我们如何在jdbc中使用prepare语句，因为它是一个接口

Question

In JDBC except DriverManager all are interfaces. How are we able to use the interfaces such as, PrepareStatement , Connection etc.?

Answer 1

The drivermanager returns a concrete implementation of the Connection . The concrete implementation of the Connection in turn returns a concrete implementation of the Statement . The concrete implementation of the Statement in turn returns a concrete implementation of the ResultSet . And so on.

Those concrete implementations are provided by the JDBC driver. To learn about the underlying implementation, do a

System.out.println(connection.getClass());

You'll see that it's not java.sql.Connection , but just the one provided by the JDBC driver used.

Interfaces are just there to define a contract the implementor has to adhere. This enables you to reuse the same JDBC code with different JDBC drivers without the need to rewrite the code (expect of maybe DB specific SQL queries, but that's not a Java/JDBC problem) whenever you'd like to reuse the same code on a different DB server.

Answer 2

DriverManager :

1. download the JDBC driver

2. put it in your JAVA projet

3. define path to the jar Driver in projet properties

Example of Connection :

public static void exampleOfConnection() {  
    try {
        /* How to instanciate a connection with a specific driver manager */
        Class.forName("org.sqlite.JDBC");
        Connection connectionDB = DriverManager.getConnection("jdbc:sqlite:~/workspace/POEC/Data/films.sqlite");
        connectionDB.setAutoCommit(false);

        /* Begin of statements */
        /* Here are use statements */
        /* End of statements*/

        connectionDB.commit();
        connectionDB.close();

    } catch (ClassNotFoundException | SQLException e) {
        e.printStackTrace();
    }
}

Example of Statement :

public static void exampleOfStatementTest(Connection conn) throws SQLException {
    String createFilmsTableQuery = "CREATE  TABLE  IF NOT EXISTS films" + "("
            + " filmId INTEGER PRIMARY KEY  AUTOINCREMENT  NOT NULL  UNIQUE ," + " filmTitle TEXT,"
            + " filmDirector TEXT," + " filmType TEXT," + " filmYear INTEGER " + ");";
    try (Statement statement = conn.createStatement()) {
        statement.execute(createFilmsTableQuery);
        statement.close();
    }
}

Example of PrepareStatement :

private static void exampleOfPrepareStatementTest(Connection conn) throws SQLException {
    String insertIntoFilmsPrepareStatementQuery = "INSERT INTO films "
            + "(filmTitle, filmDirector, filmType, filmyear) " + "VALUES (? ,? ,? ,? )";
    try (Statement st = conn.createStatement()) {
        PreparedStatement preparedStatement = conn.prepareStatement(insertIntoFilmsPrepareStatementQuery);
        preparedStatement.setString(1, "Jackie Brown");
        preparedStatement.setString(2, "Tarentino");
        preparedStatement.setString(3, "detective film");
        preparedStatement.setInt(4, 1997);
        int filmAddedQuantity = preparedStatement.executeUpdate();
        System.out.println(filmAddedQuantity + " Film(s) added");
        preparedStatement.close();
        st.close();
    }
}

Answer 3

The DriverManager (or DataSource ) is your starting point -- get the Connection etc. from it. You don't need to directly instantiate any of these.