单例模式实例：获取单例的数据库连接（同时加载配置文件，用于druid数据库连接池）

import java.io.IOException; 
import java.io.InputStream; 
import java.sql.Connection; 
import java.sql.SQLException; 
import java.util.Properties; 

import com.alibaba.druid.pool.DruidDataSource; 


public class SingletonDruidDataSource extends DruidDataSource { 
private static final long serialVersionUID = 8847473526624938692L; 
private static final SingletonDruidDataSource INSTANCE = new SingletonDruidDataSource(); 

private SingletonDruidDataSource(){ 

//InputStream propInputStream1 = this.getClass().getClassLoader().getResourceAsStream("ApplicationResources.properties"); 
InputStream propInputStream = Thread.currentThread().getContextClassLoader().getResourceAsStream("ApplicationResources.properties"); 
Properties properties = new Properties(); 
try { 
properties.load(propInputStream); 
} catch (IOException e) { 
e.printStackTrace(); 
}
this.setDriverClassName("oracle.jdbc.driver.OracleDriver"); 
this.setUsername(properties.getProperty("dbuser")); 
this.setPassword(properties.getProperty("dbpwd"));
this.setUrl(properties.getProperty("dburl")); 
this.setInitialSize(5); 
this.setMinIdle(1); 
this.setMaxActive(10); 
this.setPoolPreparedStatements(false); 
} 

public static SingletonDruidDataSource getInstance(){ 
return INSTANCE; 
} 

public static void main(String[] args) { 
if (SingletonDruidDataSource.getInstance() == SingletonDruidDataSource.getInstance()){ 
System.out.println("单例"); 
} 
DruidDataSource ds = SingletonDruidDataSource.getInstance(); 
try { 
Connection connection = ds.getConnection(); 
connection.close(); 
} catch (SQLException e) { 
e.printStackTrace(); 
} 
} 
}