Connection-采用properties配置文件建立Connecton连接

**通过编写properties配置文件对数据库url、username、userpwd进行配置，来连接oracle数据库。
方便数据库连接变更。**

第一步：在src目录下创建db.properties配置文件
（配置文件内容以 key-value/键值对的形式存放）

driver =oracle.jdbc.driver.OracleDriver
url=jdbc:oracle:thin:@localhost:1521:orcl
username=user1
password=123456

第二步：在com.wu.service包下创建ConfigManager.class类

import java.io.IOException;import java.io.InputStream;import java.util.Properties;//ConfigManager类public class ConfigManager {    private static ConfigManager configManager;    private static Properties properties;    private ConfigManager() {        String configFile = "db.properties";        properties = new Properties();//类.class：获取当前类的class对象，即“类的类”//.getClassLoader():获取类加载器，从类的字符文件        InputStream in = ConfigManager.class.getClassLoader()                .getResourceAsStream(configFile);        try {            properties.load(in);            in.close();        } catch (IOException e) {            e.printStackTrace();        }    }//单例模式：采用static修饰构造方法，整个项目运行中只有一个ConfigManager实例，所有方法调用的ConfigManager都是同一个    public static ConfigManager getInstance() {        //        if (configManager == null) {            configManager = new ConfigManager();        }        return configManager;    }//传入key，通过Properties.getProperty(Stirng key)方法获取key对应的value值    public String getValue(String key) {        return properties.getProperty(key);    }}//建立连接Connectionpublic void getConn() throws ClassNotFoundException, SQLException {     String driver = ConfigManager.getInstance().getValue(     "jdbc.driver_class");     String url = ConfigManager.getInstance()     .getValue("url");     String userName = ConfigManager.getInstance().getValue(     " username");     String password = ConfigManager.getInstance().getValue(     " password");     Class.forName(driver);     conn = DriverManager.getConnection(url, userName, password);     }