Commit and Rollback Operations in JDBC

Commit and rollback operations in JDBC are essential for managing database transactions. A transaction is a logical unit of work that consists of multiple database operations. The commit operation makes all the changes within a transaction permanent, while the rollback operation undoes the changes and restores the database to its previous state. This tutorial will guide you through the process of performing commit and rollback operations in JDBC.

Step 1: Establish a Connection

To perform commit and rollback operations, you need to establish a connection to the database using the appropriate JDBC driver and connection URL.

Connection connection = DriverManager.getConnection(url, username, password);
  

Step 2: Disable Auto-Commit

By default, JDBC operates in auto-commit mode, where each SQL statement is treated as a separate transaction and automatically committed to the database. To perform commit and rollback operations, you need to disable auto-commit mode by calling the Connection.setAutoCommit(false) method.

connection.setAutoCommit(false);
  

Step 3: Perform Database Operations

Within a transaction, you can perform multiple database operations such as insertions, updates, and deletions. These operations are grouped together and can be committed or rolled back as a single unit of work.

Statement statement = connection.createStatement();
statement.executeUpdate("INSERT INTO employees (id, name) VALUES (1, 'John')");
statement.executeUpdate("UPDATE employees SET salary = 5000 WHERE id = 1");
  

Step 4: Commit or Rollback the Transaction

After executing the desired database operations, you can choose to commit the transaction or rollback the changes.

connection.commit(); // Commit the transaction
// or
connection.rollback(); // Rollback the transaction
  

Common Mistakes with Commit and Rollback Operations:

• Forgetting to disable auto-commit mode before starting a transaction
• Not properly handling exceptions and leaving the connection in an inconsistent state
• Performing commit or rollback operations without executing any database operations
• Committing a transaction prematurely without verifying the desired changes

Frequently Asked Questions:

1. Q: What happens if I don't explicitly commit or rollback a transaction?

   A: If you don't explicitly commit or rollback a transaction, the changes made within the transaction will not be saved to the database. However, some databases may automatically rollback the transaction when the connection is closed.

2. Q: Can I perform multiple commits within a single transaction?

   A: No, a transaction can only have a single commit operation. Once a commit is performed, the changes become permanent, and subsequent commits are not allowed.

3. Q: Can I perform a rollback operation after a commit?

   A: No, once a commit is executed, the changes are permanently saved, and a rollback operation cannot undo them. The purpose of rollback is to revert the changes made within a transaction before they are committed.

Summary

Commit and rollback operations are crucial for managing database transactions effectively in JDBC. By disabling auto-commit mode, performing the necessary database operations within a transaction, and choosing to commit or rollback, you can ensure data consistency and integrity. This tutorial explained the steps involved in performing commit and rollback operations and highlighted common mistakes to avoid. Understanding and using commit and rollback operations correctly will help you build reliable and robust database applications.