Java `finally` block execution guarantee?

Java's finally Block: Guaranteed Execution?

Yes, a finally block in Java almost always executes. It's designed for cleanup actions (closing resources, releasing locks), ensuring these happen regardless of exceptions.

Exceptions: The only time a finally block might not execute is if the JVM crashes (OutOfMemoryError, StackOverflowError, etc.) before reaching it or if the finally block itself throws an uncaught exception that's not handled in the outer scope.

Example:

public void myMethod() {
  try {
    // Some code that might throw an exception
    int result = 10 / 0; 
  } catch (ArithmeticException e) {
    System.out.println("Arithmetic Exception caught: " + e.getMessage());
  } finally {
    System.out.println("Finally block executed!");
  }
}

Even with the division by zero, "Finally block executed!" prints.

Spring Boot Relevance: In Spring Boot, finally is crucial for releasing resources like database connections or file handles managed by @Autowired components, preventing leaks. Use it within @Transactional methods to ensure resources are properly released whether the transaction commits or rolls back.

Best Practice: Always use finally for resource cleanup within try-catch-finally blocks to enhance application robustness and prevent resource exhaustion. Prefer using try-with-resources (Java 7+) for simpler resource management in many cases.

try (Connection connection = DriverManager.getConnection(...)) {
    // Database operations
} catch (SQLException e) {
    //Handle exception
} // finally block not needed here as resources are automatically closed