我在使用JDBC连接池吗？

Question

我试图确定我是否实际上正在使用JDBC连接池。经过研究后，实现似乎太容易了。实际上比常规连接容易，所以我想验证一下。

这是我的连接类：

public class DatabaseConnection {

Connection conn = null;

public Connection getConnection() {

    BasicDataSource bds = new BasicDataSource();
    bds.setDriverClassName("com.mysql.jdbc.Driver");
    bds.setUrl("jdbc:mysql://localhost:3306/data");
    bds.setUsername("USERNAME");
    bds.setPassword("PASSWORD");

    try{
        System.out.println("Attempting Database Connection");
        conn = bds.getConnection();
        System.out.println("Connected Successfully");
    }catch(SQLException e){
        System.out.println("Caught SQL Exception: " + e);
    }
    return conn;
}

public void closeConnection() throws SQLException {
    conn.close();
}

}

这是真正的连接池吗？我在另一个类中使用连接是这样的：

        //Check data against database.
    DatabaseConnection dbConn = new DatabaseConnection();
    Connection conn;
    ResultSet rs;
    PreparedStatement prepStmt;

    //Query database and check username/pass against table.
    try{
        conn = dbConn.getConnection();
        String sql = "SELECT * FROM users WHERE username=? AND password=?";
        prepStmt = conn.prepareStatement(sql);
        prepStmt.setString(1, user.getUsername());
        prepStmt.setString(2, user.getPassword());
        rs = prepStmt.executeQuery();

        if(rs.next()){ //Found Match.
            do{
                out.println("UserName = " + rs.getObject("username") + " Password = " + rs.getObject("password"));
                out.println("<br>");
            } while(rs.next());
        } else {
            out.println("Sorry, you are not in my database."); //No Match.
        }

        dbConn.closeConnection(); //Close db connection.

    }catch(SQLException e){
        System.out.println("Caught SQL Exception: " + e);
    }

Answer 1

假设它BasicDataSource是来自DBCP的，那么是的，您正在使用连接池。但是，您将在每次获取连接时重新创建另一个连接池。您并不是真正地在同一个池中合并连接。您只需在应用程序启动时创建一次连接池，并从中获取每个连接。您也不应将连接保留为实例变量。您还应该关闭连接，语句和结果集，以确保在异常情况下也正确关闭了资源。Java
7的try-with- resources语句对此很有帮助，它会在try块完成后自动关闭资源。

这是一个小的重写：

public final class Database {

    private static final BasicDataSource dataSource = new BasicDataSource();

    static {
        dataSource.setDriverClassName("com.mysql.jdbc.Driver");
        dataSource.setUrl("jdbc:mysql://localhost:3306/data");
        dataSource.setUsername("USERNAME");
        dataSource.setPassword("PASSWORD");
    }

    private Database() {
        //
    }

    public static Connection getConnection() throws SQLException {
        return dataSource.getConnection();
    }

}

（如有必要，可以将其重构为抽象工厂以提高可插入性）

和

private static final String SQL_EXIST = "SELECT * FROM users WHERE username=? AND password=?";

public boolean exist(User user) throws SQLException {
    boolean exist = false;

    try (
        Connection connection = Database.getConnection();
        PreparedStatement statement = connection.prepareStatement(SQL_EXIST);
    ) {
        statement.setString(1, user.getUsername());
        statement.setString(2, user.getPassword());

        try (ResultSet resultSet = preparedStatement.executeQuery()) {
            exist = resultSet.next();
        }
    }

    return exist;
}

使用方法如下：

try {
    if (!userDAO.exist(username, password)) {
        request.setAttribute("message", "Unknown login. Try again.");
        request.getRequestDispatcher("/WEB-INF/login.jsp").forward(request, response);
    } else {
        request.getSession().setAttribute("user", username);
        response.sendRedirect("userhome");
    }
} catch (SQLException e) {
    throw new ServletException("DB error", e);
}

但是，在实际的Java
EE环境中，您应该将的创建委托DataSource给容器/应用程序服务器，并从JNDI获取它。如果是Tomcat，请另参见本文档的示例：http : //tomcat.apache.org/tomcat-6.0-doc/jndi-resources-
howto.html