PreparedStatement与Connection的“关闭”之间的关系？

Question

Javadoc says for .close() of the PreparedStatement says that it ..

Releases this Statement object's database and JDBC resources immediately instead of waiting for this to happen when it is automatically closed. It is generally good practice to release resources as soon as you are finished with them to avoid tying up database resources.

Calling the method close on a Statement object that is already closed has no effect.

Note:When a Statement object is closed, its current ResultSet object, if one exists, is also closed.

Consider the following scenario

    MyConnector databaseConnector = DBManager.instance().getConnector();

    Connection con = databaseConnector.getConnection(); // returns java.sql.Connection
    PreparedStatement pstmt = null;

    try {
        pstmt = con.prepareStatement("some query");
         ...
    } finally {  
        if (pstmt != null)
            pstmt.close();
    }

In this example, will pstmt.close() also close con ?

Answer 1

Closing a Statement doesn't close a Connection . However, closing a Connection will close a Statement .

Think of it like so:

• Connection -> creates and automatically closes -> Statement
• Statement -> creates and automatically closes -> ResultSet

So closing a Connection will automatically close any Statement s and any ResultSet s it contains.

However, it's still considered best practice to close all three manually ( ResultSet followed by Statement followed by Connection ) if possible.

Answer 2

Note: When a Statement object is closed, its current ResultSet [but not Connection] object, if one exists, is also closed.

It wont close connection, it just closes resultset object.

Answer 3

If you are using Java 7 and try-with-resources you don't need to worry about closing the connection or any of the Statement or ResultSet .

try (Connection conn = databaseConnector.getConnection();
     PreparedStatement pstmt = conn.prepareStatement("some query")) {
    ...
} catch (Exception e) {
    ...
}