from：http://www.zekkocho.com/java/91-connect-to-database-with-jdbc-singleton

——————————————————————DBConnect.java—————————————————————

package Jdbc;

import java.sql.*;

public class DBConnect{

//Static instance of connection, only one will ever exist

private static Connection connection = null;

//Returns single instance of connection

public static Connection getConnection(){

//If instance has not been created yet, create it

if(DBConnect.connection == null){

initConnection();

}

return DBConnect.connection;

}

//Gets JDBC connection instance

private static void initConnection(){

try{

Class.forName("com.mysql.jdbc.Driver");

String url = "jdbc:mysql://localhost/test";

String user = "root";

String pw = "";

DBConnect.connection =

DriverManager.getConnection(url, user, pw);

}

catch (ClassNotFoundException e){

System.out.println(e.getMessage());

System.exit(0);

}

catch (SQLException e){

System.out.println(e.getMessage());

System.exit(0);

}

catch (Exception e){

}

}

}

————————————————————————TestDB.java————————————————————————

package Jdbc;

import java.sql.*;

public class TestDB {

public static void main(String args[])

throws Exception{

//Always returns the same instance

Connection connection = DBConnect.getConnection();

ResultSet rows = null;

Statement s = connection.createStatement();

String select = "select * from people;";

rows = s.executeQuery(select);

while(rows.next()){

System.out.println(rows.getString("name"));

}

//Get connection again, still same instance

Connection connection2 = DBConnect.getConnection();

if(connection2 == connection){

System.out.println("Same Instance");

}

}

}

———————————————————new a test db：test————————————————

create table people(

id int,

name varchar(10)

);

mysql> insert into people values(1, "zhangsan");

Query OK, 1 row affected (0.04 sec)

mysql> insert into people values(2, "lisi");

Query OK, 1 row affected (0.02 sec)

mysql> insert into people values(1, "zhangsan");

Query OK, 1 row affected (0.02 sec)

mysql> select * from people;

+------+----------+

| id   | name     |

+------+----------+

|    1 | zhangsan |

|    2 | lisi     |

|    1 | zhangsan |

+------+----------+

3 rows in set (0.00 sec)

mysql>

———————————————————————run result：——————————————————————

zhangsan

lisi

zhangsan

Same Instance

C:\Users\decli\Desktop\Jdbc>dir

驱动器 C 中的卷没有标签。

卷的序列号是 5EEE-076C

C:\Users\decli\Desktop\Jdbc 的目录

2011/10/31  09:49

2011/10/31  09:49

2011/10/30  18:51               505 createDB.txt

2011/10/30  18:37               985 DBConnect.java

2011/10/31  10:34

2011/10/30  18:39               679 TestDB.java

3 个文件          2,169 字节

3 个目录 35,813,437,440 可用字节

C:\Users\decli\Desktop\Jdbc>javac  -d . *.java

C:\Users\decli\Desktop\Jdbc>C:\Users\decli\Desktop\java>java -cp .;./Jdbc/mysql-connector-java-5.0.8-bin.jar Jdbc.TestDB

zhangsan

lisi

zhangsan

Same Instance

注：如果是linux，请将 ; 换成 :即可：

gs_decli_0_231:/data/decli/java/testdb # java -cp .:./mysql-connector-java-5.0.8-bin.jar  Jdbc.TestDB   zhangsan lisi zhangsan Same Instance gs_decli_0_231:/data/decli/java/testdb #