书写简单的 JDBC 程序的顺序,JDBC Steps – Basic steps in writing a JDBC Application

 
/*
 * Import JDBC core packages. Following statement imports the java.sql package, which contains the JDBC core API.
 */
import java.sql.*;
public class RetriveAllEmployees {
  public static void main(String[] args) {
    System.out.println("Getting All Rows from employee table!");
    Connection con = null;
    String url = "jdbc:mysql://localhost:3306/";
    String db = "jdbc";
    String driver = "com.mysql.jdbc.Driver";
    String user = "root";
    String pass = "root";
    try {
      Class.forName(driver);
      con = DriverManager.getConnection(url + db, user, pass);
      Statement st = con.createStatement();
      ResultSet res = st.executeQuery("SELECT * FROM  employee");
      System.out.println("Employee Name: ");
      while (res.next()) {
        String employeeName = res.getString("employee_name");
        System.out.println(employeeName);
      }
      con.close();
    } catch (ClassNotFoundException e) {
      System.err.println("Could not load JDBC driver");
      System.out.println("Exception: " + e);
      e.printStackTrace();
    } catch (SQLException ex) {
      System.err.println("SQLException information");
      while (ex != null) {
        System.err.println("Error msg: " + ex.getMessage());
        System.err.println("SQLSTATE: " + ex.getSQLState());
        System.err.println("Error code: " + ex.getErrorCode());
        ex.printStackTrace();
        ex = ex.getNextException(); // For drivers that support chained exceptions
      }
    }
  }
}

• Loading Driver
  装载驱动
  Loading Database driver is very first step towards making JDBC connectivity with the database. It is necessary to load the JDBC drivers before attempting to connect to the database. The JDBC drivers automatically register themselves with the JDBC system when loaded. Here is the code for loading the
  装载驱动是建立数据库JDBC连接的第一步，再尝试连接数据库前，必须装载JDBC的驱动。在JDBC系统装载时，驱动会自动被注册，下面是装载的代码
  
  JDBC driver:
  Class.forName(driver).newInstance();
  
• Establishing Connection
  建立连接
  In the above step we have loaded the database driver to be used. Now its time to make the connection with the database server. In the Establishing Connection step we will logon to the database with user name and password. Following code we have used to make the connection with the database:
  前一步我们已经准备好了数据库驱动来使用。现在我们需要建立数据库连接。我们需要使用用户名和密码来登录数据库，以便建立数据库连接。
  
  con = DriverManager.getConnection(url+db, user, pass);
  
• Executing Statements
  执行语句
  In the previous step we established the connection with the database, now its time to execute query against database. You can run any type of query against database to perform database operations. In this example we will select all the rows from employee table. Here is the code that actually execute the statements against database:
  我们可以润星各种类型的语句，来让数据库执行操作。这个例子里将读取员工表格的所有行。下面是我们实际执行的语句
  ResultSet res = st.executeQuery( "SELECT * FROM employee" );
• Getting Results
  获取结果
  In this step we receives the result of execute statement. In this case we will fetch the employees records from the recordset object and show on the console. Here is the code:
  我们已经执行了语句，下面我们从结果集中获取数据，并显示在控制台上。下面是代码
  while (res.next()) {
  String employeeName = res.getInt( " employee_name " );
  System.out.println( employeeName );
  }
  
• Closing Database Connection
  关闭数据库连接
  Finally it is necessary to disconnect from the database and release resources being used. If you don’t close the connection then in the production environment your application will fail due to hanging database connections. Here is the code for disconnecting the application from database:
  最后一步必须关闭连接，释放占用的资源。如果你在正式环境不关闭链接，你将会由于挂起数据库连接而引起错误。下面是关闭数据库连接的代码。
  con.close();
  

 
C:\vinod>javac RetriveAllEmployees.java

C:\vinod>java RetriveAllEmployees
Getting All Rows from employee table!
Employee Name:
Deepak Kumar
Harish Joshi
Rinku roy
Vinod Kumar