure, leading to the error being logged.

Steps to Resolve the Issue

1. Change Connection Lifecycle Management

The first step in resolving the error is to change how connections are managed within your application. Instead of closing the connection within the executeSQL method, the connection should be closed back in the main method or wherever it is created. This way, it can remain open while multiple SQL commands are executed.

Revised Code Example:

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2. Use Traditional Looping Instead of ForEach

Using the forEach method can create complications related to exception handling, especially with checked exceptions like SQLException. Instead, consider using a traditional loop. This simplifies exception handling and allows the use of a simple try-catch block.

Revised SQL File Execution Method:

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3. Handle Exceptions Properly

Effective exception handling is crucial for developing robust applications. Instead of just logging errors, aim to provide meaningful feedback. You can propagate exceptions up the call stack, which allows for better error management.

Updated Exception Handling:

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Conclusion

By keeping the connection open for the entire duration of your SQL commands and changing your approach to looping and exception handling, you can resolve the Connection has already been closed error effectively. Adopting these practices not only solves current issues but also enhances the maintainability and reliability of your code moving forward.

In a nutshell, always ensure:

Resources are managed effectively, and those that create connections also manage their closure.

Use traditional loops for handling rows of SQL to simplify error handling.

Handle exceptions gracefully and propagate them where necessary.

By following these guidelines, your connection to PostgreSQL using JDBC should now work seamlessly!