编写配置文件

username=root
password=123456
url=jdbc:mysql://localhost:3306/myDatabase
driverClassName=com.mysql.cj.jdbc.Driver

编写测试类

import java.io.FileInputStream;
import java.io.IOException;
import java.util.Enumeration;
import java.util.Properties;

/**
 * properties配置文件的读取
 */
public class FileProperties {

    public static void main(String[] args) {
        // 配置类对象
        Properties properties = new Properties();
        try (
                // 创建输入流
                FileInputStream fis = new FileInputStream(Thread.currentThread().getContextClassLoader().getResource("jdbc.properties").getPath())
        ) {
            // 加载流文件
            properties.load(fis);

            // 获取配置文件的内容
           /* System.out.println("username: ==>" + properties.getProperty("username"));
            System.out.println("password: ==>" + properties.getProperty("password"));
            System.out.println("url: ==>" + properties.getProperty("url"));
            System.out.println("driverClassName: ==>" + properties.getProperty("driverClassName"));*/

            Enumeration<?> enumeration = properties.propertyNames();
            while (enumeration.hasMoreElements()) {
                String key = (String) enumeration.nextElement();
                String value = properties.getProperty(key);
                System.out.println(key + "==>" + value);
            }

        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }
}

结果

使用JDK提供的工具类ResourceBundle（资源绑定类）

import java.util.Enumeration;
import java.util.ResourceBundle;

public class ResourceBundleTest {
    public static void main(String[] args) {
        // 相对路径是类的根目录src,例如：jdbc.properties 的完整路劲=》 src/com/java/study/jdbc.properties
       /*  使用：不需要.properties
            ResourceBundle.getBundle("com.java.study.jdbc");
            ResourceBundle.getBundle("com/java/study/jdbc");
        */

        // 获取资源绑定器对象，这里我的jdbc.properties 就在src下，所以直接写
        ResourceBundle bundle = ResourceBundle.getBundle("jdbc");

        // 通过key获取value
        /*System.out.println(bundle.getString("username"));
        System.out.println(bundle.getString("password"));
        System.out.println(bundle.getString("url"));
        System.out.println(bundle.getString("driverClassName"));*/

        Enumeration<String> keys = bundle.getKeys();
        while (keys.hasMoreElements()) {
            String key = keys.nextElement();
            String value = bundle.getString(key);
            System.out.println(key + "=" + value);
        }
    }
}