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<users.length; 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();
}
}
}