关于 PreparedStatement

关于 PreparedStatement

If you have a SQL statement that needs to be executed multiple times, it is more efficient to use a JDBC PreparedStatement object to run it. JDBC PreparedStatement class supports the following main features:

•     SQL statements PreparedStatement objects are pre-compiled on the database server side.
•     IN parameters are supported in SQL statements in PreparedStatement objects.
•     Batch execution mode is supported to run the run SQL statement multiple times in a single transaction.

您可以使用Connection的prepareStatement()方法建立好一個預先編譯（precompile）的SQL語句，當中參數會變動的部份，先指定"?"這個佔位字元，例如：

PreparedStatement stmt = conn.prepareStatement(
    "INSERT INTO message VALUES(?, ?, ?, ?, ?)");

使用PreparedStatement也可以進行批次處理，直接來看個例子就知道如何使用：

PreparedStatement stmt = conn.prepareStatement(
    "INSERT INTO Users VALUES(?,?, ?)");
 
User[] users = ...;

for(int i=0; i
     stmt.setInt(1, users[i].getID());
     stmt.setString(2, users[i].getName());
     stmt.setString(3, users[i].getPassword());
     stmt.addBatch( );
}
 
stmt.executeBatch(); 

A PreparedStatement object should be created from a Connection object with the prepareStatement() method and executed like a regular Statement object as shown in the following program:

import java.util.*;
import java.sql.*;
import javax.sql.*;
import javax.naming.*;
public class MySqlPreparedSelect {
  public static void main(String [] args) {
    Connection con = null;
    try {
      com.mysql.jdbc.jdbc2.optional.MysqlDataSource ds
        = new com.mysql.jdbc.jdbc2.optional.MysqlDataSource();
      ds.setServerName("localhost");
      ds.setPortNumber(3306);
      ds.setDatabaseName("HerongDB");
      ds.setUser("Herong");
      ds.setPassword("TopSecret");
      con = ds.getConnection();

// PreparedStatement for SELECT statement
      PreparedStatement sta = con.prepareStatement(
"SELECT * FROM Profile WHERE ID = 2");

// Execute the PreparedStatement as a query
      ResultSet res = sta.executeQuery();

// Get values out of the ResultSet
      res.next();
      String firstName = res.getString("FirstName");
      String lastName = res.getString("LastName");
      System.out.println("User ID 2: "+firstName+' '+lastName);

// Close ResultSet and PreparedStatement
      res.close();
      sta.close();

      con.close();       
    } catch (Exception e) {
      System.err.println("Exception: "+e.getMessage());
      e.printStackTrace();
    }
  }
}