jdbc 单例

单例模式

代码

package utils;import java.io.IOException;import java.io.InputStream;import java.util.Properties;//读取数据库属性文件，获取数据库连接信息public class ConfigManager {    private  static ConfigManager configManager;    private Properties properties;    // 构造方法 方法名和类名一样    private ConfigManager() {        String configFile = "database.properties";        // 把configFile通过ConfigManager类加载器的.getResourceAsStream方法读到输入流        InputStream in = ConfigManager.class.getClassLoader().getResourceAsStream(configFile);        // IN通过properties.load方法load到properties对象里面去;        properties=new Properties();        try {            properties.load(in);        } catch (IOException e) {            // TODO Auto-generated catch block            e.printStackTrace();        } finally {            try {                if (in != null) {                    in.close();                }            } catch (IOException e) {                // TODO Auto-generated catch block                e.printStackTrace();            }        }    }    //提供给别人一个唯一的ConfigManager对象    public static ConfigManager getInstance(){        if(configManager==null){            configManager=new ConfigManager();        }        return configManager;    }    // 根据属性文件中的键获得对应的值    public String getString(String key) {        return properties.getProperty(key);    }}

饿汉单例模式

//缺点为多线程时线程不安全//上来就new一个对象在内存存着，只要调用这个方法，就把对象给人private  static ConfigManager configManager=new ConfigManager();public static ConfigManager getInstance(){        return configManager;    }

懒汉单例模式

public static synchronized ConfigManager getInstance(){        if(configManager==null){            configManager=new ConfigManager();        }        return configManager;    }

懒汉单例模式

双重锁定

public static synchronized ConfigManager getInstance(){        if(configManager==null){            synchronized (ConfigManager.class){                if(configManager==null){                    configManager=new ConfigManager();                }            }        }        return configManager;    }