Java读取Properties的方式

项目结构：经典的maven项目结构

配置文件1和2内容一致：

jdbc.driver=com.mysql.cj.jdbc.Driver
jdbc.url=mysql://localhost:3306/database?useUnicode=true&characterEncoding=utf-8&serverTimezone=Asia/Shanghai
jdbc.username=root
jdbc.password=123456

1. this.getClass().getResourceAsStream()

//读取配置文件1
public void readProperties1() throws IOException {
    //不加/会从当前包进行寻找，加上/会从src开始找
    InputStream inputStream = this.getClass().getResourceAsStream("/jdbc.properties");
    Properties properties=new Properties();
    properties.load(inputStream);
    System.out.println("jdbc.driver="+properties.getProperty("jdbc.driver"));
    System.out.println("jdbc.url="+properties.getProperty("jdbc.url"));
    System.out.println("jdbc.username="+properties.getProperty("jdbc.username"));
    System.out.println("jdbc.password="+properties.getProperty("jdbc.password"));
}
      
//读取配置文件2        
 public void readProperties1() throws IOException {
        InputStream inputStream = this.getClass().getResourceAsStream("/config/jdbc2.properties");
        Properties properties=new Properties();
        properties.load(inputStream);
        System.out.println("jdbc.driver="+properties.getProperty("jdbc.driver"));
        System.out.println("jdbc.url="+properties.getProperty("jdbc.url"));
        System.out.println("jdbc.username="+properties.getProperty("jdbc.username"));
        System.out.println("jdbc.password="+properties.getProperty("jdbc.password"));
}

2.当前类的加载器进行读取this.getClass().getClassLoader().getResourceAsStream()

//读取配置文件1
public void readProperties2() throws IOException {
    //不加/，若加了会为null
    InputStream inputStream = this.getClass().getClassLoader().getResourceAsStream("jdbc.properties");
    Properties properties=new Properties();
    properties.load(inputStream);
    System.out.println("jdbc.driver="+properties.getProperty("jdbc.driver"));
    System.out.println("jdbc.url="+properties.getProperty("jdbc.url"));
    System.out.println("jdbc.username="+properties.getProperty("jdbc.username"));
    System.out.println("jdbc.password="+properties.getProperty("jdbc.password"));
}

//读取配置文件2
public void readProperties2() throws IOException {
        InputStream inputStream = this.getClass().getClassLoader().getResourceAsStream("config/jdbc2.properties");
        Properties properties=new Properties();
        properties.load(inputStream);
        System.out.println("jdbc.driver="+properties.getProperty("jdbc.driver"));
        System.out.println("jdbc.url="+properties.getProperty("jdbc.url"));
        System.out.println("jdbc.username="+properties.getProperty("jdbc.username"));
        System.out.println("jdbc.password="+properties.getProperty("jdbc.password"));
}

• 方法1和2区别： （classpath即为target/classes 这个目录）

• Class.getResourceAsStream() 从当前类所在的位置开始查找配置文件位置。要找到jdbc.properties和jdbc2.properties必须加/从classpath下开始查找

• Class.getClassLoader().getResourceAsStream() 默认就从classpath路径下开始查找，加上/会报空指针

• 十分有必要知道java中类的加载过程！！！

3. ClassLoader类的static方法 getSystemResourceAsStream()

public void readProperties3() throws IOException {
        //InputStream inputStream = ClassLoader.getSystemResourceAsStream("config/jdbc2.properties");
        InputStream inputStream = ClassLoader.getSystemResourceAsStream("jdbc.properties");
        Properties properties=new Properties();
        properties.load(inputStream);
        System.out.println("jdbc.driver="+properties.getProperty("jdbc.driver"));
        System.out.println("jdbc.url="+properties.getProperty("jdbc.url"));
        System.out.println("jdbc.username="+properties.getProperty("jdbc.username"));
        System.out.println("jdbc.password="+properties.getProperty("jdbc.password"));
    }

4. Spring中的 ClassPathResource读取

public void readProperties4() throws IOException {
        //ClassPathResource resource = new ClassPathResource("jdbc.properties");
        ClassPathResource resource = new ClassPathResource("config/jdbc2.properties");
        Properties properties= PropertiesLoaderUtils.loadProperties(resource);
        System.out.println("jdbc.driver="+properties.getProperty("jdbc.driver"));
        System.out.println("jdbc.url="+properties.getProperty("jdbc.url"));
        System.out.println("jdbc.username="+properties.getProperty("jdbc.username"));
        System.out.println("jdbc.password="+properties.getProperty("jdbc.password"));
}

5. PropertyResourceBundle读取InputStream流

public void readProperties5() throws IOException {
        //InputStream inputStream = ClassLoader.getSystemResourceAsStream("jdbc.properties");
    	InputStream inputStream = ClassLoader.getSystemResourceAsStream("config/jdbc2.properties");
        PropertyResourceBundle bundle = new PropertyResourceBundle(inputStream);
        System.out.println(bundle.getString("jdbc.driver"));
        System.out.println(bundle.getString("jdbc.url"));
        System.out.println(bundle.getString("jdbc.username"));
        System.out.println(bundle.getString("jdbc.password"));
    }

6.ResourceBundle.getBundle()

//不用输入后缀
public void readProperties6()  {
        //ResourceBundle bundle=ResourceBundle.getBundle("jdbc");
        ResourceBundle bundle=ResourceBundle.getBundle("config/jdbc2");
        System.out.println(bundle.getString("jdbc.driver"));
        System.out.println(bundle.getString("jdbc.url"));
        System.out.println(bundle.getString("jdbc.username"));
        System.out.println(bundle.getString("jdbc.password"));
    }