Recommendation¶

Ensure that the resource is always closed to avoid a resource leak. Note that, because of exceptions, it is safest to close a resource in a finally block.

For Java 7 or later, the recommended way to close resources that implement java.lang.AutoCloseable is to declare them within a try-with-resources statement, so that they are closed implicitly.

Example¶

In the following example, the resources stmt and rs are opened but not closed.

public class CloseSql {
	public static void runQuery(Connection con, String query) throws SQLException {
		Statement stmt = con.createStatement();
		ResultSet rs = stmt.executeQuery(query);
		while (rs.next()) {
			// process result set
		}
	}
}

In the following example, the resources stmt and rs are declared within a try-with-resources block and are thus closed implicitly.

public class CloseSqlGood {
	public static void runQuery(Connection con, String query) throws SQLException {
		try (Statement stmt = con.createStatement();
				ResultSet rs = stmt.executeQuery(query)) {
			while (rs.next()) {
				// process result set
			}
		}
	}
}

Note that the Connection that is passed into the method is a long-lived object that was created elsewhere and therefore need not be closed locally. It should instead be closed by the code that created it or by a server shutdown procedure, as appropriate.

References¶

• IBM developerWorks: Java theory and practice: Good housekeeping practices.

• The Java Tutorials: The try-with-resources Statement.

• Common Weakness Enumeration: CWE-404.

• Common Weakness Enumeration: CWE-772.