How to Avoid \'Operation not allowed after ResultSet closed\' in Java JDBC MySQL?

Handling ResultSet Closure in Java JDBC MySQL Connections

When working with MySQL databases using Java JDBC, it's essential to manage the closing of ResultSets properly to avoid the error: "Operation not allowed after ResultSet closed." This error occurs when you attempt to perform operations on a closed ResultSet, leading to unexpected behavior and incorrect query results.

Understanding the Issue

In the provided code, the exception is triggered in the MySQLDonation class within the while (results.next()) loop. The actual cause is that the same Statement object (statement) is used for both the SELECT query (to retrieve the donations) and the subsequent DELETE query (to remove the processed donation record).

Solution: Create a New Statement for Each Query

To resolve the issue, you must create a new Statement object each time you execute a query. This ensures that the previous ResultSet is not automatically closed by a subsequent query execution. Here are the changes to the MySQLDatabase class:

public ResultSet query(String query) throws SQLException {
    Statement statement = connection.createStatement();
    if (query.toLowerCase().startsWith("select")) {
        return statement.executeQuery(query);
    } else {
        statement.executeUpdate(query);
    }
    statement.close(); // Optional: May not be necessary as Resources are auto-closed
    return null;
}

Additional Considerations

Besides managing Statement objects, it's crucial to follow best practices for handling JDBC resources to prevent memory leaks and ensure proper database connection handling. Here are some additional tips:

• Use try-with-resources blocks for automatic resource management.
• Initialize and close Statement, ResultSet, and Connection objects within a try-catch block.
• Handle exceptions gracefully and release resources even in the presence of exceptions.

Conclusion

By creating a new Statement for each query and adhering to resource management best practices, you can avoid the "Operation not allowed after ResultSet closed" error and ensure the correct execution of your MySQL queries. Remember to continually optimize your database interactions for efficiency and reliability.

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