java 单例模式（singleton）连接 mysql 数据库

最新推荐文章于 2025-10-29 20:37:48 发布

转载最新推荐文章于 2025-10-29 20:37:48 发布 · 2.7k 阅读

文章标签：

#MySQL

本文介绍了一个使用Java JDBC实现的单例模式数据库连接池示例。通过单例模式确保了应用程序中只存在一个数据库连接实例，有助于提高资源利用效率。文章提供了完整的代码示例，包括DBConnect类和TestDB类，演示了如何查询数据库。

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    <DIR>          .
2011/10/31 09:49    <DIR>          ..
2011/10/30 18:51               505 createDB.txt
2011/10/30 18:37               985 DBConnect.java
2011/10/31 10:34    <DIR>          Jdbc
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 #