Java单例模式读取MySql配置文件_单例模式读取配置文件

单例的数据库连接类：

import com.alibaba.druid.pool.DruidDataSourceFactory;
import javax.sql.DataSource;
import java.io.FileInputStream;
import java.sql.Connection;
import java.util.Properties;

public class Singleton {
    // 创建单例对象
    private static Singleton singleton;
    // 创建数据库获取连接的对象
    private static Connection singletonConnection = null;

    // 将构造方法私有化,防止外部new
    public Singleton() throws Exception {
        singletonConnection = Singleton.getConnection();

    }

    private static Connection getConnection() throws Exception {
        Properties prop = new Properties();
        prop.load(new FileInputStream("src\\main\\resources\\jdbc.properties"));
        DataSource dataSource = DruidDataSourceFactory.createDataSource(prop);
        Connection singletonConnection = dataSource.getConnection();
        return singletonConnection;
    }

    //  对外提供实例化的方法
    public static Connection getInstance() throws Exception {
        if (singleton == null) {
            singleton = new Singleton();
        }
        return singletonConnection;
    }
}
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测试类：

package com.gy.config;

import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.List;

public class test {
    public static void main(String[] args) throws Exception {
        Connection instance = Singleton.getInstance();
        Connection instance1 = Singleton.getInstance();
        Connection instance2 = Singleton.getInstance();
        System.out.println(instance);
        System.out.println(instance1);
        System.out.println(instance2);
        System.out.println("============================");
        Statement statement = instance.createStatement();
        String sql="select * from user";
        ResultSet resultSet = statement.executeQuery(sql);
        List<User> users=new ArrayList<>();
        while (resultSet.next()){
            String name = resultSet.getString(1);
            String password = resultSet.getString(2);
            int id = resultSet.getInt(3);
            User user = new User(name, password, id);
            users.add(user);
        }
        System.out.println(users);
    }
}
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运行结果：（成功返回单例对象）