Rule Definition
A frequent issue when dealing with database resource is resource leak. This mainly comes from an incorrect code that miss to close the connection in any cases. Incorrect resource management is a common source of failures in production applications, with the usual pitfalls being database connections and file descriptors remaining opened after an exception has occurred somewhere else in the code. This leads to application servers being frequently restarted when resource exhaustion occurs, because operating systems and server applications generally have an upper-bound limit for resources.

Remediation
You can: - close the resource in a finally block (only explicit closing is considered valid) - or annotate this resource with @Cleanup annotation (lombok.Cleanup) - or use the try with resource to declare the resource that must be closed (available in java 7) - or use Spring JDBC Template that open and close the connection for you (http://static.springsource.org/spring/docs/3.2.x/spring-framework-reference/html/jdbc.html) - or use CDI with @Dispose annotation

Violation Code Sample

String connectionURL = 'jdbc:mysql://localhost:3306/myDB';
Connection connection = null;
Statement st = null;
ResultSet rs = null;
try {
    Class.forName('com.mysql.jdbc.Driver').newInstance();
    connection = DriverManager.getConnection(connectionURL, 'root', 'admin');
    st = connection.createStatement();
    rs = st.executeQuery('Select * from EMPLOYEE_SALARIES');
    while (rs.next()) {
        System.out.println('EMPLOYEE_NAME/EMPLOYEE_SALARY');
        System.out.println(rs.getString(1) + '/' + rs.getString(2));
    } 
    rs.close(); 
    st.close();
    connection.close();
} catch (Exception ex) {
    ex.printStackTrace();
}  // VIOLATION, rs, st and connection must be closed in a finally

Fixed Code Sample

with finally
~~~~~~~~~~~~
String connectionURL = 'jdbc:mysql://localhost:3306/myDB';
Connection connection = null;
Statement st = null;
ResultSet rs = null;
try {
    Class.forName('com.mysql.jdbc.Driver').newInstance();
    connection = DriverManager.getConnection(connectionURL, 'root', 'admin');
    st = connection.createStatement();
    rs = st.executeQuery('Select * from EMPLOYEE_SALARIES');
    while (rs.next()) {
        System.out.println('EMPLOYEE_NAME/EMPLOYEE_SALARY');
        System.out.println(rs.getString(1) + '/' + rs.getString(2));
    }
} catch (Exception ex) {
    ex.printStackTrace();
} finally { // FIX
    try {
        if (rs != null && !rs.isClosed()) {
            rs.close();
        }
        if (st != null && !st.isClosed()) {
            st.close();
        }
        if (connection != null && !connection.isClosed()) {
            connection.close();
        }
    } catch (SQLException ex) {
        ex.printStackTrace();
    }
}

with Java 7
~~~~~~~~~~~~~~
String connectionURL = 'jdbc:mysql://localhost:3306/myDB';
try ( // FIX
    Connection connection =
        DriverManager.getConnection(connectionURL, 'root', 'admin');
    Statement st = connection.createStatement();
    ResultSet rs = st.executeQuery('Select * from EMPLOYEE_SALARIES');
) {
    Class.forName('com.mysql.jdbc.Driver').newInstance();
    while (rs.next())
    {
        System.out.println('EMPLOYEE_NAME/EMPLOYEE_SALARY');
        System.out.println(rs.getString(1) + '/' + rs.getString(2));
    }
}

with annotation @Cleanup
~~~~~~~~~~~~~~~~~~~~~~~~
String connectionURL = 'jdbc:mysql://localhost:3306/myDB';
@Cleanup Connection connection = null; // FIX
@Cleanup Statement st = null; // FIX
@Cleanup ResultSet rs = null; // FIX

Class.forName('com.mysql.jdbc.Driver').newInstance();
connection = DriverManager.getConnection(connectionURL, 'root', 'admin');
st = connection.createStatement();
rs = st.executeQuery('Select * from EMPLOYEE_SALARIES');
while (rs.next()) {
    System.out.println('EMPLOYEE_NAME/EMPLOYEE_SALARY');
    System.out.println(rs.getString(1) + '/' + rs.getString(2));
}

with CDI annotation
~~~~~~~~~~~~~~~~~~~~
@Produces @RequestScoped
Connection connect(User) {
   return createConnection(user.getId(), user.getPassword())
}

void close (@Disposes Connection connection) {
   connection.close();
}

http://www.java7developer.com/blog/?p=24 http://static.springsource.org/spring/docs/3.2.x/spring-framework-reference/html/jdbc.html http://projectlombok.org/features/Cleanup.html