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 afinally block.

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

Example¶

In the following example, the resourcesstmt andrs are opened but not closed.

publicclassCloseSql{publicstaticvoidrunQuery(Connectioncon,Stringquery)throwsSQLException{Statementstmt=con.createStatement();ResultSetrs=stmt.executeQuery(query);while(rs.next()){// process result set}}}

In the following example, the resourcesstmt andrs are declared within atry-with-resources block and are thus closed implicitly.

publicclassCloseSqlGood{publicstaticvoidrunQuery(Connectioncon,Stringquery)throwsSQLException{try(Statementstmt=con.createStatement();ResultSetrs=stmt.executeQuery(query)){while(rs.next()){// process result set}}}}

Note that theConnection 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.