java连接数据库（SQL Server、MySQL、Oracle）及基本查询

package com.etrol.util;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

import com.mysql.jdbc.PreparedStatement;

public class DBHelper {
//----------------------------------sqlserver----------------------------------
private static final String URL_STRING ="jdbc:sqlserver://192.168.8.3:1433;DatabaseName=SmartGrainDepot_NXQ";
private static final String DRIVER_STRING = "com.microsoft.sqlserver.jdbc.SQLServerDriver";
private static final String USER_STRING = "sa";
private static final String PASSWORD_STRING = "1hyvg32_ice";

//-----------------------------------mysql------------------------------------------
//  private static final String URL_STRING ="jdbc:mysql://localhost:3306/test";;
//  private static final String DRIVER_STRING = "com.mysql.jdbc.Driver";
//  private static final String USER_STRING = "jy";
//  private static final String PASSWORD_STRING = "jy";

//-----------------------------------oracle------------------------------------------------
//  private static final String URL_STRING = "jdbc:oracle:thin:127.0.0.1:1521:orcl";
//  private static final String DRIVER_STRING = "oracle.jdbc.driver.OracleDriver";
//  private static final String USER_STRING = "scott";
//  private static final String PASSWORD_STRING = "tiger";

private static Connection connection = null ;
private DBHelper(){

}

/**
* 获取数据库连接
* Connection
* @return
* DBHelper
*/
public static Connection getConnection(){
if (connection==null) {
try {
Class.forName(DRIVER_STRING);
try {
connection = DriverManager.getConnection(URL_STRING, USER_STRING, PASSWORD_STRING);
} catch (SQLException e) {
e.printStackTrace();
}
} catch (ClassNotFoundException e) {
e.printStackTrace();
}

}
return connection;
}

/**
* 关闭数据库连接
* void
* @param connection
* DBHelper
*/
public static void connectionClose(Connection connection){
try {
connection.close();
} catch (SQLException e) {
e.printStackTrace();
}
}

public static void main(String[] args) {
System.out.println(getConnection());
//--------------------------------sqlserver select----------------------------------------
Connection connection = getConnection();
try {
Statement st = connection.createStatement();
ResultSet reSet = st.executeQuery("select * from baseinfo_AssayResultItem;");
reSet.next();
System.out.println(reSet.getString(1));
} catch (SQLException e) {
e.printStackTrace();
}

//---------------------------------mysql select--------------------------------------------

//      try {
//          PreparedStatement ps = (PreparedStatement) connection.prepareStatement("select * from baseinfo_AssayResultItem");
//          ResultSet rs = ps.executeQuery();
//          rs.next();
//          System.out.println(rs.getString(1));
//      } catch (SQLException e) {
//          e.printStackTrace();
//      }

}

}